The United States Geological Survey Water Resources Research Act Program: Grant Details for Project 2011MT239B

Details for Project ID 2011MT239B

Methods for estimating wetland evapotranspiration through groundwater flow modeling of diurnal groundwater fluctuations

Institute: Montana
Year Established: 2011 Start Date: 2011-03-01 End Date: 2013-02-28
Total Federal Funds: $14,900 Total Non-Federal Funds: $29,800

Principal Investigators: Kevin Chandler

Project Summary: As the demand and competition for water resources increases more precise regional water budgets will be needed to better manage Montana’s limited water resources. The amount of water lost by wetlands is likely the greatest unknown in any water budget and often ignored in regional groundwater flow models. This project aims to develop methods for defining the aquifer conditions affecting evapotranspiration (ET) from wetlands by coupling MODFLOW based groundwater flow modeling with analyses diurnal groundwater fluctuations. The wetlands at Gartside Reservoir near Sidney, MT were the site of a previous hydrologic study and provide important historical data on water-level changes and information about the local hydro-stratigraphy. This site also provides a diverse set of wetland conditions with part of the area being drained for agricultural uses. Shallow monitoring wells and weirs will be installed in the wetland areas to measure water-level and surface-water flow changes during two growing seasons. Water-levels will be recorded on 15 minute intervals and consistent diurnal water level fluctuations will be analyzed for ET calculations. Meteorological data will be collected to evaluate the factors effecting wetland ET. Well bore cuttings will be analyzed to determine shallow aquifer properties. These data will be used to construct a transient groundwater flow model to simulate ET. The calculated ET rates and measured aquifer properties will be used for initial boundary conditions. Then the groundwater flow model will be calibrated to selected segments of the measured diurnal water-level curves through refinement of the initial boundary conditions.