WSP11210 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I iJJ2l:J8 4.0 DISCUSSION Erosion is, in most cases, a natural activity occurring on reservoir shorelines. However, due to numerous possible factors, the intensity of this normal erosion activity can be increased. This increase can lead to resource risks, including decreased stabilization of shoreline banks near campgrounds and roads. In these cases, erosion sites may need to be actively managed. The twenty-two erosion sites identified in this survey are located on all shores of the Williams Fork Reservoir, and are predominantly caused by normal wave activity. Only erosion sites ER02-l718, ER02-1721, and ER02-1722 present a significant resource risk, The other nineteen erosion sites present no resource risk or only minor resource risks in the form of aesthetics and/or loss of upland areas, Erosion site ER02-17l8 is located adjacent to the southern campground at the confluence of the Williams Fork River with the Williams Fork Reservoir. At this location, the river is cutting into the bank and erosion is encroaching on campsites. At the time of this erosion survey, two campsites were observed to have been partially lost to erosion of the river bank, The cause of increased intensity in this erosion site is not fully known. However, it appears that construction of the new bridge approximately 200 yards upstream of erosion site ER02-1718 has altered water flow patterns of the river, leading to increased erosion in specific areas. As water passes through the concrete footings of the bridge, its velocity is increased as it is funneled in a straight line, The straight line created by the bridge forces the water towards the bank of the river supporting the campground. As a result of the water being forced directly into the stream bank at an accelerated velocity, the intensity of erosion activity in this area has been increased. The potential for significant erosion to continue at this site is high, especially during peak flow events in the Williams Fork River. Erosion sites ER02-1721 and ER02-1722 are located in line with one another (from north to south respectively) on the eastern shore of the reservoir. Erosion at these sites has created high bluffs along the shoreline, and is continuing to encroach on upland areas located adjacent to private lands just east of the reservoir and FERC boundary line. The high bluffs at these two erosion sites continue to be eroded by bank cut processes. Waves generated within the reservoir erode the lower soil levels first, undercutting the bank. As sediment is removed at the base of the bluffs, the layers of soil above lose support and fall to the beach where they are eroded away, This active process continues to result in the loss of upland areas on this portion of the Williams Fork Project. This reservoir bank was split into two separate erosion sites, as opposed to one long continuous site, because characteristics of the two sites are different. Remediation activities have already begun on the northernmost site (ER02- \ 721), The reservoir bank at this site has been graded back to create a more gradual slope, and large cobble has been placed at the toe of the slope. At the time of this erosion survey, the grading activity had only been completed on a portion of the erosion site. No remediation activities have taken place on erosion site ER02-1722, and the upland banks on this site are much Williams Fork Res~rvolr Hydroelectri<.: Project January 2004 Stelgers CorporatIOn Erosion S\lrv~y Report Pagt' 7