Over the past 100 years, natural streamflow in Waipiyo Valley has been reduced by the transfer of water out of the valley by Upper and Lower Hamakua Ditches. The physical condition and diversion practices along the two ditch systems have varied widely over the years, and as a result, so have their effects on natural streamflow in Waipiyo Valley. Recent reno-vation and improvements to Lower Hamakua Ditch system, along with proposals for its future operation and water-diver-sion strategies, have unknown implications. The purpose of this report is to quantify the availability of streamflow and to determine the effects of current and proposed diversion strate-gies on the low-flow hydrology in Waipiyo Valley."