Land Use Planning in Maui, Hawaii, to Prevent Sedimentation of Fringing Coral Reefs

Abstract

One of the greatest threats to coral reefs of the Hawaiian Islands is sedimentation from land-based sources. Sedimentation occurs when runoff from storm events carries terrigenous sediments into the marine environment. Once in the marine environment it increases turbidity and eventually settles onto the coral, effectively smothering it. The severity of sedimentation depends on the type of sediment, the sediment load, and the residence time of the sediment. Land use that results in exposed soil, such as development, causes an increase in sedimentation. Because sedimentation begins on land, the policies addressing it must also be focused on the land. Current land use policy in Maui does not effectively address sedimentation, as it only tries to minimize the total sediment load. Land use policy does not address residence time of the sediment. Residence time is limited by wave exposure. Where wave exposure is higher, sediment is removed faster, thus having less impact on the coral. In order to effectively limit the impact of sedimentation, there must be spatially explicit land use regulations that require sediment filtration, density restriction, increased limits to total exposed soil, impervious surface restrictions, while encouraging habitat restoration and open space preservation, in areas where wave exposure is low. To better understand spatial and temporal variations in wave exposure in Maui, I created a GIS-based model of nearshore wave exposure. Using a model such as the one described here to identify critical areas that are more susceptible to sedimentation could result in more effective management of Maui’s reefs.