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Title: Determining sediment sources in the Hanalei River Watershed, Kaua'i, Hawaii

Author
item Ritchie, Jerry
item PEDONE, PAUL - USDA, NRCS
item SMITH, CHRISTOPHER - USDA, NRCS

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/7/2008
Publication Date: 3/15/2008
Citation: Ritchie, J.C., Pedone, P., Smith, C. 2008. Determining sediment sources in the Hanalei River Watershed, Kaua'i, Hawaii [abstract]. Abstracts of the 15th International Congress of the International Soil Conservation Organization (ISCO). p. 247.

Interpretive Summary:

Technical Abstract: The Hanalei River delivers suspended sediments and organic matter to Hanalei Bay with impacts on the sustainability of coral reefs and their many associated species in the Bay. Understanding the sources of sediment sources in the watershed is key for the development and design of management strategies for reducing sediment loads to the Bay. The objective of this study was to determine the source of sediments within a watershed, such as upland soils, stream bank and channel processes, and mass wasting. In order to understand the relative contribution from each of these sources, soil samples were collected from the various geomorphic surfaces within the Hanalei River Watershed and analyzed for Cesium-137 concentration. Fallout Cs-137 can be used as a tracer or fingerprint to identify sediment sources and as a marker to determine floodplain deposition patterns and rates within a watershed. For this study, recently deposited sediments on floodplains and the Hanalei bay were compared to upland sediment sources (upland soils and mass wasting sites) and stream bank samples using a simple mixing model to determine sediment sources. Cesium-137 concentration varied with upland soils > colluvial slopes > floodplain deposits > stream banks > Bay sediments. Preliminary results indicate that channel banks and mass wasting are probably the most significant sources of sediments deposited on the floodplains and in the Bay.