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Storm and Flood
Control
The Sonoma County Water Agency (SCWA) in 1958,
created eight geographical zones for the purpose of
delineating financial costs for flood control works.
The eight zones were: 1A) Laguna-Mark West, 2A) Petaluma
Creek, 3A) Valley of the Moon or Upper Sonoma Creek, 4A)
Upper Russian River [not formed], 5A) Lower Russian
River, 6A) Dry Creek [not formed', 7A) North Coastal,
8A) South Coastal, 9A) Bay. Zone funds were to cover
master plans of flood control and drainage works, initiate a
continuing maintenance program and perform emergency work
and channel clearing.
SCWA flood control work processes include
design reports and plans, environmental impact report
reviews, acquisition of property, securing federal, state
and local permits, awarding of construction contracts,
construction engineering and inspection, project accounting
and administration of grants-in-aid. The results of
the SCWA action are channelization, dams, bypass systems,
diversion systems and levees. For example, in 1963,
the SCWA took over bank protection responsibility of the
Coyote Dam works from the Corps of Engineers. SCWA continues
to remove inchannel vegetation, repair and maintains levees
and replaces unsuccessful protection devices.
Property tax rates are set annually to collect
sufficient funds to finance the flood control services
within the formed zones. In 1982, a study on financing
lead to the creation of the Benefit Assessment Act of 1982
(California Government Code Chapter 6.1 Section 54703
Division 2 Title 5) which authorizes the Board of the SCWA
by resolution or ordinance to adopt an annual assessment on
each parcel of real property except that owned by a federal,
state or local governmental agency. The amount levied on the
property is based on a class of improvement, on the basis of
property use or a combination of both. The assessment must
be properly posted or noticed and a public hearing held
prior to the Board adopting. The Board may adopt or modify
the proposed assessment. The assessment must then be
brought to the voters and needs to be approved by a majority
vote of the voters in the proposed area.
The SCWA can seek financial assistance for
supplement zone-tax revenue and can seek assistance from the
U.S. Department of Housing and Urban Development (HUD), U.S.
Natural Resources Conservation Service (NRCS), U.S. Army
Corps of Engineers, and California Department of Water
Resources (DWR).
When the SCWA was first created, the act
granted the power to control flood and storm waters within
the Agency's designated area of authority. It also has
powers over the storm waters of streams outside the area
which flow into it. They have the right to construct
drains and to acquire land needed for rights-of-way for
drains, canals, sloughs, water gates, embankments and water
courses.
The statutory rights given the SCWA were
codified into policy by subsequent resolutions.
Resolution No. DR 10073 (1964) states the SCWA would only
accept responsibility for the maintenance of drainage
facilities which satisfy their standards and specifications,
and projects accepted for maintenance became eligible for
financing through the general fund of the SCWA because some
of the accepted projects were Federally funded and therefore
outside of the zone-dependent taxing. Resolution
No. DR 17860 (1966) specified the standards and
specifications. Later revisions were included in
Resolution No. DR 42127 (1973).
Assessments for zone-taxing is based on a
benefit assessment unit derived from a "runoff
factor". For instance a runoff factor of ".0003" is
assigned to a vacant residential lot and ".90" is assigned
to a service station. Based on a unit factor (derived
from average single family parcel square footage of 9,600
and a runoff factor of .23) and the area of the assessed
parcel in areas times it's runoff factor results in a number
of units for each land parcel. Individual assessor's
parcels are provided by the SCWA. Exceptions can be given
under Government Code Section 54715(d) for railroads and
utilities or undeveloped parcels of land.
In 1995, the Editor of the local press, The
Press Democrat, called for a new public policy related to
flooding. This was in response to the flooding of 1995
and the raised speculation that land use development had
increased the volume of water runoff into the Russian
River. Construction of flood control works (as opposed
to flood management using natural land features such as
wetlands) has resulted in an increase in the volume and
speed of water in constrained channels. Flows within a
river watershed system have two general principals, that is
the rate at which water is transmitted across the land to
the water channels and the percentage of area that is made
impervious by development or natural features. Changes
in the flow pattern whether through land use development or
natural changes cause adjustments in the stream channels to
accommodate the flows or the water leaves its restrictive
banks and a flood results. An example of the percentage of
land made impervious to absorption of water pass through to
groundwater storage due to urban development shows that for
a lot size for residential use of 6,000 sq feet there is 80%
impervious surface area. An increase in total runoff
from a series of storms in an area of highly developed land
results in increased flood peaks during storm periods and
decreased low flows between storms because the water rushes
into channels during storm events and is not in the ground
for later, slow runoff.
Another way of looking at this is defining the
lag time between onset of a storm and the resultant increase
in water in the channel. Lag time is the result of two
functions of a watershed, the basin slope and the basin
length. It is influenced by the drainage area available
within the watershed basin. Lag time is altered by the
effects of urbanization on a basin's surface. Water
runs off faster from asphalt than it does from soil. Thus as
the time required to run off decreases, the peak rate of
runoff or flooding increases. Improvements of the
drainage system may reduce the lag time to one-eighth that
of the natural channels. This lag time reduction,
combined with an increased storm runoff resulting from
impervious surfaces, increases the flood peaks by a factor
that ranges from two to nearly eight.
The SCWA has dramatically altered approximately
120 stream channels through "ultimate channelizing"
(concrete, fences and Bermuda grass) and with "less than
ultimate" (rip rap and straightening.) The General
Plan Update for Sonoma County in it's 1986 form found
increased surface runoff results from the loss of
vegetation, the creation of impervious surfaces in urban
areas, and drainage improvements. Accelerated soil
loss and erosion causes increased sedimentation of
waterways. For each of the individual planning areas,
the amount of land area covered by impervious surfaces has
been estimated, based upon the extent of existing
development of residences, businesses, roads, etc. The
Plan stated that the County should request that the Water
Agency conduct specific hydrological studies in order to
determine the impact of development in the Russian River
watershed on flood elevations. Upon completion of the
studies, the County shall prepare and adopt appropriate
Master Drainage Plans which provide needed flood control and
drainage facilities or other mitigation measures. The
plan shall provide for a development fee or other financing
mechanism whereby watershed development pays the costs
associated with mitigation of flooding and drainage
impacts. By 1989 the Final Plan Public Safety Element
stated that the County shall use proposed annexations,
redevelopment agreements, revenue sharing agreements and the
CEQA process as tools to ensure that incorporated
development pays its fair share toward the studies and
mitigation of downstream flooding impacts caused by upstream
development.
Take
the premise that flooding is natural and that development in
a flood plain is the disaster. Land use planning
analysis is possible for the assessment of increased
flooding. Land use planners can measure the increase
of runoff between urbanized, sewerized land use and the base
value of a rural or undeveloped region based on currently
available data. For instance, a study by Luna Leopold
(1968), compiling data from prior studies, showed that in an
area 50 percent sewered and 50 percent impervious resulted
in the number of flows reaching or surpassing flood stage
would over a period of years be increased nearly
fourfold. The SCWA is not known to be proactive in
commenting on land use decisions on a parcel by parcel
basis, nor does it have a circulated position or policy
paper describing the increase of flooding in the counties
designated flood-assessment geographical zones. This
means that there is no oversight on impacts from land
development and its relationship to increases in area
flooding. It is also unknown what the effect is of the
inflow of the winter water from the Eel River on Russian
River flooding.
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