Water Resources Research Act Program

Principal Investigators: Leroy Heitz, Shahram Khosrowpanah

Abstract: In order to properly manage a regions water resources, it is important for water managers to know the time variability of flow in the streams of that region. Not only what are the highest flows, such as what would be available from a flood frequency study, but also how the flows vary day to day, season to season, and year to year. Studies such as water supply studies, hydropower studies and those involving sediment transport depend on this kind of long term variability data in order to develop the best management practices for a regions water resources. Guam is no different than other areas requiring water resources investigations. In order to properly carry out good water resources management, it is necessary to be able to define the variability of flow available in Guams streams. This is normally done by direct analyses of streamflow data for the stream in question or by applying some sort of inferential techniques from a gaged to an ungaged stream or from a gaged location on a stream to an ungaged location on that same stream. Of course, the most reliable means is to use actual stream flow data measured at the point of interest. The problem in Guam, as in most locations, is that stream flow information is not available for all possible sites where information is required. What is needed is a better means of predicting the variability of flow at ungaged locations that are likely to become candidate sites for water resources investigations. The flow duration curve provides us with a means of representing the variability of flow at a study site in a concise graphical fashion. Flow duration curves have proven to be useful in evaluation of surface water resources for water supply studies, hydropower design and planning studies, low flow studies such as in-stream flow requirements and other studies where it is desirable to define the variability of the flows in streams. The results of this project will be the development of a means of predicting flow duration curves at ungaged sites in Guam. All of the major streams in Southern Guam will be divided into stream reaches, or homogenous sections of a stream, that have similar flow properties. These reaches will be identified on maps developed from the detailed Geographic Information System (GIS) map inventory of Guam available at WERI. Various statistical and analytical methods, as described in the methods section below, will be applied to the existing streamflow data along with the physical characteristics of the reaches in order to predict the streamflow variability in each stream reach. The final results will be a series of GIS maps of the streams of Guam with each stream reach identified along with its average flow. A means will also be provide to predict durations curves for the various reaches along the streams. The flow duration curves that will be predicted will be useful in evaluation of surface water resources for water supply studies, hydropower investigations, low flow studies such as in-stream flow requirements, and other studies where it is desirable to define the variability of the flows in streams.