Location: Island of Guam

Problem:  Rainfall, surface-water, and ground-water information are needed for water-resource management and planning. Proper planning and management water resources require long-term information so that trends can be defined, problems discovered, and corrective actions taken. Knowledge of rainfall and runoff is necessary for the prediction and assessment of the effects of droughts and floods, the estimation of ground-water recharge, and in the design and operation of reservoirs and diversions for water supply and power generation. Long-term ground-water data are needed to determine the response of island aquifers to climatic variability as well as changes in ground-water withdrawals and land use.

Objectives: The objectives of the hydrologic data-collection program in Guam are to collect, analyze, and publish data on rainfall, surface water, and ground water from a network of sites on the island of Guam. Data are useful to Federal, State, and local planners for: (1) assessing water availability, flooding hazards, drought conditions, and ground-water/surface-water interactions, (2) estimating future conditions, and (3) managing water resources.

Relevance and Benefits:  An important part of the USGS mission is to provide scientific information to manage the water resources of the Nation. To effectively assess the Nation's water resources, the USGS collects rainfall, surface-water, and ground-water data throughout the Nation. The data are published in annual data reports, reports on water availability and hazards, and are made available on the World Wide Web (WWW). These data are used in determining long-term trends, and in development of models that allow prediction of future conditions and detection of water-supply problems. The data are critical to local, State, and regional water managers for broad-based planning and managing water-resources projects concerning water availability and hazards. The data collected in Guam are an integral part of the USGS nationwide surface-water and ground-water programs.

Approach:  A regionally representative network of rain gages, surface-water gages, and ground-water sites is maintained on the island of Guam. Data are collected using standard USGS methods. Seepage runs and low-flow partial record sites are used in place of additional surface-water gages where practical. New wells are added to the network as old wells are destroyed, new wells are drilled, local land use changes, and other needs arise.

Progress and Significant Results in Fiscal Year 2004:  Data collection, computation, and compilation continued at 7 rain gages, 15 wells, and 8 streamflow gages, 2 sediment stations, and 2 crest-stage partial-record sites. Records for previous water years were computed and finalized.