You have entered the website of the Water and Environmental Research Institute of the Western Pacific (WERI) at the University of Guam. We are currently six faculty and five staff and our mission is to seek solutions through research, teaching and outreach programs, to issues and problems associated with the location, production, distribution and management of freshwater resources in Guam, the CNMI and the FSM.
In southern Guam, there are a few watersheds with both rainfall and streamflow data. But some other watersheds have only rainfall data but no streamflow data. In the watersheds without streamflow data, it is obviously difficult to carry out watershed management studies which require streamflow data. Meanwhile, there are two problems with most of the watersheds with streamflow data. One is that the streamflow gage is not always located at the watershed outlet but a distance upstream of the outlet. The other is that there are many missing data in the streamflow data. These problems also induce difficulties to the watershed management and plans.
The objective of this study is to calibrate and validate the watershed model – LUOM (Luo, 2007) in the southern Guam watersheds in which there are both rainfall and streamflow data, and then to apply the calibrated models to the southern Guam watersheds both with and without streamflow gages to generate long term time series of streamflow for the whole watershed.
The Large-scale, Unified and Optimization Model, LUOM (Luo, 2007) is a fully physically based, two-dimensional distributed watershed model which simulates the hydrologic cycle on a watershed scale. The model discretizes the watershed into rectangular grid cells and makes use of spatial distributed GIS (Geographic Information Systems) data such as DEM (Digital Elevation Model), vegetation, and soil data. The model comprises of a series of sub-models for climate data distribution, evapotranspiration, infiltration, groundwater, surface flow, etc. The surface flow sub-model solves the two-dimensional shallow water equations using the diffusive wave approximation. With the input of climate data, mainly precipitation, temperature and wind speed, the model is able to generate not only one-dimensional output – discharge hydrographs, but also two-dimensional hydrologic quantities such as evapotranspiration, infiltration, soil moisture, groundwater table and surface water depth. Simulation of the impacts of land use (vegetation) transformation and global climate changes is within the model’s capability.
In this study, DEM, vegetation, soil, rainfall and streamflow data have been collected and processed, hydrologic watershed boundaries and stream networks have been delineated, and the LUOM (Luo, 2007) has been calibrated and validated in Ugum watershed and verified and recalibrated in the other 4 watersheds with both rainfall and streamflow data, which are Lasafua, Umatac, Inarajan, and Puliluc (at Tinago station), and the calibrated models were applied to a total of 12 watersheds including the 5 calibration watersheds and the other 7 adjacent watersheds. Fifty four (54) years of long term rainfall data have been composed from the observation data collected at the 9 climate stations in southern Guam, which have 15 years of or longer rainfall records. Using these long term rainfall data as input, the model generated long term time series of steamflow. The final output of the long term time series of streamflow is a combination of the observation streamflow data collected at the USGS gage if the watershed has one and the long term simulation result from the model.
