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Folsom Dam's outlets and penstocks now can release a maximum of 36,000 cubic feet per second. Channel capacity releases can be reached only when the lake level reaches well above the spillway crest. By this point the lake is more than 75% full and its ability to absorb inflow from a major storm is diminished. Modifications would enhance the dam's ability to release water faster, while the reservoir is still low.

Of course, levees themselves are sometimes the culprits in flooding. They cannot only fail to prevent large floods, but even if they don't fail they still can exacerbate

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Folsom Dam

damages by forcing flows into areas

where they otherwise might not go. A river constricted by streambank levees can prompt flooding both upstream or downstream (with water backing up and flooding areas upstream or funneling out downstream with the added velocity and power that can damage or overwhelm flood protection structures).

One of the way; to ease levee unreliability and damage problems is to set levees back, opening up a river's floodway and reducing the structural pressures during flood events. Set-back levees let the river occupy more of its natural floodplain, helping create a better buffer during flood events.

Inadequate dam design and flood control operations

   When it comes to flood control in California there are essentially three flaws with its dams, both in terms of design and operations: (1) Flood operation rules are not always followed; (2) Flood operation rules may be outdated or inadequate; (3) Some darns were not well designed for flood control operations because they cannot physically release water quick enough to handle large flows into their reservoirs.

Most of the dams controlling flows into the Central Valley were designed during another era. While they were billed as "multipurpose" facilities that is, structures for water storage, hydropower production, flood control and recreation -- their main purpose was to deliver water and power. They were designed to store water, not make efficient water releases during very large but infrequent storm events.

In February of 1986 at Folsom Dam on the American River, rules for making flood releases were not followed in a timely manner because of a desire to store as much water as possible for use later in the year. When the rains continued, dam operators at Folsom were suddenly forced to make unprecedented releases in order to protect the dam from overtopping.

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The American River as it winds its way through the city of Sacramento

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AMERICAN RIVER

The bright spot among the flood systems tested in 1997 was, ironically, the American River. Despite having the largest 3-day vloume of runoff ever, the existing facilities handled storm flows without any major problems.

The success of Sacramento’s flood system wasn’t a matter of luck; the storm intensity and subsequent runoff in the American River watershed was the equivalent of that occurring in other watersheds to the north and the south, including the Feather, Tuolumne and San Joaquin. Instead the lack of flooding in Sacramento resulted from prudent operation at Folsom Dam and relatively reliable levees  the result of nearly a decade of pressure on engineers and managing agencies to do something besides just demanding yet another dam on the American River.

Poor operation at Folsom Dam during the 1986 storms led to embarrassing criticism, especially from a prestigious National Research Council report released in 1994. In addition, over the last ten years, federal, state, and local governments have made major investments in Sacramento’s levee system. As a result of careful scrutiny and more investment, dam operators in 1997 made sure they promptly made required flood releases and maintained plenty of empty space in the reservoir for the seasons major storm events.

However, the American River does not represent an ideal opportunity for restoration / floodplain management. Developed areas along the river cannot provide greater floodplain storage or levee set backs. Like other parts of the state, suburban Sacramento has encroached along the rivers historic floodway to such a degree that many residents have backyard gardens planted along the toes of levees, making levee set back options extremely expensive and politically impractical.

But public safety can be improved by fixing the existing American River flood system: Folsom Dam and downstream levees. Fixing the existing flood system can be done in two principle ways: (1) stabilizing and improving levees with internal, concrete- like slurry walls, and increasing their size and resistance to erosion; (2) structurally modifying the dam at Folsom by lowering spillways and enlarging its outlet works. Those improvements, combined with earlier and more aggressive flood releases from the dam, can provide Sacramento with protection from any foreseeable floods along the American River.

Compounding that misoperation, Folsom Dam's design (specifically its spillways) would not allow operators to make full releases until about 75 percent of the reservoir was filled. In other words, because of a design flaw that had been known for years, most of Folsom Reservoir had to be filled before channel capacity releases could be made downstream; not an ideal situation when flood flows into the reservoir were already exceptionally high.

Continued In Flaws In The Existing System PartIII

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