Walnut and Grayson Creeks Desilting Project

2 Documents in Project

Summary

SCH Number
2021100347
Lead Agency
Contra Costa County
Document Title
Walnut and Grayson Creeks Desilting Project
Document Type
NOD - Notice of Determination
Received
Posted
5/18/2022
Document Description
Contra Costa County Flood Control and Water Conservation District (District), in cooperation with the Contra Costa County Public Works Department (CCCPWD), proposes to remove sediment from Walnut and Grayson Creeks that has accumulated since the last desilt operation in 2006 (Project). This work is part of periodic maintenance of these channels as required by the U.S. Army Corps of Engineers. In their current state, the hydraulic capacity of both channels is reduced from the design capacity due to siltation. The hydraulic function of these channels is critical to the operations of the District facilities in the area, and this Project will help regain the hydraulic capacity of both channels. The proposed desilt locations are as follows: Grayson Creek from Chilpancingo Parkway to Imhoff Drive; and Walnut Creek from approximately 1,200 feet downstream of Diamond Boulevard to approximately 1,300 feet downstream of Concord Avenue. These reaches were chosen due to their cost-effectiveness and ability to provide the most flood risk reduction in high-priority areas of Concord, Pleasant Hill, Pacheco, and Vine Hill while minimizing impacts to Environmentally Sensitive Areas (ESAs) such as wetlands and marshes. The vertical limit of sediment removal (2 to 7 feet) will be to the original designed geometry of the channels, derived from the as-built plans. A total of about 172,300 cubic yards (cy) of sediment will be removed; 129,800 cy from Walnut Creek and 42,500 cy from Grayson Creek. All ESAs in the vicinity will be separated from the work by a temporary fence or flagging, with an additional 2-foot berm buffering the creek channel from excavation. After desilting, the disturbed areas at all Project sites will be reseeded with a mixture of native plants. Work is proposed to occur from April to October of two consecutive years expected to start in 2023.

Contact Information

Name
Alex Nattkemper
Agency Name
Contra Costa County Flood Control and Water Conservation District
Job Title
Environmental Analyst
Contact Types
Project Applicant

Name
Syd Sotoodeh
Agency Name
Contra Costa County Department of Conservation and Development
Job Title
Planner II
Contact Types
Lead/Public Agency

Location

Cities
Concord, Pleasant Hill
Counties
Contra Costa
Regions
Citywide, Unincorporated
Cross Streets
Imhoff Dr., SR-4, I-680, Pacheco Blvd, Center Ave., 2nd Ave. S., Chilpancingo Pkwy, Concord Ave.
Zip
94520
Total Acres
36
Jobs
14
Parcel #
125-077-XXX, 125-130-XXX, 153-030-XXX, 125-076-002, 153-361-020, 125-020-XXX, 159-15C-004
State Highways
SR-4, SR-242, I-680
Railways
BART), Amtrak, UP, BNSF
Airports
Buchanan Field
Schools
Strandwood, Valhalla, Hidden Valley, Cambridge, Las Juntas Elem.
Waterways
Ellinwood, Galindo, Grayson, Walnut, Hidden Valley, Pacheco and Pine Creeks, Mallard Reservoir
Township
2N
Range
2W
Section
22,26
Base
Mt Diabo

Notice of Determination

Approving Agency
Contra Costa County Board of Supervisors
Approving Agency Role
Lead Agency
Approved On
County Clerk
Contra Costa
Final Environmental Document Available at
https://www.contracosta.ca.gov/DocumentCenter/View/73004/Final-CEQA-for-DCD-website-CP21-29?bidId=

Determinations

(1) The project will have a significant impact on the environment
No
(2a) An Environmental Impact Report was prepared for this project pursuant to the provisions of CEQA
No
(2b) A Mitigated or a Negative Declaration was prepared for this project pursuant to the provisions of CEQA
Yes
(2c) An other document type was prepared for this project pursuant to the provisions of CEQA
No
(3) Mitigated measures were made a condition of the approval of the project
Yes
(4) A mitigation reporting or monitoring plan was adopted for this project
Yes
(5) A Statement of Overriding Considerations was adopted for this project
No
(6) Findings were made pursuant to the provisions of CEQA
Yes

Attachments

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