The Central Arizona Project (CAP) is a multipurpose water resource development and management project that provides irrigation, municipal and industrial water to much of Arizona. The primary means of water conveyance is a 336-mile concrete-lined aqueduct that transports water from the Colorado River, on Arizona’s western border, across the State to Phoenix, and then southward to the aqueduct terminus near Tucson. Each year, over 1.5 million acre-feet of water is delivered to our customers.
Since its completion in 1993, the aqueduct system has experienced increasingly severe sedimentation that creates problems within the pumping plants and in the aqueduct itself. Because the sediments can decrease the flow capacity of the aqueduct, cause damage to pumps and internal systems, and restrict flow through critical filtration units, it is imperative that dredging operations occur periodically.
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| CAP forebay dredging in 2009 |
In the past, CAP performed intensive sonar based sediment studies to determine bathymetry and the amount of deposition in the forebay of each of the 13 pumping plants. The surveys show when and where dredging operations should occur. These surveys were contracted to outside companies with costs ranging from $40,000 to $120,000 annually.
In 2012, CAP began to use the sonar technology provided by BioBase to conduct its own bathymetry surveys in the pumping plant forebays. Water depths are compared to historical baseline surveys and the volume of sediment in each forebay can easily be calculated. Annual surveys allow us to compare sedimentation from year-to-year to determine loading rates and critical areas to target sediment removal. Surveys of all 13 forebays can now be accomplished in three days rather than six months, and when compared to the expensive surveys from the past, are equally as accurate.
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| Blue-scale bathymetric map of a CAP forebay. The light blue contours show an area that is extremely shallow and is in need of sediment removal. |
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| Example transect design and resultant bathymetric map coupled with the sonar log viewer. Notice the detailed image of the forebay’s trash racks produced by Lowrance HDS DownScan |
This new approach to bathymetric and sedimentation mapping saves time and money, allows us to evaluate results immediately, and makes dredging operations more efficient and timely.
Scott Bryan is the Senior Biologist for Central Arizona Project (CAP). After receiving an M.S. in Fisheries Management at South Dakota State University, Scott worked as a research biologist for Arizona Game and Fish for 10 years, then specialized in lake and stream management for seven years at a private consulting firm in Albuquerque. Scott’s current position at CAP includes a broad scope of work, including aquatic and terrestrial vegetation control, fisheries and wildlife management, invasive species research, and water quality monitoring.
