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Groundwater Availability in the Lahaina District, Maui
Between 1970 and 2006, the resident population on the island of Maui, Hawaii has increased over 250 percent. Groundwater demand for domestic supply also has increased significantly during this period. In response to increased withdrawals from the freshwater-lens system in the Lahaina area, the chloride concentrations of water pumped from wells has increased. This has led to concern over the long-term sustainability of withdrawals from existing wells in the area. To ensure prudent management of the groundwater resources in the area, and to plan for sustainable growth on the island, an improved understanding of the groundwater flow system is needed. This study will provide the information needed to better manage groundwater resources in the Lahaina area.
The objectives of this study are to estimate the effects of selected withdrawal scenarios within the Lahaina area, using a numerical groundwater flow and transport model, on water levels, the transition zone between freshwater and saltwater, and surface-water/groundwater interactions.
Relevance and Benefits
The results from this study are necessary for the proper management of the ground and surface waters in the State and, thus, the study is consistent with the mission of the USGS Science Strategy to provide citizens, communities, natural-resource managers, and policymakers with a clearer knowledge of the status of their water resources. This study will provide information needed for water-use permitting and land-use planning in an area that is rapidly being developed.
To meet the objectives of this study, a two-phased approach will be used. The two phases include: (1) collection of streamflow and groundwater data to fill in current data gaps and to further refine the conceptual model of the groundwater-flow system in the Lahaina area, and (2) enhancement of an existing numerical groundwater flow and transport model for groundwater management.
Data collection began on this study in November 2007 and continued through January 2010. To better understand the interaction between groundwater and surface water and to obtain better estimates of the potential for groundwater recharge from streamflow, discharge measurements were made or compiled for several locations along streams and diversion ditches in the Lahaina area. Continuous water-level monitoring was completed in four study area wells to provide calibration data for refining the numerical groundwater-flow model. In addition, a GPS survey of the wells was completed to verify the elevation of the water-level measuring points with respect to mean sea level. Finally, a refined numerical groundwater-flow model was constructed and calibrated to historic hydrologic data. Future pumping scenarios were developed and evaluated in collaboration with stakeholders.
Gingerich, S.B., and Engott, J.A., 2012, Groundwater availability in the Lahaina District, west Maui, Hawai'i: U.S. Geological Survey Scientific Investigations Report 2012-5010, 90 p.