Is The Restoration of Urban Streams Possible?

"It's just an urban stream," said the engineering consultant, responding to my request to vegetate the channel rather than line it with plastic geogrid. We are taught that restoring ecologically functioning urban streams and rivers is not possible, based on the belief that urban watersheds are too degraded and their landscapes too altered to support naturally functioning systems. Restoring urban streams and rivers is also not possible, we are told, because it is prohibitively expensive to practice ecological restoration in a setting where land is expensive and other land uses are valued more highly than streams. Restoration is not possible, the argument continues, because the public will not accept the flood and erosion hazards associated with uncontrolled dynamic natural streams in the interiors of cities.

Engineers, landscape architects, and planners are taught this framework in college and graduate school. The instruction includes urban stormwater literature from which students get the impression that after about a 10 to 15 percent increase in imperviousness from urbanization, it is likely that we reach a point of no return for salvaging a stable, ecologically functioning stream. Some researchers make definitive conclusions; one is that in watersheds where impervious cover exceeds 60 to 70 percent, it is not going to be impossible to restore streams (Clayton 2000).

A preponderance of urban stormwater literature shows how land use changes affect urban flood hydrographs: streams flow faster after rain, channels enlarge and erode, and large floods happen more frequently. We witness how urbanization fills in headwater streams, encases channels in concrete, puts channels and drainages in culverts, and permanently alters the drainage network of the natural stream system. Channels can incise and widen sometimes as much as eight times their original size (Hammer 1972). Eroding channels have simplified environments so that biological diversity is reduced: aquatic insects, fish, reptiles, and amphibians may barely survive and probably not thrive. Riparian plant communities are destroyed and degraded and are invaded by exotic species that can crowd out natives. The wildlife dependent on these plant communities disappears. These observations are indisputable (Bernhardt and Palmer 2007).

The rational individual therefore sees little potential in restoring urban streams, other than fostering public education and improving the urban quality of life. Even some of the most open-minded, supportive professionals who appreciate the urban environmental movement arising out of the 1980s and 1990s do not have expectations beyond increasing the aesthetic values of urban streams.

In 1982, I decided to address the issue of whether the restoration of urban streams and rivers, including the most degraded, is possible. It became clear to me that the only way to test this hypothesis was to believe that it was possible and set out to try. This book is written to record the results of this thirty-year experiment. Obviously, this effort necessarily required anyone entering this ambitious and time-consuming experiment to have a bias that it is possible to restore urban streams. I have attempted to honestly, and in some cases brutally, report project failures, ridiculous naiveté, and how better restoration practices evolved out of making mistakes. I cover the history of how the earliest smaller-neighborhood-scale projects came about and how they became the experimental settings for developing restoration design protocols. The projects described here are in urban watersheds ranging from 0.2 square mile to 16.7 square miles with limited project lengths of 200 to 750 feet. These smaller-scale projects subsequently set the stage for later large-scale projects measured in miles.

The question of whether restoring urban streams and rivers is possible must address three basic challenges. First, given the degraded urban watershed conditions and land use constraints inherent in the city, is it physically feasible to return a degraded stream to an ecologically functioning and dynamic state? Natural streams are inherently dynamic environments and require erosion, deposition, moving and adjusting plan forms, and flooding to be truly living streams. Are living streams and these urban conditions mutually exclusive concepts? The second challenge is whether it is financially feasible or reasonable to attempt to re-establish this type of dynamic ecosystem in a city. The third challenge is to ask whether enough public support can be developed to enable the sometimes inconvenient land use changes that may be necessary to allow for a functioning, live stream.

The urban stream and river case studies described in this book are organized around these questions: Did the project result in a geomorphically and biologically functioning stream? Could the project substitute for an engineered channel to provide a solution to flooding and excessive erosion? Were the identified benefits of the project achieved at a reasonable cost? How were land uses in conflict with achieving a functioning ecosystem system resolved? The case studies address these ecological, economic, and social issues and fairly answer the question of whether urban stream restoration is possible.

For the case studies to be credible, they need to be located in highly modified watersheds, represent lower- or middle-income communities with limited economic resources, and occur where the classic conflicts between city life, land use, and erosion and flood hazards exist. Without these factors, the information gained from these case studies cannot be transferable to other heavily urbanized environments. Most of the case studies in this book are therefore located in working-class, low-income, or poverty neighborhoods. They are in areas where restoration concepts conflict with housing, streets and parking, and recreational needs and in areas where the safety of children must be a concern, such as school grounds and parks. All are located where there have been flooding hazards.

How Urban Streams Differ from Streams in Other Settings

Memorable field trips taken to the rural California Sacramento and Tuolumne Rivers and their tributaries overwhelmed me with the cumulative challenges of rivers rip rapped (rocked), straightened, logged, dredged, dammed, diverted to agricultural fields, and constrained with berms and levees composed of toxic mining tailings. This widened perspective made restoring an urban stream in a city look welcomingly feasible. Streams constantly adjust and attempt to recover from human modifications, no matter what the setting is. The streams work to rebalance the sediment loads, discharges, shapes, and slopes, and sometimes the plant community recovers over time on its own. At times, stream "restoration" is a matter of a stream directing its own recovery. In other circumstances, humans intervene in an...