LDPE LINED HIGH VELOCITY CHANNELS

摘要

Temporary diversion channels are conventionally lined with riprap, especially if high flow velocities are expected. Due to the confined space and concerns about leakage, LDPE (Low Density Polyethylene Geomembrane) lined temporary diversion channels were designed and constructed for a hydropower dam decommissioning project on Vancouver Island. The constructed trapezoidal channels ranged in size from 1 m to 4 m bottom widths, 1.5 m to 4.5 m depths, with slopes of 2% to 25%. Flow velocities of up to 7 m/s were estimated, with depths of flow varying from 1 m to 2.5 m. Each channel contained a right angle bend, which was constructed with a riprap splash pad. Allowances were provided for superelevation, due to gradual bends, and cross waves. Flared inlets were required to accelerate the flow into the channel, and plunge pool outlets were required, to dissipate the energy from the high velocity flows. Two channels were constructed and then removed after the former hydropower diversion dam was decommissioned, removed and the river bed reconstructed. The author is not aware of any other LDPE lined channels of this size or with these high velocities having been designed or constructed. These lined channels have a wide range of applications for clean and contaminated water management.