Analyses of groundwater contribution to a riverine wetland

Rainfall, runoff, overbank flow and groundwater, all contribute water to wetlands. Each transport element is associated with unique modeling approaches and uncertainties. Transpiration is perhaps the hardest to quantify as it is subject to all the variability of plant growth. Transpiration causes land area to lose moisture and the loss amount depends on precipitation incidence, the temperature and type and extent of vegetation. Plants can intercept virtually all recharge during the growing season and almost none from late fall to early spring in northeastern United States. Thus, an improvement in the transpiration element can contribute considerably to an improved groundwater contribution estimate of the wetland water budget. The study site is a riverine wetland at Monmouth Battlefield State Park in Manalapan, New Jersey. Using USGS MODFLOW, a simulation is adapted to the site specific conditions of geology (from in-situ permeability tests), topography (from surveyed elevations and also USGS Topo Map) and vegetation (by assigning different evapotranspiration coefficients to different vegetation covers). Hydrologic factors (i.e. rain data) are reflected in the model. Simulation product is validated using the collected data from monitoring wells. The final product is a wetland hydrologic model for a highly localized prediction of groundwater contribution to a wetland’s water budget capable of estimating evapotranspiration. It was concluded that from 1709 millimeters (mm) of precipitation over modeling period (May 2012 to August 2013), 1000 and 835 mm or a daily average of 2.0 and 1.7 mm/day were lost to the atmosphere through evapotranspiration for forest and farm side of the study area, respectively