WRRC/Ike Wai Seminar
September 11, 12:00pm - 1:00pm
Mānoa Campus, HIG 210
Groundwater recharge-discharge imbalance, inter aquifer flow, and yet to be explained connections in Kona aquifers
Henrietta Dulai, Department of Geology and Geophysics, SOEST, UH Manoa
An island water budget has a few quantifiable moving parts, one of them being leakage of groundwater from coastal aquifers to the ocean. Quantifying this flow helps in characterizing the aquifer water budget and aids in water resources management. For this purpose, a groundwater recharge - discharge balance for the Hualalai aquifers in Kona was constructed. Here, aquifer boundaries are defined based on orographic watersheds and known geologic structures but the complex subsurface geology makes the exact region of contribution of groundwater uncertain. Therefore, groundwater geochemical signatures were used to find subsurface drainage patterns of groundwater discharging at the coast. Literature values complemented by our own measurements were compiled to account for fresh groundwater discharge along the shoreline. Discharge was then compared to recharge along the identified subsurface drainage patterns, to no surprise, resulting in large imbalances. The water budget imbalances and chemical signatures suggest that water discharging at the shore does not all originate in the basal lens and there is a connection between high level and basal aquifers. In addition, in some parts of the aquifer groundwater must originate from recharge outside of the aquifer, i.e. inter aquifer flow. The presence of inter aquifer flow is farther supported by a long-term record of hourly measurements of groundwater discharge, which shows lack of response to local precipitation and groundwater withdrawals, rather presents a very steady flow with small variations controlled entirely by sea level changes.
Water Resources Research Center/Ike Wai, Mānoa Campus