Todd Engineers

San Anselmo Flooding Litigation Support
Marin County, California

December 2005 flooding in San Anselmo

Todd Engineers provided expert analysis for litigation resulting from the December 2005 flooding along San Anselmo Creek, which is a major stream in Ross Valley and passes through central San Anselmo. Heavy rainfall in late December 2005 caused San Anselmo Creek to breach its banks, resulting in significant flooding in the towns of San Anselmo, Ross, and other downstream communities. Following the flood, numerous legal complaints were filed by flood-affected property owners alleging that public improvements (i.e., bridges) and privately- owned buildings spanning San Anselmo Creek decreased the flow capacity of the channel at various locations and contributed to flood-related damages.

Our technical analysis focused on alleged impacts of a private structure constructed on and supported by a concrete platform spanning San Anselmo Creek. Based on the analysis, we concluded that: 1) historic floods resulted in similar peak flood water elevations; 2) rainfall causing the flood represented a 100-year frequency event; 3) flooding would have occurred even if the building and bridges over San Anselmo Creek did not exist, and 4) the flow capacity of the creek beneath the building is probably equal to or greater than the natural channel. The case was settled out of court to the satisfaction of our client.

Debris Flow Mitigation for Lucas Ranch Development
Alameda County, California

View downslope to a debris barrier during mitigation work

The project objective was to limit post-development runoff to pre-development or lower peak discharges. Todd Engineers designed an upgrade to the existing stormwater control system that included revision to v-ditches and check dams on the client's property. Other key elements of the project included recontouring the surface soils, installing a subdrain system and debris barrier, and constructing a debris detention basin as a contingency in the event of future debris flows. In addition, erosion control matting was installed and the area was re-seeded with native vegetation.

Ray Will, Principal Engineer with Todd Engineers, and Lou Gilpin of Gilpin GeoSciences subsequently provided expert oversight for the design and construction. The stormwater system was installed to all parties' satisfaction.

Shallow Groundwater Mitigation Investigation
Solano County, California

Lagoon Valley lake

To stabilize the site for development, dewatering facilities are needed to drain shallow groundwater and to maintain the water table at lower levels. Todd Engineers evaluated groundwater levels and flow rates to assess the feasibility of a planned dewatering system. Pumping tests were conducted and evaluated to determine aquifer properties and discharge into proposed subdrains. In addition, it was recognized that the development itself could potentially exacerbate the shallow groundwater problems. Accordingly, Todd Engineers conducted a comprehensive water balance that evaluated the potential rise in the water table that could be anticipated. The water balance analyses identified the critical zones for the subdrain system.

Moreover, the development is required to minimize stormwater flow from the site; this will be accomplished with detention basins in the planned golf course. Todd Engineers assisted in evaluation of the amounts of water to be detained and used for golf course irrigation.

Flooding Mitigation for Rancho Verde Mobile Home Park
Sonoma County, California

Vegetation in and along Hinebaugh Creek

After years of flooding, the Rancho Verde community was concerned that local planned development (including a casino) would increase flooding problems. Todd Engineers was first retained to review and provide comments on the DRAFT Environmental Impact Statement (DEIS) and supporting references for the nearby proposed Graton Rancheria Casino and Hotel. Through a series of meetings, Todd Engineers personnel worked with casino consultants to develop plans that would reduce the potential for flooding. These plans included innovative ideas such as a flood bypass system and wetland detention basins.

Subsequently between 2003 and 2007, Todd Engineers provided field inspection and analysis of Hinebaugh Creek, including preparation of cross-sections. One of the initial tasks was to map the local storm drain system; Todd Engineers confirmed the location of several culvert outfalls discharging from Rancho Verde into Hinebaugh Creek. Todd Engineers' field inspection indicated that sediment buildup had reduced the creek capacity between 17 and 33 percent. Moreover, vegetation -- including willow trees, grasses and brush -- was extremely dense along the banks and channel near Rancho Verde. This resulted in blockage of the overall channel and Rancho Verde's culverts, resulting in backup of floodwaters in the mobile home park.

Based on the field work and analysis, Todd Engineers proposed stormwater mitigation measures including modifications to the RVMHP property and Hinebaugh Creek to redirect peak flows or increase flow capacity in the channel. Todd Engineers coordinated with the local flood control agency to identify critical choke points along the creek and to define measures to reduce the flooding potential. We also worked closely with the Laguna de Santa Rosa Foundation, which is concerned with the proliferation of non-native vegetation (e.g., Ludwigia species) in local creeks. The resulting collaborative flood control measures, including Ludwigia control and sediment removal, have proven successful through subsequent storm events.

Eden Shores Community Buffer Zone Channel
City of Hayward, California

Todd Engineers directed a team of engineers, biologists, and hydrologists to address design criteria for the channel. Project concerns included determination of a viable water supply source, definition of water quality objectives, and evaluation of available biological and engineered aquatic systems. For the final design, the team recommended the use of groundwater for water supply, nutrient absorptive aquatic planter pockets and aeration and circulation systems for water quality control, and an automated water level monitoring system.