A Water-Budget Model and Assessment of Groundwater Recharge for the Island of Hawai?i

iiiConcern surrounding increasing demand for groundwa-ter on the Island of Hawai'i, caused by a growing population and an increasing reliance on groundwater as a source for municipal and private water systems, has prompted a study of groundwater recharge on the island using the most current data and accepted methods. This report documents the development of a daily water-budget model for computing groundwater recharge for the entire Island of Hawai'i and the application of the model to estimate mean recharge for various land-cover and rainfall conditions. The development of a submodel for the Kona area and the application of the model to estimate historical groundwater recharge in the Kona area during the period 1984-2008 also are documented. Recharge estimates from this study are compared to recharge estimates used by the State of Hawai'i Commission on Water Resource Management (CWRM) in setting the sustainable yields (maximum allow-able pumping rates) of Hawai'i aquifer systems in the 2008 version of the Water Resource Protection Plan (2008 WRPP).