Flood Control Features
Tempe Town Lake is part of the Salt River channel and as such, is subject to receiving water from upstream. When snow melts from the north or rains fall across our state, water is released from the SRP dam systems into the lower Salt River and then through the Tempe Town Lake.
The dam system that forms the Town Lake was designed to handle a wide range of water flows and occasional large floodwater events on the Salt River and Indian Bend Wash. Prior to construction of the lake the Salt River was channelized and deepened to pass through the maximum expected 500-year flood event in this reach of the river. Two levee systems were also constructed: A cement stabilized alluvium lower levee that carries the 100-year flood event (approximately 180,000 cfs), and a rock gabion upper levee designed to contain the 500-year flood event (approximately 250,000 cfs).
Town Lake utilizes eight rubber bladders that form two inflatable dams segments that contain the water on the east and west ends of the lake. These dams can be rapidly deflated or inflated in 45 minutes or less to release flood waters flowing down the Salt River, or to capture and store the tail end of flood water flows in the lake. Water that is released or passed through the lake during storms can be replaced with the tail end of local flood waters, or by flood waters released or spilled from full reservoirs upstream on the Salt and Verde Rivers.
Pictured above: An example of a movable crest steel gate dam, which has been selected as the future Town Lake downstream dam system
Tempe plans to replace the inflatable rubber dams with a movable crest steel gate system in 2015. The city is moving to the steel gate technology because the harsh desert environment has caused excessive aging of the rubber dams and has shortened their useful life.
Here is a general guide to understanding water flows to Town Lake:
River flows of less than 10,000 cubic feet per second (cfs) normally do not result in any change to standard operations at Town Lake. The dam control system automatically adjusts to increasing discharge rates in the river to maintain a constant lake elevation. If flows exceed 10,000 cfs, the City of Tempe would expect some debris to pass and would address that situation. At river flow rates between 10,000 cfs to 30,000 cfs, the dam control system will continue to maintain a relatively constant lake level while adjusting to pass increasing discharge rates. When flows exceed 30,000 cfs, dams are lowered partially to safely pass through flood flows. At least one or two dam segments are lowered completely when flows exceed 36,000 cfs. As the flood peak passes and flows drop, the inflatable dam segments are completely re-inflated when flows drop to 10,000 cfs or less, capturing the tail end of the flood event to re-fill the lake.
The Town Lake dam system in Tempe is rated to safely pass the 200-year flood event flow rate of approximately 210,000 cubic feet per second (cfs).
The gauges at Priest Dr. and Curry Rd. account for the water passing through Tempe Town Lake. Anyone can monitor the water flow in current time by clicking on Salt River at Priest Dr. and Indian Bend Wash at Curry Rd.