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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 involved, including:

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 mitigation fees.

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.

City Administration
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