Shallow Water Habitat for Pallid Sturgeon
By John Remus
U.S. Army Corps of Engineers
Editor’s Note: This is a continuation of articles on issues facing the Missouri River Mainstem System and efforts by the Omaha District of the U.S. Army Corps of Engineers to address them. This series of articles began in the last issue of the Water Current and conclude in this issue. The UNL Water Center particularly wants to thank Rose Hargrave and Mary Roth at the Corps for their involvement in this project - SWR.
Several methods in the Missouri River to provide shallow water habitat for endangered pallid sturgeon have been introduced by the U.S. Army Corps of Engineers (Corps).
Before development, the Missouri River ’s natural features offered a wide range of flows, depth and water velocity for native species such as pallid sturgeon.
At that time, the river channel and adjacent flood plain consisted of a main channel, secondary channels, side channels, emergent and submerged sandbars, backwater areas and oxbow lakes. The continuous meandering of the river and large floods kept these natural features of the river intact.
After the Corps developed the river to support navigation and flood control a number of changes affecting native species began to occur.
Development confined the river to a single channel, prevented it from meandering and removed larger floods from the hydrologic cycle. The result is a nearly uniform channel in the lower 735 miles of the river.
In 2000, U.S. Fish and Wildlife Service issued a biological opinion (BiOp) requiring the Corps to provide 20-30 acres of shallow water habitat per river mile from Sioux City , Iowa to the mouth.
There are several ways the Corps can meet BiOp objectives. Currently, there are about 3,000 acres of shallow water habitat in the lower river. In addition, modifying discharges from Gavins Point Dam can create a maximum of 1,200 acres of shallow water habitat, or less than two acres per river mile. The goal is an overall increase in depth and velocity diversity across the cross section with at least 20-30 acres in the five-foot deep range and 2.5 feet per second range.
Finally, the remaining 14-25 acres per mile of habitat are being provided through a reconstruction of the Bank Stabilization and Navigation Project. The Corps has begun using techniques designed for depth diversity.
Success of the shallow water habitat program relies on the ability of these methods to sustain habitat over time. This will require continued monitoring and assessment. The Corps is in the beginning stages of a comprehensive monitoring and evaluation plan that will verify the effectiveness of these treatments and aid in developing new activities.
Shallow Water Habitat Construction Techniques Used by the Army Corps of Engineers in 2004
Type |
Construction |
Benefits |
Projects Completed in 2004 |
Dike Notches |
Part of an existing dike is removed or a lowered section is left un-repaired. Generally are 50 feet wide and 3-5 feet below the normal water surface elevation. |
Allows flow into and out of the dike fields at a wider range of flows, can create complex sandbar/side channel habitats, provide for a sandy rather than silt substrate, and develop greater overall depth and velocity diversity. |
420 dike notches, (about 492 acres of SWH) |
Revetment Notches |
Part of an existing revetment or kicker structure is removed a lowered section is left un-repaired. Vary from 50 to 100 feet wide and are typically 5 feet below the normal water surface elevation |
Connect existing pool areas to the main channel at lower flows, provide for a sandy rather than silt substrate, and develop greater overall depth and velocity diversity. |
91 revetment notches, (about 120 acres of SWH) |
Bank Notches and Type B Notches |
Remove part of an existing dike and excavation of the high bank. Vary from 50 to 100 feet wide; are generally at least 75 feet long. Depths vary but are generally 5 feet below the normal water surface elevation. |
Create new habitat immediately and afterwards. Introduce sediment to the river and increase the alluvial dynamics. Allow flow into and out of the dike fields at a wider range of flows, can create complex sandbar/side channel habitats, provides for a sandy rather than silt substrate, and develops greater overall depth and velocity diversity. |
200 notches (about 460 acres of SWH)
|
Major Dike Modifications |
Remove a large part of the dikes in a bend and the construction of additional structures in the main channel (chevrons). This treatment is a major top width widening technique. |
Creates new habitat immediately and afterwards. Introduces sediment to the river and increases the alluvial dynamics. Can create complex sandbar/side channel habitats, provides for a sandy rather than silt substrate, and develops greater overall depth and velocity diversity. |
16 miles (about 8 acres of SWH). However, this technique created greater depth diversity of the entire channel that other techniques, and it is expected to create 8-15 acres per mile once the areas mature. |
Pilot Channels |
Excavated trenches between two or more revetment notches. The purpose is to provide SWH along the outer sides of the bends where the water is generally deeper and velocities are faster |
Creates new habitat immediately and afterwards. Introduces sediment to the river, increases the alluvial dynamics, and develops greater overall depth and velocity diversity. |
Nearly 11,000 feet pilot channels (about 43 acres of SWH). |
Chutes |
Excavated trenches between two or more pool areas or a channel excavated across a point bar. Provide off channel habitat that would be similar to the side chutes in the natural river. |
Creates new habitat immediately and afterwards. Introduces sediment to the river, increases the alluvial dynamics, and develops greater overall depth and velocity diversity. Can also create a small delta area in the vicinity of their outlet that also has SWH benefits. |
Three chutes (about 78 acres of SWH). |
Dredged Backwater Areas |
Dredging remnant backwater and oxbow lakes to create shallow off channel areas. |
Creates habitat immediately and introduces sediment to the river. Areas are not dynamic. |
4 backwater areas (about 135 acres of SWH.) |
