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Surface-Water Loss in Honouliuli Stream near the Ewa Shaft on Oahu
Changes in land use in the Ewa area of Oahu have increased current and projected demand for potable water. Groundwater from the Ewa Shaft could potentially be used to meet future potable water needs in the Ewa area. The Honolulu Board of Water Supply is concerned with the possibility of bacteria in the water pumped from the Ewa Shaft. Although potential sources of bacteria in the pumped water are not fully understood, existing accounts indicate that surface water may be lost to the subsurface near the site.
The objective of the study is to evaluate the location and quantity of surface-water loss in Honouliuli Stream near the Ewa Shaft to improve understanding of potential sources of bacteria in the pumped water. The scope of the work includes (1) the collection of new water-level and seepage-run information, and (2) an analysis of the extent of the surface-water loss in the study area.
Relevance and Benefits
The results from this study are necessary to determine if surface water may be infiltrating near the study area. Information generated by this study is needed to make an informed decision on how to best manage groundwater resources. Therefore, the study is consistent with the USGS Science Strategy and its broader theme of developing a Water Census of the United States to provide the public and decision makers with information on freshwater resources.
To meet the objectives of this study, the USGS will (1) compile existing discharge records and collect new discharge measurements from Honouliuli Stream to evaluate streamflow loss rates, (2) measure water levels in Ewa Shaft to evaluate the relation between surface-water discharge and the water level in the Ewa Shaft, and (3) analyze the location and quantity of surface-water loss in the Honouliuli Stream near the Ewa Shaft.
Rosa, S.N., 2017, Measuring surface-water loss in Honouliuli Stream near the ‘Ewa Shaft, O‘ahu, Hawai‘i: U.S. Geological Survey Scientific Investigations Report 2017-5042, 14 p., https://doi.org/10.3133/sir20175042.