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• 1.0 INTRODUCTION This report presents the design of a river b.~utk stabilization project on the Williams Fork River at the RAG Empire Corporation, Eagle Mines. The Eagle Mines Site is located adjacent to Colorado Route 13 approximately 6 miles south of Craig, Colorado as shown on Figure 1-1. The principal objective of the design is to control stream bank erosion on the Williams Fork River in order to protect the rail spur to the mine. Stream meandering has advanced in one segment such that continued erosion would threaten the railroad embankment as indicated on Drawing 1. The reach of the Williams Fork River near its mouth is a meandering alluvial channel with an average slope of 0.0021. From the survey of the channel performed on April 16, 1999, the slope of the channel thalweg was found to quite variable while the slope of the water surface was more uniform as shown in Figure 1-2. The bank erosion that threatens the rail spur appeazs to be due to natural shifting of the channel course which occurs even in stable streams. Faster moving water on the outside of the bend continues to erode the bank at the base until the bank collapses. During the site visit in February 1999, it was evident that seepage from the cut bank during low flows also reduces the stability of the bank along with the absence of bank vegetation. The steep bank, approximately 6-feet in height, appeared along the west side of the channel from just downstream of the access road bridge to the last meander bend before the railroad bridge. Sediment deposition was occurring on the east side of the channel creating a gentle but irregular channel side slope with prominent gravel bars on the inside of the meander bends. Although covered with snow at the time of the site visit, little vegetation emerged from the snow on the gravel bars which are undoubtedly submerged during high flow. • AHA Filenarnc EmpveDesigi doc 1 07/30/99