ALBERT

Description: Many studies have empirically confirmed the relationship between urbanization and changes to the hydrologic cycle and degraded aquatic habitats. While much of the literature focuses on extent and configuration of impervious area as a causal determinant of degradation, in this article I do not attribute causes of decreased watershed storage on impervious area a priori . Rather, adapting the concept of variable source area (VSA) and its relationship to incremental storage to the particular conditions of urbanized catchments, I develop a statistically-robust linear regression-based methodology to detect evidence of VSA-dominant response. Using the physical and meteorological characteristics of the catchments as explanatory variables, I then use logistic regression to statistically analyze significant predictors of the VSA classification. I find that the strongest predictor of VSA-type response is the percent of undeveloped area in the catchment. Characteristics of developed areas, including total impervious area, percent developed open space, and the type of drainage infrastructure do not add to the explanatory power of undeveloped land in predicting VSA-type response. Within only developed areas, I find that total impervious area (TIA) and percent developed open space both decrease the odds of a catchment exhibiting evidence of VSA-type response and the effect of developed open space is more similar to that of TIA than undeveloped land in predicting VSA response. Different types of stormwater management infrastructure, including combined sewer systems (CSS) and infiltration, retention, and detention infrastructure are not found to have strong statistically significant effects on probability of VSA-type response. VSA-type response is also found to be stronger during the growing season than the dormant season. These findings are consistent across a national cross-section of urbanized watersheds, a higher resolution dataset of Baltimore Metropolitan Area watersheds, and a subsample of watersheds confirmed not to be served by (CSS). This article is protected by copyright. All rights reserved.

Description: Abstract Actual pumping tests may involve continuously decreasing rates over a certain period of time, and the hydraulic conductivity (K) and specific storage (Ss) of the tested confined aquifer cannot be interpreted from the classical constant‐rate test model. In this study, we revisit the aquifer drawdown characteristics of a pumping test with an exponentially decreasing rate using the dimensionless analytical solution for such a variable‐rate model. The drawdown may decrease with time for a short period of time at intermediate pumping times for such pumping tests. A larger ratio of initial to final pumping rate and a smaller radial distance of the observation well will enhance the decreasing feature. A larger decay constant results in an earlier decrease, but it weakens the extent of such a decrease. Based on the proposed dimensionless transformation, we have proposed two graphical methods for estimating K and Ss of the tested aquifer. The first is a new type curve method that does not employ the well function as commonly done in standard type curve analysis. Another is a new analytic method that takes advantage of the decreasing features of aquifer drawdown during the intermediate pumping stage. We have demonstrated the applicability and robustness of the two new graphical methods for aquifer characterization through a synthetic pumping test.

Description: In our previous study, Faulkner et al. (2009) developed a Stokes-Darcy (SD) model for flow in a karst aquifer with a conduit bedded in matrix. Beavers-Joseph (BJ) interface condition was used to describe the matrix/conduit interface. Cao et al. (2010) studied the mathematical well-posedness of a coupled continuum pipe-flow (CCPF) model as well as convergence rates of its finite element approximation. In this study, to compare the SD model with the CCPF model, we use numerical analyses to validate finite element discretization methods for the two models. Using computational experiments, simulation codes implementing the finite element discretizations are then verified. Further model validation studies are based on the results of laboratory experiments. Comparing the results of computer simulations and experiments, we conclude that the SD model with the BJ interface condition is a valid model for conduit/matrix systems. On the other hand, the CCPF model with the value of the exchange parameter chosen within the range suggested in the literature perhaps does not result in good agreement with experimental observations. We then examine the sensitivity of the CCPF model with respect to the exchange parameter, concluding that, as has previously been noted, the model is highly sensitive for small values of the exchange parameter. However, for larger values, the model becomes less sensitive and, more important, also produces results that are in better agreement with experimental observations. This suggests that the CCPF model may also produce accurate simulation results, if one chooses larger values of the exchange parameter than those suggested in the literature. Copyright © 2011 John Wiley & Sons, Ltd.

Description: This study presents an analytical solution of dam-break floods in a trapezoidal channel with detailed solution procedure. An approach predicting the peak discharge of floods caused by embankment dam failures was derived from the aforementioned analytical solution with a database of 27 historical dam failures. The prediction performance of this approach has been proved by comparing with other 14 straightforward equations for estimating the peak discharge. The proposed model with a small uncertainty of predicted peak flow rates, has a high coefficient of determination and a small standard error, being ranked in the top four of the 15 methods considered in this paper. The robustness and predictive capability of the proposed model are further demonstrated in two case studies, both were considered in the previous analyses performed by other investigators. This method provides a simple and transparent tool for engineers to predict the peak discharge and is easy to implement for trial and error calculation. This article is protected by copyright. All rights reserved.

Description: Soil macropore networks are subsurface connected void spaces caused by processes such as fracture of soils, micro-erosion, and fauna burrows. Axial X-ray computed tomography (CT) scanning provides a convenient means of recording the spatial structure of soil macropore networks. The objective of this study were to (1) based on CT technique and GIS digitized image method, construction a new technique for tracing, visualizing and measuring the soil macropore networks; (2) investigate the effects of farming activities on soil macropore networks characteristics. Our technique using left-turning and nine-direction judgment methods, a combination of the layer-by-layer analysis method and the up-down tracking algorithm. The characteristics for the overall structure patterns of macropores, the spatial distribution of the macropore networks and each single macropore network can conveniently identify by our technique. Eight undisturbed soil columns from fields with two distinct land uses (under cultivation and not been cultivated) and four different depths (0-20 cm, 20-40 cm, 40-60 cm and 60-80 cm) were investigated. The soil columns were scanned using X-ray CT at a voxel resolution of 0.075 mm × 0.075 mm × 3.000 mm. Results indicate that farming activities can destroy the initial structure of macropores and those remaining are mainly small and medium-sized networks with lower extension and hydraulic conductivity. The network properties show a significant difference between upper and lower layer. The results can provide beneficial reference to further research centered on non-equilibrium flow prediction and chemical transport modeling in field soils. This article is protected by copyright. All rights reserved.

Description: Partitioning evapotranspiration ( ET ) into evaporation ( E ) and transpiration ( T ) in wetlands is important for understanding the hydrological processes in wetlands and the contribution of wetland ET to local and regional water cycling and for designing effective wetland management strategies. Stable water isotopes are useful in the application of ET partitioning through the evaluation of the isotopic compositions of E ( δ E ), T ( δ T ) and ET ( δ ET ) obtained from observation or modelling methods. However, this approach still suffers from potentially large uncertainties in terms of estimating the isotopic endmembers. In this study, we modified the traditional isotope-based ET partitioning methods to include leaf-level biological constraints to separately estimate the relative contributions of T from Scirpus triqueter and Phragmites australis and the relative contributions of E from the standing surface water in a semi-arid marsh wetland in northeastern China. The results showed that although the δ T values of Scirpus triqueter and P. australis were rather similar, the mean δ T values of the two species were different from the values of δ E , making it possible to distinguish the relative contributions of E and T through the use of isotopes. The simulation of leaf water using a non-steady-state model indicated obvious deviations in leaf water enrichment ( δ Lb ) from isotopic steady states (ISS) for both species, especially during early mornings and evenings when relative humidity was highest. The isotopic mass balance showed that E accounted for approximately 60% of ET , and T from Scirpus triqueter and P. australis each contributed approximately 20% to ET ; this implied that the transpiration of one reed was equivalent to that of 5.25 individuals of Scirpus triqueter . Using the estimated ratio of T to ET and the measured leaf transpiration, the total ET was estimated to be approximately 10 mm d -1 . Using the NSS- T r method, the estimated ET was higher than the water loss calculated from the water level gauge. This indicated that the river water and surrounding groundwater were the sources of the marsh wetland, with a supply rate of 8.3 mm d -1 .

Description: The concentration and isotopic composition of nitrate were analyzed to improve an understanding of nitrate sources and transformation processes in a typical karstic agricultural field in the Houzhai catchment, Guizhou Province, Southwest China. The results revealed that no distinct spatial pattern of content and isotopic composition of nitrate exists in this karst catchment. Nitrate in surface stream (SFS) had slightly lighter isotopic composition and lower concentration compared to nitrate in subterranean stream (STS) during the dry season. Concentrations of SFS nitrate increased to concentrations similar to those of STS during the wet season. The isotopic values indicated that nitrate were mainly impacted by manure sources during the dry season, and influenced by a mix of chemical fertilizer and manure during the wet season. The denitrification rates were roughly estimated based on the isotopic compositions of nitrate after considering volatilization and ignoring assimilation. The calculated result showed approximately 1/5 of nitrate load was removed by denitrification in the catchment. Annual nitrate flux from the outlets accounted for 14.2% of applied total fertilizers used in the catchment, approximately 85% of total transported flux from the catchment in the wet season. Furthermore, chemical weathering processes were enhanced by using nitrogen fertilizer because liberated protons and enhanced HCO 3 − flux were produced through by nitrification. This article is protected by copyright. All rights reserved.

Description: The aim of this study is to understand the canopy interception of Qinghai spruce forest under conditions of different precipitation characteristics and canopy structures in the upper reach of Heihe River basin, northwestern China. Based on a continuous record covering our investigating period by an automatic throughfall collecting system, we analyzed the relationships between the canopy interception and the precipitation characteristics. Our results support the well-established exponential decay relationship between the gross precipitation and the interception percentage after the canopy is saturated. But, our results sufficiently illustrate a notable point that the variations in the interception percentage are almost independent from the variations in the gross precipitation before the canopy is saturated. Our examination into the relationship between the interception and the 10 min-average intensity of precipitation demonstrates a divergent relationship and the divergent relationship is bracketed by an upper “dry line” indicating that 100% of gross precipitation was intercepted before saturation and by a lower “wet line” suggesting that the actual canopy storage capacity reached the maximum and evaporation was the only component of the interception. To search for the relationship between canopy structures and interception, we grouped the canopy covers over the 90 throughfall-collecting tanks into 10 categories ranging from 0 (no cover) to 0.9 (nearly completely covered) and the corresponding canopy interception was calculated by subtracting the averaged throughfall of each canopy-cover category from the gross precipitation. The results show that the interception percentage increases faster with increasing canopy cover under intermediate rainfall conditions than that under heavy rainfall conditions. Unexpectedly, under light rainfall conditions the increasing rate of interception percentage with increasing canopy cover and also with increasing plant area index is not faster than that under the intermediate rainfall conditions simply because the tank-measured percentage of interception was extremely high at near-zero canopy cover conditions. Copyright © 2013 John Wiley & 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: Much of the nonlinearity and uncertainty regarding the flood process is because hydrologic data required for estimation are often tremendously difficult to obtain. This study employed a back-propagation network (BPN) as the main structure in flood forecasting to learn and to demonstrate the sophisticated nonlinear mapping relationship. However, a deterministic BPN model implies high uncertainty and poor consistency for verification work even when the learning performance is satisfactory for flood forecasting. Therefore, a novel procedure was proposed in this investigation which integrates linear transfer function (LTF) and self-organizing map (SOM) to efficiently determine the intervals of weights and biases of a flood forecasting neural network to avoid the above problems. A SOM network with classification ability was applied to the solutions and parameters of the BPN model in the learning stage, to classify the network parameter rules and to obtain the winning parameters. The outcomes from the previous stage were then used as the ranges of the parameters in the recall stage. Finally, a case study was carried out in Wu-Shi basin to demonstrate the effectiveness of the proposal. Copyright © 2009 John Wiley & Sons, Ltd.