ALBERT

Description: [No abstract available]

Description: [No abstract available]

Description: It is known that the maximum danger of flutter‐type aerodynamic instability for suspension bridges occurs during the early erection phases of the deck. The effectiveness of two different provisional measures for increasing the instability critical windspeed in such conditions is evaluated for a long span suspension bridge with flat box stiffening girder. Copyright © 1981 John Wiley & Sons, Ltd

Description: [No abstract available]

Description: This paper illustrates the design of a four‐storey, three‐bay, moment‐resisting, planar steel frame. Non‐linear step‐by‐step integration is used as the analysis technique within the design process itself rather than as a check at the end of the design process. The method of design directly quantifies the accepted seismic‐resistant design philosophy that a properly designed structure: (1) resists moderate ground motion without structural damage, and (2) resists severe ground motion without collapse. Actual ground motion accelerograms are selected and scaled to levels representing moderate and severe ground motions. Constraints quantifying structural damage and limited non‐structural damage are constructed for the case of moderate ground motion, along with constraints quantifying collapse and limited structural damage for the case of severe ground motion. In addition serviceability constraints are imposed on structural behaviour under gravity loads only. Objective functions include the minimization of structural volume as well as the minimization of response quantities such as storey drifts and inelastically dissipated energy. A sophisticated optimization algorithm is utilized to solve the resulting mathematical programming problem. Comparative results concerning the computational phase as well as performance of both preliminary and final designs are presented. The practicality and reliability of the design method are assessed. Copyright © 1983 John Wiley & Sons, Ltd

Description: The peak dynamic responses of two mathematical models of a fifteen‐storey steel moment resisting frame building subjected to three earthquake excitations are computed by the response spectrum and time history methods. The models examined are: a ‘regular’ building in which the centres of stiffness and mass are coincident resulting in uncoupled modes with well‐separated periods in each component direction of response; and an ‘irregular’ building with the mass offset from the stiffness centre of the building causing coupled modes with the translational modes having closely spaced periods. Four response spectrum modal combination rules are discussed and are used to predict the peak responses: (1) the square root of the sum of the squares (SRSS) method; (2) the double sum combination (DSC) method; (3) the complete quadratic combination (CQC) method; and (4) the absolute sum (ABS) method. The response spectrum results are compared to the corresponding peak time history values to evaluate the accuracy of the different combination rules. The DSC and the CQC methods provide good peak response estimates for both the regular and irregular building models. The SRSS method provides good peak response estimates for the regular building, but yields significant errors in the irregular building response estimates. The poor accuracy in the irregular building results is attributable to the effects of coupled modes with closely spaced periods. It is concluded that the DSC and CQC methods produce response estimates of equivalent accuracy. Both methods are recommended for general use. In addition to the DSC and CQC rules, the SRSS method is recommended for systems where coupled modes with closely spaced periods do not dominate the response. Copyright © 1983 John Wiley & Sons, Ltd

Description: To study the characteristic features of the in‐plane free‐field response, two actual sites of nuclear power plants, a soft and a rock site, are analysed, by varying the location of the control point and the nature of the wave pattern. Harmonic and transient seismic excitations are examined. The conclusions reached in the vast parametric study of Reference 6 are confirmed for the actual sites. These apply to the range of possible apparent velocities and the associated motions, the spatial variations with depth and in the horizontal direction. If only one component of the control motion, e.g. the horizontal, is matched, then it can be associated either with a body wave or with a surface wave. In the latter case, a specific mode is used up to the frequency at which the next higher mode starts, since for a given frequency, the higher modes attenuate less. The other component of the motion follows. If both components are prescribed, the motion can be interpreted as arising from a combination of a P‐ and an SV‐wave (with a common apparent velocity). Surface waves alone cannot be used to match both components. A body wave has to be included, at least up to the frequency at which the second mode starts. For the soft site, the surface waves decay significantly, especially in the range of higher frequencies, where the apparent velocity is considerably smaller than the shear‐wave velocity of the rock. For this site, it seems sufficient to examine only (extremely shallow) body waves. For a rock site, however, Rayleigh‐waves exist which attenuate little, leading to smaller apparent velocities than extremely shallow body waves. Copyright © 1983 John Wiley & Sons, Ltd

Description: An experimental study of a Coulomb friction damped aseismic base isolation system with fail‐safe characteristics is described in this paper. The base isolation system utilized commercially made natural rubber bearings and a skid system which comes into operation at preset‐levels of relative horizontal displacement between the structure and the foundation. The fail‐safe skid provides hysteretic damping and prevents failure of the isolation system in the event of displacements larger than those assumed in the original design. The isolation system can be designed for an earthquake which can be reasonably expected within the lifetime of the structure; in the event of an earthquake of unanticipated intensity the failsafe system will prevent collapse of the structure. The testing of the system involved an 80,000lb model, approximately 1/3 scale to a real structure mounted on the 20′ × 20′ shaking table at EERC and subject to a variety of earthquake inputs. The results show that the hysteretic effect of the fail‐safe system does not greatly increase the accelerations experienced by the structure but considerably reduces the relative displacements at the isolation bearings. The action of the fail‐safe system was tested by using an earthquake input that produced a resonant response in the isolated mode of the model. The stability limit of the isolation system was exceeded and the bearings failed but complete failure of the isolation system and thus collapse of the model was prevented by the fail‐safe system. The implementation of the system in full scale structures poses no technical or construction problems. An equivalent linearization technique was developed for this system for design purposes using response spectra. The accuracy of this approach was verified by comparison with the experimental results. Copyright © 1983 John Wiley & Sons, Ltd

Description: An analysis is presented of the transient flexural vibrations of an elastic column supported by an elastic half‐space under the condition that an arbitrarily shaped free‐field lateral acceleration and displacement are given as inputs. Applying Laplace transformations with respect to time and numerical inverse Laplace transformations, the time histories of the column acceleration at the interface and free end, and the column and half‐space displacement distributions are obtained. After the input free‐field acceleration terminates, slightly damped and almost harmonically variable acceleration is observed. The acceleration frequency after the disappearance of the input acceleration nearly coincides with the resonant frequency of the system. The slight damping with the first resonant frequency, even if the half‐space is soft compared with the column, is characteristic of the transient flexural vibrations of a column supported by a half‐space. Such a phenomenon is not typical of the transient longitudinal vibration problem. Therefore, it may be concluded: when buildings and structures are subjected to an earthquake or an explosive force, their flexural vibrations will continue with their first resonant frequencies, even if their foundations are soft. Copyright © 1983 John Wiley & Sons, Ltd

Description: A dynamic response analysis procedure for an x‐braced tubular steel offshore platform frame is described, including details of the mathematical model adopted to represent the dynamic buckling behaviour of the brace member. Results obtained with this mathematical technique are compared with experimental data measured during shaking table tests of a 5/48 scale model frame. The agreement between experiment and analysis is excellent for different levels of response, ranging from linearly elastic to cyclic brace buckling. Copyright © 1983 John Wiley & Sons, Ltd

Description: Theoretical and experimental studies were undertaken to gain insight into physical parameters controlling the flocculation and settling properties of mud floes in the Changjiang Estuary, China. The Rouse equation is applied to vertical profiles of suspended sediment concentration to determine the bulk mean settling velocity (w s) of sediment suspended in the Changjiang Estuary. Both in situ point-sampled and acoustically measured profiles of suspended mud concentrations were fit selectively. The calculated settling velocities ws mainly ranged from 0.4 to 4.1 mm. s -1 for the point-sampled data set, and from 1.0 to 3.0 mm s-1 for the acoustically measured data set. Furthermore, the settling velocities of mud flocs increased with mean concentration (C) of mud flocs in suspension and were proportional to increasing bottom shear stress (τb) of tidal flow. The best equation for the field settling velocity of mud flocs in the Changjiang Estuary can be expressed by the power law: ws, = m Cn (m, 1·14-2·37; n, 0.84-1·03). It is suggested that C and τb were the dominant physical parameters controlling the flocculation and ws of mud flocs in suspension. © 2004 John Wiley and Sons, Ltd.

Description: Changes in nutrient budgets and hydrological processes due to the natural disturbance of pine wilt disease (PWD) were monitored in a small, forested watershed in Japan. The disturbance caused changes in soil nitrogen transformations. Predisturbance, mineralized, nitrogen remained in the form of NH4+, whereas in disturbed areas most mineralized nitrogen was nitrified. Stream NO3 - concentrations increased following PWD. There was a delay between time of disturbance and the increase of NO3 - in ground and stream waters. Stream concentrations of NO3- and cations (Ca2+ + Mg 2+) were significantly correlated from 1994 to 1996, whereas the correlation among NO3-, H+, and SO42- was significant only in 1995. Although both cation exchange and SO42- adsorption buffered protons, cation exchange was the dominant and continuous mechanism for acid buffering. SO42- adsorption was variable and highly pH dependent. The disturbance also resulted in slight delayed changes of input-output nutrient balances. The nitrogen contribution to PWD litter inputs was 7·39 kmol ha-1, and nitrogen loss from streamwater was less than 0·5 kmol ha-1 year-1 throughout the observation period. This large discrepancy suggested substantial nitrogen immobilization. © 2004 John Wiley and Sons, Ltd.

Description: Laboratory tests performed on 181 rock samples from boreholes drilled in different areas of the Betic Cordillera allow us to calculate their hydraulic conductivity and open porosity values. Higher values are generally associated with Miocene calcareous sandstones, although hydraulic conductivity reaches its highest values in some isolated limestone and dolostone samples. Lower values were found in marly limestones and marbles. Specific yield ranged from 0 to 0.0798, with a mean value of 0.00579. A total of 79 samples did not release water during the specific yield test, while another 11 samples released water for more than 30 min. Such wide ranges of variation show the great diversity of behaviour that the matrix of the carbonate rocks can have, referring to water storage and transfer, and its influence on pollutants spread, for example. A weak relation between interconnected porosity and hydraulic conductivity was found. The relation between interconnected porosity and specific yield is slightly stronger, except in the case of the dolomites, where a high correlation was found. No dependence on depth was found for hydraulic conductivity and interconnected porosity. © 2004 John Wiley and Sons, Ltd.

Description: The hydrological model TOPMODEL is used to assess the water balance and describe flow paths for the 9·73 ha Lutz Creek Catchment in Central Panama. Monte Carlo results are evaluated based on their fit to the observed hydrograph, catchment-averaged soil moisture and stream chemistry. TOPMODEL, with a direct-flow mechanism that is intended to route water through rapid shallow-soil flow, matched observed chemistry and discharge better than the basic version of TOPMODEL and provided a reasonable fit to observed soil moisture and wet-season discharge at both 15-min and daily time-steps. The improvement of simulations with the implementation of a direct-flow component indicates that a storm flow path not represented in the original version of TOPMODEL plays a primary role in the response of Lutz Creek Catchment. This flow path may be consistent with the active and abundant pipeflow that is observed or delayed saturation overland flow. The 'best-accepted' simulations from 1991 to 1997 indicate that around 41% of precipitation becomes direct flow and around 10% is saturation overland flow. Other field observations are needed to constrain evaporative and groundwater losses in the model and to characterize chemical end-members posited in this paper. Published in 2004 by John Wiley and Sons, Ltd.

Description: A model of rainfall-runoff relationships is an essential tool in the process of evaluation of water resources projects. In this paper, we applied an artificial neural network (ANN) based model for flow prediction using the data for a catchment in a semi-arid region in Morocco. Use of this method for non-linear modelling has been demonstrated in several scientific fields such as biology, geology, chemistry and physics. The performance of the developed neural network-based model was compared against multiple linear regression-based model using the same observed data. It was found that the neural network model consistently gives superior predictions. Based on the results of this study, artificial neural network modelling appears to be a promising technique for the prediction of flow for catchments in semi-arid regions. Accordingly, the neural network method can be applied to various hydrological systems where other models may be inappropriate. © 2004 John Wiley and Sons, Ltd.

Description: This paper, the second in the series, uses the entropy theory to describe the spatial variability of groundwater quality data sets. The application of the entropy theory is illustrated using the chloride observations obtained from a network of groundwater quality monitoring wells in the Gaza Strip, Palestine. The application involves calculating information measures, such as transinformation, the information transfer index and the correlation coefficient. These measures are calculated using a discrete approach, in which contingency tables are used. An exponential decay fitting approach was applied to the discrete models. The analysis shows that transinformation, as a function of distance, can be represented by the exponential decay curve. It also indicates that, for the data used in this study, the transinformation model is superior to the correlation model for characterizing the spatial variability. © 2004 John Wiley and Sons, Ltd.

Description: High-resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonate chemistry parameters of groundwater at two adjacent locations within the peak cluster karst of the Guilin Karst Experimental Site in Guangxi Province, China, were made with different types of multiparameter sonde. The data were stored using data loggers recording with 2 min or 15 min resolution. Waters from a large, perennial spring represent the exit for the aquifer's conduit flow, and a nearby well measures water in the conduit-adjacent, fractured media. During flood pulses, the pH of the conduit flow water rises as the conductivity falls. In contrast, and at the same time, the pH of groundwater in the fractures drops, as conductivity rises. As Ca2+ and HCO3- were the dominant (〉90%) ions, we developed linear relationships (both r2 〉 0.91) between conductivity and those ions, respectively, and in turn calculated variations in the calcite saturation index (SIC) and CO2 partial pressure (PCO2) of water during flood pulses. Results indicate that the PCO2 of fracture water during flood periods is higher than that at lower flows, and its SIC is lower. Simultaneously, PCO2 of conduit water during the flood period is lower than that at lower flows, and its SIC also is lower. From these results we conclude that at least two key processes are controlling hydrochemical variations during flood periods: (i) dilution by precipitation and (ii) water-rock-gas interactions. To explain hydrochemical variations in the fracture water, the water-rock-gas interactions may be more important. For example, during flood periods, soil gas with high CO2 concentrations dissolves in water and enters the fracture system, the water, which in turn has become more highly undersaturated, dissolves more limestone, and the conductivity increases. Dilution of rainfall is more important in controlling hydrochemical variations of conduit water, because rainfall with higher pH (in this area apparently owing to interaction with limestone dust in the lower atmosphere) and low conductivity travels through the conduit system rapidly. These results illustrate that to understand the hydrochemical variations in karst systems, considering only water-rock interactions is not sufficient, and the variable effects of CO2 on the system should be evaluated. Consideration of water-rock-gas interactions is thus a must in understanding variations in karst hydrochemistry. © 2004 John Wiley and Sons, Ltd.

Description: Regimes are useful tools for characterizing the seasonal behaviour of river flow and other hydroclimatological variables over an annual cycle (hydrological year). This paper develops and tests: (i) a regime classification method to identify spatial and temporal patterns in intruannual hydroclimatological response; and (ii) a novel sensitivity index (SI) to assess river flow regimes' climatic sensitivity. The classification of regime shape (form) and magnitude considers the whole annual cycle rather than isolating a single month or season for analysis, which has been the common approach of previous studies. The classification method is particularly useful for identifying large-scale patterns in regimes and their between-year stability, thus providing a context for short-term, small-scale process-based research. The SI provides a means of assessing the often-complex linkages between climatic drivers and river flow, as it identifies the strength and direction of associations between classifications of climate and river flow regimes. The SI has the potential for application to other problems where relationships between nominal classifications require to be found. These techniques are evaluated by application to a test data set of river flow, air temperature and rainfall time-series (1974-1999) for a sample of 35 UK river basins. The results support current knowledge about the hydroclimatology of the UK. Although this research does not seek to yield new, detailed physical process understanding, it provides perspective at large spatial and temporal scales upon climate and flow regime patterns and quantifies linkages. Having clearly demonstrated the regime classification and SI to be effective in an environment where the hydroclimatology is relatively well known, there appears to be much to gain from applying these techniques in parts of the world where patterns and associations between climate and hydrology are poorly understood. © 2004 John Wiley and Sons, Ltd.

Description: In this paper a new and efficient control method based on fuzzy logic is proposed for real-time operation of spillway gates of a reservoir during any flood of any magnitude up to the probable maximum flood. Artificial neural networks are used to model the non-linear relationship among the main variables of the reservoir under consideration. In order to demonstrate the performance of the proposed method, we simulate the control system using different probable overflow hydrographs. The results of the proposed control method are compared with the results of the conventional control methods. The results obtained from the simulations indicate that the proposed method exhibits superior performance over the conventional reservoir flood operation, with much more flexible results. © 2004 John Wiley and Sons, Ltd.

Description: This paper adopts standard tests developed in temperate catchment research to determine the total phosphorus (TP) and the algal available (base-extractable) phosphorus (NaOH-P) content of a wide range of glaciofluvial sediments from the Northern Hemisphere. We find that the TP content of these sediments is broadly similar to the P content of major rock types in Earth's crust (230-670 μgP/g) and so the TP yields of glacier basins may be high owing to the efficacy of suspended sediment evacuation by glacial meltwaters. We show that this is best achieved where subglacial drainage systems are present. The NaOH-P pool of the sediments is found to be low (1-23 μP/g) relative to the TP pool and also to the NaOH-P pool of suspended sediments in temperate, non-glacierized catchments. This most probably reflects the restricted duration of intimate contact between dilute meltwaters and glacial suspended sediments during the ablation season. Thus, despite the high surface-area: volume ratio of glacial suspended sediments, the potential for P adsorption to mineral surfaces following release by dissolution is also low. Further, sorption experiments and sequential extraction tests conducted using glacial suspended sediments from two Svalbard catchments indicate that the generation of reactive secondary minerals (e.g. Fe- and other hydroxides) with a strong capacity to scavenge P from solution (and thereby promote the continued dissolution of P) may also be limited by the short residence times. Most P is therefore associated with poorly weathered, calcite/apatite-rich mineral phases. However, we use examples from the Svalbard glacier basins (Austre Brøggerbreen and Midre Lovénbreen) to show that the high sediment yields of glaciers may result in appreciable NaOH-P loading of ice-marginal receiving waters. Again, the importance of subglacial drainage is highlighted, as it produces a major, episodic release of NaOH-P at Midre Lovénbreen that results in a yield (8.2 kg NaOH-P/km2/year) more than one order of magnitude greater than that at Austre Brøggerbreen (where subglacial drainage is absent and the yield is 0.48 kg NaOH-P/km2/year). Therefore, as since both detrimental and beneficial effects of sediment-bound P loading in ice marginal receiving waters are possible (i.e. either reduced primary productivity owing to increased turbidity or P fertilization following desorption) there is a pressing need to assess the ambient P status of such environments and also the capacity for ice-marginal ecosystems to adapt to such inputs. © 2004 John Wiley and Sons, Ltd.

Description: A model was developed for estimating the delay between a change in climatic conditions and the corresponding fall of water level in large lakes. The input data include: rainfall, temperature, extraterrestrial radiation and astronomical mid-month daylight hours. The model uses two empirical coefficients for computing the potential evaporation and one parameter for the soil capacity. The case studies are two subcatchments of the Altiplano (196 000 km2), in which the central low points are Lake Titicaca and a salar corresponding to the desiccation of the Tauca palaeolake. During the Holocene, the two catchments experienced a 100 m fall in water level corresponding to a decrease in water surface area of 3586 km2 and 55 000 km2, respectively. Under modern climatic conditions with a marked rainy season, the model allows simulation of water levels in good agreement with the observations: 3810 m a.s.1. for Lake Titicaca and lack of permanent wide ponds in the southern subcatchment. Simulations were carried out under different climatic conditions that might explain the Holocene fall in water level. Computed results show quite different behaviour for the two subcatchments. For the northern subcatchment, the time required for the 100 m fall in lake-level ranges between 200 and 2000 years when, compared with the present conditions, (i) the rainfall is decreased by 15% (640 mm/year), or (ii) the temperature is increased by 5.5 °C, or (iii) rainfall is distributed equally over the year. For the southern subcatchment (Tauca palaeolake), the time required for a 100 m decrease in water level ranges between 50 and 100 years. This decrease requires precipitation values lower than 330 mm/year. © 2004 John Wiley and Sons, Ltd.

Description: Winter wheat (Triticum aestivum L.) is the major crop in the North China Plain (NCP). The monsoon climate in this region causes most rain to fall in the summer season, but during the winter-wheat growing season (October-May) the rainfall is far less than the water requirements for the crop. The efficiency of soil water use by winter wheat needs to be improved to reduce the need for irrigation. In this paper, we report the results of two seasons' work on soil water utilization, root growth and distribution, root water uptake by the crop under different irrigation treatments, and possible ways to improve soil water-use efficiency. The field experiments were carried out at Luancheng Station (37°53′N, 114°41′E) from 1996 to 1997 and 1998 to 1999, two growing seasons of winter wheat. Five treatments for each season: rain-fed and irrigated winter wheat with different irrigation numbers from 1 up to 4, were set up in a randomized plot design. Soil available water-holding capacity at the experimental site was about 454 mm for the top 2 m soil profile. Root sampling results showed that winter wheat had a prolific root system with an average maximum rooting depth of 2 m. Most of the root system was concentrated in the upper 40 cm of soil. Root length density in the top layer of soil (0-20 cm) was very high, with values over 5 cm cm-3 . The distribution of water uptake from the soil profile under high soil moisture conditions was the same as the distribution of root length density. The roots in the top layer of soil played an important role in soil water uptake. When root length density was less than 0.8 cm cm-3, the root was the main factor limiting the complete utilization of soil water by crops. The scarcity of roots in the deep soil layers restricted the full utilization of soil water by the crops. Thus, at maturity, over 100 mm of available water remained in the root zone for the rain-fed treatment, although the upper layers had already entered water deficit. The crop took up 80% of the total available soil water in the treatment without irrigation in a dry season. For irrigated wheat, from 40 to 50% of crop water uptake was from the stored soil water. Available stored soil water played an important role in the higher production of wheat crops in the NCP. Effective measures to increase the utilization of stored soil water could improve crop performance under conditions of limited water supply. Results showed that deep tillage to break the soil pan improved root growth in the deeper soil layers, and sowing the crop evenly also enhanced water uptake from the top soil layer to compete with soil evaporation. © 2004 John Wiley and Sons, Ltd.

Description: Surface energy fluxes above the canopies of well-irrigated winter wheat and maize in the North China Plain were measured by the Bowen-ratio energy balance technique in 1999-2000. Seasonal variation of the ratio of latent heat flux λE to available energy Rn - G showed that the ratio of λE to Rn - G exceeded 83% when leaf area index (LAI) varied from 2.0 to 6.0. The seasonal trend of evaporative fraction (EF) for winter wheat was similar to that of LAI before senescence stage, which is a critical factor controlling EF, which itself reflects the partitioning of available energy into λE. The Priestley-Taylor parameter α over the wheat and maize canopies changed greatly over the course of a growing season, and the seasonal average α of winter wheat was 1.17 and 1.26, and that of maize was 1.06 and 1.09 in the two consecutive years. α for winter wheat was exponentially correlated to 0-20 cm surface soil moisture, but not for maize and with the increase of soil depths, the correlation between α and soil moisture was weak. Under different soil moisture conditions, a linear correlation between extractable soil water and leaf water potential ψ for winter wheat was found. Copyright 2004 John Wiley and Sons, Ltd.

Description: In arid and semi-arid regions there is usually a shortage of irrigation water; thus, wastewater water, as well as other low-quality water resources, may become an important source of water and nutrients. However, (pre)treated wastewater may contain elements and compounds that can damage the environment. It also has the potential to affect water quality adversely in an aquifer that may be the source of drinking water in the area. In order to assess the impacts of wastewater on the enviromnent, groundwater samples were taken and analysed in typical croplands in the North China Plain, where urban wastewater or groundwater have been used for irrigation for several decades. Concentrations of nitrate (NO3-) in groundwater in the study area varied from 50 to 130 mg 1-1 in the croplands irrigated by wastewater, but in the croplands irrigated by pumping wells, away from the Dongming Canal, NO3- concentrations are less than 35 mg 1-1. It was found that values of δ15N ranged from +5 to +13‰, and dominantly from +7 to +11‰, and the NO3- concentration in most wells with depths of less than 40 m was higher than the drinking water standard set by the WHO. Cluster analysis was used to classify the spatial distribution of nitrates resulting from the wastewater. Identification of chemical patterns is found to be effective for the comprehensive assessment of the spatial distribution of groundwater quality. It is also emphasized that the wastewater in this area controls the NO3- distribution in the groundwater, and should be used carefully to protect both soil and groundwater from NO3- pollution. © 2004 John Wiley and Sons, Ltd.

Description: Effective management of limited water resources in the North China Plain requires reliable calculation of historical groundwater balances at local, sub-watershed scales. These calculations typically are hindered by poorly constrained recharge estimates. Using a simple soil-water balance model, we independently calculated annual recharge from irrigated cropland to unconfined alluvial aquifers underlying Luancheng County, Hebei Province, in the western part of the North China Plain, for 1949-2000. Model inputs include basic soil characteristics and daily precipitation, potential evapotranspiration, irrigation, crop root depth, and leaf-area index; model outputs include daily actual evapotranspiration and areal groundwater recharge. Results indicate that areal recharge is not a constant fraction of precipitation plus irrigation, as previously assumed, but rather the fraction increases as the water inputs increase. Thus, model-calculated recharge rates range from 5 to 109 cm year-1, depending on the quantity of precipitation and irrigation applied. The important implication is that, because this drainage recharges the underlying aquifer, improving irrigation efficiency by reducing seepage does not save water. This explains why successful efforts to reduce groundwater pumping for irrigation have had no effect on water-table declines. So long as crop cover is extensive and all crop-water requirements are met-which has been the case in Luancheng County since the 1960s-groundwater levels will continue to decline at a steady rate. Potential solutions include reducing the irrigated area, reintroducing fallow periods, and shifting water from agriculture to other, less consumptive uses. © 2004 John Wiley and Sons, Ltd.

Description: The Yellow River basin of China, located in the semi-humid, semi-arid and arid climatic zones, is now confronted with serious problems of water deficit. With regard to intensified human activities and climatic change, knowledge about changes in the regional hydrological cycle should be seen as a key requirement in searching for an adaptation strategy in water resource use. This paper attempts to detect trends associated with hydrological cycle components in the region. The hydrological cycle components are derived from monthly precipitation and runoff date, based on the schemes proposed herein. Two methods, including linear regression and Mann-Kendall, have been applied to the detection of trends in the hydrological cycle components. For the Lanzhou station, only surface runoff showed a decreasing trend. As for Huayuankou station, the results have shown that natural runoff, surface runoff and groundwater runoff all have significant decreasing trends, whereas the decreasing trend of the other components is not significant. Impacts of human activities, climatic change and annual runoff coefficient change on the hydrological cycle components are also discussed. The study suggests that increasing water resources development and utilization is the most important factor in causing the frequent drying-up in the main course of the Yellow River. Moreover, the similarities of the trends in precipitation and natural runoff suggest a linkage between climatic change and hydrological cycle change. © 2004 John Wiley and Sons, Ltd.

Description: The lower reaches of the Yellow River are basically a discharge zone with a high salt content, and the study area of Yucheng in Shandong Province became arable only after the water diversion project from the Yellow River was implemented in 1972. The sustainability of agriculture in this area is examined through the redistribution of soil moisture and solutes in the vertical profile based on the measurement of soil moisture, potential and solute content in a maize field at the Yucheng Experimental Station. Diurnal moisture fluctuations appear in the surface layers at 30 and 50 cm depths, and the daily water content at 90 cm depth decreases about a month after planting, due mainly to the effect of root water extraction, even reaching a level lower than that at 70 cm depth. Soil moisture obviously increases for the three layers at 30, 50, 90 cm depth, and the relevant peak-time shifts from the surface 30 cm depth to the deep layer at 120 cm depth with a varied time lag in response to rainfall events, but there is little or no signal for the other layers due to the effects of soil properties, roots, and soil storage. The existence of a convergent zero flux plane may explain to some extent the accumulation of moisture and solutes in the layer at 120 cm. depth. Though the chemical facies along the profile from the unsaturated surface to the deep saturated zone generally evolves in a direction of decreasing SO42- and Cl-, a strong driving force upward and the accumulation of solute at 120 cm may change the redistribution pattern and three groups of this pattern were classified according to the evolution and concentration distribution profiles. The main factors affecting the moisture, solute and their distributions for the three groups are varied: rainfall, irrigation and evapotranspiration for the surface layer till 70 cm depth, root extraction for the accumulation layer of 70-120 cm depth, and the fluctuation of the groundwater table for the deep layer at 120-200 cm depth. The agriculture appears sustainable as long as diverted water from the Yellow River is available, but the high content of solute accumulation in the layer at about 120 cm depth is a potential risk. Copyright 2004 John Wiley and Sons, Ltd.

Description: The nature of intra-annual variability in the non-advective heat fluxes affecting streams and rivers in Devon, UK was investigated through detailed monitoring of study reaches in an upland moorland catchment, below a regulating reservoir, and flowing through deciduous woodland and coniferous forest during the period May 1995 to April 1996. A clear pattern of seasonal variation was evident, whereby net radiation provided a heat source during the summer but a heat sink in the winter, as incoming short-wave radiation declined and outgoing long-wave radiation increased. Sensible transfer added heat to the study reaches in the summer but removed it during the winter, and bed conduction acted as a heat sink in the summer period but as a heat source in the winter months. Friction and evaporation added and removed heat, respectively, from the study reaches throughout the year, but the magnitude of these fluxes reflected seasonal variations in discharge and in wind speed. Water temperature generally followed the net non-advective heat energy budget, which was positive in summer but negative in winter. Although a general pattern of seasonal variability in the non-advective heat energy budget was evident, detailed differences in the nature and extent of intra-annual variability were apparent between the study reaches and particularly between forested and non-forested sites. © 2004 John Wiley and Sons, Ltd.

Description: The impact of vegetated filter strips (VFS) on sediment removal from runoff has been studied extensively in recent years. Vegetation is believed to increase water infiltration and decrease water turbulence thus enhancing sediment deposition within filter media. In the study reported here, field experiments have been conducted to examine the efficiency of vegetated filter strips for sediment removal from cropland runoff. Twenty filters with varying length, slope and vegetated cover were used under simulated runoff conditions with an average sediment concentration of 2700 mg/L. The filters were 2, 5, 10 and 15 m long with a slope of 2·3 and 5% and three types of vegetation. Three other strips with bare soil were used as a control. The experimental results showed that the average sediment trapping efficiency of all filters was 84% and ranging from 68% in a 2·m filter to as high as 98% in a 15-m long filter compared with only 25% for the control. The length of filter has been found to be the predominant factor affecting sediment deposition in VFS up to 10 m. Increasing filter length to 15 m did not improve sediment trapping efficiency under the present experimental conditions. The rate of incoming flow and vegetation cover percentage has a secondary effect on sediment deposition in VFS. © 2004 John Wiley and Sons, Ltd.

Description: Motion-sensing radio transmitters were implanted in cobbles (72-92 mm diameter) and placed in a stream in southwest Idaho for 43 days during a snowmelt period. The radios transmit different pulse rates depending on whether the rocks are at rest or in motion. Every 30 s, a datalogger samples the receiver and records the pulse rate of the transmitters. Such information can be used to assess numerous properties of particle transport that are beyond the capabilities of conventional tracking methods. Conclusions include: (i) rocks are more likely to move on rising hydrograph limbs than on failing hydrograph limbs; (ii) the average Shields' parameter is 0·046; (iii) rocks move only a fraction of the time between initial and final motion during an event; (iv) the distributions of motion and rest periods are best modeled by gamma functions rather than exponential, but the distributions approach exponential as the tails are trimmed. © 2004 John Wiley and Sons, Ltd.

Description: The impact of landfill contaminated groundwater along a reach of a small stream adjacent to a municipal landfill was investigated using stable carbon isotopes as a tracer. Groundwater below the stream channel, groundwater seeping into the stream, groundwater from the stream banks and stream water were sampled and analysed for dissolved inorganic carbon (DIC) and the isotope ratio of DIC (δ13 CDIC). Representative samples of groundwater seeping into the stream were collected using a device (a 'seepage well') specifically designed for collecting samples of groundwater seeping into shallow streams with soft sediments. The DIC and δ13 CDIC of water samples ranged from 52 to 205 mg C/L and -16·9 to +5·7‰ relative to VPDB standard, respectively. Groundwater from the stream bank adjacent to the landfill and some samples of groundwater below the stream channel and seepage into the stream showed evidence of δ13 C enriched DIC (δ13 CDIC = -2·3 to +5·7‰), which we attribute to landfill impact. Stream water and groundwater from the stream bank opposite the landfill did not show evidence of landfill carbon (δ13 CDIC = -10·0 to -16·9%). A simple mixing model using DIC and δ13 CDIC showed that groundwater below the stream and groundwater seeping into the stream could be described as a mixture of groundwater with a landfill carbon signature and uncontaminated groundwater. This study suggests that the hyporheic zone at the stream-groundwater interface probably was impacted by landfill contaminated groundwater and may have significant ecological implications for this ecotone. © 2004 John Wiley and Sons, Ltd.

Description: The caesium-137 method of quantifying soil erosion is used to provide field data for validating the capability of the SHETRAN modelling system for predicting long-term (30-year) erosion rates and their spatial variability. Simulations were carried out for two arable farm sites (area 3-5 ha) in central England for which average annual erosion rates of 6·5 and 10·4 t ha-1 year-1 had already been determined using caesium-137 measurements. These rates were compared with a range of simulated values representing the uncertainty in model output derived from uncertainty in the evaluation of model parameters. A successful validation was achieved in that the simulation range contained the measured rate at both sites, whereas the spatial variability was reproduced excellently at one site and partially at the other. The results indicate that, as the caesium-137 technique measures the erosion caused by all the processes acting at a site, it is relevant to hydrologically based models such as SHETRAN only if erosion by wind, agricultural activities and other processes not represented in the model are insignificant. The results also indicate a need to reduce the uncertainty in model parameter evaluation. More generally, the caesium-137 technique is shown to provide field data that improve the severity of the validation procedure (accounting for internal as well as outlet conditions) and that add spatial variability to magnitude as a condition for identifying unrealistic parameter sets when seeking to reduce simulation uncertainty. © 2004 John Wiley and Sons, Ltd.

Description: Winter-forest processes affect global and local climates. The interception-sublimation fraction (F) of snowfall in forests is a substantial part of the winter water budget (up to 40%). Climate, weather-forecast and hydrological modellers incorporate increasingly realistic surface schemes into their models, and algorithms describing snow accumulation and snow-interception sublimation are now finding their way into these schemes. Spatially variable data for calibration and verification of wintertime dynamics therefore are needed for such modelling schemes. The value of F was determined from snow courses in open and forested areas in Hokkaido, Japan. The value of F was related to species and canopy-structure measures such as closure, sky-view fraction (SVF) and leaf-area index (LAI). Forest structure was deduced from fish-eye photographs. The value of F showed a strong linear correlation to structure: F = 0.44 - 0.6 × SVF for SVF 〈 0·72 and F = 0 for SVF 〉 0·72, and F = 0·11 LAI. These relationships seemed valid for evergreen conifers, larch trees, alder, birch and mixed deciduous stands. Forest snow accumulation (SF) could be estimated from snowfall in open fields (So) and to LAI according to SF = So - (1 - 0·11 LAI) as well as from SVF according to SF = So (0·56 + 0·6 SVF) for SVF 〈 0·72. The value of SF was equal to So for SVF values above 0·72. The value of sky-view fraction was correlated to the normalized difference snow index (NDSI) using a Landsat-TM image for observation plots exceeding 1 ha. Variables F and SF were related to NDSI for these plots according to: F = -0·37NDSI + 0·29 and SF = So (0·81 + 0·37NDSI). These relationships are somewhat hypothetical because plot-size limitation only allowed one sparse-forest observation of NDSI to be used. There is, therefore, a need to confirm these relationships with further studies. © 2004 John Wiley and Sons, Ltd.

Description: An integrated flow determination algorithm is proposed to calculate the spatial distribution of the topographic index to the channel network. The advantages of a single flow direction algorithm and other multiple flow direction schemes are selectively considered in order to address the drawbacks of existing algorithms. A spatially varying flow apportioning factor is introduced to distribute the contributing area from upslope cells to downslope cells. The channel initiation threshold concept is expanded and integrated into a spatially distributed flow apportioning algorithm to delineate a realistic channel network. The functional relationships between the flow apportioning factors and the expanded channel initiation threshold (ECIT) are developed to address the spatially varied flow distribution patterns considering the permanent channel locations. A genetic algorithm (GA) is integrated into the spatially distributed flow apportioning algorithm (SDFAA) with the objective function of river cell evaluation. An application of a field example suggests that the spatially distributed flow apportioning scheme provides several advantages over the existing approaches; the advantages include the relaxation of overdissipation problems near channel cells, the connectivity feature of river cells and the robustness of the parameter determination procedure over existing algorithms. © 2004 John Wiley and Sons, Ltd.

Description: An adequately tested soil and water assessment tool (SWAT) model was applied to the runoff and sediment yield of a small agricultural watershed in eastern India using generated rainfall. The capability of the model for generating rainfall was evaluated for a period of 18 years (1981-1998). The watershed and subwatershed boundaries, drainage networks, slope, soil series and texture maps were generated using a geographical information system (GIS). A supervised classification method was used for land-use/cover classification from satellite imageries. Model simulated monthly rainfall for the period of 18 years was compared with observations. Simulated monthly rainfall, runoff and sediment yield values for the monsoon season of 8 years (1991-1998) were also compared with their observed values. In general monthly average rainfall predicted by the model was in close agreement with the observed monthly average values. Also, simulated monthly average values of surface runoff and sediment yield using generated rainfall compared well with observed values during the monsoon season of the years 1991-1998. Results of this study revealed that the SWAT model can generate monthly average rainfall satisfactorily and thereby can produce monthly average values of surface runoff and sediment yield close to the observed values. Therefore, it can be concluded that the SWAT model could be used for developing a multiple year management plan for the critical erosion prone areas of a small watershed. © 2004 John Wiley and Sons, Ltd.

Description: The temporal and spatial continuity of spatially distributed estimates of snow-covered area (SCA) are limited by the availability of cloud-free satellite imagery; this also affects spatial estimates of snow water equivalent (SWE), as SCA can be used to define the extent of snow telemetry (SNOTEL) point SWE interpolation. In order to extend the continuity of these estimates in time and space to areas beneath the cloud cover, gridded temperature data were used to define the spatial domain of SWE interpolation in the Salt-Verde watershed of Arizona. Gridded positive accumulated degree-days (ADD) and binary SCA (derived from the Advanced Very High Resolution Radiometer (AVHRR)) were used to define a threshold ADD to define the area of snow cover. The optimized threshold ADD increased during snow accumulation periods, reaching a peak at maximum snow extent. The threshold then decreased dramatically during the first time period after peak snow extent owing to the low amount of energy required to melt the thin snow cover at lower elevations. The area having snow cover at this later time was then used to define the area for which SWE interpolation was done. The area simulated to have snow was compared with observed SCA from AVHRR to assess the simulated snow map accuracy. During periods without precipitation, the average commission and omission errors of the optimal technique were 7% and 11% respectively, with a map accuracy of 82%. Average map accuracy decreased to 75% during storm periods, with commission and omission errors equal to 11% and 12% respectively. The analysis shows that temperature data can be used to help estimate the snow extent beneath clouds and therefore improve the spatial and temporal continuity of SCA and SWE products. © 2004 John Wiley and Sons, Ltd.

Description: Effects of the catchment runoff coefficient on the performance of TOPMODEL in simulating catchment rainfall-runoff relationships are investigated in this paper, with an aim to improve TOPMODEL's simulation efficiency in catchments with a low runoff coefficient. Application of TOPMODEL in the semi-arid Yihe catchment, with an area of 2623 km2 in the Yellow River basin of China, produced a Nash-Sutcliffe model efficiency of about 80%. To investigate how the catchment runoff coefficient affects the performance of TOPMODEL, the whole observed discharge series of the Yihe catchment is multiplied with a larger-than-unity scale factor to obtain an amplified discharge series. Then TOPMODEL is used to simulate the amplified discharge series given the original rainfall and evaporation data. For a set of different scale factors, TOPMODEL efficiency is plotted against the corresponding catchment runoff coefficient and it is found that the efficiency of TOPMODEL increases with the increasing catchment runoff coefficient before reaching a peak (e.g. about 90%); after the peak, however, the efficiency of TOPMODEL decreases with the increasing catchment runoff coefficient. Based on this finding, an approach called the discharge amplification method is proposed to enhance the simulation efficiency of TOPMODEL in rainfall-runoff modelling in catchments with a low runoff coefficient. © 2004 John Wiley and Sons, Ltd.

Description: By applying the technique of conformal transformation of the metric, widely used in general relativity and cosmology, the analysis of groundwater flow in an anisotropic aquifer (in which the hydraulic conductivity is a tensor) is reduced to the case of an isotropic one. This reduction is achieved for a particular conformal factor of the transformation. Examples of application of this technique are given. © 2004 John Wiley and Sons, Ltd.

Description: Two-component hydrograph separations were performed for three, nested, snowmelt-dominated catchments in Sequoia National Park. The purpose of the hydrograph separations was to: (i) differentiate between the old and new water contributions to discharge during snowmelt using δ18O signatures; (ii) identify the fraction of snowmelt that travelled through the subsurface (reactive) compartment during the snowmelt period using silica or sodium; and (iii) investigate the impact of changing end-member signatures on the separations. 'Old' water refers to water that was stored in the watershed during the previous year, whereas 'new' water is current snowmelt. Hydrograph separations were performed for both a high-accumulation (1998, annual precipitation 2·4 m) and an average year (1999, 1·3 m). The proportion of old water contribution to discharge during the rising limb of the hydrograph was 10-20%, with 80-100% of snowmelt being reactive, i.e. passing through soil and talus. Estimates of old and new soil water and direct snowmelt entering the stream varied among the catchments in 1999. Differences between these components were minimal in 1998, regardless of varying topography and differing proportions of soil, rock and talus. Using time-dependent rather than constant δ18O meltwater and silica soil-water signatures made a meaningful impact on both new and old water, and reactive and unreactive, estimates. © 2004 John Wiley and Sons, Ltd.

Description: Discharge, especially during flood periods, is among the most important information necessary for flood control, water resources planning and management. Owing to the high flood velocities, flood discharge usually cannot be measured efficiently by conventional methods, which explains why records of flood discharge are scarce or do not exist for the watersheds in Taiwan. A fast method of flood discharge estimation is presented. The greatest advantage of the proposed method is its application to estimate flood discharge that cannot be measured by conventional methods. It has as its basis the regularity of open-channel flows, i.e. that nature maintains a constant ratio of mean to maximum velocities at a given channel section by adjusting the velocity distribution and the channel geometry. The maximum velocity at a given section can be determined easily over a single vertical profile, which tends to remain invariant with time and discharge, and can be converted to the mean velocity of the entire cross-section by multying by the constant ratio. Therefore the mean velocity is a common multiple of maximum velocity and the mean/maximum velocity ratio. The channel cross-sectional area can be determined from the gauge height, the water depth at the y-axis or the product of the channel width multiplied by the water depth at the y-axis. Then the most commonly used method, i.e. the velocity-area method, which determines discharge as the product of the cross-sectional area multiplied by mean velocity, is applied to estimate the flood discharge. Only a few velocity measurements on the y-axis are necessary to estimate flood discharge. Moreover the location of the y-axis will not vary with time and water stage. Once the relationship of mean and maximum velocities is established, the flood estimation can be determined efficiently. This method avoids exposure to hazardous environments and sharply reduces the measurement time and cost. The method can be applied in both high and low flows in rivers. Available laboratory flume and stream-flow data are used to illustrate accuracy and reliability, and results show that this method can quickly and accurately estimate flood discharges. © 2004 John Wiley and Sons, Ltd.

Description: It is common for runoff and erosion models to be run at coarse time steps (e.g. daily) owing to limited data availability. However, such models are unable to capture adequately the small-scale surface runoff and erosion processes that are dominated by, for example, precipitation characteristics at time-scales of minutes. This dilemma calls for the development of approaches that appropriately capture short time-scale processes when running the models at daily scales. In this paper, we assess two scaling approaches that are simple and are intended to preserve prediction quality as time scales become coarser: (i) use of effective rates of precipitation and runoff, and (ii) use of a rainfall disaggregation scheme. Runoff and erosion are simulated using a six-parameter surface runoff model and a one-parameter erosion model. A downhill simplex optimization algorithm is applied for parameterization at 2 min and daily time steps, using measured 2 min and daily precipitation data respectively, against measured daily runoff and erosion. The 2 min simulation results are aggregated to daily values to make comparisons with the measured plot-scale daily runoff and erosion data for 2 years (1997-98) from six sites in the Jhikhu Khola catchment in Nepal. The runoff and erosion simulation results calibrated from the 2 min precipitation data are good (E = 0.92 for runoff and 0.80 for erosion, all sites collectively), whereas other results, particularly the erosion simulation from the calibrated daily model, are very poor. These results are taken as the reference to compare with the two different scaling approaches. The effective rate approach is poor compared with the 2 min estimates but is a considerable improvement over daily erosion estimates. The rainfall disaggregation scheme is comparable to the 2 min estimates and produces better results than the effective rate approach. This study illustrates that rainfall scaling has significant scope for temporal scaling of hydrologic processes, particularly where continuous simulation is preferred. © 2004 John Wiley and Sons, Ltd.

Description: Snow cover from a 3 year (1992/93-1994/95) simulation of the Canadian Regional Climate Model (CRCM; operational version 3·5·3) driven by National Centers for Environmental Prediction analysis data over eastern Canada was evaluated using passive-microwave-derived snow cover information from the daily Special Sensor Microwave/Imager (SSM/I) data. The presence of snow on the ground was derived from 19 and 37 GHz normalized difference brightness temperature series to which a low-pass filter was applied to remove day-to-day noise, and thresholding was also applied at different levels for taking into account the variation in vegetation density. The thresholds calibrated for four density classes with surface observations show a mean residual underestimation in the SSM/I number of days with snow cover during seasonal transition of -7 days. Compared with the SSM/I-derived information, the CRCM was found to delay systematically the onset of the snow cover (typically 50 days late) and to ablate snow too quickly during the spring melt period (typically 30 days early). These systematic errors were attributed to the single-layer force-restore representation of the soil-snow layer and contributed to snow cover extent underestimations in the order of 9% relative to the total area. © 2004 John Wiley and Sons, Ltd.

Description: Statistical downscaling techniques have been developed to address the spatial scale disparity between the horizontal computational grids of general circulation models (GCMs), typically 300-500 km, and point-scale meteorological observations. This has been driven, predominantly, by the need to determine how enhanced greenhouse projections of future climate may impact at regional and local scales. As point-scale precipitation is a common input to hydrological models, there is a need for techniques that reproduce the characteristics of multi-site, daily gauge precipitation. This paper investigates the ability of the extended nonhomogeneous hidden Markov model (extended-NHMM) to reproduce observed interannual and interdecadal precipitation variability when driven by observed and modelled atmospheric fields. Previous studies have shown that the extended-NHMM can successfully reproduce the at-site and intersite statistics of daily gauge precipitation, such as the frequency characteristics of wet days, dry- and wet-spell length distributions, amount distributions, and intersite correlations in occurrence and amounts. Here, the extended-NHMM, as fitted to 1978-92 observed 'winter' (May-October) daily precipitation and atmospheric data for 30 rain gauge sites in southwest Western Australia, is driven by atmospheric predictor sets extracted from National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis data for 1958-98 and an atmospheric GCM hindcast run forced by observed 1955-91 sea-surface temperatures (SSTs). Downscaling from the reanalysis-derived predictors reproduces the 1958-98 interannual and interdecadal variability of winter precipitation. Downscaling from the SST-forced GCM hindcast only reproduces the precipitation probabilities of the recent 1978-91 period, with poor performance for earlier periods attributed to inadequacies in the forcing SST data. © 2004 John Wiley and Sons, Ltd.

Description: Presenting a critical review of daily flow simulation models based on the Soil Conservation Service curve number (SCS-CN). this paper introduces a more versatile model based on the modified SCS-CN method, which specializes into seven cases. The proposed model was applied to the Hemavati watershed (area = 600 km 2 ) in India and was found to yield satisfactory results in both calibration and validation. The model conserved monthly and annual runoff volumes satisfactorily. A sensitivity analysis of the model parameters was performed. including the effect of variation in storm duration. Finally, to investigate the model components, all seven variants of the modified version were tested for their suitability. © 2004 John Wiley and Sons, Ltd.

Description: This work evaluated the spatial variability and distribution of heterogeneous hydraulic conductivity (K) in the Choushui River alluvial fan in Taiwan, using ordinary kriging (OK) and mean and individual sequential Gaussian simulations (SGS). A baseline flow model constructed by upscaling parameters was inversely calibrated to determine the pumping and recharge rates. Simulated heads using different K realizations were then compared Willi historically measured heads. A global/local simulated error between simulated and measured heads was analysed to assess the different spatial variabilities of various estimated K distributions. The results of a MODFLOW simulation indicate that the OK realization had the smallest sum of absolute mean simulation errors (SAMSE) and the SGS realizations preserved the spatial variability of the measured K fields. Moreover, the SAMSE increases as the spatial variability of the K field increases. The OK realization yields small local simulation errors in the measured K field of moderate magnitude, whereas the SGS realizations have small local simulation errors in the measured K fields, with high and low values. The OK realization of K can be applied to perform a deterministic inverse calibration. The mean SGS method is suggested for constructing a K field when the application focuses on extreme values of estimated parameters and small calibration errors, such as in a simulation of contaminant transport in heterogeneous aquifers. The individual SGS realization is useful in stochastically assessing the spatial uncertainty of highly heterogeneous aquifers. © 2004 John Wiley and Sons, Ltd.

Description: The layered structure of a snowpack has a great effect on several important physical processes, such as water movement, reflection of solar radiation or avalanche release. Our aim was to investigate what factors are most important with respect to the formation and persistence of distinct layers in a subalpine environment, We used a physically based numerical one-dimensional model to simulate the development of a snowpack on a subalpine meadow in central Switzerland during one winter season (1998-99). A thorough model validation was based on extensive measurement data including meteorological and snow physical parameters. The model simulated the snow water equivalent and the depth of the snowpack as well as the energy balance accurately. The observed strong layering of the snowpack, however, was not reproduced satisfactorily. In a sensitivity analysis, we tested different model options and parameter settings significant for the formation of snow layers. The neglection of effects of snow microstructure on the compaction rate, and the current description of the water redistribution inside the snowpack, which disregard capillary barrier effects, preferential flow and lateral water flow, were the major limitations for a more realistic simulation of the snowpack layering. Copyright © 2004 John Wiley and Sons. Ltd.

Description: Nitrate concentrations in streamwater of agricultural catchments often exhibit interannual variations, which are supposed to result from land-use changes, as well as seasonal variations mainly explained by the effect of hydrological and biogeochemical cycles. In catchments on impervious bedrock, seasonal variations of nitrate concentrations in streamwater are usually characterized by higher nitrate concentrations in winter than in summer. However, intermediate or inverse cycles with higher concentrations in summer are sometimes observed. An experimental study was carried out to assess the mechanisms that determine the seasonal cycles of streamwater nitrate concentrations in intensive agricultural catchments. Temporal and spatial patterns of groundwater concentrations were investigated in two adjacent catchments located in south-western Brittany (France), characterized by different seasonal variations of streamwater nitrate concentrations. Wells were drilled across the hillslope at depths ranging from 1.5 to 20 m. Dynamics of the water table were monitored and the groundwater nitrate and chloride concentrations were measured weekly over 2 years. Results highlighted that groundwater was partitioned into downslope domains, where denitrification induced lower nitrate concentrations than into mid-slope and upslope domains. For one catchment, high subsurface flow with high nitrate concentrations during high water periods and active denitrification during low water periods explained the higher streamwater nitrate concentrations in winter than in summer. For the other catchment, the high contribution of groundwater with high nitrate concentrations smoothed or inverted this trend. Increasing bromide/chloride ratio and nitrate concentrations with depth argued for an effect of past agricultural pressure on this catchment. The relative contribution of flows in time and correlatively the spatial origin of waters, function of the depth and the location on the hillslope, and their chemical characteristics control seasonal cycles of streamwater nitrate concentrations and can influence their interannual trends. © 2004 John Wiley and Sons, Ltd.

Description: The hydraulic conductivity (K) of many low permeability materials is strongly scale-dependent. In raised mires and other types of peat deposit the effects of features such as abandoned infilled ditches, root holes and localized woody material, cause K to be heterogeneous and scale-dependent. Despite this, field measurements are routinely made using auger hole (slug) tests at the scale of only a few tens of centimetres. Such measurements are locally valid, but where the regional subsurface movement of water through peat bogs is simulated using groundwater models, typically at the scale of hundreds of metres, they give rise to a systematic underestimate of flows and an overprediction of water table elevations. Until now, techniques to obtain values at a scale sufficiently large to include the effects of localized features of higher permeability have not been applied routinely. Research at Thorne Moor, a large raised mire, demonstrates that the K of peat varies over several orders of magnitude when measured at different scales, using a variety of techniques. Laboratory and auger hole tests cannot be relied upon to provide results that represent the hydraulic conductivity of large expanses of peatland. This has significant implications for the management and long-term restoration of peatlands where both regional and local control of water levels is crucial. For groundwater models to be used successfully to plan such schemes, it is essential to apply the K values relevant to the scale of the simulation. This paper describes and tests novel techniques, using ditches, for the derivation of K at large scales which overcome many of the problems that have been identified with conventional techniques and are capable of producing estimates that are appropriate to the application of physically based regional flow models. © 2004 John Wiley and Sons, Ltd.

Description: This paper examines several issues related to hydrological boundaries and their border zones. In a two-dimensional space, a boundary is a line that separates two domains possessing different hydrological properties or dominated by different hydrological processes, and a border is an area that experiences an edge effect owing to transitions or mixing of processes. Hydrological boundaries may be static, such as drainage divides, or dynamic, such as the edges of a seasonal snow cover. They may be open or closed to the transfer of matter and energy, although most boundaries tend to be perforated, permitting different rates of movement across different segments. Borders may be narrow or the edge effect can affect large areas, as happens to the sensible heat flux over a highly fragmented melting snowfield. The introduction of artificial boundaries, notably the grid patterns of remote sensing pixels, digital elevation models and land surface schemes, gives rise to problems of mismatch with the natural hydrological boundaries. Incorrect demarcation, omission and generalization of boundaries can produce errors that are hard to rectify. Serious biases are involved when point observations are used to calibrate parameters or to validate model outputs integrated over a bounded area. Examples are drawn mainly from cold climate hydrology to illustrate the boundary issues but the questions transcend disciplinary areas. The intent of this presentation is to stimulate discussions that could be a prelude to finding solutions to many boundary problems which have thus far eluded hydrological investigations. © 2004 John Wiley and Sons, Ltd.

Description: The effects of small water bodies or lakes on the surface sensible and latent heat fluxes and the transport of heat and water vapour in the atmospheric boundary layer (ABL) over the Mackenzie River Basin (MRB) are studied from two cases, which occurred on 2 and 8 June 1999 during the warm season. The synoptic condition for the cases is representative of about 33% of the synoptic situation over the MRB. The two events are simulated using the Canadian mesoscale compressible community (MC2) model. A one-way nesting grid approach is employed with the highest resolution of 100 m over a domain of 100 km2. Experiments were conducted with (LAKE) and without (NOLAKE) the presence of small water bodies, whose size distribution is obtained through an inversion algorithm using information of their linear dimension determined from aircraft measurement of surface temperature during MAGS (the Mackenzie GEWEX (Global Energy and Water Cycle Experiment) Study) in 1999. The water bodies are assumed to be distributed randomly in space with a fractional area coverage of 10% over the MRB. The results show that, in the presence of lakes, the domain-averaged surface sensible heat flux on 2 June 1999 (8 June 1999) decreases by 9·3% (6·6%). The surface latent heat flux is enhanced by 18·2% (81·5%). Low-level temperature advection and the lake surface temperature affect the air-land/lake temperature contrast, which in turn controls the sensible heat flux. In the absence of lakes the surface wind speed impacts the latent heat flux, but in the presence of lakes the moisture availability and the atmospheric surface layer stability control the latent heat flux. The enhancement is smaller on 2 June 1999 as a result of a stable surface layer caused by the presence of colder lake temperatures. The domain-averaged apparent heat source and moisture sink due to turbulent transports were also computed. The results show that, when lakes are present, heating and drying occur in the lowest 100 m from the surface. Above 100 m and within the ABL, there was apparent cooling. However, the apparent moistening profiles reveal that lakes tend to moisten the ABL through transfer of moisture from the lowest 50-100 m layer. © 2004 John Wiley and Sons, Ltd.

Description: This paper reports results from field experiments and hydrological modelling on the dynamics of runoff generation in highly convergent parts of the landscape in a logged and burnt eucalypt forest in south-eastern Victoria, Australia. Large-scale rainfall simulation experiments were conducted to explore runoff generating mechanisms from harvested areas, and to assess the effectiveness of standard water quality protective measures, here a disturbed filter strip, in preventing accession of sediment to near-stream areas. We then examined the likely effects of varying antecedent moisture conditions on surface and subsurface runoff generating mechanisms. Very small volumes of surface runoff were generated only at very high rainfall intensity rates that exceeded a 100 year recurrence interval event during the simulated experiments. There was little or no identifiable impact of either compaction from logging operations or fire-induced hydrophobicity on surface infiltration or generation of surface runoff. Measured soil hydraulic properties and soil depths explained the paucity of surface runoff, and the dominance of subsurface storm flow as the prime runoff generating mechanism. Deep lateral subsurface flow was observed from the cut-face of a fire access track and into a streamhead downslope of the experimental plots. Water balance modelling using Topognamic indicated the conditions under which saturated overland flow in this environment could be generated are rare, but that care should be taken in siting of roads and tracks in lower parts of convergent landscapes. © 2004 John Wiley and Sons. Ltd.

Description: Lateral subsurface flow is generally assumed to occur as a result of the development of a saturated zone above a low-permeability interface such as at the soil-bedrock contact, and it is often augmented by macropore flow. Our objective was to evaluate the development of lateral subsurface flow and soil saturation at a semiarid ponderosa pine forest in New Mexico with respect to the conceptual model of saturation building above the soil-bedrock contact. At this site, we have long-term observations of the water budget components, including lateral flow. A 1·5 m deep by 7 m long trench was constructed to observe lateral subsurface flow and development of saturation directly. Our observations are based on flow resulting from a melting snowdrift. The edge of the drift was about 7 m upslope from the trench. Lateral subsurface flow only occurred from root macropores in the Bt soil horizon. Saturation developed and grew outward from flowing root macropores, rather than growing upward from the soil-bedrock interface. This macropore-centred saturation resulted in a highly heterogeneous distribution of water content until enough macropores began flowing and individual macropore saturated zones grew large enough to coalesce and saturate large volumes of the soil. Our observations are based on one snowmelt event and a relatively short hillslope flow path, and thus do not represent a full range of hydrologic conditions. Nevertheless, the observed behaviour did not conform to the traditional model of soil-bedrock control of saturation and lateral flow. © 2004 John Wiley and Sons, Ltd.

Description: In 1998 a wild fire struck a paired catchment research area under long-term monitoring of hydrological and nutrient budgets. Streamwater quality as concentrations of dissolved and suspended particulate matter was monitored during 1.5-2.5 years after the fire in streams from seven different catchments. As the catchments, due to earlier experimental treatments, had different vegetations, varying effects related to different fire intensities were observed. The highest, mean stormflow, suspended sediment concentrations resulted from intensive fire in secondary vegetation that had experienced severe soil disturbance in previous treatments (crawler tractor timber extraction 10 years earlier). Stormflow concentrations were typically still about 400 mg 1-1 in 1999 (10-21 months after the fire), which was about the maximum recorded concentration in streams during initial soil disturbance in 1988. Forest fire in natural forest resulted in less than half as high stormflow concentrations. For dissolved elements in streamwater there was a positive relation between fuel load (and fire intensity) and concentration and longevity of effects. Stream baseflow dissolved nutrient concentrations were high in the months following the fire. Mean baseflow K concentrations were 8-15 mg 1-1 in streams draining catchments with intensive fire in secondary vegetation with large amounts of fuel. After controlled fire for forest plantation establishment in 1988 corresponding concentrations were 3-5 ing 1-1, and after forest fire in natural forest in this study about 2 mg 1-1. This study shows differences in response from controlled fire for land management, forest fire in natural forests and wild fires in manmade vegetations. These differences relate to resistance and resilience to fire for the involved ecosystems. There is reason to believe that wild fires and repeated wild fires during or after droughts, in successions caused by human influence, may lead to larger losses of ecosystem nutrient capital from sites compared with forest fires in natural forests. As fire in the humid tropics becomes more common, in an increasingly spatially fragmented landscape, it will be important to be aware of these differences. © 2004 John Wiley and Sons, Ltd.

Description: A chain of connected macropores, which develops nearly parallel to the impermeable subsurface layer, is commonly found in hillslopes and referred to as a soil pipe. Field observations have revealed that water flow in such a pipe (pipe flow) has large hydrogeomorphic effects, since it contributes to rapid transfer of storm water and subsurface soil erosion. This study proposed a simple simulation method to describe water dynamics in a piped hillslope. The applicability of the method was examined using data obtained from a bench-scale experiment using pseudo soil pipes. Results of the experiment showed that (1) the flume-bed pore water pressure became small around the upper ends of the pipes; (2) when pipe outlets were connected to a stream channel (the open pipe condition), the flume-bed pore water pressures in the whole slope were much lower than those under the 'no pipe' condition; (3) when pipe outlets were not connected to a stream channel (the closed pipe condition), the flume-bed pore water pressure at the pipe outlets was higher than that under the 'no pipe' condition. These results were reproduced by solving the two-dimensional Richards equation assuming an equivalent soil matrix layer for the original 'pipes plus soil matrix' part, which had a larger saturated hydraulic conductivity than the surrounding soil matrix. This simple simulation method has an advantage over previous pipe flow models: both the pipe flow and the interaction between the soil pipes and the surrounding soil matrix can be computed by solving the Richards equation without using any further assumptions for the boundary conditions between the soil pipes and the soil matrix. Results of numerical experiments using the simple method showed that (1) under the closed pipe condition, the flume-bed pore water pressure at the pipe outlets increased as the pipe length increased, and (2) once the open pipes clogged, flume-bed pore water pressures in the whole slope increased, and the greatest increase occurred at the boundary between the clogging and non-clogging parts. © 2004 John Wiley and Sons, Ltd.

Description: Hydrological monitoring was conducted in high-relief watersheds in the Japan Alps to investigate the relationship between hillslope hydrological processes and landform evolution in steep granite and shale mountains. In the Koshibu watershed, underlain by Mesozoic shale, the drainage density and frequency was significantly lower than in the Yotagiri watershed underlain by granite. Drainage micro-morphology analysis showed that hillslopes in the watersheds K1 and K6 (Koshibu basin) are mostly combinations of talus and bedrock exposures. In contrast, watershed Y1 (Yotagiri basin) is composed of several zero-order streams with hollows. Infinite slope stability analysis indicates that the regolith shear strength in the K6 watershed (Koshibu basin) is lower than that of the Y1 hillslope, but groundwater levels were higher in the Y1 hillslope than in the K6 hillslope during storm events. These data suggest that, although the shear strength of the soil is stronger in the Yotagiri watershed, the slopes are unstable because of the groundwater conditions, whereas deep-seated landslides may occur episodically in the Koshibu watershed associated with extreme stroms and very high antecedent soil moisture. These differences would strongly contribute to the different observed hillslope processes and drainage characteristics. © 2004 John Wiley and Sons, Ltd.

Description: Suspended solids (SS) discharge from a tropical rain forest was observed at the Bukit Tarek Experimental Watershed in Peninsular Malaysia in order to elucidate mechanisms of SS production and transport. Peaks of water discharge and electrical conductivity (EC)lagged further behind rainfall peaks than did dissolved oxygen (DO), indicating that the discharge in the early stage of a storm is mainly formed by rain water with high DO. Stream water showing a high value of EC originating from subsurface water formed the main storm flow and lagged behind the rainfall. SS concentrations rose to a peak quickly and, like DO, the peak preceded that of water discharge. A clockwise hysteresis loop in the relationship between SS and water discharge exists, and the magnitude of hysteresis loop is in proportion to storm size. The values of SS concentration correlate positively with the values of rainfall intensity on logarithmic axes. The time intervals between peaks of rainfall and SS concentrations are assumed to be a delivery term expressing distance from sediment source to measuring point. Immediate transport of SS from the source to the sampling site, the short time gap between the peaks of rainfall and SS concentrations, and the high rate of infiltration on the hillslope suggest that the sources of high SS concentrations are located close to the stream. The calculated source area is located at a gentler part of the stream, where wet riparian areas exist. The strong relationship between water discharge and SS concentration during the small storm proves that the source areas of SS and water were the same. In contrast, the source area of SS disappeared when rainfall ceased, whereas the source area of water discharge was still expanding in the larger storm. These phenomena may produce clockwise loops in the SS concentration-water discharge relationship. © 2004 John Wiley and Sons, Ltd.

Description: Landslides are natural processes triggered by complex relationships between many conditioning factors. In Rio de Janeiro city, intense rainstorms combined with steep slopes, usually occupied by slums, create favourable conditions for landslide generation. In general, slope failures are related to high positive pore-pressures inside soil mantles, which are associated with topographic hollows and hydraulic discontinuities inside the deep weathered profile. This study aims to characterize the role played by spatial variations in saturated soil hydraulic conductivity Ksat on landsliding in the Papagaio Basin (2.5 km2), triggered by intense rainstorms (250 mm in less than 2 days) in February 1996. Field measurements, using the Guelph permeameter, were conducted along soil profiles (up to 5.0 m depth), around and inside landslide scars representing different geomorphological domains. Also, soil physical properties (grain size, total porosity, macroporosity, microporosity, etc.) were evaluated at the 87 sites where Ksat was measured. Despite the many geological and pedological variations inside the basin, including changes in lithology, fracture density, vegetation type and succession stage, soil characteristics and weathering stage, and human activities, 94% of the Ksat values varied by only two orders of magnitude (1.0 x 10-6-9.0 x 10-5 m s-1). However, abrupt changes in Ksat were observed along some of the soil profiles studied, e.g. an increase of two orders of magnitude in only 0.30 m. These hydraulic discontinuities may contribute locally to the development of high pore pressures during intense rainstorms, leading to landsliding. The results also suggest that different Ksat variation patterns coexist inside the basin, which should be considered in mathematical models of landslide prediction. © 2004 John Wiley and Sons, Ltd.

Description: A comparison between commonly used techniques for hydrograph recession analysis, namely the semi-logarithmic plot of a single recession segment, the master recession and a relatively new approach based on wavelet transform was carried out. These methods were applied to a number of flood hydrograph events of two catchments in West Java, Indonesia. The results show that all the methods tested produce reasonable and comparable results. However, problems arise in the semi-logarithmic plot and the master recession, i.e. determining the recession parameter K is not an easy task especially where the plotted data on a semi-logarithmic plot is not a linear but a curved line. On a curved line, the end of direct flow or starting point of baseflow is not clear and it is quite difficult to identify. Hence, the best line as a basis for computing the recession parameter K becomes uncertain. The wavelet transform approach, however, produces promising results and minimizes a number of problems associated with hydrograph recession analysis. The end of direct flow and the location of the baseflow component are easily determined through the wavelet maps. © 2004 John Wiley and Sons, Ltd.

Description: A physically based distributed slope stability model is described that utilizes a combined surface-subsurface kinematic wave module to assess groundwater fluctuations related to slope stability. A total of 82 major rainstorms from 1972 to 1990 in Carnation Creek, British Columbia, were examined to determine the influence of different characteristics of rainstorms (such as mean and maximum hourly intensity, duration, and rainfall amount) on the slope stability. These rainstorms vary in mean intensity from 16 to 112 mm h-1, storm duration from 11 to 93 h, and maximum hourly intensity from 34 to 35 mm h-1. Four synthetic 'uniform intensity' rainstorms were also tested against real storms to assess the effect of short-term hourly rainfall intensity peaks on landslide occurrence. Altogether, 602 simulations were conducted. The combined influence of mean and maximum hourly intensity, duration, and total rainfall amount of rainstorms were important in generating landslides. The temporal distribution of short-term intensity also influenced the landslide occurrence. When saturated hydraulic conductivity of the soil was lowered or soil depth was raised, most rainstorms produced larger numbers of landslides. For the most part, actual rainstorms produced less stable conditions than their synthetic 'uniform intensity' counterparts. For all landslide-producing storms, slope failure usually occurred after some threshold of cumulative rainfall and maximum hourly rainfall intensity. These simulations provide insights into the distributed behaviour of landslide occurrence during large rainstorms with varying characteristics. Copyright © 2004 John Wiley and Sons, Ltd.

Description: Runoff and sediment transport were observed in two mountainous watersheds with different lithologies. One watershed is underlain by chert and the other by sandstone and shale. The chert watershed consists of bedrock cliffs and shallow regolith (0-2 m), whereas the sandstone-shale watershed is covered with a deeper regolith (1-5 m). In the sandstone-shale watershed, a large spring located in the channel head contributed to storm runoff. Tensiometric response in regolith above the spring showed negative pressure head throughout storm runoff, thus implying that the subsurface flow in bedrock predominated even during storm runoff. In the chert watershed, the runoff coefficient was larger than in the sandstone-shale watershed. Tensiometric response in regolith showed positive pressure head during storm runoff, indicating generation of rapid subsurface stormflow. Concentration of subsurface flow from side slopes increased peak streamflow in the downstream direction. In these two watersheds, different subsurface flowpaths, including bedrock fractures, facilitated different modes of sediment transport. Groundwater outflow at the spring caused seepage erosion in the sandstone-shale watershed, whereas peak streamflow transported bedload supplied by rockfall in the chert watershed. © 2004 John Wiley and Sons, Ltd.

Description: A novel method of visualizing and understanding the internal functional behaviour of an artificial neural network (ANN) river flow model is presented. The method hypothesizes that an ANN is able to map a function similar to the flow duration curve while modelling the river flow. A mathematical analysis of the hypothesis is presented, and a case study of an ANN river flow model confirms its significance. The proposed approach is also useful within other models that improve the performance of an ANN. The reasons why these models improve a raw ANN can be clearly understood using this approach. While the field of ANN knowledge-extraction is one that continues to attract considerable interest, it is anticipated that the current approach will initiate further research and make ANNs more useful to the hydrologic community. © 2004 John Wiley and Sons, Ltd.

Description: Multivariate statistical analysis was used to explore relationships between catchment topography and spatial variability in snow accumulation and melt processes in a small headwater catchment in the Spanish Pyrenees. Manual surveys of snow depth and density provided information on the spatial distribution of snow water equivalent (SWE) and its depletion over the course of the 1997 and 1998 melt seasons. A number of indices expressing the topographic control on snow processes were extracted from a detailed digital elevation model of the catchment. Bivariate screening was used to assess the relative importance of these topographic indices in controlling snow accumulation at the start of the melt season, average melt rates and the timing of snow disappearance. This suggested that topographic controls on the redistribution of snow by wind are the most important influence on snow distribution at the start of the melt season. Furthermore, it appeared that spatial patterns of snow disappearance were largely determined by the distribution of snow water equivalent (SWE) at the start of the melt season, rather than by spatial variability in melt rates during the melt season. Binary regression trre models relating snow depth and disappearance date to terrain indices were then constructed. These explained 70-80% of the variance in the observed data. As well as providing insights into the influence of topography on snow processes, it is suggested that the techniques presented herein could be used in the parameterization of distributed snowmelt models, or in the design of efficient stratified snow surveys. © 2003 John Wiley and Sons, Ltd.

Description: This paper describes the preliminary development of a network-index approach to modify and to extend the classic TOPMODEL. Application of the basic Beven and Kirkby form of TOPMODEL to high-resolution (2·0 m) laser altimetric data (based upon the UK Environment Agency's light detection and ranging (LIDAR) system) to a 13·8 km2 catchment in an upland environment identified many saturated areas that remained unconnected from the drainage network even during an extreme flood event. This is shown to be a particular problem with using high-resolution topographic data, especially over large appreciable areas. To deal with the hydrological consequences of disconnected areas, we present a simple network index modification in which saturated areas are only considered to contribute when the topographic index indicates continuous saturation through the length of a flow path to the point where the path becomes a stream. This is combined with an enhanced method for dealing with the problem of pits and hollows, which is shown to become more acute with higher resolution topographic data. The paper concludes by noting the implications of the research as presented for both methodological and substantive research that is currently under way. © 2004 John Wiley and Sons, Ltd.

Description: Stable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice-sheet, West Greenland. The samples were collected at frequent intervals during the period 20-28 July 2000 in a small (〈20 L s-1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ18O is related to the composition of oxygen isotope provenances, mainly near-marginal local superimposed ice and basal up-sheared ice further up-glacier; (ii) a relationship is seen between all base cations (Na+, K-, Ca2+, Mg2+), SO42- and δ18O, indicating that solute acquisition is provided by solid-solution contact with the up-sheared ice-as the relationship with Cl- is weak the influence of seasalt-derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ18O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ18O-a short residence time leads to a delayed decrease in ion concentrations. © 2003 John Wiley and Sons, Ltd.

Description: A theory of pressure sensor response in snow is derived and used to examine the sources of measurement errors in snow water equivalent (SWE) pressure sensors. Measurement errors in SWE are caused by differences in the compressibility of the pressure sensor and the adjacent snow layer, which produces a shear stress along the perimeter of the sensor. When the temperature at the base of the snow cover equals 0 °C, differences in the snowmelt rate between the snow-SWE sensor interface and the adjacent snow-soil interface may also produce a shear stress along the sensor's perimeter. This shear stress perturbs the pressure field over the sensor, producing SWE measurement errors. Snow creep acts to reduce shear stresses along the SWE sensor's perimeter at a rate that is inversely proportional to the snow viscosity. For sustained periods of differential snowmelt, a difference in the mass of snow over the sensor compared with the surrounding soil will develop, producing additional permanent errors in SWE measurements. The theory indicates that SWE pressure sensor performance can be improved by designing a sensor with a high Young's modulus (low compressibility), low aspect ratio, large diameter and thermal properties that match those of the surrounding soil. Simulations of SWE pressure sensor errors using the theory are in close agreement with observed errors and may provide a means to correct historical SWE measurements for use in hydrological hindcast or climate studies. Published in 2003 by John Wiley and Sons, Ltd.

Description: Soil moisture is a significant variable in its importance to the validation of hydrological models, but it is also the one defining variable that ties in all components of the surface energy balance and as such is of major importance to climate models and their surface schemes. Changing the scale of representation (e.g. from the observation to modelling scale) can further complicate the description of the spatial variability in any hydrological system. We examine this issue using soil moisture and vegetation cover data collected at two contrasting spatial scales and at three different times in the snow-free season from a cutover peat bog in Cacouna, Québec. Soil moisture was measured using Time Domain Reflectometry (TDR) over 90 000 m2 and 1200 m2 grids, at intervals of 30 and 2 m respectively. Analyses of statistical structure, variance and spatial autocorrelation were conducted on the soil moisture data at different sampling resolutions and over different grid sizes to determine the optimal spatial scale and sampling density at which these data should be represented. Increasing the scale of interest without adequate resolution in the measurement can lead to significant inconsistency in the representation of these variables. Furthermore, a lack of understanding of the nature of the variability of soil moisture at different scales may produce spurious representation in a modelling context. The analysis suggests that in terms of the distribution of soil moisture, the extent of sampling within a grid is not as significant as the density, or spacing, of the measurements. Both the scale and resolution of the sampling scheme have an impact on the mean of the distribution. Only approximately 60% of the spatial pattern in soil moisture of both the large and small grid is persistent over time, suggesting that the pattern of moisture differs for wetting and drying cycles. © 2003 John Wiley and Sons, Ltd.

Description: The aim of this study is to identify, in a small catchment area located within a tropical forest, the pedological compartments in which the export of nutrients and chemical erosion of solutes occur during a stormflow event. The catchment area displays two types of lateral flow: (i) overland flow at the surface of the soil in the litter and root mat and (ii) groundwater flow in a macroporous subsurface horizon. We interpret the variations of stream-water chemistry during a storm-flow event using the separation of storm-flow hydrograph data between overland and groundwater flow, and (Cl-) as a chemical parameter characterizing the residence time of water in the soil. It appears that K+ especially was released into the throughfall, whereas Ca++, Mg++ and Na+ were clearly released from the litter. K+ disappeared rapidly from soil solution, whereas Ca++ and Mg++ were more progressively absorbed by the vegetation. The Ca++ and Mg++ contents in groundwater increased with increasing residence time owing to the transpiration of trees. The export of H4SiO4 in the overland flow was moderate, i.e. 24% of total H4SiO4 export in the stream flow, as overland flow represented 39% of total runoff. The subsurface horizon-where active groundwater flow occurs-was successively affected by chemical erosion during the storm-flow peak, and then by neoformation of kaolinite favoured by increasing water residence time. © 2003 John Wiley and Sons, Ltd.

Description: Different commonly used predictive equations for the reaeration rate coefficient (K2) have been evaluated using 231 data sets obtained from the literature and 576 data sets measured at different reaches of the River Kali in western Uttar Pradesh, India. The data sets include stream/channel velocity, bed slope, flow depth, cross-sectional area and reaeration rate coefficient (K2), obtained from the literature and generated during the field survey of River Kali, and were used to test the applicability of the predictive equations. The K2 values computed from the predictive equations have been compared with the corresponding K2 values measured in streams/channels. The performance of the predictive equations has been evaluated using different error estimation, namely standard error (SE), normal mean error (NME), mean multiplicative error (MME) and coefficient of determination (r2). The results show that the reaeration rate equation developed by Parkhurst and Pomeroy yielded the best agreement, with the values of SE, NME, MME and r2 as 33·387, 4·62, 3·58 and 0·95, respectively, for literature data sets (case 1) and 37·567, 3·57, 2·6 and 0·95, respectively, for all the data sets (literature data sets and River Kali data sets) (case 2). Further, to minimize error estimates and improve correlation between measured and computed reaeration rate coefficients, supplementary predictive equations have been developed based on Froude number criteria and a least-squares algorithm. The supplementary predictive equations have been verified using different error estimates and by comparing measured and computed reaeration rate coefficients for data sets not used in the development of the equations. © 2003 John Wiley and Sons, Ltd.

Description: Snow water equivalent (SWE) sensors can experience errors when the base of the snow cover is at the melting temperature, the snow can support shear stresses (assumed to occur at densities greater than 200 kg m -3 ), and the rate of snowmelt on the sensor is different than on the surrounding ground. Either undermeasurement or overmeasurement errors may occur at critical times when the snow cover transitions from winter to spring conditions and at the start of periods of rapid snowmelt. Parameters to determine the onset of SWE sensor undermeasurement errors are defined by a negative rate of change for SWE, a negative rate of change for snow density, and an increasing snow depth. For the onset of overmeasurement errors, the rate of change for SWE will be positive while snow depth decreases and the snow density rate of change exceeds a defined positive threshold. When the snow temperature and density error conditions and the three under- or over-measurement error-indicator parameters are satisfied at the same time, an SWE sensor error has started. Real-time correction of the errors is done by multiplying the average snow cover density, set at the start of the error, with the snow depth. Once the error event ends, when the corrected SWE and SWE sensor data intersect, SWE is again determined from SWE sensor measurements. SWE sensor errors were accurately detected and corrected for five different sensors located in maritime and intermountain climatic zones when high-quality SWE sensor, snow or air temperature, and snow depth measurements were available. Implementation of the error detection and correction method requires simultaneous measurements of SWE, snow depth, and snow temperature near the ground. Improved error correction can be achieved by incorporating precipitation data and estimates of snow density due to retained rain or snow melt. Copyright © 2004 John Wiley & Sons, Ltd.