Section 32 Program. Streambank Erosion Control Evaluation and Demonstration. Work Unit 2-Evaluation of Existing Bank Protection. Field Inspection of the Fisher River Channel Realignment Project near Libby, Montana

摘要

In September 1967, NPS conducted an inspection of the completed groins in channel changes and prepared a report on the findings. Construction records indicated that 28 groins were in place prior to the spring 1967 runoff. Four of these groins were badly damaged, three to the extent that they were hardly recognizable, and the remaining twenty-four all appeared to have been modified to varying degrees, mostly in the weir sections. Stone weighing less than 200 lb generally appeared to have been moved out of the groin and swept downstream. The groins were considered to be effective in reducing erosion and adequate, but not ideal, in the creation of suitable aquatic conditions. The report further indicated that the ability of the groins to direct water flows had been reduced by the spring runoff and their useful life would probably average less than 10 years. In many cases the digging action of the water flowing over the groins had created good fish habitat; however, there was concern that these pools would only be temporary features of the stream, unless steps could be taken to place material that could resist peak discharges. It was recommended that the groins should be constructed of stone ranging from 200 to 2,000 lb, with 50 percent of the stone weighing over 1,000 lb. At the time of the WES inspection visit, the project reach was stable; no serious channel degradation or aggradation was noted. Although groin rock was scattered downstream at some locations, many of the groins were intact. No riprap blankets placed on side slopes had failed.