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- Info
Sediment reduction in urban stormwater runoff from construction sites
| Author: |
Sturm, Terry W.; Kirby, Ronald E., Jr. |
| Date: |
1991 |
| Periodical: |
Atlanta, GA: Georgia Institute of Technology, School of Civil Engineering in cooperation with: Environmental Resources Center. Technical Completion Report for US Department of the Interior, Geological Survey, Project 14-08-0001-G1556 |
| Abstract: |
This research has focused on an evaluation of current design criteria and best-management practices for controlling sediment in runoff from construction sites in response to recent Georgia legislation which established an effluent limit on turbidity. The research approach has been two-pronged with an analysis of field data collected by Georgia EPD and of numerical data generated by a computer simulation model. The field data were collected at landfill sites which had a sediment basin. Regression relations between suspended solids in mg/1 and turbidity in NTU were developed for each landfill site and were found to be dependent on the soil types at each site, which included clay loam, loam, and sandy loam. The field data indicated that the sediment basins at two of the landfill sites met the turbidity discharge standard for all storm events sampled while the sediment basin at a third site did not. It is apparent from the field data that the probability of meeting the turbidity discharge standard is dependent on rainfall characteristics, the hydrologic condition and size of the watershed contributing to the receiving stream, soil properties and soil conservation measures on the disturbed watershed, and the sediment basin design. Computer simulation results were obtained from the model SEDCAD+ for disturbed watersheds with sediment basins designed according to the Georgia Erosion and Sediment Control Manual. The results showed that sediment basins can be very effective in reducing suspended sediment in construction-site runoff. However, for a disturbed area with significant soil-conservation treatment, the peak sediment concentration in the sediment-basin outflow exceeded the undisturbed peak concentration for a meadow land use. This was the case for storm recurrence intervals from 2 to 25 years and for all three soils tested. For an undisturbed land use of 1/3 agriculture, 1/3 woods, and 1/3 pasture, disturbed sediment concentrations in the sediment-basin outflow were less than the undisturbed values. Sediment-basin trap efficiencies obtained from the numerical model varied from approximately 45 percent for the clay loam soil to 80 percent for the sandy loam soil. The trap efficiencies decreased with increases in surface loading rate. The numerical results suggest that an improvement in the design criteria for sediment basins would be to re-define the surface loading rate and to specify lower allowable values for soils with high percentages of clay. The numerical results also quantitatively demonstrate the importance of applying soil conservation measures so as to prevent as much sediment as possible from ever reaching the sediment basin. |
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