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Hydrologic Response: Kaho'olawe, Hawaii

Dep. of Geological and Environmental Sciences, Stanford Univ., Stanford, CA 94305.

^* Corresponding author (keith{at}pangea.stanford.edu).

ABSTRACT

Kaho'olawe, the eighth largest island in the Hawaiian chain, has experienced major surface erosion during the last century due to overgrazing and military activity. In this paper we report the results from a series of physically-based numerical simulations of hydrologic response, to large rainfall events, that were performed for Kaho'olawe. An event-based rainfall-runoff and erosion model (i.e., KINEROS) was applied, in a geographic information system (GIS) framework, to make quantitative and distributed estimates of infiltration, Horton overland flow generation, and erosion. A digital elevation model (DEM) was employed to delineate individual catchments across the island, and define areas of uniform slope within each catchment. A Landsat MSS scene of Kaho'olawe was used to classify the island into three distinct landcover categories via the normalized difference vegetation index (NDVI). The landcover categories were then used to further approximate the spatial pattern of near-surface soil hydraulic properties across the island. Distributed estimates of saturated hydraulic conductivity and sorptivity were obtained by ordinary kriging of 135 field measurements from the island. Sensitivity analysis was performed to characterize what impact the uncertainty in soil-hydraulic property and rainfall data had on simulated runoff. Horton overland flow and the related transport limited erosion were shown to be highly variable. The introduction of vegetation to denuded areas on Kaho'olawe was found to significantly reduce erosion.