WATER-LEVEL MANAGEMENT OPPORTUNITIES FOR ECOLOGICAL BENEFIT, POOL-5 MISSISSIPPI RIVER

This paper examines the potential to manage Mississippi River water le vels for ecological benefits. The study focuses on the Weaver Bottoms, a 4,000 acre backwater marsh in southeastern Minnesota (Pool 5) highl y valued for fish and wildlife habitat. The Weaver Bottoms has suffere d increasing loss of aquatic vegetation and associated habitat degrada tion since the 1960s, largely due to persistent high water, sedimentat ion, wave re-suspension of sediments, and poor light penetration. In o ther reaches of the Mississippi River, water level reductions exposing backwater sediments have produced strong vegetative responses due to subaerial exposure of seeds and sediment compaction. Water level manag ement scenarios for Pool 5 were developed using the HEC-2 water surfac e profile model. Results indicate that in many years it would be possi ble to reduce water levels sufficiently to expose much of the Weaver B ottoms, generating a substantial vegetative response. Additional benef its could be expected since both sediment compaction and increased veg etation would reduce re-suspension of sediments. Shifting management p riorities to improve habitat would temporarily impact many river users , including both commercial and recreational boaters. Water level redu ctions must be coordinated with their needs.