River and floodplain rehabilitation

River and floodplain rehabilitation

cbec identifies implementable designs, which enhance ecosystem health and achieve water quality objectives, while minimizing flood risks and the need for future maintenance.

Innovative and sustainable flood management techniques, along with the latest technologies, are paired with creative rehabilitation techniques to solve complex hydrodynamic challenges.

cbec staff has worked on a number of large scale multi-objective levee setback and floodplain enhancement projects in addition to many dam removal, in-stream habitat enhancement, and localized floodplain rehabilitation projects.

cbec staff has numerous design engineers licensed in states such as California, Washington, Oregon, Colorado, Nevada, Mississippi, Indiana, Kentucky, Virginia. cbec staff routinely develop project designs from initial feasibility, through concept to final design. cbec staff also regularly provide construction engineering support. A recent project at Cordova Creek in the Lower American River Parkway, Sacramento, California, was completed in late 2016 and is flourishing. In April 2017, the project won an award from Sacramento Environmental Commission for Outstanding Environmental Stewardship. http://www.emd.saccounty.net/sec/pages/environmentalawards.aspx

Flooding in Pescadero, California has been a huge problem for decades. Now through a combination of upstream floodplain and stream restoration, flood risk is being reduced by using non-developed land upstream as floodplain storage.


This model animation graphic shows how floodplain inundation is being increased as a result of floodplain and stream restoration.

Photos taken during and after construction show the rock ramp designed by cbec ecoengineers used to raise the thalweg elevation to increase floodplain connectivity.

Photos taken during and after construction show the wood structures designed by cbec ecoengineers used to raise the thalweg elevation to increase floodplain connectivity.

Various approaches are available for river and floodplain rehabilitation, especially if the floodplain is heavily disconnected from the river channel as a result of channel incision. Channel incision is typically caused by hydromodification effects, such as upstream urbanization, or impacts of dams, grazing, deforestation, or other land use changes. This results in the loss of the vital floodplain “sponge effect” whereby floodplain flows run off the floodplain rather than infiltrate into the substrates and gradually feed back into the river channel. The river channel can be “reconnected” to its floodplain either by raising the thalweg elevation of the channel or lowering the floodplain through mass grading. At the Butano Creek project, near Pescadero, on California’s Central Coast, the river channel was raised using a series of engineered wood structures and riffles.

Construction commenced on the Southport Levee Setback Project in West Sacramento, California in May 2017. This aerial photo taken by cbec shows clearing and grubbing work starting for construction of the new levee. The old levee alignment (shown by the levee top road) will remain but will be breached at various locations to expose up to 150 acres of floodplain. The project is unique in that large areas of floodplain will be lowered to provide borrow material for levee construction, while dramatically increasing floodplain connectivity to the Sacramento River. This will be highly beneficial for anadromous fisheries rearing habitat.

Graphic impression of the new levee setback at Southport (by cbec) showing a dense riparian forest and wetland swales.

The Central Valley of Northern California represents an enormous flood challenge and is at risk from catastrophic flooding. As a result, substantial efforts are underway, such as the Central Valley Flood Protection Plan, to improve California’s levee system. Recently, new levee construction has involved setting back the levee to provide opportunities for improved riverine processes, such as meandering, as well as improved and enhanced floodplain riparian and aquatic habitats. cbec staff has worked on several recent such projects, including the Bear and Feather River Levee Setback Projects, as well as most recently, the Southport Levee Setback Project on the Sacramento River in West Sacramento. This project is probably one of the largest and most important levee setback projects located in a major city in California. cbec staff have not only worked on the geomorphic design for the project but have lead the ecosystem restoration components the of the project on the exposed/setback floodplain.

Tidal wetland rehabilitation

Tidal wetland rehabilitation

Rehabilitating tidally influenced wetlands poses unique challenges due to the complex interaction between coastal and riverine processes.

Equipped with considerable experience and a variety of modeling and design tools, cbec is distinctly qualified to handle the design and implementation of tidal wetland rehabilitation projects.

Staff is expertly trained in the application of hydrodynamic and sediment transport models, which are used to identify opportunities and constraints.

cbec has worked on many high profile tidal and estuarine projects in California, including the salt ponds of San Francisco Bay and the Sacramento-San Joaquin Delta. Other projects include tidal environments along the west coast of the USA from San Diego to the Puget Sound and in the Gulf states, such as in the Apalachicola region of Florida.

2- and 3-dimensional modeling is routinely applied to tidal wetland rehabilitation projects by cbec hydrologists and engineers to determine hydrodynamic circulatory patterns, inundation regimes, particle tracking, and residence times. Tidal hydrodynamics and sediment transport are highly complex, particularly in lagoonal zones. This video shows an animation of 2-dimensional model output of water depth at the Santa Clara River Estuary. The right hand pane shows bed level change over time for the coupled sediment transport model.

Estuarine hydrodynamics must often be modeled at very large scales. cbec modelers have in recent years modeled estuarine systems on the east and west coast of the US. Here for example is shown a model animation from the Puget Sound, Washington, indicating tidal water levels on flood and ebb tide.

2-dimensional hydrodynamic tidal model at a site in the Delta showing tidal velocities and depths for a restoration project.

The Sacramento-San Joaquin River Delta represents highly threatened and important regional habitat for Delta Smelt and other anadromous species. Enormous efforts are underway to try to slow, arrest and reverse the decline in the habitats of the Delta for the benefits of aquatics species, and cbec are involved to a large degree in these projects. cbec staff are involved in numerous projects in the Yolo Bypass and the Northern Delta, at key locations like McCormick-Williamson Tract, Lower Yolo Restoration Project, Prospect Island Tidal Habitat Restoration Project, and others throughout the Cache Slough Complex.

Fisheries habitat rehabiliatation

Fisheries habitat rehabiliatation

cbec’s fisheries expertise extends from threatened and endangered species (e.g., Chinook salmon, steelhead, Lahontan Cutthroat trout, and tidewater goby) of the North American west coast to the Atlantic Salmon in the Northern UK (Scotland).

Typical considerations and design elements for fisheries projects include channel dimensions, substrate size, large wood structures, channel/floodplain connectivity, off-channel habitats, bank vegetation and structure, as well as other hydraulically controlling features that are critical to creating ecologically productive environments for a variety of life stages.

A thorough understanding of the hierarchy of physical controls on in-stream habitats and the ability to link sediment transport processes to the quality of aquatic habitats has qualified cbec to be involved in many high profile fisheries enhancement projects.

We have designed projects in nearly every major river in California’s Central Valley, as well as many along the west coast.

Aerial of redds constructed by spawning fish on the Lower American River in Sacramento, California. The second image show the results of habitat suitability index modeling for spawning. Overlayed on this are actual surveyed redds showing how successful both the modeling and design were.

Model output relating Habitat Suitability Indices to velocity. Post construction monitoring of redd locations has indicated that the suitability for spawning has been predicted through modeling, then constructed on site, with remarkable success.


Millions of dams exist across the US, including small dams constructed privately for various water delivery purposes. Many are old and present major barriers to anadromous fish. cbec has successfully designed and implemented dam removal projects, such as at Branciforte Creek in Santa Cruz County, California.


Gravel augmentation projects represent a fantastic opportunity to augment the sediment supply to rivers starved of their sediment through upstream dams while vastly improving fish spawning conditions. cbec not only designs these projects, but also supervises construction. For example, cbec has prepared gravel augmentation designs for 8 locations on the Lower American River since 2008.

cbec frequently uses watershed assessments to identify and prioritize fish passage obstructions and barriers. Shown here is a recent concept sketch for a fish passage improvement project in the Coon Creek watershed in California.”

Identifying the complex interactions between aquatic and terrestrial ecology and physical processes (hydrology, hydraulics and geomorphology) is key to developing and designing successfully functioning seasonal wetlands.

cbec’s seasonal wetlands expertise includes floodplain wetlands, high elevation meadows, seasonal wetlands at the tidal interface (brackish) and vernal pools.

cbec engineers and hydrologists use a variety of different tools for these purposes including relatively simple water budget calculators, surface water – groundwater models, and complex 1- and 2-dimensional hydrodynamic models.

cbec develop project designs from initial feasibility, through conceptual design, to final design plans, specifications and bid documents. Often seasonal wetland elements are combined with other rehabilitation elements such as river channel, floodplain, tidal, estuarine and coastal rehabilitation. Understanding the linkages between ecological and physical processes is key and cbec have been dedicated in creating these important linkages in the successful implementation of seasonal wetland projects.

The Calero Ponds project in the Santa Clara Valley of northern California is a heavily impacted landscape located on County Parks property that is bisected by water supply conveyance features and used for decades for dryland grazing. In 2016, a portion of the County Parks property it was identified for rehabilitation and cbec staff, working with biologists, ecologists and permitting specialists, developed concept and final designs, specifications and bid documents. cbec engineers provided construction support to complete the successful project. Calero Ponds is just one example of the many types of seasonal wetland projects that cbec staff has completed.

FEFLOW model of a seasonal wetland

cbec staff have been involved in the design of many seasonal wetland projects since 2007. cbec is particularly specialized in the design of vernal pool complexes and have developed a surface water – groundwater model to analyze vernal pool hydrology. Vernal pools have a unique type of ecology that requires a thorough understanding of the associated hydrologic regime to create successfully functions. Chris Campbell, Director, is an industry leader in vernal pool hydrology.

Seasonal wetlands often occur at the interface with tidal marshes. At these interfaces it is important to understand how the tidal inundation affects the seasonal wetlands and the nature of the brackish/freshwater marsh. Projects involving such seasonal wetlands have been created in several locations by cbec and partners in the Yolo Bypass. The design graphic shown here provides an example of one such marsh.

Bank stabilization should not be considered in isolation. It should be considered as part of a whole watershed approach. At cbec we address the “cause” and the “symptoms”. A “band-aid” approach will only be a temporary measure. A sustainable solution is by far the preferred approach.

Biotechnical bank stabilization (sometimes referred to as bioengineering) has been in use for many years and is now widely preferred to traditional, “hard” civil engineering approaches (using concrete or rip rap). Wherever possible, cbec design engineers will always default to biotechnical approaches over traditional approaches.

There are numerous types of biotechnical approaches depending on the severity of the erosion problem and the forces (flow, velocity, bed and bank shear) at play. cbec hydrologists and engineers use sophisticated modeling tools (1-, 2- and 3-D models) to analyze hydrodynamic forces and provide design parameters for the appropriate selection of techniques.

cbec develop project designs from initial feasibility, through conceptual design, to final design plans, specifications and bid documents. cbec Directors, Dr. Chris Bowles and Dr. Chris Hammersmark regularly teach courses in Fluvial Geomorphology and Biotechnical Bank Stabilization where they encourage identifying the causes to correctly address the symptoms. They emphasize the whole watershed approach.

At Arcade Creek in Sacramento, California, cbec engineers developed biotechnical bank stabilization for this heavily impacted stream deep in the urban core. Unfortunately, a watershed approach was not possible since the watershed is so heavily impacted by urbanization. Constraints included adjacent urban areas, a playground and walking trails. It was important that the meandering creek did not erode into these features. Therefore, it was necessary to develop designs that would be resilient to a range of hydrologic conditions. 1- and 2-dimensional modeling was used to develop design parameters. A robust approach was developed that included longitudinal peak stone toe protection (LPSTP), rood wads, coir fabric, willow poles and native seeding.

A more reach scale approach was adopted at Butano Creek near Pescadero on the Central Coast of California. At a watershed level it was identified that reconnecting Butano Creek to its floodplain upstream of a problematic sediment depositional area (bridge crossing) could be highly beneficial to reduce sediment loading as well as enhance ecological function of the upstream floodplain. Raising the channel was used to reconnect the creek channel to the floodplain using engineered wood structures and riffle grade control structures. These forms of biotechnical approach have proven to be highly effective, and since the project was completed in Fall 2016, the floodplain has inundated frequently, forming large sand crevasse splays.