Missouri’s Oxbow Lakes Georganne Bowman Water Protection Program DNR January 24, 2006

Oxbow Lakes n How do oxbows form? n Missouri’s oxbows: –What’s the water like? –What are they good for? n How should we manage oxbows?

How Do Oxbows Form? n Large river flood plains. n Snake-like meanders. n Maintains gradient and velocity.

1) The water on the inside of the loop, travels slower than the water on the outside edge. This leads to deposition of sediment in the corners. How Do Oxbows Form?

2) Meanwhile, water on the outside of the turn flows faster, which erodes the banks making the meander even wider. 3) The neck of the “yoke” closes in. How Do Oxbows Form?

4) During a high flow event, the meander cuts off from the main channel. A horseshoe shaped oxbow lake forms. How Do Oxbows Form?

n The new lake is cut off from the river. n Flooding brings in nutrients and fish. n Sedimentation occurs with each flood event. n Short life span.

Missouri’s Oxbows n Missouri and Mississippi floodplains. n Smaller rivers. n Approximately 24 classified

What is the water like? n n Very Shallow. – –most oxbows are less than 3 meters deep. n n High nutrient loads. n n Can Be Very Productive. – –Unless light limited. n n Constantly Mixed. n n Where’s the watershed?

What is the water like?

n n Four oxbow lakes sampled monthly summers from – –Cooley, Sunshine, Teteseau, and Dalton. – –Surface area ranged from 17 – 323 ha. – –Mean depth at normal elevation for these oxbows was < 1 meter.

What are they good for?

Big Lake State Park: n n Big Lake is the largest remaining oxbow lake in Missouri. n n The shallow lake has a long history as a recreational area (prior to 1932). n n Created one of the first public recreation areas in northwest Missouri. What are they good for?

n Current river management: –Channelization keeps meanders from forming. –Levees prevent floods from refilling. –Runoff leads to eutrophication. –No new oxbows formed. How Do We Manage Oxbows?

Lake Dredging: “As a part of the Page Avenue Extension, MoDOT will dredge the main body of the lake. The dredging will restore the lake to a minimum depth of 10 feet.” -Creve Coeur ($10,000,000) Pumping: “The state will spend up to $2,000 per year — to ease the costs of pumping — at some oxbow lakes.” - St Joseph News Press Water level control for waterfowl hunting.

Oxbow lakes united State officials should work St. Joseph News-Press (11/20/05) Oxbow lakes pose a very tricky conundrum for the state of Missouri and the people who live on the shores of those lakes. The lakes belong technically to the state. But when it comes to keeping the lakes from drying up, the burden lands mainly on local landowners. How Do We Manage Oxbows?

n n Blessing and Curse: – –High wildlife and recreation value. – –Limited resource. – –Long history. n n BUT: – –Will never be “high quality H 2 O”. – –Must be maintained - very costly. – –Probably not used for swimming.

How Do We Manage Oxbows? n n Setting Nutrient Criteria Values. – –Maintain hypereutrophic values? – –Allow these lakes to function as wetlands? – –Other ideas/comments?