Sand Deposits Offshore Oahu, Hawaii

Abstract

The value of sand as aggregate for concrete for the construction industry and as sediment for artificial beach replenishment at tourist destinations on Oahu has increased following a legislative moratorium on the mining of beach sand. Concern for future shortfalls of sand supply prompted prospecting for offshore deposits. Sand channels extend offshore from major valleys and coastal embayments on Oahu. Most of these accumulations join sinuous deposits of sediment ponded on ancient terraces that parallel the coastline. Sand cores were collected from these mapped deposits. Statistical analysis of particle size distributions of 279 samples from these cores reveals local areas that are promising for future exploitation. In some areas, variations of grain size can be related to water depth and distance from shore, but in most areas, grain sizes are not simply related to the geographic distribution of sampled sand. Along the leeward Oahu coast, size distributions are related to depth in core : 5 ft of fine sand covers medium and coarse sand. Comparisons between samples from different locales reveals relationships primarily to submarine geomorphology and secondarily to coastal wave climate.