Hawaii Regional Sediment Management (RSM) : regional sediment budget for the West Maui Region

Abstract : This Technical Report provides a description of the Regional Sediment Management (RSM) investigations performed by the U.S. Army Corps of Engineers (USACE), Honolulu District (POH), along the West Maui coastal region of the Island of Maui, Hawaii. The methodology for determining volume change rates as well as numerical modeling is discussed, including the particle tracking modeling, in support of identifying sediment pathways for the development of the regional sediment budget for the West Maui coast. The West Maui Region incorporates a thin coastal margin backed by steep mountainous terrain that has been vastly altered by agricultural and urbanized development. Shoreline hardening is being proposed along portions of the regions coastline. Shoreline change for this area was quantified by the U.S. Geological Survey (USGS). All sub-regions were found to be erosional in the long and short-term, based on average rates. The dynamics of the area are complex with a wave climate affected by intricate bathymetry, wind, and island sheltering. Currents vary from nearshore to offshore and within the water column. Coastal morphology includes headlands and reefs with a very limited supply of sediment. Wave and current models indicate that large waves in the summer and winter drive the majority of sediment transport (northward-directed in summer and southward-directed in winter). Because of these seasonal patterns, the net transport of sediment is small. There is evidence of nearshore eddy formation that increases the complexity of sediment transport in the region with sediment pathways changing on short-term (hours) to longer term (weeks to months) temporal scales. This is a very dynamic and seasonally affected shoreline, and the present RSM study is one tool that will help inform future shoreline management in the region.