Environmental Assessment, Emergency Streambank Protection, South Raccoon River, 8-Inch Water Supply Line, Stuart, Iowa

摘要

The purpose of this study was to assess various measures to provide streambank protection along the left descending (i.e., north) bank of the South Raccoon River in Dallas County, Iowa. A water pipe, which conveys domestic water to Stuart, Iowa, in neighboring Guthrie County, underlies the riverbank and riverbed and is being threatened by bank erosion. Concrete-Filled Mattress, Riprap Protection, and No Action were considered as alternatives to control the erosion at the study site. Of these alternatives, Riprap Protections was chosen as the selected plan because of its lower construction cost and because it was more environmentally sound. The selected plan entails grading and shaping 150 linear feet of the eroded riverbank (75 feet on either side of the buried water line) to provide a uniform slope of 1V on 2H, and placing an 18-inch layer of Iowa Class D riprap as shown on plates 2 and 3. An estimated 600 tons (i.e., 400 cubic yards) of graded riprap is needed to construct the streambank protection project. Approximately 142 cubic yards of material will be placed below the ordinary high water elevation of 901.5 feet National Geodetic Vertical Datum (NGVD). An environmental review of the proposed action indicates that the proposed project would not result in significant effects on the environment. Therefore, an environment impact statement will not be prepared. (fr)