This chapter describes the models that simulate the diversion of water. A diversion is any infrastructure or operational action that removes water from its natural course (a river, stream, lake, or aquifer) and conveys it to another location or use. Diversions can be temporary (seasonal) or permanent, and can range from small irrigation headgates to major interbasin transfer projects. Common types of diversions include the following:
Interbasin transfers: moving water from one watershed to another
Operational diversions: routing flood flows to bypass channels, floodways, or storage areas
Diversions serve many purposes:
Irrigation and agricultural supply
Purpose: Deliver reliable water to farmland when rainfall is insufficient or poorly timed.
Example: Irrigation diversions from the Colorado River to the Imperial and Palo Verde Valleys in Southern California.
Example: Extensive canal networks in the Indus Basin (Pakistan/India) divert river flows to agricultural command areas.
Municipal and industrial (M&I) water supply
Purpose: Move water to cities or industries located away from major sources, or to improve reliability and water quality.
Example: Los Angeles Aqueduct (diverts water from the Owens Valley to Los Angeles).
Example: Colorado-Big Thompson Project transfers water from the Colorado River headwaters (west slope) to cities and farms on the Front Range (east slope).
Hydropower generation (run-of-river or storage-based)
Purpose: Route water through turbines; sometimes water is returned to the river downstream (but not always at the same location or time).
Example: Hydropower diversions in steep terrain (common in the Alps, Pacific Northwest, and Himalayas) where water is diverted into a penstock to a powerhouse and then returned to the river.
Flood risk management and emergency operations
Purpose: Reduce flood stages by diverting a portion of high flows into bypasses, floodways, or designated storage areas.
Example: Yolo Bypass in California: during high flows, water is diverted from the Sacramento River system into a flood bypass to protect Sacramento and surrounding areas.
Example: Bonnet Carré Spillway in Louisiana: diverts Mississippi River floodwaters into Lake Pontchartrain to reduce pressure on levees protecting New Orleans.
Environmental restoration, habitat management, and water quality control
Purpose: Re-route or supplement flows to improve habitat, temperature, salinity, or water quality; or to provide minimum instream flows.
Example: Managed diversions or releases used to improve salinity control and habitat conditions in the Sacramento–San Joaquin Delta.
Navigation and channel maintenance
Purpose: Maintain depths and flows for shipping channels or keep water where it supports navigation needs.
Example: Diversion structures and training works in large river systems can be used to maintain navigation channels (often coupled with locks/dams).