Stream bank erosion is causing concern about sediment buildup in parts of Perry Lake, a new study shows.

The reservoir is collecting sediment twice as fast as the U.S. Army Corps of Engineers predicted when the dam was built and the lake opened in 1969.

“As sediment accumulates, it reduces the water storage capacity,” said Kyle Juracek, hydrology researcher for the U.S. Geological Survey in Lawrence. “To address the problem, you have to have a pretty good understanding of where the sediment and erosion is coming from.”

Most of that sediment is coming from eroding banks along stream channels that lead into the lake, the study found. The primary stream is the Delaware River and its tributaries. The most affected area of the lake is upstream from the causeway, Juracek said.

The latest two-year study follows an earlier study, the results of which were released in 2003. That study was to determine how serious the sedimentation problem was, while the latest study determined the general cause of the problem.

The earlier study found that sedimentation had taken away 23 percent of the water conservation pool in the lake. The conservation pool is the normal pool level the Corps of Engineers prefers to maintain for multipurpose use. An estimate in 2006 increased that to 26 percent.

“The annual rate is less than 1 percent (increase) per year, but it is filling in twice as fast as the Corps predicted,” Juracek said.

The lake still has many decades of use remaining, Juracek said. But there is reason for concern because the state not only uses its reservoirs for flood control but it also spends millions of dollars purchasing water for storage – and that storage capacity is being reduced.

Eventually something will have to be done, Juracek said. Dredging is one option. At John Redmond Reservoir near Burlington, the level of the conservation pool was raised because of sedimentation.

“That’s just a temporary solution,” Juracek said. “You can’t keep raising the pool because you’ll run out of dam.”

Still to be determined at Perry is specifically where the main erosion problems are along the inflow stream channels. That would take another study, but none is planned.

Once erosion problem areas are identified, ways to slow runoff sediments and control bank erosion can be developed. That is something the Kansas Water Office is interested in, said Earl Lewis, operations manager. The water office split the cost of the latest study – $200,000 – with USGS and the Kansas Department of Health and Environment.

“Over the last five or six decades, the state and federal governments have spent a lot of money on soil conservation to try to keep soil on the land from washing down into the streams,” Lewis said. “We haven’t really seen the sediment reduction that you normally think of.”

While stream bank erosion has been identified as the main problem for Perry Lake, runoff from fields is still a concern farther up the basin, Lewis said.

“We need to figure out how much we’re looking for additional research and how much we are going to work with local stakeholders to identify those areas that need improvement,” Lewis said.