The Littoral Sand Budget, Hawaiian Islands

Abstract

Profile surveys were made across 80 selected Hawaiian beach and nearshore environments at quarterly intervals for one and one-half years during 1962-63. Also 70 additional beaches were measured at less frequent intervals. Using these profiles, supplemented by water-jet borings and measurements from aerial photographs, the total sand volume of each of the major Hawaiian beach systems was computed. The seasonal fluctuations of these volumes were also computed and related to the wave and littoral current regimes. The volume of littoral sand was found to be considerably less than the volume for many sandy continental areas. About 4.0 X 10^7 cu yd of sand is held in beach reservoirs on the seven major island s of the Hawaiian group; most is concentrated on Kauai ( 1.4 X 10^7 cu yd) and on Oahu (1.0 X 10^7 cu yd). Individual beaches containing more than 1 X 10^6 cu yd are Keawanui on Niihau; Hanalei, Polihale-Barking Sands, and Kekaha-Nohili-Bonham on Kauai; Bellows-Waimanalo on Oahu; and Papohaku on Molokai. The beaches on the island of Hawaii hold the smallest volumes of sand. Seasonal rates of erosion and accretion of beach sand reservoirs were found to be generally on the order of a few tens of cubic yards of sand per linear yard of beach per month . The higher rates were on exposed north and west coasts, with a maximum rate of several hundred cubic yards of sand per linear yard of beach per month recorded for Lumahai Beach, Kauai during 1962-63.