Measured and predicted sediment yield from a subtropical, heavy rainfall, steep-sided river basin: Hanalei, Kauai, Hawaiian Islands

To determine the sediment yield of the 54.4 km(2) Hanalei River basin, we e mploy three methods: (1) the Universal Soil Loss Equation (USLE), which use s natural characteristics of the basin such as the amount of rain, slope st eepness and length values, and soil types to predict sediment erosion in a basin; (2) the thickness and calibrated radiocarbon age of fluvial deposits cored from the coastal plain; and (3) field measurements of suspended sedi ment in the river. Method 1 (USLE) provides a model prediction of sediment yield that we test with observational data of methods 2 and 3. Several curv es, including one by the US Soil Conservation Service, predict a sediment d elivery ratio (measured sediment yield: gross erosion) between approximatel y 15% and 50%. With 5260 +/- 2210 Mg (metric tons) yr(-1) of suspended sedi ment in the Hanalei River and 2300 +/- 700 Mg yr(-1) deposited on the coast al plain, however, the delivery of sediment in the Hanalei basin ranged bet ween 45% and 101% of the maximum predicted USLE value (88 +/- 103 Mg km(-2) yr(-1)). This higher than predicted yield may be the result of mass moveme nt. We are not able to differentiate, however, between erosion and mass mov ement as the principle agent of denudation. Our measurements indicate a tot al sediment yield of 140 +/- 55 Mg km(-2) yr(-1) for the Hanalei Valley. (C ) 1999 Elsevier Science B.V. All rights reserved.