Contra Costa County Flood Control and Water Conservation District
Contra Costa County
San Ramon and Walnut Creeks
Public or private land?
Lower Walnut Creek, north of Highway 4 and East of I-680. North of the City of Concord, and east of the City of Martinez. The specific limits are the mouth of Susuin Bay upstream to the BNSF Railroad (2.5 miles) plus an additional 1.5 miles of the lowest reach of Pacheco Creek.
This project incorporates a new way of approaching the traditional methods of operating and maintaining a flood control facility. This alternative approach moves away from the single purpose, environmentally insensitive USACE design, to a sustainable plan that will prove appropriate floodplains and create floodplains and habitat. These features have all been lost upon the construction and subsequent management of the LWC system.
Transform Lower Walnut Creek from an antiquated, difficult to maintain, U.S. Army Corps of Engineers (USACE) facility into a sustainable, environmentally sensitive creek. Project will include modification of project levees, acquisition of flowage easements and possible reconfiguration of the channel conveyance to better accommodate sediment and habitat. Also includes robust public participation and recreational components.
Drinking Water Supply
Water Quality Improvement
Habitat Protection and Restoration
This project will preserve and enhance in-stream and adjacent marshland habitat while maintaining or improving the design level of flood protection. It also provides a direct water quality improvement by expanding constructed wetlands providing stormwater treatment benefits.
The project will acquire flowage easements to ensure vacant lands within the creek's floodplain are protected from development and instead receive the nourishing, periodic flooding they have traditionally enjoyed.
This project has partnership opportunities with regard to habitat restoration and maintenance of restored areas, as well as recreation features that can be added and managed by other partners.
perhaps, but this represents the District's largest-cost capital project, so excess funds are unlikely.
Project will use wetlands for conveyance, recharge and flood storage.
Part 2 - Detail
The Walnut Creek watershed is the largest in Contra Costa County, draining over 150 square miles, and containing eight cities and over 300,000 residents. The lowest, or most downstream, portion of this watershed is called Lower Walnut Creek, and it consists of a wide trapezoidal earth channel with levees on one or both sides. It is populated with a diverse assortment of wildlife both in the water and in the adjacent marshlands.
The channel is heavily impacted by sediment and has partially silted up, which affects its flood carrying capacity. But removing the sediment also removes the habitat and wildlife, and the sediment would quickly return.
In essence, the project is transforming this legacy facility into a a sustainable channel that provides critical flood protection in a way that is more compatible with the plants and animals that call the creek home.
This can be accomplished by:
Creating additional wetlands, riparian habitat, and revegetation potential
Moving back the channel levees in the lower reaches to provide additional capacity for floodwaters
Reducing de-silting costs, and finding reuse sites for excess sediment from the project.
Restoring the design level of flood protection by expanding conveyance and securing flowage easements over low risk parcels currently protected by the levees.
Other objectives include expanding recreation and educational opportunities along the creek.
This project was built by the Corps in the 1960s and has been problematic since it was constructed. In 2003, after decades of wrangling with the Corps, the Flood Control District partnered with the Corps on a General Reevaluation Project. This produced excellent technical data (such as sediment studies, hydraulic model, wetland delineation and salmonid viability studies), but when Congress eliminated earmark funding, the project stalled.
In response, the Flood Control District took the unusual step to request Congress deauthorize the lowest 4 miles of the 22 mile Walnut Creek system. This request was granted in the 2014 WRRDA legislation, and, now in local control, planning can begin in earnest.
The Flood Control District retained Environmental Science Associates (ESA) to lead the local planning effort. This effort in well underway with technical analyses and comprehensive stakeholder engagement proceeding simultaneously.
The likely preferred alternative will consist of breaching or lowering approximately 3 miles of project levees to restore flood flows to wetland areas. This would augment habitat, allow accumulated sediment (and habitat) to remain in the channel, and would restore the design level of flood protection.
Lower Walnut Creek is proud to be one of the demonstration projects included in the "Flood Control 2.0" program being let by SFEI.
Flood Control Zone 3B master plan
The District has on file a vast number of Lower Walnut Creek studies. They include wetland delineations, biological assessments, levee certifications, sediment analyses, hydraulics and hydrology modelling reports.
Lower Walnut Creek, which drains directly into Suisun Bay
Overview: Lower Walnut Creek today looks significantly different than when it was channelized over 60 years ago. Even back in 1963, when the Corps began its efforts in the watershed, Lower Walnut Creek was far from pristine and untouched. Development: When farms and fields are developed into commercial, residential, and industrial uses, areas where water used to drain into the soil became paved over. This new impervious surface meant that less water soaked into the ground and more ran off into creeks. Natural processes had formed the creeks to a certain size, and this additional runoff meant the creeks flooded more often. To make matters worse, some of the most desirable flat lands for farming and development were near the creek in its historic floodplain. The high value of this land set up tremendous pressures to reduce flood damages and tame the creek. Channelization: Historic aerial photos from 1939 show the alignment of Walnut Creek to be significantly different from when the Corps began work in 1963. In the 1940s and 1950s, the natural creek was channelized by neighboring landowners to help keep stormwater in the creek and to pass it through the system efficiently. When the Corps was asked to help the situation in the 1960s, the resulting project further widened the already channelized creek and constructed levees to allow the water to rise higher without escaping. The newly-formed Flood Control District (District) was the non-federal sponsor for this work by the Corps of Engineers and signed agreements saying they would own and maintain the channel in perpetuity. Calculations at the time showed the channel would need minimal maintenance, and sufficient funds were available to perform this maintenance. Sediment: Soon after Lower Walnut Creek was handed over to the Flood Control District for maintenance, it became clear that much more sediment was depositing in the creek than was originally calculated by the Corps. The Corps returned in 1973 and participated in dredging the lower channel, removing over 850,000 cubic yards of sand and mud. When the District prepared to dredge the channel again in the early 1990s, it because clear that significant habitat for wildlife had formed in the channel since the last invasive dredge and getting regulatory permits necessary to do this work would prove difficult and enormously costly. This difficulty was compounded by the reduction in the district’s property tax funds as a result of the passage of Prop 13 in 1978. Unfortunately, leaving the habitat in place was not an acceptable maintenance practice in the eyes of the Corps of Engineers . This conflict put the District in a no-win situation:
Should the District remove all the vegetation and habitat in the channel to restore it to its 1960s configuration? Should the District allow the sediment, vegetation and habitat to remain but be out of conformance with the Corps maintenance requirements?
The District ultimately chose a third option, which was to deauthorize the project from the Federal system, and proceed with a local project without the Corps oversight or assistance.
If the project is not implemented, opportunities for the habitat improvement would be lost, and continued sediment accumulation would reduce flood carrying capacity. This would eventually lead to increased flood risk for neighboring property owners and for after a flood, increased demands to "clean out that creek!" Instead, the District's project provides a sustainable balance between flood protection and habitat improvement that makes the creek work better for all.
i. Water Supply (conservation, recycled water, groundwater recharge, surface storage, etc.)
ii. Water Quality
...Currently, the habitat present in the stream help to slow and filter stormwater, improving water quality.
iii. Flood and Stormwater Management
...The Lower Walnut Creek channel is the primary drain for 150 square miles and 300,000 residents. It serves an extremely critical role in the drainage protection of large commercial, industrial and residential areas.
iv. Resource Stewardship (watershed management, habitat protection and restoration, recreation, open space, etc.)
...A fundamental component of the Lower Walnut Creek Restoration is the preservation of the habitat that has developed in the channel and to implement a project that would allow this habitat to remain. A very exciting part of the project is the recreational opportunities afforded by this project. Implementing Lower Walnut Creek paves the way for a long awaited EBRPD Iron Horse Trail Extension which would add the northen-most six miles to make the new terminus at the shore of Suisun Bay at the mouth of Walnut Creek. It also would intersect with the Great Delta Trail and support the new staging area and interpretative experience at Pacheco Marsh.
Increases Water Supply Reliability
Advances/ Expands Conjunctive Management of Multiple Water Supply Sources
Increases Water Use and/or Reuse Efficiency
Provides Additional Water Supply
Promotes Water Quality Protection
Reduces Water Demand
Advances/Expands Water Recycling
Promotes Urban Runoff Reuse
Addresses Sea Level Rise
Addresses other Anticipated Climate Change Impact (e.g. through water management system modifications)
Improves Flood Control (e.g. through wetlands restoration, management, protection)