Much of Hawai‘i’s surface water infrastructure was developed by sugar plantations during the late 1800s and early 1900s. With the collapse of the sugar industry, many aging irrigation systems have fallen into disrepair. Through the efforts of Hawai‘i’s congressional delegation, federal funding has been made available to examine these agricultural water systems, estimate the cost of restoring them, evaluate their future prospects, and identify opportunities for water reclamation. CTAHR’s Ali Fares, Carol Ferguson, and Tomoaki Miura have led the latest phase of this agricultural water plan for the Hawai‘i Department of Agriculture.

The water plan addresses 10 previously studied irrigation systems located on five islands. For each system, prime agricultural lands, soil types, and current land uses and crops were mapped, as were potential sources of reclaimed water for irrigation. Preliminary maps were developed for an additional 11 irrigation systems. For the 10 systems studied, the irrigation needs for 27 crops were estimated based on historical climate data, soil properties, crop-specific water use traits, and growing seasons. The software employed to calculate these crop water duties is a flexible tool through which irrigation managers, farmers, and regulators can predict specific crop water requirements depending on when and where the crop is grown. Previous records, maps, site visits, and the input of an expert panel were used to evaluate the 10 systems, including the impact of proposed rehabilitation works.

To project water demands to the year 2030, macroeconomists were surveyed to develop three scenarios—most likely, optimistic, and pessimistic— for Hawai‘i agriculture. A panel of agriculturalists was asked to project crop acreages, from which irrigation demands were estimated. The potential for bioenergy crops was assessed using a separate survey and geographical analysis of available lands. The results will help Hawai‘i’s counties develop water plans for their jurisdictions. The Agricultural Water Use and Development Plan is still in draft form; official release of the water plan is anticipated in spring 2008.