FLOOD07777

• County: Statewide
• Community: Southern California
• Basin: Statewide
• Title: Urban Sprawl and Flooding in Southern California
• Date: 1/1/1970
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

3. The diversion, wherever possible, of
sediment-laden waters onto areas where
sediment can be deposited and excess water can
percolate into the ground-water reservoir.
4. The realinement, enlarging, and paving of
permanent channels to convey excess runoff to
the ocean.
5. Such measures are possible in the
mountain areas to retard erosion and surface
runoff through the prevention of forest fires. the
reseeding of areas denuded by fire, the
regulation of land use, and the stabilization of
channels.

Flood control on a major scale in southern
California had its inception in 1915 with the
organization of the Los Angeles County Flood
Control District. That district, organized under
the laws of the State, had as its objective the
control of the waters of the Los Angcles and San
Gabriel Rivers, the Rio Hondo, Ballona Creek,
and major tributaries and washes of Los Angeles
County. This task was much later described by
an eminent engineer as being "well-nigh
impossible of complete solution on the one hand
and a necessity on the other." Impetus to the
flood-control activities in the region followed
the passage of several Federal flood-control acts,
the first of which was approved in 1936. Those
acts provided the U.S. Army Corps of Engineers
with the authority and funds for the
construction of flood-control basins, debris
basins, and several hundred miles of
levee-and-channel improvement.

In Los Angeles County, the Corps of
Engineers and the Los Angeles County Flood
Control District have constructed all 20 of the
flood-control reservoirs and 61 of the] 06 debris
basins planned for the county. They have also
improved more than 350 miles of stream
channel for the conveyance of floodwaters. The
improvement is usually made by fully lining a
reach of channel with reinforced concrete or by
constructing levees faced with concrete or
rip-rap. The improvement of an additional 275
miles of channel is planned in the county. The
storage capacities of the nood-control reservoirs
are maintained, as much as possible, by' sluicing
debris through them during periods of low flow,
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but periodically some must be cleane_
mechanically. The debris basins, too, must b_
cleaned mechanically; the material must be
removed and then must be transported by truck
to disposal areas. That process becomes
increasingly costly as nearby disposal areas are
filled and longer trucking hauls are required to
reach new disposal areas.

Another important function of the Los
Angeles County Flood Control District is the
construction and maintenance of a supplemental
system of storm drains in the urbanized areas of
the county to collect storm waters close to their
source and carry them to the main system of
flood-conveyance channels. About 950 miles of
storm drain have been built at a cost of about
$700 million, and it is estimated that $1 billion
more will be needed to provide the additional
625 miles of storm drain that are planned. The
eventual total cost of the entire supplemental
storm-drain system will far exceed that of the
main system of flood-conveyance channels.

East of Los Angeles County, in the 3lnta Ana.
River basin, the Corps of Engineers has
undertaken the protection of the urban areas of
Orange, San Bernardino. and Riverside Counties.
They have constructed five of eight authorized
flood-control reservoirs and many miles of flood
channels, such as those on Lytle Creek and
Cajon Creek. The flood-control program of the
Corps of Engineers for the Santa Ana River
basin has been augmented by the work of
flood.control districts in the three counties
involved. These organizations cooperate in
integrating the nood-control programs, in
consolidating local levee and storm-drainage
districts, and in building storm drains and nood
channels.

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West of Los An,geles County, the Ventura
County Flood Control District has constructed
Matilija Reservoir, and along the Ventura River
downstream from th.at reservoir the Corps of
Engineers has built 13,000 feet of levees. On the
Santa Y nez River in Santa Barbara County the
U.S. Bureau of Reclamation has built CachumaA
Reservoir downstream from the older Juncal and"
Gibraltar Reservoirs.

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