USING SEDIMENT FINGERPRINTS TO ASSESS SEDIMENT-BUDGET ERRORS, NORTH HALAWA VALLEY, OAHU, HAWAII, 1991-92

Reliable estimates of sediment-budget errors are important for interpr eting sediment-budget results. Sediment-budget errors are commonly con sidered equal to sediment-budget imbalances, which may underestimate a ctual sediment-budget errors if they include compensating positive and negative errors. We modified the sediment 'fingerprinting' approach t o qualitatively evaluate compensating errors in an annual (1991) fine (<63 mu m) sediment budget for the North Halawa Valley, a mountainous, forested drainage basin on the island of Oahu, Hawaii, during constru ction of a major highway, We measured concentrations of aeolian quartz and Cs-137 in sediment sources and fluvial sediments, and combined co ncentrations of these aerosols with the sediment budget to construct a erosol budgets. Aerosol concentrations were independent of the sedimen t budget, hence aerosol budgets were less likely than sediment budgets to include compensating errors. Differences between sediment-budget a nd aerosol-budget imbalances therefore provide a measure of compensati ng errors in the sediment budget. The sediment-budget imbalance equall ed 25 per cent of the fluvial fine-sediment load. Aerosol-budget imbal ances were equal to 19 per cent of the fluvial Cs-137 load and 34 per cent of the fluvial quartz load. The reasonably close agreement betwee n sediment- and aerosol-budget imbalances indicates that compensating errors in the sediment budget were not large and that the sediment-bud get imbalance is a reliable measure of sediment-budget error. We attri bute at least one-third of the 1991 fluvial fine-sediment load to high way construction. Continued monitoring indicated that highway construc tion produced 90 per cent of the fluvial fine-sediment load during 199 2. Erosion of channel margins and attrition of coarse particles provid ed most of the fine sediment produced by natural processes. Hillslope processes contributed relatively minor amounts of sediment. (C) 1998 J ohn Wiley & Sons, Ltd.