Conservation zoning for groundwater source protection
Lau, L. Stephen, and John F. Mink
Conservation zoning in Hawaii dedicates lands for the protection of watersheds and water sources. The designated lands include forest and vacant areas but exclude areas for major uses such as urban and agricultural. This has been the practice on the island of Oahu, Hawaii, USA (land area 593 mi2 [1535 km2]; 1990 population about 840,000) since the 1920s. The sizable conservation district (about 40 percent of the island land) in high-rainfall mountains ensures the recharge needed for groundwater sources that provide over 99 percent of the drinking water supply for Oahu. Is this policy wise, or is it too inflexible and draconian to be applicable to water source protection for other communities?
This paper presents the hydrological paradigm that optimal groundwater recharge takes place in undisturbed natural forests in Hawaii and discusses aquifer sustainable yields and groundwater quality. The Hawaii land use law, which was the first in the United States to regulate land use on a statewide basis, and its ramifications are also discussed. Finally, the recent (1992) five-year review of the conservation districts is presented from the hydrological perspective. The review not only confirms the necessity of the existing conservation districts but also recommends considerable expansion, especially in certain areas of the sparsely populated neighbor islands that are threatened with urbanization. The current status of the recommended changes is discussed.