Bob Dimmitt, a geotechnical engineer of the U.S. Corps of Engineers
Kansas City District, right, explains a recently assigned safety
rating of Pomona dam to Jim Green, Pomona, during an open house
last week at the project office.
Wayne White | Managing Editor
POMONA LAKE—The dam at Pomona Lake is significantly inadequate
with moderate to high risk, but nobody downstream should worry.
The official dam safety classification was released last week
during an open house at the Pomona Lake project office.
As explained at the open house March 2, the U.S. Army Corps of
Engineers implemented a national program for evaluating dams’
risks nationwide. Based on screening results, dams were rated
according to the Dam Safety Action Classification system on a
I to V classification. Normal and adequately safe dams are represented
by a V rating; I is a dam that is critically near failure or extremely
Pomona Lake dam is rated as III, meaning it is significantly inadequate
or moderate to high risk. The one-day inspection was conducted
in April 2009 by a team of experts.
According to the Corps, the results of the inspections of more
than 600 dams nationwide will be used to prioritize dam rehabilitation
“We want to put money where the dams are most at risk,”
said Bob Dimmitt, a geotechnical engineer of the Corps’
Kansas City District.
Dimmitt said that although the inspection of Pomona dam resulted
in identified concerns, the dam is not in danger of breach, and
it will continue to serve its purposes for many years.
The identified concerns are: Foundation rock is jointed and may
have small cavities that allow seepage during high pool; rip rap
on the dam face is weathered and degraded that could result in
erosion during extreme floods; and the dam has less drainage features
than newer dams, resulting in more concerns about stability and
Dimmitt said Pomona dam has a known seep on the left abutment
that is monitored daily.
“All dams leak. There’s never been a dam built that
doesn’t leak,” Dimmitt said. “As long as it
is controlled, it’s not a problem.”
Following the inspections, the Corps has budgeted for work at
Pomona Lake, including measuring seepage, surveying the drainage,
updating emergency action plans, scheduling coordination meetings
with emergency management officials, and public communication.
Dimmitt said on-site personnel inspect the dam daily looking for
unusual or changed conditions. More thorough inspections are conducted
monthly. In addition to annual inspections, Pomona dam is also
scheduled for a detailed five-year inspection in October.
The only other Kansas Corps dam to be rated as III was at Wilson
Lake. The primary concern at Wilson is seepage.
Nearby Melvern Lake dam was one of seven Kansas Corps dams rated
as IV, or inadequate with low risk or moderately safe. No risk
reduction measures are required for dams rated IV.
According to Dimmitt, the highest or safest rating of V applies
primarily to newly constructed dams and no dams in Kansas have