Linked hydrologic, hydraulic, and ecological models can facilitate planning and implementing water releases from reservoirs to achieve ecological objectives along rivers. We applied a flow‐ecology model, the Ecosystem Functions Model (HEC‐EFM), to the Bill Williams River in southwestern USA to estimate areas suitable for recruitment of riparian tree seedlings in the context of managing flow releases from a large dam for riparian restoration. Ecological variables in the model included timing of seed dispersal, tolerable rates of flow recession, and tolerable duration of inundation following germination and early seedling establishment for native Fremont cottonwood and Goodding's willow, and non‐native tamarisk. Hydrological variables included peak flow timing, rate of flow recession following the peak, and duration of inundation. A one‐dimensional hydraulic model was applied to estimate stage‐discharge relationships along ~58 river kilometres. We then used HEC‐EFM to apply relationships between seedling ecology and streamflow to link hydrological dynamics with ecological response. We developed and validated HEC‐EFM based on an examination of seedling recruitment following an experimental flow release from Alamo Dam in spring 2006. The model predicted the largest area of potential recruitment for cottonwood (280–481 ha), with smaller areas predicted for willow (174–188 ha) and tamarisk (59–60 ha). Correlations between observed and predicted patches with successful seedling recruitment for areas within 40 m of the main channel ranged from 0.66 to 0.94. Finally, we examined arrays of hydrographs to identify which are most conducive to seedling recruitment along the river, given different combinations of peak flow, recession rate, and water volume released. Similar application of this model could be useful for informing reservoir management in the context of riparian restoration along other rivers facing similar challenges.
Abstract.Although flooding can lead to many types of severe consequences, the primary objective of the US Army Corps of Engineers (USACE) dam and levee safety programs are to manage risk to the public who rely on those structures to keep them reasonably safe from flooding. Thus, reducing the risk associated with loss of life is paramount. USACE employs a scalable approach to estimating loss of life, where the goal is to invest an appropriate amount of resources to answer the question at hand. Given the large number of dams and levees within the USACE SRUWIROLR RYHU GDPV DQG PLOHV RI OHYHHV D ³RQH VL]H ILWV DOO´ DSproach does not work. Screening-level risk assessments are carried out to initially characterize risk. That initial risk characterization informs prioritization of additional efforts such as interim risk management activities and more detailed risk assessments. More detailed risk assessments inform investment in long-term risk reduction measures, which include analysis and selection of major modification activities and implementation of non-structural measures including emergency management and evacuation planning. This paper describes the USACE scalable approach for estimating loss of life from flood events.
This paper describes the development and application of a reservoir management decision support system for evaluating floodplain benefits and socioeconomic trade-offs of reservoir management alternatives in the Connecticut River watershed. The decision support system is composed of a reservoir system simulation model, an ecological model, and two river hydraulics models. The reservoir model simulated current operations at 73 reservoirs and flows at locations of interest in the Connecticut River watershed. Regulated flows from the reservoir model were compared with unregulated flows, both statistically and spatially, for a suite of environmental flow metrics based on inundation patterns related to floodplain vegetation communities. Analyses demonstrate use of the decision support system and show how its use illuminates (1) trends in existing hydrologic alteration for the Connecticut River mainstem and one of its tributaries, the Farmington River, and (2) management scenarios that might have ecological benefits for floodplain plant communities. The decision support system was used to test two management scenarios to assess potential floodplain benefits and associated trade-offs in hydropower generation and flood risk. The process described shows the usefulness of large-scale reservoir management decision support systems that incorporate environmental considerations in assisting with watershed planning and environmental flow implementation.
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