Comparative Analysis of Current Methodologies for Watershed Impact Analysis

Three modeling techniques were used in an effort to assess impacts to local hydrology from drinking water withdrawals and wastewater discharges for a proposed mixed-use residential development.  Since the drainage basin of the study area located in southeast Massachusetts is composed entirely of stratified drift, stream flow is highly dependent on groundwater contributions to the river.  Due to this unique hydrology, both surface water and groundwater modeling techniques were used as a basis to assess this complex flow system.  The applied methodologies include groundwater flow models developed by the USGS (MODFLOW and the Stream Depletion Model), and a watershed model developed by Limbrunner, Vogel, and Chapra (2005).  Remarkably similar results were generated through these three methods despite variations in their approach, level of sophistication, limitations imposed by requisite simplifying assumptions, and hydrologic and geologic data needs.  A brief description of local site hydrology and modeling methodologies is presented followed by a discussion of the results and conclusions of the study supporting the assertion that the proposed changes to the hydrologic cycle within the basin will not have a significant impact to streamflow of the nearby river.