From October 1972 through September 1977, the effects of highway construction in the 38 square mile Blockhouse Creek basin were studied. Water discharge, suspended-sediment discharge, and stream-temperature data were collected at four stations in the basin. The 5-year period included 1 year before construction, 2 years during construction, and 2 years after construction. The effects of stream relocation and sediment-control methods used in the highway construction were also investigated.
During the period of data collection, about 35,500 tons of suspended sediment was transported by Blockhouse Creek and Steam Valley Run. The data indicate that 9,100 tons was introduced to the stream from construction areas. The normal sediment yield for the two basins was determined to be 80 tons per square mile per year. Most of the sediment was transported by the streams during high flows and probably passed through Blockhouse Creek, as little deposition was observed below the construction area. Stream temperature seemed to be relatively unaffected by the stream relocations and diversions.
Stream relocation and diversion methods were successful in limiting the amount of sediment discharged by the new channels. Physical sediment-control methods limited sediment discharge during baseflow periods and small storms. Coarse sediments especially were controlled by these methods. The most effective method of sediment control was limiting the amount of time that the construction-area soils were exposed. (USGS)
