E/E-21a

Strategic focus area:

Description:

OBJECTIVES: The objectives are to 1) explore the extent to which stream restoration design alternatives are capable of mitigating watershed-scale changes in hydrologic response associated with urbanization, and 2) establish explicit criteria for hydrologic performance that can be tested through modeling and field monitoring. The primary goal of the research is to quantify the physical controls on channel/floodplain storage and surface-water residence time in urban streams through field measurements and numerical hydrodynamic simulations of the performance of restoration designs. The motivating questions follow. 1) Is it possible to use stream restoration along the channel and riparian zone to counteract or mitigate the hydrologic changes imposed on the watershed by intensive urban development? If so, what design alternatives have the best chance of achieving this goal? 2) How do channel and riparian zone conditions affect surface water residence time and how can residence time metrics be used to assess stream restoration success? METHODOLOGY : The proposed research includes both field-based and modeling efforts. Supplemental pressure transducers upstream of a longer-term stream gage will quantify discrete hydrologic responses from different areas of the watershed. LIDAR data and field surveys will be used to construct high-resolution topographic representations of the domain. Dimensions of debris jams and culvert/bridge openings will also be surveyed. The 2-d depth-averaged hydrodynamic model TUFLOW will be used for each site to provide a high-resolution spatio-temporal representation of the flow field and interaction with hydraulic structures. After calibration to existing conditions, hydrodynamic models representing alternative channel and floodplain conditions will be modeled for the domain for both low and high flows. Metrics such as changes in volume in storage, peak discharge, hydrograph time base, velocity, wave celerity, residence time, and shear stress will be quantified for the site to demonstrate how channel and riparian zone conditions affect transient storage. RATIONALE: Chesapeake Bay tributary management strategies mandate new approaches to mitigate the negative impacts of urbanization, including stream rehabilitation and reforestation. Despite hundreds of millions of dollars spent in the Bay Watershed, the performance of stream restoration projects remains poorly understood. Clearly articulated success criteria, detailed site characterization, and mechanistic modeling efforts are all needed in the planning phase to define the unique spatial and temporal context of each project to maximize the probability of project success. Enhanced strategies for stream restoration will improve the hydrologic and ecologic regime for both the local watershed and receiving water bodies, and will not waste valuable taxpayer dollars on unsuccessful projects. A planned restoration project for a degraded headwater urban stream in Baltimore County provides a special opportunity to extensively test designs to improve project success. Evaluating strategies for improving stream restoration projects falls directly into the strategic plan of the Maryland Sea Grant.