Restoring Neighborhood Streams

Planning, Design, and Construction

Ann L. Riley

• Publisher: Island Press
• Year: 2016
• Print ISBN: 9781610917407, 9781610917391
• eBook ISBN: 9781610917414
• Subtopic: Environmental Science

Thirty years ago, the best thinking on urban stream management prescribed cement as the solution to flooding and other problems of people and flowing water forced into close proximity. Urban streams were perceived as little more than flood control devices designed to hurry water through cities and neighborhoods with scant thought for aesthetics or ecological considerations. Stream restoration pioneers like hydrologist Ann Riley thought differently. She and other like-minded field scientists imagined that by restoring ecological function, and with careful management, streams and rivers could be a net benefit to cities, instead of a net liability. In the intervening decades, she has spearheaded numerous urban stream restoration projects and put to rest the long-held misconception that degraded urban streams are beyond help.

What has been missing, however, is detailed guidance for restoration practitioners wanting to undertake similar urban stream restoration projects that worked with, rather than against, nature. This book presents the author's thirty years of practical experience managing long-term stream and river restoration projects in heavily degraded urban environments. Riley provides a level of detail only a hands-on design practitioner would know, including insights on project design, institutional and social context of successful projects, and how to avoid costly and time-consuming mistakes. Early chapters clarify terminology and review strategies and techniques from historical schools of restoration thinking. But the heart of the book comprises the chapters containing nine case studies of long-term stream restoration projects in northern California. Although the stories are local, the principles, methods, and tools are universal, and can be applied in almost any city in the world.

Chapter 1

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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 riprapped (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 effort to hasten or redirect the recovery process. In some cases, restoration occurs because of the intervention of animals such as beavers. Environmental management professionals need to keep in mind that the channel evolution and recovery processes we observe in more rural environments are also present in urban environments. The variables making up stream dynamics—including topography, rainfall, discharges, sediment loads and sizes, vegetation, and valley and channel slopes—are present, even for the streams encased in concrete. That means that the restoration practitioner in an urban environment may be able to reasonably describe how a stream may respond to changes in discharges, sediment supplies, channel slopes, and vegetation removal. Diagnostic assessments can be carried out to identify watershed and stream system problems such as risk of flood damages or excessive erosion, and they help remedy the causes of the imbalances, not just put a Band-Aid on them.

Many professionals promote stereotypes or unquestioned assumptions about urban streams or rivers. One of the most notorious symbols of the highly degraded urban river in the United States is the Los Angeles River, encased in concrete since the 1930s. A number of Los Angeles flood control engineers state that this river cannot feasibly recover any natural functions because the upstream debris basins and concrete channels prevent river sediment transport. Without a sediment supply, the river cannot conceivably begin to express natural channel forms or river dynamics. A field trip to the Los Angeles River not only reveals a channel filled with a wide range of sediment sizes ranging from sands to cobbles and boulders, but also a sediment supply sufficient for creating channel complexity and allowing willow thickets to re-establish (fig. 1.1). I was also led by local officials to the rectangular concrete channel Coyote Creek (fig. 1.2) and the trapezoidal channel San Jose Creek (fig. 1.3), both tributaries to the San Gabriel River, the other degraded urban river draining the Los Angeles area. We observed channels with substantial sediment supplies that have been transported and deposited to form a single-thread meandering channel with a floodplain that supports riparian vegetation. This situation is occurring to the consternation of flood control officials who view this re-creation of natural depositional forms within the flood control channel as an unfortunate maintenance problem. Many other flood control engineers administering to other similar flood control channels sympathize with this commonly occurring “problem.”

FIGURE 1.1 The North Fork Los Angeles River is re-forming in a dirt-bottom flood control channel at Glendale Narrows, Los Angeles.

FIGURE 1.2 Coyote Creek in the San Gabriel watershed, Los Angeles County, is recovering ecological functions within a rectangular, concrete flood control channel through sediment transport, deposition, and recovery of riparian vegetation.

Water quality conditions can also take an ironic twist in urban areas. The Los Angeles San Gabriel Watershed Council monitoring program shows high levels of coliform bacteria in the more natural upper watershed areas used for recreation than in downstream reaches in urbanized Los Angeles (Belden 2008). Similar findings from a water quality agency study on Wildcat Creek in Richmond, California, indicate pockets of pollution located in the protected open-space regional and local parklands. That pollution can be attributed to the large number of dog walkers who do not clean up the excrement of their pets (Surface Water Ambient Monitoring Program 2008).

Many highly urbanized streams still have access to sediment supplies from less developed or underdeveloped steep headwater areas and the bed and banks of the channels. Some receive regular supplies from naturally unstable hillsides, landslides, and fault zones or alluvial fans. Although urban streams in highly developed environments can be expected to have lower sediment supplies than they did as natural systems, it is not good practice to universally assume that urban streams are cut off from all supplies or that sediment supply is automatically a limiting factor precluding the return of some of the natural functions of both erosion and deposition and sediment transport.

FIGURE 1.3 San Jose Creek in the San Gabriel watershed, Los Angeles County, is recovering a channel, floodplain, and riparian corridor in a trapezoidal flood control channel.

In a case like the Los Angeles River, increasing the sediment transport and deposition functions may well be one of the important strategies for increasing the functioning of a highly urbanized river corridor. The Los Angeles River contains 8 miles of a dirt-bottom river through the Glendale Narrows section of the river. This reach flows downstream between the city of Burbank, upstream of Griffith Park, and Taylor Yard, a defunct railroad maintenance yard located just above downtown Los Angeles. The Taylor Yard reach near Glendale and the 101 Freeway in figure 1.4 is also referred to as Frog Town by locals because this dirt-bottom channel supports vegetation and a braided channel type with the physical complexity sufficient to support an amazing number of insects, amphibians, and bird species. No flood problems have occurred along these dirt-bottom reaches, and they provide a model for removing the concrete channel inverts along the other reaches of the river.

Although many planning efforts focused on identifying restoration options for the Los Angeles River have struggled with design strategies for bringing life back to the river, one obvious model for restoration already exists in the Glendale Narrows section. Short floodwalls can be added to the higher terrace to contain the expected higher water-surface elevations for the largest flood flows, which are caused by the changes in the river cross sections as it fills with sediment and vegetative growth. Concrete reaches can emulate the dirt-bottom sections with removal of the concrete invert and use of grade controls to support the concrete sides while allowing the river to have a functioning ecosystem in the bottom portion of the channelized system (Friends of the Los Angeles River 1995). My favorite location along the Los Angeles River is shown in figure 1.5 near Frog Town, where the dirt-bottom channel transitions again to a concrete bottom and the river is carving out a single-thread “active channel” transporting water and sediment through the concrete.

FIGURE 1.4 The Los Angeles River at “Frog Town,” Los Angeles, supports birds and aquatic habitat for amphibians in a dirt-bottom flood control channel at the 101 Freeway. Credit: Los Angeles Department of Water and Power.

The Los Angeles River was historically represented by a number of channel and wetland types, including a single-thread and braided channel with freshwater floodplain marshes and tidal marshes. In some areas, the river would meander up to 7 miles. The river will most likely never return to its original historic form, although the information on the historic landscape is being used to set new restoration objectives in opportunity areas (Stein et al. 2007). The current constraints on the Los Angeles River do not mean, however, that it cannot function as a different type of river within its confined state and provide ecological “services” as well as improved aesthetics, as illustrated in figure 1.6 (Garrett 1993).

By the 1980s, tertiary treated recla...

Table of contents

• Cover
• About Island Press
• Title Page
• Copyright
• Dedication
• Contents
• Foreword
• Acknowledgments
• Chapter 1. Is The Restoration of Urban Streams Possible?
• Chapter 2. Defining Restoration
• Chapter 3. Neighborhood-Scale Restoration Projects
• Chapter 4. What Neighborhood Projects Teach
• Appendix. Regional San Francisco Bay Restoration Plant Survivors and Plants Associated with More Risk to Survival (Common and Latin Names)
• About the Author
• Island Press | Board of Directors