Upstream Hydrologic Effects of Dam Installation and Removal

0438749 Loague河流的筑坝会引起河流水文和地貌状况的深刻变化。随着大坝的老化，拆除大坝的做法变得越来越普遍，预计这也会导致水和沉积物在系统中流动的方式发生重大变化。大坝的建设导致上游集水区基准面的上升，导致水流深度和速度的改变，水位升高，泥沙沉积。在某些情况下，水坝的存在会改变集水区的生态水文学，包括在水坝直接影响区建立湿地生态系统。大坝下游河道形态受泥沙减少和洪峰流量减缓的影响，本研究建议采用综合水文模型模拟大坝和大坝拆除对近地表水文地貌的影响。所使用的模型，InHM，是非常适合的任务，因为它模拟三维可变饱和地下流体流动和二维地表水流动，使用一个完全耦合的方法。这使得它成为研究地下水-地表水相互作用的理想工具，例如由水坝引起的相互作用。作为研究计划的一部分，InHM将增加一个基于物理的多物种沉积物输运算法，允许模拟高地侵蚀（雨溅和漫流），渠道运输，水库沉积，以及水库沉积物的侵蚀后大坝拆除。在现有的InHM的完全耦合水力学的驱动下，泥沙输运算法将提供比具有简单水文基础的模型更准确的泥沙通量估计。传输算法将考虑到由植被等引起的粗化和凝聚力的影响，将在俄克拉荷马州的R-5集水区对扩展模型进行测试，选择该实验地点是因为该实验地点具有丰富的长期/空间可变数据，包括降雨和气候记录、水和沉积物排放数据以及土壤含水量数据。将在R-5现场证明InHM模拟泥沙输运的长期水文响应的能力。InHM然后将被用于一个应用模式，以模拟小流域的Searsville大坝在沿海范围的加州。建于1891年的Searsville大坝遭受了许多旧大坝的命运，因为它的水库现在几乎完全被沉积物填满。因此，正在考虑拆除该大坝。本研究的目的是解决有关的问题，Searsville大坝的影响和潜在的去除水文制度，包括湿地生态系统的可持续性，已形成附近的湖泊和沉积物侵蚀和运输下游。利用现有的地形，土地利用，土壤，地质和气候的历史数据，增加了额外的现场数据的泥沙输运通量率，通道水文地貌参数和近地表水力特性，我们将进行建模工作，定量评估替代大坝管理策略的影响，包括模型假设和数据误差所造成的预测不确定性的分析。对有水坝的一般假设集水区进行更多的模拟将扩大研究范围，并为评估进一步的研究需求提供一个坚实的基础。这项研究的结果将以特定地点和广泛基础的方式提出，以便他们能够接触到包括公众在内的各种利益相关方。

0438749LoagueThe damming of a river causes profound changes to the hydrologic and geomorphologic regime of the river. Dam removal, a practice becoming increasingly common as our population of dams grows older, is similarly expected to cause major changes to the manner in which water and sediment move through the system. Dam construction causes a rise in base level for the upstream catchment, resulting in altered streamflow depths and velocities, higher water tables, and sediment deposition. In some cases the presence of a dam brings about changes to the ecohydrology of the catchment, including the creation of wetland ecosystems in the dam's immediate zone of influence. Downstream of the dam channel morphology is affected by the reduction in sediment load and the moderation of peak flows.This study proposes to use a comprehensive hydrologic model to simulate the effects of dams and dam removal on near surface hydrology and geomorphology. The model to be used, InHM, is well suited to the task as it simulates 3D variably-saturated subsurface fluid flow and 2D surface water flow using a fully-coupled approach. This makes it ideal for studying groundwater- surface water interactions, such as those caused by dams. As part of the research plan InHM is to be augmented with a physically based multiple species sediment transport algorithm, allowing simulation of upland erosion (both by rainsplash and overland flow), channel transport, and reservoir deposition, as well as erosion of reservoir sediments following dam removal. Driven by the fully-coupled hydraulics in the existing InHM the sediment transport algorithm will provide more accurate sediment flux estimates than models with simpler hydrologic underpinnings. The transport algorithm will take into account the affects of armoring and cohesion caused by, for example, vegetation.The expanded model will be tested at the R-5 catchment in Oklahoma, an experimental site chosen due to the wealth of long-term / spatially-variable data, including rainfall and climate records, water and sediment discharge data, and soil-water content data. The ability of InHM to simulate long-term hydrologic response with sediment transport will be proven at the R-5 site. InHM will then be used in an application mode to simulate the small watershed impounded by Searsville Dam in the coastal range of California. Searsville Dam, constructed in 1891, has suffered the fate of many old dams in that its reservoir is now almost completely filled with sediment. Consequently dam removal is being considered for this dam. This study aims to address questions related to the impact of Searsville Dam and its potential removal on the hydrologic regime, including the sustainability of a wetland ecosystem that has formed near the lake and sediment erosion and transport downstream. Using existing historical data on topography, land use, soils, geology, and climate, augmented with additional field data on sediment transport flux rates, channel hydrogeomorphologic parameters, and near-surface hydraulic properties, we will undertake a modeling effort to quantitatively assess the impacts of alternate dam management strategies, including an analysis of prediction uncertainty caused by model assumptions and data error. Additional simulations of generic hypothetical catchments with dams will broaden the scope of the study and provide a sound footing for assessing further research needs. The results from this study will be presented both in site- specific and broad- based terms so that they can reach a wide variety of interested parties including the general public.