ALBERT

Description: The Kosi River is an important tributary of the Ganges River, which passes through China, Nepal and India. With a basin area of 71 500 km2, the Kosi River has the largest elevation drop in the world (from 8848 m of Mt Everest to 60 m of the Ganges Plain) and covers a broad spectrum of climate, soil, vegetation and socioeconomic zones. The basin suffers from multiple water related hazards including glacial lake outburst, debris flow, landslides, flooding, drought, soil erosion and sedimentation. This paper describes the characteristics of water hazards in the basin, based on the literature review and site investigation covering hydrology, meteorology, geology, geomorphology and socio-economics. Glacial lake outbursts are a huge threat to the local population in the region and they usually further trigger landslides and debris flows. Floods are usually a result of interaction between man-made hydraulic structures and the natural environment. Debris flows are widespread and occur in clusters. Droughts tend to last over long periods and affect vast areas. Rapid population increase, the decline of ecosystems and climate change could further exacerbate various hazards in the region. The paper has proposed a set of mitigating strategies and measures. It is an arduous challenge to implement them in practice. More investigations are needed to fill in the knowledge gaps.

Description: A comprehensive approach estimating sediment yield from a watershed is needed to develop better measures for mitigating sediment disasters and assessing downstream impacts. In the present study, an attempt has been made to develop an integrated method, considering sediment supplies associated with soil erosion, shallow landslide and debris flow to estimate sediment yield from a debris-flow-prone watershed on a storm event basis. The integrated method is based on the HSPF and TRIGRS models for predicting soil erosion and shallow landslide sediment yield, and the FLO-2D model for calculating debris flow sediment yield. The proposed method was applied to potential debris-flow watersheds located in the Sioulin Township of Hualien County. The available data such as hourly rainfall data, historical streamflow and sediment records as well as event-based landslide inventory maps have been used for model calibration and validation. Results for simulating sediment yield have been confirmed by comparisons of observed data from several typhoon events. The verified method employed a 24-h design hyetograph with the 100-yr return period to simulate sediment yield within the study area. The results revealed that the influence of shallow landslides on sediment supply as compared with soil erosion was significant. The estimate of landslide transport capacity into a main channel indicated the sediment delivery ratio on a typhoon event basis was approximately 38.4%. In addition, a comparison of sediment yields computed from occurrence and non-occurrence of debris flow scenarios showed that the sediment yield from an occurrence condition was found to be increasing at about 14.2 times more than estimated under a non-occurrence condition. This implied watershed sediment hazard induced by debris flow may cause severe consequences.

Description: To control severe soil erosion on the Loess Plateau, China, a great number of soil conservation measures have been adopted since 1950s and subsequently, the "Grain for Green" project has been implemented from 1999. The measures and the project result in a large scale land use/cover change (LUCC). Understanding the impacts of the measures and the project on streamflow, sediment load and their dynamic relation is essential as the three elements are closely related to the sustainable catchment management strategy on the Loess Plateau. The data for seven selected catchments in the middle reaches of the Yellow River were used and standardized with precipitation and the controlling area for analysis. Nonparametric Mann-Kendall test and Pettitt test were employed to detect trends and change points of the annual streamflow and annual sediment load. Simple linear regressions for the monthly streamflow and sediment load from May to October were made to express their dynamic relation. Based on the change point identification and the time when the project began to implement on the Loess Plateau, the whole time for the data records was divided into three periods to compare the change extents in streamflow, sediment load and their dynamic relation between catchments. Results show that there are three types of responses in streamflow, sediment load, and their dynamic relations for the seven catchments. The effects of the LUCC on streamflow, sediment load, and their dynamic relation are greatest in the three transition zone catchments with the two rocky mountain catchments followed. The effects are much weaker in the two loess hilly-gully catchments. In general, the change extents for sediment load are much greater than those for streamflow, which results in the increasingly weakening trends of statistical significance for the dynamic relation between the periods.

Description: To control severe soil erosion on the Loess Plateau, China, a great number of soil conservation measures have been implemented since 1950s and subsequently, the "Grain for Green" project was implemented in 1999. The measures and the project resulted in a large scale land use/cover change (LUCC). Understanding the impacts of the measures and the project on streamflow, sediment load and their dynamic relation is essential because the three elements are closely related to the sustainable catchment management strategy on the Loess Plateau. The data for seven selected catchments in the middle reaches of the Yellow River were used and standardized with the precipitation and the controlling area for analysis. The nonparametric Mann-Kendall test and the Pettitt test were employed to detect trends and change points of the annual streamflow and annual sediment load. Simple linear regressions for the monthly streamflow and sediment load from May to October were made to express their relationship. Based on the change point identification and the time when the project began to be implemented on the Loess Plateau, the complete time for the data records was divided into three periods to compare the change degrees of streamflow, sediment load and their relation for the catchments. Results show that there are three types of responses in streamflow, sediment load, and their dynamic relations for the seven catchments. The effects of the LUCC on streamflow, sediment load, and their relationships are greatest in the three transition zone catchments followed by the two rocky mountain catchments. The effects are much weaker in the two loess hilly-gully catchments. In general, the change degrees for sediment load are much greater than those for streamflow, which results from the decreased streamflow and weakening trend of their dynamic relation period by period in catchments.

Description: Continuous measurements of airborne particles and their chemical compositions were conducted in May, June, October and November 2014 at an urban site in Wuhan, Central China. The results indicated that the particle concentrations stayed at a relatively high level in Wuhan, with the averages of 135.1 ± 4.4 (mean ± 95 % interval) and 118.9 ± 3.7 μg/m3 for PM10, and 81.2 ± 2.6 and 85.3 ± 2.6 μg/m3 for PM2.5 in summer and autumn, respectively. Moreover, PM2.5 frequently exceeded the National Standard Level II (i.e., daily average of 75 μg/m3), and six PM2.5 episodes were captured during the sampling campaign. The composition analysis found that secondary inorganic ions and carbonaceous aerosols dominated the constituents of PM2.5. It is noteworthy that potassium (K) (2060.7 ± 82.3 ng/m3, 47.0 ± 2.2 %) was the most abundant element, implying the biomass burning in/around Wuhan. During the episodes, carbonaceous aerosols increased significantly, a signature of combustion activities as well. The source apportionment confirmed that biomass burning was the main cause of PM2.5 episodes except for case 2, with the contribution ranging from 48.0 ± 1.0 % in case 5 to 70.1 ± 0.5 % in case 3. Fugitive dust and oil refinery/usage were the main contributors to PM2.5 in case 2. In addition to biomass burning, the contribution of oil refinery/usage also increased in case 5. Furthermore, the mass and proportion of NO3− peaked in case 6. It was found that the high levels of NOx and NH3, and low temperature in case 6 were responsible for the increment of NO3−. We also found that SOC formation was dominated by the aromatics and isoprene in autumn, and the contribution of aromatics increased during the episodes.