Hydrolink 2017/4. Multi Reservoir Systems Operations

Topic: Multi Reservoir Systems Operation

Reservoir delineation and cumulative impacts assessment in large river basins: A case study of the Yangtze River Basin

Ph.DDOCTOR OF PHILOSOPH

Water Quality in the Yangtze River at Shanghai and the Role of Coastal Reservoirs in Shanghai’s Water Supply

Shanghai is the largest city in China and third largest in the world. It is home to more than 24 million people and is the largest commercial and industrial centre in China. Challenges to water supply in coastal mega cities are becoming apparent worldwide, and Shanghai was predicted to be among one of the most likely to suffer severe water crisis. To meet its rapidly growing demand for municipal water supply, Shanghai has turned to the enormous fresh water resource provided by the Yangtze River at its estuary. Coastal reservoirs have been constructed to capture, store and protect water supplies in the estuary; these reservoirs now provide around 70% of Shanghai’s water supply. This thesis is designed to examine the implications of using coastal reservoirs in Shanghai’s municipal water supply system by describing relevant water quality characteristics of the Yangtze River at points of diversion to Shanghai’s coastal reservoirs and evaluating the effect of water quality processes in these reservoirs on downstream water treatment operations. A critical literature review covering Shanghai’s municipal water supply and the water quality at the Yangtze River Estuary was undertaken. From literature sources, data on key water quality parameters at the estuary and the Qingcaosha Reservoir, Shanghai’s largest coastal reservoir, has been collected. The data has been assembled and compared with relevant standards, and Mann-Kendall analysis applied to trends in key nutrients and total suspended solids concentrations. The settling characteristics of the Qingcaosha Reservoir have been assessed by treating the reservoir as an ideal settling basin and potential algal growth behaviour analysed using the lake ecology model PCLake+. Potential management options for algal blooming in the Qingcaosha Reservoir are explored

Assessing the impact of land use change on hydrology and sediment yield in the Xiangxi Catchment (China) using SWAT

This dissertation describes the application of the eco-hydrological model SWAT to a watershed in the Three Gorges Region, which is located in Hubei Province and Chongqing Municipality in Central China. The region is heavily influenced by the construction of the Three Gorges Dam on Yangtze River, which was completed in 2009. The dam was constructed for reasons of flood protection, hydropower production and navigation benefits. It exerts substantial influence on water resources in the affected sub-watersheds of Yangtze River. In the Three Gorges Region, the construction of the Three Gorges Dam induced a large-scale land use change. This can mostly be attributed to the inundation of agricultural areas, villages and towns, which necessitated the resettlement of more than 1 million people and the relocation of agriculturally used areas from the valley bottoms to steep, formerly forested slopes. The clearance of forest on steep slopes and their use for agricultural production is expected to strongly increase the risk of erosion and diffuse sediment inputs to surface waters. Soil erosion results in the removal of nutrient-rich topsoil, which leads to an irreversible degradation of soils and to undesired off-site effects in surface waters. The sediment reduces the life span of the Three Gorges Reservoir due to siltation and carries large amounts of nutrients to the water bodies. At the same time, flow velocities are reduced and the residence time of water is prolonged in the reservoir. In combination, the increasing sediment and nutrient inputs and the altered flow regime are expected to exacerbate the risk of eutrophication and thereby hamper the usability of water resources. Especially in the backwater areas of Yangtze River tributaries, an increasing occurrence of algae blooms has been observed in recent years. The current situation in the Three Gorges Region indicates a strong need for sustainable water resources management. This dissertation aimed at identifying a suitable tool for assessing the impact of land use change in the Three Gorges Region on water quantity and quality to support the development of integrated watershed management plans. Therefore, the eco-hydrological model SWAT (Soil and Water Assessment Tool) was applied to the Xiangxi Catchment in Hubei Province. The Xiangxi Catchment comprises an area of 3200 km2 as is considered to be representative of the eastern part of the Three Gorges Region. Land use in the watershed is dominated by forest. Agriculturally used areas are restricted to relatively small areas, which are characterized by severe soil erosion. SWAT was used in this dissertation to simulate water balance, streamflow and sediment yield under past, current and possible future land use conditions. Also, the most important sources of model error were identified in this study. Results indicate that the model performs very well with regard to streamflow and water balance, whereas the prediction of sediment yield is more problematic. SWAT output was analyzed at different spatial levels ranging from the entire watershed to individual Hydrologic Response Units. Generally, there is considerable uncertainty associated with the SWAT predictions in the Xiangxi Catchment, because of a low amount of data available for model parameterization, calibration and validation. Nevertheless results of the basic model calibration were considered a sufficient basis for the simulation of land use scenarios. The forested area in the Xiangxi Catchment has increased in the recent past which led to a decrease of fast flow components and sediment yield. Scenario simulations demonstrate that a further increase in forest would result in a continuation of the trends observed in the past, whereas an increase of agriculturally used areas would induce a strong increase in sediment yields. The scenario simulations indicate a high potential for conflicts between environmental protection and agricultural production, which is aggravated by conservation efforts of the Chinese government, e.g. the Sloping Land Conversion Program (SLCP). Through compensation and subsidy payments, SLCP encouraged farmers to convert sloping cropland to forest or grassland. While this is an effective means of reducing soil erosion on the afforested areas, it increases the pressure on the remaining cropland. The results of this dissertation suggest that in the future the application of selected Best Management Practices may be more effective for realizing sustainable watershed management plans than continuing to reallocate land use types within the Xiangxi Catchment. SWAT has already been used successfully for assessing the effects of Best Management Practices on water resources in a number of studies. However, the data currently available for the Xiangxi Catchment does not allow for a sufficiently detailed parameterization and calibration of land use and management. Future studies in the Xiangxi Catchment should focus on improving the data base by obtaining additional relevant input data. This can help to reduce the uncertainty in model results and facilitate the simulation of Best Management Practices. By testing the applicability of SWAT to the Xiangxi Catchment and identifying the main sources of uncertainty, this dissertation laid the groundwork for further research in the Three Gorges Region, which can help to preserve natural resources in this unique and sensitive ecosystem

Soil erosion and sediment yield in the upper Yangtze, China

Soil erosion and sedimentation are key environmental problems in the Upper Yangtze because of the ongoing Three Gorges Project (TGP), the largest hydro-power project in the world. There is growing concern about the rapid increase of soil erosion over the last few decades and its consequence for potential sedimentation in the reservoir. The study aims to examine controls on the spatial and temporal distributions of sediment transfer within the Upper Yangtze and the hydrological consequences of land use changes, using varied approaches at different catchment scales. First, soil erosion and sedimentation are examined using the radionuclide Cs-137 as a tracer within a small reservoir catchment in the Three Gorges Area. The results indicates that soil erosion on sloping arable land and the rates of reservoir sedimentation have been severe during the past 40 years, mainly due to cultivation on steep slopes. Changes in reservoir sedimentation rates are mainly attributed to land use changes. The suitability of the Cs-137 techniques for investigating soil erosion and sedimentation in intensely cultivated subtropical environments is also considered. The use of the technique for erosion investigation may have limitations due to the abundance of coarse soil textures, uncertainty about fallout deposition rates and the high incidence of human disturbance, but the technique shows promising perspectives for sedimentation investigation since a few dating horizons might be identified. Second, sediment and runoff measurement data for around 30 years from over 250 hydrological stations within the Upper Yangtze have been examined within a GIS framework. The dataset has been integrated with catchment characteristics derived from a variety of environmental datasets and manipulated with Arc/Info GIS. The analysis of the sediment load data has permitted identification of the most important locations of sediment sources, the shifting pattern of source areas in relation to land use change and sub-catchments exhibiting trending sediment yields corrected for hydrological variability. The study demonstrates the importance of scale dependency of sediment yield in both the identification of temporal change and the modelling of relationships between sediment yield and environmental variables, suggesting that the treatment of the scale problem is crucial for temporal-spatial studies of sediment yield

Spatial Estimations of Soil Properties for Physically-based Soil Erosion Modelling in the Three Gorges Reservoir Area, Central China

Soils present a central medium for processes between the environmental spheres, and therefore play a key role in the functioning of terrestrial ecosystems. However, soil erosion as a natural force of landscape evolution adversely affects the capacity of soils to support ecosystem services. Moreover, inadequate agricultural practices, deforestation, and construction activities amplify natural soil loss rates and transform soil erosion to a major threat for managed ecosystems worldwide. Particularly, the Three Gorges Reservoir Area in China is highly susceptible to soil erosion by water. This is attributable to unfavorable environmental conditions, such as rainfall events of high intensity and steep slope inclinations in areas of extensive, but small-scale crop cultivation. Moreover, in the course of the impoundment of the Yangtze River in the area of the Three Gorges, resettlements and accompanied deforestation reinforced the risk of hazardous soil erosion, which attenuates soil productivity and threatens the functioning of the reservoir. Therefore, conservation measures to stabilize steep sloping surfaces have been implemented to mitigate the hazardous effects of soil erosion. However, to assess the conservation measures an efficient tool is required to identify spatial soil erosion patterns in small, mountainous, and data scarce catchments within the Three Gorges Reservoir Area. The present thesis aims to provide an efficient modelling framework that facilitates a detailed quantification of sediment reallocations due to erosive rainfall-runoff events. Therefore, Digital Soil Mapping techniques based on Latin Hypercube Sampling and Random Forest regression were applied to derive spatially distributed data on soil properties and to furnish a physically- and event-based soil erosion model. The soil sampling design was optimized to address the difficult terrain, an integrative use of legacy soil samples, and a reduced sample set size. Furthermore, the present thesis introduces a spatial uncertainty measure, which was used to identify areas for additional sampling to further refine initially processed soil property maps. In addition, continuous data on rainfall, runoff, and sediment yields were obtained to identify erosive rainfall-runoff events and to calibrate the physically-based soil erosion model EROSION 3D. Evaluation of the hypercube sampling design was conducted by comparing it to a simulated Latin Hypercube design without constraints in terms of operability and efficiency adjustments. Using the optimized sample set size of n = 30, the proposed sample design adequately reproduced the variation of terrain parameters, which served as proxies on the target soil properties of coarse, medium, and fine topsoil sand contents. Furthermore, the validity of the approach was assessed by estimating the spatial distribution of the target soil properties and validating the results independently. The results show convincing accuracies with R²-values between 0.59 and 0.71. The adequacy of the uncertainty-guided sampling for refining initial mapping approaches was evaluated by comparing the refined maps of topsoil silt and clay contents to the initial and further mapping approaches that exclusively used random samples from the entire study area. For the comparative analysis, the quality of the approaches was assessed by independent, bootstrap-, and cross-validation. The refined mapping approach performs best, showing a reduced spatial uncertainty of 31% for topsoil silt and 27% for topsoil clay compared to the initial approaches. Using independent validation, the accuracy increases by similar proportions, showing an accuracy of R² = 0.59 for silt and R² = 0.56 for clay. The EROSION 3D model runs were evaluated using the measured sediment yields. The model performs well for large events (sediment yield > 1 Mg) with an average individual model error of 7.5%, while small events show an average error of 36.2%. The focus of analysis was led on the large events to evaluate reallocation patterns. Soil losses occur on approximately 11.1% of the study area with an average soil loss rate of 49.9 Mg ha-1. Soil loss mainly occurs on crop rotation areas with a spatial proportion of 69.2% for ‘corn-rapeseed’ and 69.1% for ‘potato-cabbage’. Deposition occurs on 11% of the study area. Forested areas (9.7%), infrastructure (41%), cropland (corn-rapeseed: 13.6%, potato-cabbage: 11.3%), and grassland (18.4%) are affected by deposition. Since the vast majority of annual sediment yields (80.3%) were associated to a few large erosive events, the modelling framework can be recommended to identify sediment reallocations and to assess conservation measures in small catchments in the Three Gorges Reservoir Area

River channel change in the Middle Yangtze River in the last 50 years: A case study in the Jianli sub-reach

Master'sMASTER OF SOCIAL SCIENCE

Managing Water Resources in Large River Basins

Management of water resources in large rivers basins typically differs in important ways from management in smaller basins. While in smaller basins the focus of water resources management may be on project implementation, irrigation and drainage management, water use efficiency and flood operations; in larger basins, because of the greater complexity and competing interests, there is often a greater need for long-term strategic river basin planning across sectors and jurisdictions, and considering social, environmental, and economic outcomes. This puts a focus on sustainable development, including consumptive water use and non-consumptive water uses, such as inland navigation and hydropower. It also requires the consideration of hard or technical issues—data, modeling, infrastructure—as well as soft issues of governance, including legal frameworks, policies, institutions, and political economy. Rapidly evolving technologies could play a significant role in managing large basins. This Special Issue of Water traverses these hard and soft aspects of managing water resources in large river basins through a series of diverse case studies from across the globe that demonstrate recent advances in both technical and governance innovations in river basin management