Hydrologic Characterization of Potential Sites for Restored and Constructed Wetlands, Montana

Problem:

The Montana Department of Transportation (MDT) works with the Montana Interagency Wetlands Group to avoid, minimize, or mitigate damage to wetlands that might result from highway construction. In the event that damage to wetlands cannot be avoided, new wetlands are constructed to replace those that are lost. Under this program, the MDT is responsible for developing, constructing, and monitoring the new or restored wetlands. At some localities nationally, inadequate pre-construction hydrologic analyses have resulted in unsuccessful attempts to create or restore wetlands. In order to ensure success in any future wetland creation or restoration efforts, the MDT needed hydrologic information and analysis for potential wetland sites.

Objective:

The overall objective of this project is to provide a framework and database within which the USGS can assist the MDT in developing and maintaining a successful wetland mitigation program by providing technical assistance with the hydrologic aspects of wetland construction. Specific objectives are to: 1) assist the MDT in developing a water budget for each wetland prior to construction; 2) provide information about probable water availability under a range of scenarios; 3) identify possible pre- and post-construction water-quality concerns; 4) monitor wetland systems after construction. Monitoring results will be used to evaluate the success of wetland mitigation, guide project management, and assess hydrologic impacts on the project areas.

Approach:

The study area and scope of work for each proposed site will be determined based on discussions between the MDT and USGS. All available topographic, hydrologic, geologic, and soils data will be compiled for each site. The water budget for the sites will be determined by the MDT with assistance from the USGS by estimating or measuring surface-water and groundwater flow into and out of the wetland. Precipitation and evapotranspiration will be estimated based on available climatic data or measurements made on site. Potential water-quality problems will be identified in general terms, based on the quality of water discharging from or to the site along with possible transformations of specified constituents through natural biological and chemical processes. Where water-quality is a potential concern, water-quality parameters will be measured in water from multiple locations at the proposed wetland site. Field parameters to be measured include: temperature, pH, specific conductance, and dissolved oxygen. In addition, water samples may be collected and analyzed for selected constituents to improve understanding of the geochemical processes that occur in response to changing hydrologic and biologic regimes.

Status:

Monitoring of groundwater levels and stream discharge and stage continues at several sites in Montana. Monthly water levels are being measured at sites near Laurel (Wagner Pit and Kindsfather Pit), Libby (Shrieber Meadows and McGinnis Meadows), Creston (MDT wetland), Nine Mile (Amon Ranch), Sula (Camp Creek), Big Hole (Sportsman Campground and Big Hole Grazing Association), Townsend (Hahn Ranch), Bozeman (East Interchange), Shields River (Easton Ranch), Emigrant (Murphy Ranch), Chinook (Reed Ranch), and Roscoe (Lazy EL Ranch). At some of these sites with active stream channels, seasonal stream flow measurements are also made. These sites include Shrieber Meadows, Bozeman East Interchange, Big Hole Grazing Association and the Easton Ranch on the Shields River.

Publications: none

Cooperator: Montana Department of Transportation

Project Chief: Sean M. Lawlor