|CITY COUNCIL AGENDA ITEM NO. 22
Meeting Date: August 26, 2008
Subject/Title: Informational Report regarding habitat use of Contra Costa
County Flood Control detention basins and request for staff direction.
Prepared by: Debra Galey, Management Analyst
Submitted by: Bailey Grewal, Director of Public Works/City Engineer
Informational Report regarding habitat use of Contra Costa County Flood
Control detention basins and request for staff direction.
At the August 12, 2008, City Council meeting, staff was requested by the
City Council to provide information regarding habitat use of Contra Costa
County Flood Control detention basins.
As requested by the City Council, the following summarizes information and
issues surrounding habitat use of detention basins and provides an update on
staff work to date on the topic.
Detention Basins are master planned, constructed, owned and maintained by
the Contra Costa County Flood Control and Water Conservation District
(“Flood Control District”). The primary, intended purpose is to hold storm
water, prevent flooding of developed areas and prevent the effects of large
volumes of storm water directly entering the creeks during a storm event.
Modifying these detention basins for additional habitat use creates very
real concerns for the multiple jurisdictional agencies that would be
Capacity: Retaining water year round in the detention basin decreases the
capacity to hold the storm water, thereby requiring larger detention basins
and additional acreage.
Environmental: Retained water eventually creates a habitat for wildlife that
through regulation, limits the use of the area with the intent of protecting
the habitat. Various regulatory permits would be required for any activity
associated with a habitat site including; maintenance, discharge of storm
water into and out of the detention basin, silt removal, etc. The permit
would have associated conditions such as time of year and how activities may
be performed, (i.e. manual maintenance rather than mechanical) as well as
mitigation for any impact on the habitat, including the payment of
Liability: Retaining water in a basin year-round incurs additional liability
for the property owner, or responsible maintenance party, due to safety
issues such as drowning associated with allowing public access or
trespassing, as well as public health issues such as vector control. The
unmanaged wetland vegetation in a habitat area can also create nuisance
issues such as odors, collection of trash, and homeless sites. Retaining
water year-round also increases the risk of flooding and its associated
liability. It may be possible to control the water level with gates or
valves, but this also adds to maintenance time and expense.
Cost: Increased maintenance time, expense and any additional mitigation
required by jurisdictional agencies.
Storm water detention basins containing wildlife habitat would be monitored
and regulated by State agencies including California Department of Fish and
Game and Regional Water Quality Control Board.
Previously, City staff has been successful in coordinating efforts with the
Flood Control District to modify design of a few detention basins to be more
aesthetically pleasing and incorporate recreation use. Heron Park is an
example of a detention basin that is more naturally pond shaped, though this
was agreed to by the Flood Control District only after much coordination and
the use of park acreage for storm water capacity during a very large storm
event. Creekside Park (south of Balfour Road adjacent to Marsh Creek) and
Fairview Avenue soccer fields (south of Buena Vista Street) are other
examples of detention basins that are used as recreation facilities during
the dry season. If not used as joint facilities, these detention basins
would be similar to the rectangular detention basins along Sellers Avenue
(south of Chestnut Street) and Fairview Avenue (south of Lone Tree Way).
Currently, discussions continue with the Flood Control District for
modification and habitat use of existing and future detention basins. City
staff has been researching the viability of using County Habitat
Conservation Funds for the construction and maintenance of the habitat use
of storm water/habitat detention basins. The Flood Control District is the
agency charged with the task of providing regional storm drain planning and
facilities, as well as the owner and maintenance party. As the responsible
agency, the Flood Control District is willing to modify detention basin
design and use as long as the issues outlined above are addressed
satisfactorily. One alternative discussed was for the Flood Control District
to turn over ownership and maintenance of detention basins to the City,
though the Flood Control District did not plan to transfer the Brentwood
portion of their County wide flood control maintenance property tax along
with the transfer of maintenance responsibility.
At this time, staff is requesting direction of the City Council as to their
desire for next steps.
The only associated impact pursuing this further with other agencies would
be staff time. The full cost and funding source associated with habitat use
of flood control detention basins are unknown and would be largely dependent
upon conditions of other regulatory agencies. However, the Flood Control
District has conveyed that any additional cost of maintenance, liability or
mitigation will be borne by the City resulting from retention of any water
in these detention basins.