The Piti-Asan Watershed is considered one of three “priority watersheds” (Kottermair, 2012), which contains several conservation areas and two large proposed developments. Within the Piti- Asan Watershed there was an estimated 2103 people during the 2000 census, which was estimated to have grown to 2454 by 2010. Furthermore, increased construction within the watershed and around the rest of the island is expected to occur as a result of the current population trends. These expected changes will have an effect on the dynamic hydrologic behavior of the watershed. Furthermore, sediment carried to the Piti and Asan Bay outlets from the watershed can adversely affect nearby coastal and marine communities.

This project performed an analysis of the potential impact of existing and proposed natural and human activities on the watershed behavior and suggested recommendations to manage such activities in order to reduce the impacts on the watershed. This study analyzed the hydrologic behavior of the Piti- Asan Watershed through measurements of rainfall, stream level, stream flow, and river turbidity over the course of one year. Estimates of erosion contribution by areas within the watershed were conducted using the GIS erosion model developed by Park (2007).

A correlation between the collected hydrologic data was made. The product of the research was a stage discharge curve for the Masso and Asan Rivers. The study determined the areas contributing the most potential erosion and the major causes of soil erosion in the Piti-Asan Watershed. Such causes of erosion included: erosive soils, poor vegetative soil cover, bank erosion, steep slopes, heavy rainfall events, improperly managed construction, and lack of erosion management on existing buildings. Management strategies to address these problems were suggested.