Magnitude of Winter Rains

By Tom Ellis

U.S. Army Corps of Engineers surveys in the late 1800’s determined the following facts:

• Anticipated peak flood flows from the Sacramento River would be 600,000 cubic feet per second (cfs).
• That flow was ten times the expected peak flows from the San Joaquin River.
• Intensity of flood conditions in the Sacramento Valley were greater that in any other American river system.
• The ratio of flood flows in cfs to the land area expressed in square miles to receive those flows for the Sacramento River is 22 cfs to one square mile of land; in the Mississippi River, it is 1.5 to 1; in the Columbia River it is 5.8 to 1.
• Areas of the Sacramento Valley to accept the bulk of those flows were the Colusa, Sutter, American (Natomas Area), and Yolo Basins - basically, the low lands from the Sutter Buttes south to Rio Vista.

Prior to beginning the reclamation efforts in the Sacramento Valley, engineers realized a choke point existed in the Horseshoe Bend area near Rio Vista.  They made the channel wider, deeper, and straighter for 12 miles from lower Cache Slough to Collinsville.  To do this, they moved more soil than was excavated to create the Panama Canal.  Currently, this area needs cleaning to assure continued movement of peak flows into Suisun Bay.

In 1907 and 1909, there were levee breaks at Moon’s Bend, down river from the city of Colusa, which convinced engineers that levees alone could not protect the area from the ravages of flooding.  The January 1909  event was the most devastating, unleashing 118,000 cfs of flood water into the Colusa Basin on the west side of the river.  It flooded the entire Colusa Basin in 5 or 6 days, overtopped the Knights Landing Ridge and continued down into the Yolo Basin.  This continued for 30 days.  Of course, this event occurred before any dams were built.

Engineers saw that levees were not the answer so they developed the Sacramento River Flood Control Project - a joint Federal and State effort featuring channel cleaning and levee construction on the main stem of the River, and development of a bypass system to handle the peak flood events.  The system consisted of a series of weirs and designated flood channels designed to relieve the peak flows from the main stem of the River during flood events.  The main stem of the River could handle 25% of the peak flows passing Colusa, so the bypass was designed large enough to handle the remaining 75% of the flows.  This ratio is basically maintained throughout the entire system.

The result of this effort was the reclamation of vast tracts of excellent farmland and urbanization of the Sacramento area.  It allowed a flourishing agriculture, a vibrant economy, and the establishment of Sacramento as the capital of California in an area Mother Nature had designed as overflow land.

Today, this flood control system is being compromised.  Strict interpretation of the Endangered Species Act (ESA) has pitted human activity against wildlife - animals and plants against people.  The result has been that sediment and vegetative buildup has occurred as river meander is encouraged in the main stem of the River.  Similar buildup has occurred within our bypasses, where wildlife refuges have been developed in these designated floodways.  Our safety valves for major flood events have been compromised, as their design capabilities have been reduced.

The very important Sacramento River Flood Control Project designed and built in the early 20th century by pioneer valley residents who saw the dynamic river system running wild, has been compromised by ecosystem restoration efforts.  The Sutter National Wildlife Refuge which is located inside the north end of the Sutter Bypass, has significant growth of weeds, underbrush and trees that adversely affect the ability to move high volume flood flows through this important channel.  Many feel this refuge was a contributing factor to the levee failure that occurred a few hundred yards upstream, flooding the Meridian area in 1997.  We must remember these bypass channels are much like the rain gutters on our homes in that they are very flat and must be cleaned on a regular basis for them to function properly when a storm hits.

The Sacramento city area is very dependent upon the proper functioning of the entire bypass system.  Capacity of the main stem of the River through the downtown area is 110,000 cfs.  When flowing at this rate, there is about 5-times that amount flowing south in the parallel channel of the Yolo Bypass (capacity 500,000 cfs) west of the city.  There is no way the main stem of the River could ever handle that huge flow so doing anything that reduces the capacity of these facilities is not good policy!  One could say that in this era of concern about Global Warming with the accompanying increase in rainfall and reduction of the snow pack, maintaining our ability to move those huge flood flows through the area is imperative!

As recently as 1986, the Flood Control Project, which has a total design capacity of 600,000 cfs, actually moved a record measured peak flow of 650,000 cfs down through the Sacramento area into Suisun Bay.  During that event, Shasta, Oroville and Folsom Dams held back about 260,000 cfs off the peak flows.  If you combine that with the 650,000 cfs the River and Bypass handled, you have a peak valley flow over 900,000 cfs!  For sure, the dams saved the day for our valley!  Maybe we have not seen the greatest flood event yet, so we must not compromise our flood control system in any way!

Return to Flood Control Main Page

Home | Top