Underground water banking: how water is captured and stored

The diagram of the Granite Reef Underground Storage Project (GRUSP) below illustrates how underground water banking works, and how the Granite Reef Diversion Dam allows water to reach the SRP canal system. Below the diagram, you can read a step-by-step description of the processes.

This diagram shows how GRUSP works

Underground storage

SRP's water banking projects, such as GRUSP and the New River-Agua Fria River Underground Storage Project (NAUSP), put water into storage in large underground aquifers. Both facilities are operated by SRP on behalf of the facility owners. GRUSP is owned by SRP, Chandler, Gilbert, Mesa, Phoenix, Scottsdale, and Tempe. NAUSP is owned by SRP, Avondale, Chandler, Glendale, and Peoria.

Most of the water stored in GRUSP -- illustrated in the diagram above -- is from the Colorado River. The process is described below. Each numbered step corresponds to that feature in the diagram above.

  1. Water from the Colorado River is brought to the CAP Canal
  2. From the CAP Canal, the water flows to SRP's South Canal
  3. Water is then released to the GRUSP delivery channel
  4. Then carefully measured and fed into recharge basins
  5. In these basins, the water quickly soaks into the porous sand and gravel
  6. The water then travels down to increase the amount of water already in the saturated layers of sand, silt and gravel below

How Granite Reef Diversion Dam works

The Granite Reef Diversion Dam (7), also illustrated above, spans the Salt River (8).

The dam is used to raise the river water level which allows the water to flow into SRP's canal system. The steps below describe how the dam works. Numbers correspond to the features in the diagram above.

  • The Arizona Canal (9) carries water to lands north of the river and the South Canal (2) supplies lands to the south. At this same location, Central Arizona Project (1) crosses the Salt River and the SRP system.
  • Just north of the Salt River, the CAP Canal becomes a pair of enormous pipes that siphon (10) the Colorado River water under the Salt River.
  • The CAP water reappears at the end of the siphon on the bluff south of the Salt River, where it is lifted by a CAP pumping plant (11), continuing its trip south to Pinal County and the Tucson area.

CAP water can also be run into the SRP canals for transport to GRUSP, to cities, or to other water users.

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