Native forests provide many societal benefits, including protecting freshwater resources that provide drinking water and sustain culturally, economically, and ecologically valuable springs, streams, and groundwater dependent ecosystems. The objectives of this report are to: (1) model future management scenarios for Kaua‘i’s native forests that are co-developed with The Nature Conservancy (TNC) to quantify the impact of conservation efforts on water resources; (2) estimate gallons of groundwater recharge saved with existing or expanded (existing + proposed) watershed conservation efforts using a spatially explicit water balance model; and (3) to estimate conservation costs associated with management units and associated return on investment in terms of gallons of recharge per dollar spent. Building on previous work for Maui, O‘ahu, and Hawai‘i Island that examined the economic benefits of hydrologic services from watershed protection and restoration, this project studies 16 major (> 200 acres) completed and proposed fence areas that fall within the Kaua‘i Watershed Alliance. Land cover, evapotranspiration (ET), and recharge-to-runoff ratio data are combined with State and TNC conservation cost information to estimate the gallons of recharge saved per dollar invested in watershed conservation. Over a 50-year time horizon and given an invasive canopy spread rate of 3% and a discount rate of 3%, 593 gallons of groundwater recharge are saved on average per dollar invested in existing fence units, spanning from 85 gal/$ up to 2625 gal/$ depending on the specific fenced region. When proposed fences are included, the average ROI falls slightly to 567 gal/$, with a range of 60-2641 gal/$ across various units. This study demonstrates the importance of taking a long-term view on conservation ROI, as conservation costs are often front-loaded because of initial fence construction and ungulate removal costs, while annual water benefits grow continuously as the avoided loss of recharge increases over time.
