Balancing in-and off-stream uses of water in the Hawaiian Islands

Abstract

The island of Kaua'i is the oldest of the main Hawaiian Islands and has roughly 70,000 inhabitants. Sugar plantations historically dominated the island's economy but have been largely supplanted by tourism in recent years. The surface water resources in the Waimea River watershed on Kaua'i were diverted at the beginning of the twentieth century by former sugar plantations into roughly 77 kilometers of transmission ditches, tunnels, flumes, and siphons of the Kekaha Ditch Irrigation System (KEDIS) and the Koke'e Ditch Irrigation System (KODIS). These ditch systems were constructed to transport water to the arid, fertile lands of the Mana Plain that required irrigation water to grow sugarcane. A 2013 petition by community groups to the State of Hawai'i Commission on Water Resource Management (CWRM) demanded that stream flow be restored and that interim instream flow standards for the Waimea River and its headwater and tributaries be established. The current amount of water diverted into the two ditch systems exceeds present-day agricultural needs, which are dominated by corn seed crops. However, the island's electric utility has developed plans to use the water stored in the existing high elevation reservoirs on KODIS to produce electricity using pumped hydropower storage technology. Pumped hydropower would allow the utility to "store" excess energy produced by the island's rapidly expanding utility-scale photovoltaic array systems with the ultimate goal of producing all of the island's electricity using renewable resources. The physical condition and volume of water currently diverted by both ditch systems was evaluated and measured by Element Environmental (E2). CWRM is using the information collected to establish water diversion guidelines that strike a balance between off-stream uses (agriculture and hydroelectric power production) and instream uses of this water, including maintenance and restoration of stream and riparian habitat and ecosystems as well as protection of traditional and customary Hawaiian rights.