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#           Exploring: Reservoir Capacity And Sedimentation Of The Fena Valley Reservoir Guam      

  Completed

      By California Water Science Center      December 10, 2018    

            -              Overview           
            -              Publications           
            -              Partners           

The Fena Valley Reservoir, located in southern Guam, is the primary source of water for the United States Naval Base Guam and nearby village residents. At full capacity, the reservoir surface area extends approximately 0.30 mi2, and drains a watershed area of about 5.88 mi2.  After reservoir construction, periodic bathymetric surveys, coupled with sedimentation models, can be used to produce estimates of sedimentation rates to evaluate the potential impacts of climate change.

Since the construction of the Fena Dam in 1951, sediment has accumulated in the reservoir and reduced its storage capacity. The reservoir was surveyed previously in 1973, 1979, and 1990 (Kennedy Engineering Inc., 1973; Curtis, 1984; Nakama, 1992) in order to estimate the loss in storage capacity. To determine the current storage capacity, the United States Geological Survey in cooperation with the United States Navy resurveyed the bathymetry of the reservoir in February 2014. This project was part of a comprehensive study to investigate the future of water resources on Guam.

Two methods were used to survey reservoir bathymetry. The first involved use of an integrated Acoustic Doppler Current Profiler and Global Positioning System (ADCP-GPS) (using a Sontek M9 HydroSurveyor ADCP). Horizontal positions were provided by the GPS and bed elevations were computed from ADCP-measured depths and known reservoir water surface elevations at the time of survey. Navigation and data processing were accomplished using Sontek's HydroSurveyor software package. Speed of sound measurements were made with a Conductivity-Temperature-Depth (CTD) profiler and were integrated into the bathymetric survey. The Sontek M9 ADCP is a 5-beam system with 50 degree swath, thus providing increased spatial coverage over single-beam sonar without the additional complexity [e.g. Inertia Measurement Unit (IMU)] of multi-beam sonar equipment.

View Media Details

Reservoir bathymetry was also measured with a multi-frequency, single-beam sonar system with the capability for sub-bottom profiling, i.e. mapping the thickness of deposited sediment within the reservoir. Concurrent with the ADCP surveying, the BSS+3 sub-bottom profiler was deployed (Specialty Devices, Inc.), along with differential GPS (Trimble R10) for positioning. This system was developed specifically for reservoir bathymetry and sediment mapping, and the methods have proven successful for a range of reservoir surveying applications (Dunbar and others, 1999, Obhiambo and Boss, 2004, Anderson and others, 2013). Mapping the sediment deposit with sonar provides an independent check of volume changes computed from historical surveys, which used different methods and may contain much more uncertainty than surveys using modern techniques. The BSS+3 system measures water depth with a 200 kHz transducer and sediment thickness with two additional lower-frequency transducers. Thus, the system provides redundancy with an ADCP survey for reservoir bathymetry as well as sub-bottom profiling capabilities.

 

### Contacts

#### Mathieu Marineau

##### Program Chief, Watershed Sciences

California Water Science Center

mmarineau@usgs.gov

916-278-3179

####             Scott A Wright (Former Employee)          

##### Hydrologist

California Water Science Center

### Explore Search

                      - Drinking-Water
                      - Surface Water Quality
                      - Surface Water Supply
                      - Water Quality Monitoring
                      - Water Use
                      - Measuring and Monitoring
                      - Surface Water
                      - Water Quality
                      - Water
                      - water quality methods

View All **

Below are publications associated with this project.

October 19, 2015

####                 Storage capacity of the Fena Valley Reservoir, Guam, Mariana Islands, 2014              

Water Resources Mission Area, California Water Science Center, Pacific Islands Water Science Center

September 30, 2019

####                 Water resources on Guam—Potential impacts of and adaptive response to climate change              

Water Resources Mission Area, Pacific Islands Water Science Center

June 28, 2017

####                 Daily reservoir sedimentation model: Case study from the Fena Valley Reservoir, Guam              

Water Resources Mission Area, California Water Science Center

January 1, 1992

####                 Storage capacity of Fena Valley Reservoir, Guam, Mariana Islands, 1990              

January 1, 1984

####                 Sedimentation survey of Fena Reservoir, Guam, Mariana Islands, 1979              

Below are partners associated with this project.

#### U.S. Navy

The Fena Valley Reservoir, located in southern Guam, is the primary source of water for the United States Naval Base Guam and nearby village residents. At full capacity, the reservoir surface area extends approximately 0.30 mi2, and drains a watershed area of about 5.88 mi2.  After reservoir construction, periodic bathymetric surveys, coupled with sedimentation models, can be used to produce estimates of sedimentation rates to evaluate the potential impacts of climate change.

Since the construction of the Fena Dam in 1951, sediment has accumulated in the reservoir and reduced its storage capacity. The reservoir was surveyed previously in 1973, 1979, and 1990 (Kennedy Engineering Inc., 1973; Curtis, 1984; Nakama, 1992) in order to estimate the loss in storage capacity. To determine the current storage capacity, the United States Geological Survey in cooperation with the United States Navy resurveyed the bathymetry of the reservoir in February 2014. This project was part of a comprehensive study to investigate the future of water resources on Guam.

Two methods were used to survey reservoir bathymetry. The first involved use of an integrated Acoustic Doppler Current Profiler and Global Positioning System (ADCP-GPS) (using a Sontek M9 HydroSurveyor ADCP). Horizontal positions were provided by the GPS and bed elevations were computed from ADCP-measured depths and known reservoir water surface elevations at the time of survey. Navigation and data processing were accomplished using Sontek's HydroSurveyor software package. Speed of sound measurements were made with a Conductivity-Temperature-Depth (CTD) profiler and were integrated into the bathymetric survey. The Sontek M9 ADCP is a 5-beam system with 50 degree swath, thus providing increased spatial coverage over single-beam sonar without the additional complexity [e.g. Inertia Measurement Unit (IMU)] of multi-beam sonar equipment.

View Media Details

Reservoir bathymetry was also measured with a multi-frequency, single-beam sonar system with the capability for sub-bottom profiling, i.e. mapping the thickness of deposited sediment within the reservoir. Concurrent with the ADCP surveying, the BSS+3 sub-bottom profiler was deployed (Specialty Devices, Inc.), along with differential GPS (Trimble R10) for positioning. This system was developed specifically for reservoir bathymetry and sediment mapping, and the methods have proven successful for a range of reservoir surveying applications (Dunbar and others, 1999, Obhiambo and Boss, 2004, Anderson and others, 2013). Mapping the sediment deposit with sonar provides an independent check of volume changes computed from historical surveys, which used different methods and may contain much more uncertainty than surveys using modern techniques. The BSS+3 system measures water depth with a 200 kHz transducer and sediment thickness with two additional lower-frequency transducers. Thus, the system provides redundancy with an ADCP survey for reservoir bathymetry as well as sub-bottom profiling capabilities.

 

### Contacts

#### Mathieu Marineau

##### Program Chief, Watershed Sciences

California Water Science Center

mmarineau@usgs.gov

916-278-3179

####             Scott A Wright (Former Employee)          

##### Hydrologist

California Water Science Center

### Explore Search

                      - Drinking-Water
                      - Surface Water Quality
                      - Surface Water Supply
                      - Water Quality Monitoring
                      - Water Use
                      - Measuring and Monitoring
                      - Surface Water
                      - Water Quality
                      - Water
                      - water quality methods

View All **

Below are publications associated with this project.

October 19, 2015

####                 Storage capacity of the Fena Valley Reservoir, Guam, Mariana Islands, 2014              

Water Resources Mission Area, California Water Science Center, Pacific Islands Water Science Center

September 30, 2019

####                 Water resources on Guam—Potential impacts of and adaptive response to climate change              

Water Resources Mission Area, Pacific Islands Water Science Center

June 28, 2017

####                 Daily reservoir sedimentation model: Case study from the Fena Valley Reservoir, Guam              

Water Resources Mission Area, California Water Science Center

January 1, 1992

####                 Storage capacity of Fena Valley Reservoir, Guam, Mariana Islands, 1990              

January 1, 1984

####                 Sedimentation survey of Fena Reservoir, Guam, Mariana Islands, 1979              

Below are partners associated with this project.

#### U.S. Navy