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Rivers and Streams Most California rivers historically had wide seasonal flow variatiolls, and many plant and animal species were adapted to these patterns. r,' ',,,c:~--\\.] -- f:>1IriI ~ ~1.:~ IZ'O "" .J#' ~ I ~ ~ ~"1 !-- .... .. '" 18 i'-~ ;11 Left uncontrolled by levees and dams, most rivers follow meandering courses across the land, paying no attention to property lines or political boundaries. At one time, the Los Angeles River regularly inundated large areas of the coastal plain between Santa Monica and Long Beach that is now urbanized and protected by extensive flood-control channels, Before 49 dams were built on its mainstem and tributaries, the Colorado River's fan-like floodplain could extend from the river's terminus at the Gulf of California (south of Yuma, Ariz,) northward into California and Arizona, And the Sacramento River, swollen with winter rains and spring snowmelt, regularly drove early settlers of its namesake city from their homes during the Gold Rush era. To protect the growing urban areas of California and support the vast agricultural industry so important to its economy, a network of dams and levees was built to regulate and contain flows in the rivers, Dams allowed water flows to be controlled for both flood ~ _..., . ~I'- ~. "'"'... .' ;-" ., .~. "~ - . :-~ .l'! r::I ~r ... "'......,>i'. IT... r" ~".Y' .,;V -." " .~.. P'" ,: , . . -" ~ I:' :...... ~";S" ~" 0; 'h~ , .. ... r'..ro: ... "!' ... p .' ~ fJ -all! control and allocation of irrigation and drinking water. Levees helped minimize unpredictable flooding of valuable agricultural and urban land, But the benefits of tlood control and reliable water deliveries did not come without environmental con. sequences. Reservoirs now store about 30 million acre-feet of water from the Sacramento-San Joaquin river systems, but the reservoirs also reduce sedi. ment transport needed to maintain riparian areas and fish-spawning areas on those rivers and their tributaries by an estimated 83 percent, according to CALFED, More than 5,000 miles of levees have been constructed in California that protect against flood- ing but also increase flow velocities and prevent rivers from depositing nutrient. rich sediment in flood- plain areas. Dams altered the flow patterns and temperature gradients of some rivers to the detriment of fish. Gravel mining along rivers removed fish- spawning habitat and allered streambed contours. Experiments with floodplain restoration in the Yolo Bypass near Sacramento and the Cosumnes River suggest that rewatering riverine floodplains has significant benefits for native plant and animal species, One ot the most promising and cost-effec- tive habitat restoration strategies has been to modify existing flood-control bypasses and create new ones along major rivers that store and dissipate flood waters. Besides keeping flood waters away from urban areas, bypasses also can provide important habitat for waterfowl and spawning and rearing areas for fish, A 3,500-acre habitat-restoration project in the Yolo Bypass along the Sacramento River just west of Sacramento is one example of how the bypass strategy can provide simultaneous flood control and habitat benefits. Excess winter flows from the Sac- ramento River are diverted to the bypass, where they inundate an area that effectively doubles the wetted surtace area of the Delta, While the water gradually evaporates or flows to the Delta, it provides shallow water habitat for watertowl and fish, Once the water drains off, portions of the sediment-enriched soil are used for seasonal farming. The habitat area is man- aged by a consortium of state and federal agencies, .... CALFED planners believe that bypasses like Yolo can be flooded during most years at a relatively modest cost. The success of the Yolo Bypass could become a model for use elsewhere, perhaps even the San Joaquin River system, where bypasses are not an existing feature. However, bypasses could be controversial because water sent to them is not available for downstream uses. i I , ~