Shell Creek Watershed Improvement Group Exploring Innovative Bio-Engineering Approaches to Stream Restoration
Facing ongoing challenges with erosion, water quality and flooding, the Shell Creek Watershed Improvement Group (SCWIG) is looking at some innovative approaches to improving the health of this watershed in northeast Nebraska.
SCWIG, a group of landowners and farmers that formed in 1999, has seen considerable success in promoting no-till, buffer strips and other Best Management Practices to help improve the quality of the water draining into Shell Creek. Now, the group is ready to tackle some of the major structural issues with the creek itself.
Like many Midwestern streams, Shell Creek has been altered significantly from its historical norm. Land use changes and channel straightening have resulted in much steeper slopes in the creek’s channel, which has increased water velocity. This in turn has led to greatly increased bed and bank erosion.
To determine the scope of these problems, SCWIG worked with EA Engineering, Science, and Technology, Inc. to establish the Shell Creek Watershed Environmental Enhancement Plan, which includes a “geomorphic assessment” report for Shell Creek. The report, prepared by Interfluve Inc., an engineering firm specializing in river restoration, was finalized in late July 2014.
The report found that the creek has cut its way down 10-25 feet below its historic elevation along much of the 100+ miles of the system, which has made restoration efforts more challenging. Banks have become high and steep in many places, cut off from their former floodplain. Floodwaters, trapped in the creek’s deeper channel, have become faster, causing rapid downstream flooding and increasing erosion rates even further.
The creek is also widening, with bank erosion rates of up to 6 feet per year in some areas in the lower end of the watershed near the Platte River. Overall, approximately 50 acres were lost to bank erosion from 1993-2012.
To deal with these issues, SCWIG is exploring several options that will be presented to the public as part of the Shell Creek Watershed Environmental Enhancement Plan at a public Open House on September 18th in Platte Center.
As a result of input from SCWIG and other project partners, including the Nebraska Department of Environmental Quality and the Lower Platte North Natural Resources District, three kinds of structural improvements to the creek have been identified as priorities.
To help reduce bank erosion, the group is looking at “log cribwall stabilization,” a bioengineering alternative to the traditional rip-rap method. The log cribwall approach involves placing stacked layers of logs, rocks, and soil along the edges of a creek. This lattice-like structure helps reestablish a natural floodplain for the creek and provides a bed for native vegetation to grow, which also improves aquatic habitat.
Another practice under consideration is “bench wetland restoration” to reduce further cutting of the creek channel and to provide an outlet for confined floodwaters. This would involve reconnecting orphaned oxbows to the creek by excavating them down to the current flood level. This design would allow high-water events (typically 2-3 times per year) to flow into the oxbows and help establish wetlands that would provide wildlife and aquatic habitat, flood storage, groundwater recharge, and filtering of water pollutants.
Tributary stabilization is the third structural measure being considered. Along the lower reaches of many of Shell Creek’s tributaries, “knickpoints” have formed - areas where mini-waterfalls have resulted from the tributaries trying to cut their way down to the main creek’s level. Grade-control structures could help stabilize these knickpoints, reduce erosion rates, and prevent further downcutting in the tributaries.
Ongoing promotion of Best Management Practices throughout the watershed will continue to be a priority for SCWIG as well, with cost-share programs available to assist landowners with a variety of conservation practices.
An Open House was held in Platte Center in September 2014 to update landowners, farmers, and city and county officials on the Environmental Enhancement Plan.
To move forward with restoration plans, SCWIG is pursuing grant funds from several partners this fall, including the Nebraska Department of Environmental Quality, the Nebraska Environmental Trust, and the Lower Platte North NRD. If approved, design and permit work could begin as early as April 2015, with construction beginning the following year. Specific project locations have not yet been determined, but will likely focus on bridges, roads, and other important infrastructure. The project partners are encouraging property owners to assist with project siting and plan implementation.