How Much Water Flows Through The Sacramento River During a Flood Event?
Relationship of Flood Flows in the Sacramento River Flood Control System and the Magnitude of Water Produced
Written by Tom Ellis
The rate of flow in a river in cubic feet per second (cfs) can readily be converted to volume in acre-feet produced within 24 hours by doubling the rate of flow. That means 1,000 cfs is equal to 2,000 acre-feet per day which is enough water to cover 2,000 acres (approximately 3 square miles) one foot deep.
To get a feel for the amount of water that is produced during a major flood event on the Sacramento River every 24 hours, you can double the design capacity of 600,000 cfs. That equals 1,200,000 acre-feet in one day, or enough water to cover 1,200,000 acres one foot deep.
As an example of how quickly water can accumulate, consider the larger storage facilities on the River system if they were empty. Shasta Lake has a capacity of 4.5 million acre-feet. Therefore, a flood flow of 600,000 cfs would fill Shasta Lake in 3.75 days. Oroville Reservoir’s capacity of 3.5 million acre-feet would fill in less that 3 days and Folsom Reservoir, with a capacity of 975,000 acre-feet, would fill in about 19.5 hours.
During the 1986 flood of record for the Sacramento Valley, measured peak flow through the Sacramento River Flood Control Project facilities was 650,000 cfs, which was 50,000 cfs greater than the design capacity. If you were to assume a flow of 500,000 cfs passing through the system, which is not uncommon during winter storms in the Valley, this would be equivalent to flooding one million acres, approximately 1,500 square miles, one food deep in 24 hours.
An excerpt from the 1916 House of Representatives Report on Floods of the Mississippi and Sacramento Rivers compares the rate of flow of 600,000 cfs for the Sacramento River to the area in our valley to receive this flow, which is 26,000 square miles --- a ratio of 23 cfs to 1 square mile of land area. The major portion of this area lies south of the Sutter Buttes, extending down through the Rio Vista area, including the Colusa, Sutter, American and Yolo Basins. For comparison, this report also gives the similar ratio for the lower Mississippi as 1.5 cfs for 1 square mile and the Columbia River as 5.8 to 1.
These facts underscore the need to maintain the ability to move the Sacramento River’s large volume of floodwater through the existing bypass system unimpeded. It is absolutely imperative if we are going to have urban development and a continued flourishing agriculture in areas that could be subject to flood.
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