Application of MODFLOW to Determine the Effectiveness of Flood Protection System Upgrades in West Springfield, Massachusetts

The West Springfield Massachusetts Flood Protection System (FPS) at the confluence of the Connecticut and Westfield Rivers is comprised of levees, relief wells and toe drain systems at two locations designated the Riverdale FPS and the Westfield River FPS.  Each was constructed in the 1940’s by the United States Army Corps of Engineers (USACE) to protect West Springfield from river flooding during 500 year flood stages.  Recent review of current conditions by the Federal Emergency Management Agency (FEMA) and USACE led to the conclusion that these systems were in need of upgrades.  Proposed FPS upgrades were modeled using three-dimensional (3D) MODFLOW and the model was based on previously compiled engineering and USACE reports and field data, which provided proper parameter inputs for MODFLOW to refine the design upgrades.  The model was designed to encompass the drainage basin around West Springfield with the Connecticut and Westfield Rivers influencing the main head values for the region, representing proposed upgrades and the 500 year flooding conditions.  The model grid was independently refined at each FPS to provide detail of modeled parameters and conditions required by the project’s engineers.  Following refinement and calibration, the model was run under several scenarios, each with 500 year simulated flood stage and varying relief well designs.  Output of each scenario was reviewed with respect to drawdown equipotential lines surrounding each FPS in order to summarize the functional efficiency of the proposed upgrades. The final working model provided insight and understanding of proposed upgrades to the FPS not originally available to the project’s engineers.  Additionally, MODFLOW illustrated subsurface condition interactions at each FPS, showing no adverse impacts were present during flood stages due to refinement of FPS design and removal of relief wells in key locations along the levees.