Simulation of groundwater flow in the shallow aquifer system of the Delmarva Peninsula, Maryland and Delaware

Abstract

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Hydrogeologic controls on groundwater discharge and nitrogen loads in a coastal watershed

“…S1), which is consistent with a water-budget-based recharge estimate for another Delmarva location of 33 cm/yr (Johnston, 1976). Sanford et al (2012) prescribed drain boundaries at root depths associated with different land uses (0.6-1.8 m below land surface), whereas we prescribed drains at the land surface in the current study. They considered the additional water removed by prescribing drains below land surface to be evapotranspiration (ET), so the recharge they applied included this ET component.…”

“…They considered the additional water removed by prescribing drains below land surface to be evapotranspiration (ET), so the recharge they applied included this ET component. The current study applied a net recharge value that excluded the ET component, so the reduction to 75% of the value applied by Sanford et al (2012) is reasonable. Average recharge applied to the calibrated Reference model is 43% of the 113 cm/yr mean annual precipitation recorded at the nearest NOAA rain gage (NOAA, 2010).…”

“…Geological Survey model of the Delmarva Peninsula (Sanford et al, 2012;Ward Sanford, personal communication 3/17/2011) and adjusted during calibration (see Section 3.3; Fig. S1).…”

“…This model was a simplified representation of the heterogeneous system in which three aquifers were represented by 7 layers ranging in thickness (Sanford et al, 2012;Ward Sanford, personal communication 4/1/2011) were used to delineate groundwater flow divides. These were generally coincident with the surface watershed boundary (McKenna et al, 2007).…”

“…In coastal watersheds, transit times can average on the order of several decades for discharge to streams (Sanford, 2011;Sanford et al, 2012) and coastal waters (Robinson and Reay, 2002;Tait et al, 2014). Transit times of groundwater discharging to streams increases in the downstream direction (Modica et al, 1998(Modica et al, , 1997, so it likely follows that SGD (which occurs downstream of the stream mouth) would tend to be older than groundwater discharging to streams.…”