MODFLOW-2005 model used to simulate the regional groundwater flow system in the updated New Jersey Coastal Plain model, 1980-2013

A third revision of the New Jersey Coastal Plain (NJCP) groundwater flow model, using MODFLOW-2005 (version 1.12.00), was completed to maintain the model’s usefulness for water-resource managment and development. The regional groundwater-flow model was initially developed for the U.S. Geological Survey (USGS) Regional Aquifer System Analysis (RASA) program. Periodic revision of the model is required as the result of changing hydrologic stresses, different and more complex water management needs, and increased knowledge of hydrologic conditions. The RASA model was initially constructed in the 1980’s as a quasi-3D model with 10 aquifers. The 9 intervening confining units were simulated using vertical leakage parameters at the aquifer contacts. The model was revised in the late 1990’s by (1) rediscretizing the model parameters with smaller grid spacing, (2) rediscretizing the stream cells for a better representation of streams, (3) using a spatially variable recharge rate based on studies conducted by the New Jersey Water Science Center since the model was initially developed, and (4) updating groundwater withdrawal data to 1998. For this study, the USGS, in cooperation with the New Jersey Department of Environmental Protection, again revised the model, updating the hydrogeologic framework, hydraulic parameters, and groundwater withdrawals. The revised 21-layer, fully three-dimensional, NJCP groundwater-flow model extends into Delaware and parts of Maryland and simulates 11 aquifers and 10 intervening confining units. The revisions include spatially and temporally variable recharge estimated using a Soil-Water-Balance (version 1.0.1) model; updated hydrologic parameters using UCODE_2014 (version 1.004) including the confining units in New Jersey and the hydrogeologic units in Maryland and Delaware; updated boundary flows from the North Atlantic Coastal Plain groundwater-flow model; groundwater withdrawals from 1980-2013 for the New Jersey Coastal Plain and from 1980-2010 for the modeled areas in Delaware and Maryland; and additional model layers to refine the simulated flow in Atlantic and Cape May Counties, New Jersey. The revisions to the model allows for (1) refined boundary flows for local models, (2) improved simulated interaction between water levels in southern New Jersey and withdrawals in Delaware, (3) simulation of the unconfined Kirkwood-Cohansey aquifer system and confined Rio Grande water-bearing zone, and (4) the ability to do particle tracking to determine regional sources of flow and times of travel. The groundwater flow model provides water managers with a tool to better understand the groundwater system of the New Jersey Coastal Plain, evaluate groundwater budget components, and make informed water-resource management decisions. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20235066).

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Organization: Department of the Interior