THE ASHLU HYDROELECTRIC PROJECT: A CASE STUDY OF A RUN-OF-RIVER HYDROELECTRIC PROJECT IN SOUTHWEST BC

摘要

The Ashlu Hydroelectric Project is a run-of-river hydro scheme in southwest BC, Canada. The project is on Ashlu Creek, upstream of the confluence with the Squamish River. The project uses a head difference on Ashlu Creek from the intake to the powerhouse. The project straddles the "hanging valley" where the Ashlu enters the Squamish valley. The intake and powerhouse are at the upstream and downstream extremes of a steep-sided, narrow canyon. The powerhouse is tucked into the base of the steep valley but the intake is above the narrow section of the creek where the valley opens up.The intake structure consists of an earthfill/rockfill embankment, a spillway with an Obermeyer gate and a sluiceway/intake. The spillway and most of the intake are founded on bedrock but the embankment and the sluiceway are founded on alluvial sediments. To avoid excavating a trench down to bedrock or installing a pile cut-off wall, an upstream blanket was designed to control seepage. As there are no sources of low permeability soil at the site, a geomembrane was used for the impervious unit of the upstream blanket. To prevent seepage from lifting the geomembrane, the geomembrane joints are not sealed so that pressures can be relieved. Minor seepage through the overlaps of the geomembrane is not a serious concern. This is one of the first applications of this design.This paper presents the design and construction of the unique aspects of Ashlu Hydro Project with particular focus on the intake/spillway/embankment structure on Ashlu Creek.