Upstream Hydrologic Effects of Dam Installation and Removal

[04:38 . 74]筑坝使河流的水文和地貌状况发生了深刻的变化。随着水坝的老化，拆除大坝的做法变得越来越普遍，同样预计会导致水和沉积物在系统中移动的方式发生重大变化。大坝建设导致上游集水区水位上升，导致水流深度和流速改变，水位升高，泥沙淤积。在某些情况下，大坝的存在会给集水区的生态水文带来变化，包括在大坝直接影响区域内创造湿地生态系统。大坝下游河道形态受泥沙负荷减少和洪峰流量缓和的影响。本研究提出利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InHM模型非常适合这项任务，因为它使用全耦合方法模拟了3D变饱和地下流体流动和2D地表水流动。这使得它成为研究地下水和地表水相互作用的理想选择，比如大坝引起的相互作用。作为研究计划的一部分，InHM将增加一种基于物理的多物种沉积物运输算法，允许模拟高地侵蚀（由雨水飞溅和陆地水流）、河道运输和水库沉积，以及大坝拆除后水库沉积物的侵蚀。在现有InHM中全耦合水力学的驱动下，泥沙输移算法将比具有简单水文基础的模型提供更准确的泥沙通量估计。传输算法将考虑到装甲和内聚造成的影响，例如，植被。扩展后的模型将在俄克拉何马州的R-5集水区进行测试，选择这个实验地点是因为这里有丰富的长期/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水分含量数据。在R-5站点将验证InHM模拟沉积物输运的长期水文响应的能力。然后，InHM将在应用程序模式下用于模拟加利福尼亚州沿海地区的Searsville大坝所蓄水的小流域。建于1891年的Searsville大坝遭遇了许多老水坝的命运，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。本研究旨在解决与Searsville大坝及其潜在拆除对水文制度的影响相关的问题，包括在湖泊附近形成的湿地生态系统的可持续性以及沉积物的侵蚀和下游运输。利用现有的关于地形、土地利用、土壤、地质和气候的历史数据，再加上关于泥沙输送通量、河道水文地貌参数和近地表水力特性的额外现场数据，我们将进行建模工作，定量评估备用大坝管理策略的影响，包括分析由模型假设和数据误差引起的预测不确定性。对一般假设的水坝集水区进行更多的模拟，将扩大研究的范围，并为评估进一步的研究需求提供坚实的基础。这项研究的结果将以具体地点和广泛的术语来介绍，以便他们能够接触到各种各样的兴趣团体，包括公众。

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.