Guthrie Lake and Liberty Lake receive fair conditions on dam inspections
The City of Guthrie recently released their annual dam inspection reports for Guthrie Lake and Liberty Lake as required by the Oklahoma Water Resources Board. Both dam reports received “fair” conditions.
Myers Engineering inspected the dams in December 2014.
The lake level was too low to access the intake structure during the inspection but was in fair condition during the 2013 inspection and was rehabilitated recently.
For Guthrie Lake, the west abutment and west spillway both received “poor” conditions. The abutment showed large tree growth along the downstream face and numerous animal burrows on the upstream face. The spillway had cracking and spalling of concrete as well as overgrowth of trees and brush. Many of the trees were cut but were left in the spillway. The report says by allowing the debris to remain on the spillway, it will trap moisture and cause freeze/thaw spalling to occur.
The upstream side of the dam was in fair condition with ample riprap armor, adequate to poor grass cover, excessive animal burrows and cleared of trees.
The downstream slope of the dam, east abutment, northeast spillway and the crest were given “satisfactory” conditions.
The downstream slope did not have adequate grass cover according to the report. A few trees were present as was animal burrows.
The east abutment on the upstream side was adequately protected with riprap and had moderate condition grass cover. The report says small saplings present on the downstream side that should be mowed.
The northeast spillway had trees and cattails in the spillway and need to be removed, the stilling basin should be cleared of vegetation and lined with riprap to dissipate energy and the joints should be resealed in the spillway and stilling basin.
The west stilling basin showed signs of spalling, scaling, and exposed reinforcement. The west stilling basin is insufficient to dissipate energy and has resulted in a large scour at the end of the stilling basin. The engineer company recommended to evaluate demolishing the west spillway and stilling basin and reconstructing the west abutment.
The crest was ruled as “satisfactory” condition. Cracking was found in the pavement that was caused by thermal expansion and contraction and normal wear.
Liberty Lake Dam Inspection
The intake structure was not inspected due to low lake levels. The locations of the pipe penetrations through the embankment were inspected and did not show signs of seepage or leaking.
The emergency spillway (east spillway) was in good condition, but the downstream slope was listed as being in poor condition.
The report found inadequate grass cover and numerous bare spots, but no severe erosion was observed on the slopes of the dam.
The crest of the dam was received a satisfactory condition with no signs of cracking, depressions, arching, settlement, erosion or livestock or animal burrows.
Several categories listed at the dam received “fair” conditions, including upstream side, downstream slope, abutment contacts and the concrete spillway.
There was no evidence of erosion on the upstream side of the dam, but had some small brush and a number of small trees.
The east abutment on the downstream side of the dam showed signs of erosion. No seepage was noted. The report suggests the area of erosion should be filled with compacted soil and lined with rip rap to prevent further scour.
Some spalling at joint s and minor cracking was noted during the inspection on the concrete spillway (west spillway). Engineers say the leakage at the joint s does not appear to have increased since last year’s inspection. This leakage should be reevaluated once the reservoir pool reaches the normal operating pool.