A Wanapum Dam drawdown on the Columbia River is highlighting concerns for fish protection, irrigation, and hydro power generation. After a 65-foot horizontal crack was spotted at one of the dam's 12 spillways in February, a drawdown was put into effect by its owner, Grant County Public Utility District. The Dalles Chronicle reported March 15 that the drawdown is the steepest one since the dam went into operation back in 1964.
The reservoir drawdown was placed behind the hydro project to reduce the amount of pressure put on the faulty spillway. Grant PUD said the cracked spillway is stabilized with a drawdown at a minimum of 541-feet elevation.
Given this is the steepest drawdown since Wanapum Dam began operating, the decreased "head" has meant hydro production is performing at only half what it was before since water pressure "drives" the turbines.
“There isn’t as much force, potential energy, above the dam,” said Chuck Allen, Grant spokesman.
Gravity-fed fish ladders are a major concern as well with the Wanapum Dam drawdown. There are plans to modify two fish ladders at the dam to allow migrating fish to pass through during the spring and summer months. Grant PUD is also weighing options for capturing fish and transporting them around the reservoir, the report added.
Irrigators with land-use authorizations for withdrawing water from Wanapum reservoir will be provided details and technical information on how they need to prepare for the irrigation season. According to the report, 11 orchard irrigators affected by the Wanapum Dam drawdown have already been contacted individually by the utility. Irrigators seeking information from the Dept. of Ecology can visit this page HERE.
No date has been mentioned about when water levels will be raised. Grand PUD and contractors are examining the spillway's damage to determine the best way to repair it. The evaluation is expected to continue until next week and also involves independent consultants and officials with the Federal Energy Regulatory Commission to determine what method will be used in repairing the cracked spillway pier. Water levels can hopefully be raised to intermediate levels during the repair phase.
A number of others are impacted with the drawdown since Grant PUD is also working with Chelan PUD in addition to other dam operators on the Columbia River. Government agencies and tribes have also been affected by the drawdown of Wanapum Dam.
Copyright © 2014 Heather Tooley
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