How do droughts affect Lake Red Rock?

With the flood event of recent years, people are more familiar with high lake levels and dam outflows at Red Rock; however, the lake and dam have an important job to during drought conditions as well.

In addition to flood control, Lake Red Rock and Saylorville Lake were designed to provide “Low Flow Augmentation” – at their normal lake levels, or “conservation pools,” the two reservoirs store water to ensure at least minimum outflows. THese flows help maintain the river’s water quality for Des Moines downstream of Saylorville and from Red Rock downstream to Ottumwa.

While the drought of 1988 is fresher in memory, the drought that caused the greatest impact to Red Rock occurred in 1977. The lake’s conservation pool (normal lake level) at that time was 725 mean sea level (msl); however, due to low precipitation, Red Rock saw a record low pool of 719.68 msl. The lowest outflow through the dam on record occurred from June through August that same year when the dam released only 200 cubic feet per second (cfs), equal to about 1,500 gallons/second. This is very low compared to current outflows on March 6, 2012 of 3,650 cfs (approx. 27,000 gal/sec), and the record high outflow in July 1993 of 104,000 cfs (approx. 780,000 gal/sec).

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