| Popis: |
Rock check dams are commonly installed in construction site ditches to reduce the potential erosion that can occur during runoff events. Recent tests at field sites have suggested that check dams constructed of fiber materials, such as coir, straw, and excelsior may outperform rock in reducing ditch erosion, and adding polyacrylamide (PAM) can significantly reduce turbidity. This paper describes tests of three check dam types for turbidity reduction under controlled conditions. These included standard rock, rock wrapped in an excelsior blanket, and excelsior wattles. A series of three check dams were installed in a 24 m, lined ditch with a 5-7% slope. A simulated storm was introduced to the ditch for 20 minutes, with sediment added and a peak flow of 56 liter s-1 (2 cfs). Samples were taken on the downhill side of each check dam and analyzed for turbidity. The excelsior wattles with PAM produced significantly lower turbidity than the rock check dam, although adding PAM to that greatly reduced turbidity as well. When compared to untreated check dams, PAM reduced turbidity by 61-93%, down from a range of 350-1300 nephelometric turbidity units (NTU) to 47 – 229 NTU. The rock + excelsior and excelsior wattle dams maintained substantial flocculation potential after three events, but the rock dam did not. The maximum potential concentration of PAM was 5 mg L-1, well below levels known to be non-toxic, but an indirect measurement indicated concentrations more than 100 fold lower after mixing with suspended sediment. |
