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Outline

Urban Stream Restoration Techniques Prepared by the Center for Watershed Protection

In This Presentation The effects of urbanization on stream channels Initial effects Long-term effects An assessment of urban stream restoration practices About the Center’s study Bank protection practices Grade control practices Flow deflection/concentration practices Bank stabilization practices Summary of results Keys to success Future research needs

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The Balance of Stream Dynamic Equilibrium (Lane, 1955)

The Initial Effects of Urbanization on Stream Channels Channel becomes straighter Channel becomes shallower Channel slope becomes steeper Higher stream velocities Increased sediment load Decreased ability to support aquatic life

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The Balance of Stream Dynamic Equilibrium (Lane, 1955)

The Long-Term Effects of Urbanization on Stream Channels Channel enlargement Stream incision Decreased ability to support aquatic life

"Channel Enlargement as a Function..." Channel Enlargement as a Function of Impervious Cover in Alluvial Streams

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Urban Stream Restoration Techniques:  An Initial Assessment

About the Study Focused on performance of individual stream restoration practices Examined more than 20 different types of stream restoration practices Assessed more than 450 individual practice installations

Practice Groups Bank protection practices Grade control practices Flow deflection/concentration practices Bank stabilization practices

Study Methodology Each practice was evaluated in the field according to four criteria: Structural integrity Function Habitat enhancement Vegetative stability

Study Limitations Age of the practice – most were installed in last 3-4 years Lack of standardization – practices were installed by a wide range of public and private entities with differing methods and design objectives Influence of adjacent practices – the influence of any nearby practices was not directly assessed Sample size – the sample size of some practices is small, with some used on only a single project Defining success – this study did not measure aquatic community response

Study Design 20 projects were selected out of an inventory of 40 3/4 in Baltimore/Washington DC metropolitan area 1/4 in the NE Illinois metropolitan area Minimum 15% impervious cover in watershed Projects at least 2 – 3 years old No limits on size or extent of project

Assessment Methodology Assessment Parameters: Percent intact movement or dislocation unintended erosion or deposition Design objective Unintended benefits or impacts Habitat enhancement Plant material survival Planting area erosion

Bank Protection Practices Rootwad Revetments Imbricated Rip-Rap Boulder Revetments Lunkers A-Jacks

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Grade Control Practices Rock Vortex Weirs Rock Cross Vanes Rock Weirs Step Pools Log Drops & V-Log Drops

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Flow Deflection/Concentration Practices Wing Deflectors – Single and Double Log Vanes Rock Vanes – Straight Vanes and J-Vanes Cut-off Sills Linear Deflectors

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Bank Stabilization Practices Coir Fiber Logs Live Fascines Brush Mattresses Bank Regrading and  Vegetative Stabilization

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Summary Most practices, when correctly designed and installed, work reasonably well Only two practices, rock weirs and log drops, have questionable value The majority of practice failures resulted from: improper overall project design inappropriate channel conditions for practice type poor construction techniques

Keys to Success Overall project design: A good understanding of stream adjustment processes and an accurate assessment of current and future channel conditions The recognition that urban streams behave differently than natural channels

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Keys to Success Inappropriate conditions for practice type: Most practices have a fairly narrow range of suitable channel conditions Selecting the right practice for the channel conditions is essential

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Keys to Success Poor construction techniques: Designers and contractors need to communicate effectively and work as a team Maintain flexibility during construction

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Future Needs More research into relationships between channel geometry and flow regime, sediment transport, and landscape processes in the urban environment is necessary.