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Synoptic Groundwater-Level Measurements for the Central Maui Area (includes Iao and Waihee)

What Are Synoptic Groundwater-Level Measurements?

Synoptic groundwater-level measurements are a special type of measurement in which water levels in wells are measured within a relatively short period and under specific hydrologic conditions. Synoptic water-level measurements provide a “snapshot” of heads (and an indication of freshwater storage) in an aquifer. Synoptic measurements commonly are taken when data are needed for mapping the elevation of the water table or potentiometric surface, determining hydraulic gradients, or defining the physical boundaries of an aquifer. Regional synoptic measurements are made periodically for selected aquifers to complement more frequent measurements made from a smaller number of wells.

Periodic water-level measurements are made by manually using electronic-sensor tapes or chalked metal tapes and may contain errors associated with (1) the measuring tapes used, (2) the measuring-point elevations at the top of the well, and (3) the plumbness of the well. Each of these sources of error is discussed briefly here.

Available Data for the Central Maui Area

Synoptic water-level measurements for the Central Maui area are summarized in the following table and maps. Water-level measuring tapes used in the survey were calibrated during May 2004 and during July and August 2011. Water levels for the synoptic survey of August 29, 2012 reflect measuring-point elevations resurveyed to a common datum established by the National Geodetic Survey using differential Global Positioning System (GPS) methods during 2003. In August 2012, a few of the newer Iao-Waihee area wells were tied into the existing well network using reference marks established in the 2003 GPS survey and digital leveling equipment.

Water levels measured on May 17, 2005 in central Maui were lowest in the central isthmus and were highest in the Iao aquifer area. In general, water levels measured on August 29, 2012 were lowest near the coastal, northern part of the Iao-Waihee area and were highest in the inland, southern part of the area. Continuous water-level measurements in wells 6-5430-05, 6-5431-01 and 6-5731-05 provide temporal context for the synoptic water-level measurements.

Water-level measurements were made possible with the assistance of the County of Maui Department of Water Supply and the State of Hawaii Commission on Water Resource Management

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