Map of Great Egg Hrbor and Mulica River Basins in New Jersey.

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Great Egg Harbor-Mullica River Basin model., NJ

Project Title: Great Egg Harbor-Mullica River Basin model., NJ
Project Number: 2454C1Q
Project Chief:
Project Start Date: 01-MAY-2005
Project End Date: 31-DEC-2009

Project Objectives

• Understand the nature of groundwater-surface water interactions and the effects of the withdrawals from the underlying confined aquifers.on the Kirkwood-Cohansey aquifer system in the Great Egg Harbor and Mullica River basins.
• Understand the present use of both groundwater and surface water (including agricultural needs) in the basins and the likely increased future demand.
• Collect data to support calibration of a groundwater flow model of the Great Egg Harbor and Mullica River Basins.
• Develop a groundwater flow model having sufficient resolution to be used as a tool to predict baseflow effects from pumpage in the Kirkwood-Cohansey aquifer and confined aquifers.
• Collaborate with NJDEP, county and local stakeholders to develop several water management alternatives that can be used to demonstrate the potential affects of various water management approaches. These alternatives will include full-allocation, growth in deep confined aquifers, growth in shallow aquifer, and seasonal conjunctive use of shallow and deep aquifers.
• Simulate and evaluate the possible hydrologic effects of the alternatives. These findings will be presented to NJDEP and stakeholders.
• Prepare a report summarizing the project’s findings which will include hydrogeology, water use, ground-water flow model development and calibration, and the results of the simulation of water-management alternatives. All or portions of this report may be incorporated into a regional water-supply planning document to be prepared by NJDEP.

Statement of Problem

In the Atlantic Coastal basins (fig. 1), ground water is both an important water supply and has a critical role in maintaining the health of freshwater and estuarine ecosystems. Issues related to water-availability have been raised during the recent droughts. The major sources of ground water in the area are the unconfined Kirkwood-Cohansey aquifer and the confined Atlantic City 800-foot Sand aquifer.

The unconfined and confined aquifer systems each have different water-supply concerns. The major concern about the unconfined aquifer system is related to increasing withdrawals causing streamflow depletion and affects on wetlands. A major concern about the confined aquifers is that water levels in the Atlantic City 800-foot Sand aquifer have been steadily declining and were more were 80 ft below sea level in fall 2003.

Demand for water in the southeast New Jersey area is expected to increase as growth continues in the area. Supplying these demands while maintaining adequate streamflow and protecting the long-term resources in the Atlantic City 800-foot sand will require effective water resource management. Potential water-supply alternatives that can be evaluated include; increased withdrawals from the 800-foot Sand or Kirkwood-Cohansey aquifer at sustainable rates and seasonal conjunctive use of the shallow and deep aquifers at sustainable rates. A ground-water flow model that can adequately simulate the interaction between ground water and surface water for the region on a monthly scale is needed.

Strategy and Approach

The general approach to complete this project will be to initially collect specific hydrologic data relevant to understanding the relationship between surface and ground water in the study area. These data combined with data from network observation wells and gages, and available information on the hydrogeology and water use will be used to develop and calibrate a ground-water flow model. The flow model will then be used to evaluate the conditions and consequences of various water management schemes.

These specific hydrologic data needed to be collected is synoptically-measured shallow-aquifer water levels with concurrent streamflow measurements.

Recent water-use data including the 1999 to 2002 drought period and that coinciding with the synoptic measurement periods in the spring of 2005 and the fall of 2006 will be used for model calibration purposes will be complied from NJDEP and USGS files. Users and purveyors will be contacted to resolve problems with the data. Agricultural water use will constitute a particular focus in this data compilation effort. Additionally, the permitted full allocation pumpage will be compiled from NJDEP files to provide a baseline for the preparation of future demand scenarios.

A ground-water flow model will be developed to simulate ground-water-surface water interaction in the Kirkwood-Cohansey aquifer and will be based on the MODFLOW 2000 model computer code. Currently available ground-water flow models of the area focus on the confined aquifer systems and do not handle the interconnection with streams at a resolution sufficient for the needs of this project. The model will be developed with available GIS data on recharge, evapotranspiration, etc. Of particular value will be information about the hydrogeologic framework available from NJGS and USGS files. USGS will collaborate with NJGS to develop the hydrogeologic framework for the model. The particular areas of focus for this aspect will be the nature of the unconfined part of the Kirkwood-Cohansey aquifer system, the nature and location of the pinch out of the confining bed above the Atlantic City 800-foot sand aquifer, and the nature and extent of the Rio Grande water-bearing zone.