Nine sedimentation surveys conducted from 1983 to 1998 at Waimaluhia Reservoir determined the rate of sediment accumulation in the reservoir during H-3 Highway construction upstream of the reservoir. Rates of storage-capacity loss ranged from 1.1 acre-feet per year between 1983 and 1988 to 4.9 acre-feet per year between 1988 and 1992. The average loss rate during the period of intensive construction between 1983 to 1992 was 2.7 acre-ft per year. The average loss rate during the study period between 1983 and 1998 equals the design loss rate of 2.0 acre-feet per year. The average bulk density of deposited sediments was 29 pounds per cubic foot. From the bulk density data, loss of storage capacity, and suspended-sediment data collected downstream of the reservoir, a total of 26,950 tons of sediment was delivered to the reservoir from 1983 to 1998, of which 19,100 tons were trapped in the reservoir. From these sediment loads, a sediment yield of 565 tons per square mile per year and trap efficiency of 71 percent were computed. A trap efficiency of 60 percent, bulk density of 65 pounds per cubic foot, and sediment yield of 1,500 tons per square mile per year were used to compute the design loss rate of 2.0 acre-feet per year.
