Design of Low-Flow Ecosystem Features for Urban Flood Control Structures
How can ecosystem features be designed within urban flood control channels to increase habitat diversity and complexity without raising flood stage?
Urban rivers have been extensively channelized to meet flood control needs, thereby resulting in uniform hydraulics at low to medium flows that provide minimal habitat value. This research proposal addresses how to rework the channel bed and banks, or add features such as flow deflectors and pools/riffles, to provide increased flow complexity and habitat heterogeneity. The primary constraints will be the existing channel top width and flood stage at high flows. Ideally, increasing channel width, floodplain area, and stormwater detention would all be aspects of a comprehensive urban stream restoration project. However, these elements are outside the scope of the proposed research because they are often not feasible to implement in highly confined urban environments. The proposed research will focus on designing ecosystem features within the existing channel footprint.
Need and Benefit
Need: As watersheds throughout the western United States have become increasingly urbanized over the last century, Reclamation facilities and lands such as reservoirs, canals, and rivers have been impacted. Urban streams have perhaps suffered the greatest decline in biological habitat values and species diversity as rivers have been channelized and confined. Threats to native aquatic species may jeopardize the ability of Reclamation and its stakeholders to continue to deliver water and manage these degraded river systems. There are several urban rivers managed by Reclamation or its partners that have a need for the results from this proposed research.
Reclamation provided Title XVI funds to re-use most of the recycled water that currently makes up base flow for the Los Angeles River, where ESA-listed species such as the southern steelhead, red-legged frog, Santa Ana sucker, and unarmored three-spine stickleback used to thrive. Title XVI states that appraisal investigations shall be conducted to identify opportunities for water reclamation and reuse, including environmental restoration, fish and wildlife, and recreation. Reclamation manages the Rio Grande through Albuquerque, New Mexico. There are documented cases of fish kills of the endangered Rio Grande silvery minnow resulting from poor conditions at the confluence between flood control channels and the Rio Grande. Rivers in the MP Region that transit heavily urbanized areas are important for salmon migration (e.g., CALFED Bay-Delta Program, San Joaquin Program). The Phoenix Area Office is also interested in habitat restoration measures for urban channels in the Phoenix, AZ area. It is likely that there is a Reclamation partner or stakeholder in every region that manages an urban flood control or water supply channel that would benefit from this proposed study.
Benefit: The outcome of this research will provide tools that managers can use to enhance the ecological function of urban streams, thereby minimizing conflicts between environmental needs and water supply demands. These tools and the supporting data will allow for an efficient and economical approach to urban stream restoration with a full understanding of the effects of potential methods. Unanticipated consequences with large costs will be prevented or minimized as a result of this study.
Urgency: A comprehensive literature review has not identified any studies that simultaneously quantify ecosystem benefits and flood control effects. Reclamation and its partners currently have the option of allowing urban stream habitat values to continue to decline, or attempting to implement urban restoration features without data that addresses the benefits and risks.
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