CCRC presented with new reservoir design similar to original plan

A new task order was presented to Clarke County Reservoir Commission (CCRC), and it’s on par to the original design of a new reservoir.

During a June 16 CCRC meeting, Mark Duben, water section manager and vice president of HDR Inc. of Des Moines, presented a report on updated future water demands and hydrology and hydraulics at dam site 4B, the location of the reservoir.

For the current and future raw water demands for Clarke County, the total average raw water demand used for design projected for 2037 is 2.79 million gallons per day.

Of that, West Lake has been projected to satisfy .8 million gallons per day of that demand.

The new projected reservoir design source would have a supply capacity of 1.99 million gallons per day of raw water demand. The original reservoir designs have projected 2.2 million gallons per day.

“With that, we did a similar analysis to what we presented a few months ago on a smaller alternative,” Duben said.

The reservoir

The original plan was for CCRC to build a reservoir project located in northwest Clarke County.

The reservoir was to provide a water supply for Osceola and Southern Iowa Rural Water Association (SIRWA) with an 816-acre lake, which could provide 2.2 million gallons of water per day.

West Lake, the current water source, doesn’t meet the needs of Clarke County and SIRWA. Funding for the project includes many sources, especially funding from the local-option sales tax.

However, there have been legislative setbacks and issues with landowners and eminent domain, which has caused CCRC to look into reducing the design of the reservoir.

January alternative

In January, Duben presented alternative spillway concept resulted in an estimated cost increase of nearly $22 million, including structural and overall construction contingencies.

Another drastically changed design feature was the volume of the available water supply volume, measured in acres-feet. The original design had 11,780 acres-feet. The new modified design has 3,850 acres-feet.

The available water supply in million gallons per day went from 2.2 million to 1.2 million.

CCRC members weren’t in favor of that plan.

June alternative

In the June presentation, many things stayed the same, including the top of dam still being 1,021 feet.

The only major change in the new analysis was the normal pool dropping by a foot. The normal pool storage drops from 13,685 acres-feet to 12,880 acres-feet.

The sediment pool and sediment storage still remains the same.

The available water supply in acres-feet went from 11,780 in the original design to 10,975 to the current proposed design.

A cost analysis wasn’t available during the CCRC meeting.

Duben said the important thing to notice in the new task order was the available water supply in million gallons per day only went from 2.2 to 1.99.

“So, very little change here,” Duben said. “The footprint of the reservoir itself, top of dam remains the same, that footprint remains the same. Very little change in that 400-foot buffer due to the smaller pool, but a little bit of change there. So really, one foot lower normal pool.”