Water Resources Research Act Program

Details for Project ID 2011GU197B

Sediment Analysis and Modeling of the Ugum Watershed in Southern Guam

Institute: Guam
Year Established: 2011 Start Date: 2011-03-01 End Date: 2012-02-29
Total Federal Funds: $17,415 Total Non-Federal Funds: Not available

Principal Investigators: Charles Luo, Shahram Khosrowpanah

Abstract: Guam Waterworks Authority (GWA) has collected turbidity data in the Ugum Watershed for several years. The simplicity of taking turbidity measurements allows for the continuous in-situ gathering of such data. This is very useful when monitoring rapidly varying turbidity conditions in tropical rivers. However, turbidity is not the same as the suspended sediment concentration (SSC), which is an important quantity from engineering perspective. A correlation is therefore needed between turbidity and SSC. Luckily, USGS has 4 years of daily sediment data (October 1 2005 to September 30, 2009) from the Ugum River gauging station located above Talofofo Falls (ID: 16854500). The SSC data are recorded in milligrams per liter and suspended sediment discharges in tons per day. Unfortunately, there are several data gaps in the USGS 2005 and 2006 records. However, by using the available USGS daily SSC data in combination with GWA’s turbidity data, it should be possible to estimate the missing values using linear regression and other methods of regression analysis. A large-scale, unified and optimization model - LUOM (Luo, 2007) – has recently been developed. This two-dimensional distributed watershed model predicts various hydrological components of a watershed. Another model, LUOM-SED (Luo, 2003), is a basin-wide distributed sediment production and transportation model that was developed from LUOM (Luo, 2007) and employs diffusive wave model equations to govern the surface water flow. Sediment is produced from each grid relating to rainfall intensity, flow velocity, slope, vegetation, and soil types. The concentration continuity equation is utilized to govern the sediment transportation across the basin. Then, the sediment gradually reaches and accumulates in the channel it falls into and is computed in two transportation patterns: bed load and suspended load, according to the flow capacity. One dimensional equations are adopted to simulate the sediment movements in the river and riverbed change, and finally output the time series of sediment volume at selected locations. This model will be calibrated using the data available for the Ugum watershed. The objectives of this project are: 1) To find the correlation between the turbidity and SSC data sets collected by GWA and USGS respectively; 2) Use this correlation to estimate the 2005 and 2006 missing SSC data; and, 3) Calibrate and validate the LUOM-SED using the SSC data with the missing data added. The benefits of this project will be enormous not only to Guam but also to other islands in the Western Pacific. It provides not only the correlation of turbidity and SSC, but also the calibrated model LUOM-SED, both of which could be applied to water quality studies in any watersheds in Guam with similar geological and hydrological conditions. The calibrated model could also be used for environmental evaluation for badland regeneration and/or deterioration. Researchers studying the impact of various watershed management practices could generate sediment output with the calibrated model. Additionally, turbidity data at various section of a watershed could also be used to produce SSC data. By providing a clearer understanding of the sediment situation in Guam’s rivers and streams, GWA will also be better positioned to determine which surface water sources in southern Guam could best be tapped for drinking water purposes.