|
<br />
<br />RETHINKING LEVEE CONSTRUCTION
<br />
<br />Levee construction and reconstruction continues
<br />throughout California. Levees are being strength-
<br />ened along the Sacramento and Feather rivers in
<br />northern California. More levees are proposed for
<br />reconstruction on the San Joaquin, Sacramento,
<br />American and Mokelumne rivers, along with
<br />hundreds of other smaller streams throughout the
<br />state, Nearly $200 million in federal funds was spent
<br />to repair and upgrade levees along the Sacramento
<br />and San Joaquin river systems following the 1997
<br />New Year's flood. New levees are being constructed
<br />and rebuilt along the Santa Ana River in southern
<br />California,
<br />
<br />Levees along constricted rivers pose major problems.
<br />The San Joaquin River system levees, for example,
<br />were built close to the river's edge to channel
<br />seasonal snow melt. In 1997, levees overwhelmed
<br />by high flows caused flooding in parts of Fresno,
<br />Madera, Manteca, Stanislaus and San Joaquin
<br />counties.
<br />
<br />Environmental awareness plays an increasing role
<br />in determining how to construct and rehabilitate
<br />levees. Setting back levees and constructing water-
<br />side berms, which give rivers more breathing room
<br />and improve riparian habitat, are now accepted flood
<br />management measures_ In 1997, five and one-half
<br />miles of levees were intentionally breached and
<br />abandoned at the Cosumnes River Preserve to
<br />widen fhe floodplain and f100dway to improve riparian
<br />habitat and increase flood protection, DWR and the
<br />Corps have been experimenting with waterside
<br />berms, which replace sloped levees with a bench or
<br />L-shaped berm, The flat bottom of the water side
<br />berm is inundated during the tidal cycle, which
<br />encourages the proliferation of riparian vegetation
<br />that benefits fish,
<br />
<br />A consortium of state and federal agencies, which
<br />are working on finding a long-term solution to the
<br />Bay.Delta water supply and ecosystem problems,
<br />recommend creating set back levees and widening
<br />managed f1oodways, This group, known as CALFED,
<br />also promotes coordinating flood management with
<br />ecosystem needs, such as combining levee repair
<br />and stability with needed wildlife habitat improve-
<br />ments where practical.
<br />
<br />Local reclamation districts are concerned about
<br />impacting endangered species as they operate and
<br />maintain levees. Many programs have been altered
<br />to avoid disturbing these species. Of chief concern
<br />
<br />CHANNELIZED, LEVEED RIVER
<br />
<br />COll~rcle.Groul.
<br />
<br />~~~~
<br />
<br />SET-BACK LEVEES
<br />
<br />
<br />Riprap
<br />
<br />
<br />
<br />is a reclamation district manager's potential liability
<br />under the federal Endangered Species Act (ESA) if
<br />an endangered species is harmed or "taken," Flood
<br />control officials say the need to avoid endangered
<br />species has increased maintenance costs and in
<br />some instances prevented the proper clearing on
<br />some rivers. However, others point out that needed
<br />expedited levee repairs were exempted from ESA
<br />requirements after the 1997 floods.
<br />
<br />A set back lel'ee allows the
<br />river to occupy the flooplain
<br />and reduces the threat of
<br />levees overtopping. The
<br />design of a setback leree
<br />l'llries depending on whether
<br />it is a delta, river or
<br />tidallevl>e.
<br />
<br />
<br />
<br />-.. ~~---
<br />
<br />,,. ~" "~" ":
<br />..~>"",.rtt~,J
<br />~t."-i""'Y't.~,:~
<br />....," ,,' ,.e'~'.-,,''''#l'.i'
<br />.'~.o~;:_ ,.~t l!l",'- ,..;,
<br />_:./\'<::..: r "~-'.":..~~., --Hi. -
<br />
<br />,i,l~
<br />,:f... ,..,
<br />::::'.fV:Fff
<br />
<br />-;.1;.
<br />
<br />.~ :~~.~ ~{:fi;~:~~~.,~.,;,
<br />~: .'
<br />
<br />',',
<br />
|