Projects>Restoration Plan in Grant County Washington
Confluence was hired by Ducks Unlimited to develop five conceptual design alternatives for restoring aquatic habitat, riparian vegetation, and wetland habitat along four miles of Wilson Creek in the channeled scabland region of central Washington. The BLM had recently acquired 4,000 acres along Wilson Creek, and utilized Confluence’s restoration alternatives analysis to determine a course of action for restoring the project area.
Confluence employed two methodologies to estimate various flood return intervals within the project area. StreamStats, a USGS program available online http://streamstats.usgs.gov was used to delineate the watershed boundary upstream of the project site. This program computes various return intervals using regional regression equations for regions in Washington and was used to determine flood intervals at each of the two gage sites and at the downstream end of the project area. Existing data from the two USGS gages were used to develop estimated flood intervals at the project site using a drainage/area relationship.
Discharges in the Wilson Creek bypass channel were measured to determine base flow conditions. Discharges were measured using a Marsh McBirney digital velocity gage and incorporated into a velocity/area spreadsheet to calculate flow. Base flows were measured at five locations along the project reach to determine the effects of groundwater and irrigation diversions through the project reach.
In order to further understand subsurface soil and groundwater characteristics, six groundwater piezometers were installed throughout the project area. Installation of each piezometer included boring a 6” diameter hole to a depth of approximately 10 feet or to bedrock, whichever occurred first. A 4-inch screened PVC piezometer was installed in each hole and backfilled with bentonite. Each well casing was covered with a steel cap to prevent damage from livestock. Pressure transducers were later installed in each piezometer to provide continuous groundwater elevations.
Confluence developed at-a-station hydraulic scenarios for each restoration option involving reconstructing a new stream channel and floodplain through the project reach. Hydraulic parameters and proposed cross section dimensions were adjusted to design for floodplain connectivity at regular flood return intervals.
Five conceptual restoration design alternatives were proposed including reconstructing the channel through its historic floodplain, converting the riparian corridor from fallow agricultural fields to native riparian vegetation, and utilizing existing topography to enhance and construct wetlands. The conceptual design plans were submitted to the Bureau of Land Management to assist in developing a resource management and restoration plan for newly acquired parcels in the Wilson Creek watershed. The preferred alternative will be utilized as a tool for restoration planning and funding efforts of these parcels.
Nearly the entire valley floor had been converted to agricultural production beginning in the 1940s. Many of the formerly cropped areas were fallow for several years, resulting in a dense stand of undesirable species, including mustard, whitetop, japanese brome, and whitetop. As part of each restoration alternative, Confluence developed a revegetation plan to recover native species indicative of wetland, riparian, and streamside zones. An unfarmed reference vegetation area was identified within the project area, indicating former dominancy by bunchgrass species such as bluebunch wheatgrass, and basin wildrye.
The revegetation plans for the Wilson Creek valley included:
- Regrading altered topography to restore historic water table depths and areas prone to flooding.
- Aerial spraying of all fallow crops which had overgrown with undesirabe mustard and brome species.
- Discing and drill seeding of upland and riparian herbaceous species.
- Establishment of native riparian shrubs by transplanting or nursery stock.
- Establishment of food plots adjacent to newly constructed wetland features for waterfowl production.
- A comprehensive list of recommended upland and riparian grasses, forbs and woody shrubs commonly found along perennial streams of eastern Washington.