Lake Red Rock: Past, Present & Future

In 1965, the United States Army Corps of Engineers had embarked on a project to build a dam on the Des Moines River in Marion County approximately 35 miles from Des Moines to control flooding in southeast Iowa and on the Mississippi River. The project, Red Rock Dam, was completed in 1969 and the resulting reservoir was christened Lake Red Rock. Red Rock dam and lake were architectural marvels, creating the largest flood control structure and largest lake in Iowa respectively. The project cost approximately 88 million dollars but expenses were quickly recuperated from the prevention of destruction cause by seasonal flooding annually.

The dam itself is a gravity fed flood control structure meaning there is no pumping or movement of water by mechanical means from the reservoir to the river below. Red Rock dam consists of five flood or tainter gates each with a maximum outflow capacity of 20,000 cubic feet per second and 14 submerged sluice gates. The tainter gates are the emergency method of flood control when the reservoir becomes filled to beyond flood stage and beyond the capabilities of the sluice gates. The sluice gates are submerged in the area beneath the tainter gates in an area known as the stirring or outlet basin. Each sluice gate has maximum outflow capacity of 1,000 cubic feet per second making the maximum outflow capacity of the dam approximately 114,000 cubic feet per second. The reservoir, Lake Red Rock has a normal surface area of approximately 15,520 acres that, in times of flooding, can expand to more than 70,000 acres. Large concrete obstructions called baffles were installed below the sluice gates to slow the water as it came through the dam in order to prevent erosion. Each baffle weighed several tons and was the size of a car. The reservoir was created when the dam was completed flooding the surrounding area including the former town, and name sake of the project, of Red Rock.

The town of Red Rock is located about five miles north of Knoxville. The city itself was established on and the Des Moines River and as a result, many homes were displaced in the surrounding river valley were displaced following the construction of Red Rock dam. The evidence of these homes and farmsteads can still be seen in times of low water on Lake Red Rock. The previous highway 14 bridge just a few miles north of Knoxville that previously ran through Lake Red Rock is largely intact and is also visible during periods of low water.

Upon construction, the dam was built with the intended lifespan of 100 years. After this period, the dam would be evaluated and the decision would be made to either decommission the dam or continue its operation. Several factors would be involved in determining the continued operation of the dam including: overall condition, functionality, cost of repairs and possible upgrades, and the viability of the dam as a flood control structure. Many forces are currently working against the existence of the dam and lake and may have an impact on the lifespan of the project, the main force being the decreasing amount of storage capacity in the reservoir due to infiltration and build up of top-soils and silts. According to an interview with Bill Ehm, the Department of National Resources Water Resource Policy Director, in an article published by Jason Johnson on the United States Department of Agriculture’s Natural Resources Conservation Service website, “the amount of sediment flowing into the lake is equal to 456,000 dump truck loads of soil runoff into the lake annually.” Top-soil runoff comes primarily from agriculture fields but can also come from construction sites and bare soil areas with little vegetation. The continued build-up is reducing the amount of floodwater the reservoir can hold and also introducing agricultural chemicals into the surrounding ecosystem and food chains. Ehm continues to describe the amount of topsoil infiltrating the reservoir, “sediment buildup in the lake is an innate problem, however, because of the number of acres that drain into Red Rock. More than 500 acres of land sheds water for every acre of lake. To put that in perspective, most lakes have a 20 or 40 to one ratio.” This problem, however, has not gone unnoticed and the DNR is working on erosion control methods along tributaries that dump into the Des Moines River. Some farmers are also doing their part but implementing erosion control methods including the installation of tiling and terraces. Some farmers have even switched to no-till farming methods that preserve the topsoil by not plowing and disking agriculture fields.

           The future of operations at Red Rock is dependent on controlling the topsoil influx primarily. Whether or not the dam will continue to function up to or after its planned lifespan rests on whether or not the reservoir can continue to be a viable flood control structure. Despite the grim outlook, the future looks bright for Red Rock Dam, literally. A hydroelectric power plant is slated to be installed in the pre-existing structure of the dam with construction starting in late 2013 and being completed by 2016. According to a press-release from the US Army Corps of Engineers website, the power plant will generate power for 8,000 homes in the Marion, Mahaska, and Jasper county area. The project will create 500 new jobs over the construction period and will create an economic benefit of $250 million to the surrounding area. Hopefully with continued work on preserving topsoil upstream, and preservation of natural forms water retention downstream, Iowa’s largest lake will continue exist, and the dam, continue to function.