Design Criteria for Sediment Basins

About the report:

The need for controlling construction induced sediment to keep it from entering the nation's waterways is generally accepted. Efficient means and methods for sediment control, however, are not simple, and in some cases have not been developed to a high degree. A look at the overall picture of sediment control shows two distinct approaches: (1) Control of erosion, and (2) interception of errant soil once erosion has taken place. Obviously erosion control (mainly by vegetation) is the preferred approach. However, during periods of active construction and before vegetation is established, erosion is inevitable. The problem is then to intercept the waterborne sediment produced and confine it to the construction area. According to William M. Smith, County of Fairfax Public Works, flows below 15 CFS based on a 10-year rain can be controlled by berms, and straw and brush dams, which are less expensive than silt ponds or basins. On the other hand flows in excess of 400 CFS (again based on the 10-year storm) are too large for the practical design of silt basins, so efforts should be concentrated on protecting the stream from construction by placing traps, berms, and barriers along the stream banks, So, in essence, use of the siltation pond or basin is limited to situations where high flows will range from perhaps somewhat less than 15 CFS to a maximum of 400 CFS, based on the 10-year storm event. Finally, this short report will consider only the volume aspects, or trap efficiency, of the ponds and not the design of the dam, riser pipe, spillway, etc.

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