1a. Objectives (from AD-416):
Determine the rates of potential groundwater recharge in the sugar cane production system including seepage from irrigation canals and reservoirs. Seepage in these areas is critical for recharging aquifers that supply water to the Island of Maui. Quantifying the rates of recharge is needed to assess water supplies for potential biofuels production.
1b. Approach (from AD-416):
Categorize the existing 75 miles of irrigation canals by similar soils, geology, and slope and whether the canal is lined or unlined. Within specific sample areas of similar geology, slope, soils, and canal type (line or unlined), use geophysical methods to assess potential for seepage. In areas of potentially high seepage, install seepage meters to give more quantitative rates of water loss within the canal system.
3. Progress Report:
The Navy's dependence on oil (petroleum) strains operational planning. Its focus is on securing a sustainable fuel supply. ARS research and models will help determine how best to manage natural resources to allow Office of Naval Research (ONR) sustainability in fuel supply while also promoting ecological services and the local economy in Hawaii. Seepage under irrigation canals and water supply reservoirs has been identified as potential sources of water loss. A geophysical technique called resistivity was applied to six irrigation reservoirs at varying elevations and geology to determine areas of active seepage. Initial results show a perched water table approximately 3 feet to 20 feet from the surface that flows downslope. To quantify the rate of seepage, a seepage meter was designed, developed, and applied to the six reservoirs that were analyzed using resistivity. Contrary to current understanding, all reservoirs showed a net influx of water, shifting focus on management of the perched water table to minimize seepage losses. Also, state-of-the-art doppler flow meter technology is being tested on canals to determine seepage losses. The methodology is currently being developed and refined for conditions on the HC&S (Hawaiian Commercial & Sugar Company) plantation.