Washington State’s Dam Safety Office in the Department of Ecology (DSO) took advantage of the drawdown of the Lake Tapps Reservoir to do its proscribed evaluation of the dikes surrounding the reservoir in February.
The reservoir was originally created by flooding four small lakes and is held in place as “Lake Tapps” by a series of 15 dikes. These earthen dikes are inspected at least once every five years to determine safety and security. The DSO inspected the reservoir (water) side of 13 of the dikes.
Later this year, DSO will return to inspect the landward side of these dikes. This inspection, when the reservoir is full, will enable DSO to assess any seepage through the dikes. The DSO typically provides Cascade with a report on the condition of the dikes following the final inspections. Cascade will then plan to implement any required improvements necessary to ensure the integrity of the dikes.
The reservoir had been drawn down to allow for Cascade’s installation and testing of repaired, rehabilitated and new valves at the Powerhouse. Active refill began last week. The reservoir is rising rapidly – as much as three to four inches per day (two to 2.5 feet per week). At this fill rate, Cascade anticipates the reservoir will reach full recreational level of elevation 541.5 feet by mid-March.
Cascade will, for a short time during the spring, raise the level up to elevation 543 feet, which is the maximum permissible level for Lake Tapps, to remind residents of the legal high water mark. This is done every year during the spring. Cascade will maintain Lake Tapps at an approximate elevation of 542.6 to 542.8 feet throughout the summer and early fall.