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- Info
Design of an urban, ground-water-dominated wetland
| Author: |
Winston, Richard B. |
| Date: |
1996 |
| Periodical: |
Wetlands |
| Abstract: |
In the Barney Circle wetland in southeast Washington DC, a proposed site for wetland enhancement and creation, ground water supplied over 80% of the flow into the wetland from 25 March to 17 August 1994. In most months, the primary outflow from the wetland occurred as ground-water flow, but in April, almost all the outflow was surface water. Rain, runoff, and changes in storage account for less than a third of the observed surface-water discharge from the wetland to the Anacostia River in April and May. This indicates that ground-water inflow was the major source of water. Although it is only a first order basin, the wetland had a small but definite flood-control function. Peak surface-water discharges out of the wetland during a storm event were reduced by 38 to 80% compared to surface-water inflow into the wetland. The time during which storm outflow occurred was much longer than the time of storm inflow. Proposed construction of a highway will result in a 13% reduction in the recharge area of the Barney Circle watershed. A calibrated ground-water flow model of the watershed suggests that this will result in a 27% decrease in base flow discharge from the wetland. The hydro period of the wetland will only be slightly affected, however. By modifying the calibrated watershed model, it was possible to design a modified topography of the wetland that will favor desired plant communities. However, modifying the hydro period will require a much greater depth of excavation than would have been predicted based on the average hydro period either before or after highway construction. Excavation of the wetland will cause ground water in the surrounding uplands to drain more quickly than previously. This change in the hydrology had to be taken into account in the design. This study illustrates how failure to consider the effects of site alteration on local hydrology could result in project failure. |
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