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Credit River, MN Final Report - Fluvial Geomorphic Assessment

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Credit River, MN Final Report - Fluvial Geomorphic Assessment Credit River, MN Final Report - Fluvial Geomorphic Assessment March 5, 2008 Prepared for: Scott County Community Development Natural Resources Department Government Center 14 200 Fourth Avenue West Shakopee, MN 55379-1220 3602 Atwood Avenue Suite 3 Madison, WI 53714 2007 Inter-Fluve Inc. Credit River Geomorphic Assessment 2 TABLE OF CONTENTS 1. Introduction.....................................................................................................................3 1.1. Review of Fluvial Geomorphology Principles.......................................................5 2. Data Collection / Methods ............................................................................................10 2.1. Existing data.........................................................................................................10 2.2. Fluvial Geomorphology .......................................................................................10 2.3. Hydrology.............................................................................................................10 3. Results...........................................................................................................................12 3.1. Geology, topography and soils.............................................................................12 3.2. Historic Conditions..............................................................................................13 3.3. Existing Geomorphology .....................................................................................18 3.4. Surface Water Hydrology.....................................................................................31 4. Management Recommendations...................................................................................34 4.1. Project Type - Natural Channel Restoration/Relocation ......................................34 4.2. Project Type - Grade Control ...............................................................................38 4.3. Project Type – Floodplain Management ..............................................................38 4.4. Project Type – Riparian Management..................................................................38 4.5. Project Type – Crossing. ......................................................................................39 4.6. Project Type - Bank Stabilization ........................................................................40 4.7. General Recommendations...................................................................................42 4.8. Specific Potential Projects....................................................................................42 5. References........................................................................................................................43 6. Appendices.......................................................................................................................44 2007 Inter-Fluve Inc. Credit River Geomorphic Assessment 3 1. Introduction conditions by reach for the main stem and In the spring of 2007, the Scott County tributaries. This report is supplemented by Natural Resources Department contracted with completed project forms which the County will Inter-Fluve to conduct a fluvial geomorphic integrate into the Scott County GIS platform. assessment of the Credit River Watershed. The This fluvial geomorphic assessment was project is an attempt to locate channel stability geared toward project identification so that Scott problems, assess overall stream condition and County can eventually develop a long term address the concerns of landowners regarding restoration and watershed management strategy. erosion, flooding and threats to infrastructure. This type of assessment typically results in a large Through several meetings, Inter-Fluve and number of total projects; in this case 48 County officials identified the following significant projects were identified on the Credit objectives: River mainstem. In order to prioritize these projects for funding allocation, a ranking system 1) Conduct a reconnaissance level geomorphic assessment that collects for potential restoration projects was developed information regarding channel stability, for the watershed. This ranking system scores infrastructure, fish habitat, and general stream health potential project sites based on 11 metrics (Table 2) Identify potential restoration or 1). Each metric contributes a value of 1 through 7 reclamation projects in the watershed for the site, and the total of all of the metrics is 3) Create a system of prioritization for the potential project score. Each project can be identified projects ranked by a single metric or multiple metrics, so 4) Integrate the results of the study with the that priority can be a result of any combination of existing Scott County Geographic metrics chosen by Scott County staff. Information System (GIS) platform In this system, metrics refer mainly to the degree that a completed project will affect each Scott County staff assisted with collection of metric. For example, an infrastructure risk score existing data (aerial photographs, maps etc.) and of 1 reflects that if nothing is done, there will still created field maps. Inter-Fluve scientists be no risk to infrastructure from channel identified distinct study reaches within the Credit instability, either because no infrastructure exists River watershed. Fieldwork commenced in June at the site, or risk is extremely low. Conversely, a and July 2007, and Inter-Fluve met with score of 7 indicates that if nothing is done, public interested landowners on site and with officials safety and property are under immanent risk. This from the City of Savage. project did not include any formal structural The report that follows is a brief summary of engineering survey or risk assessment. If the data collected, and outlines general stream infrastructure is determined in this survey to be at 2007 Inter-Fluve Inc. Credit River Geomorphic Assessment 2007 Inter-Fluve Inc. 2007 Inter-Fluve Inc. Cred Table 1: Metrics for scoring potential projects. Metric Score: 1 3 5 7 Low to moderate infrastructure risk Infrastructure at moderate but not immedi- Infrastructure at high or immanent risk No risk to infrastructure with no action, Infrastructure risk and minimal risk to public safety with ate risk, moderate public safety risk, or of failure with no action. Public safety or no infrastructure present no action, or inf. value <$100,000 infrastructure value <$200,000 at risk or infrastructure value >$200,000 Minimal improvement to overall stream Low to moderate improvement of 250- Moderate improvement 1000-2500 ft of Significant improvement to overall Erosion/channel stability stability and function, <250 ft of channel 1000 ft of channel bank channel bank stream stability and function or >2500 ft bank Groundwater and surface water issues, Surface water restoration, engineering Moderately complex, no specialty engi- Elementary solution, shelf design, vol- professional specialty design services Project complexity plans required, earthwork involved, neering required, minor earthwork, some unteer and hand labor implementation, required, heavy oversight, major earth- significant permitting basic permitting no permits work, EAW/EIS permitting Location Mouth to lower ¼ of watershed Lower 1/4 to 1/2 of watershed 1/2 to upper 3/4 of watershed Upper 3/4 to headwaters Some minor reduction in sediment Moderate reduction in bank erosion and Major erosion control through signifi- Sediment/nutrient load- No load reduction resulting pollution, increased filtration of nutri- surface runoff entering stream through cant BMP installation, stormwater ing ents buffer or other BMPs > 30 ft detention, infiltration or buffer filter. Project cost > $300K $201 - $300K $51 - 200K $0 - $50K Aesthetic impact No impact Low impact Moderate positive impact High positive impact Low impact (eg. improve depth Moderate impact (removes perch or other Fish passage No impact on fish passage through culvert, minimal velocity small barrier, natural bottom culvert re- High impact (dam removal) it River GeomorphicAssessment it reduction) placement) High value - Easy access, cooperating Low value - Poor site access, difficult Moderate value - Good access, moderate Public Education No public education value landowner, good demonstration and to see, small project demonstration value high visual impact In-stream Ecological Moderate benefit - subreach based, moder- High benefit - Reach based, >1000 ft of No in-stream ecological benefit Low benefit - Spot location, small size Benefit ate sized project stream Riparian Ecological Moderate benefit - subreach based, moder- High benefit - Reach based, large ripar- No riparian ecological benefit Low benefit - Spot location, small size Benefit ate sized project ian areas, floodplain scale 4 5 some risk, we advise local officials to conduct 1.1. Review of fluvial geomorphology principles their own formal structural engineering In order to fully visualize the relationships assessment. This scoring does not reflect any risk between habitat formation and stream ecology, it from flooding. Other metrics gauge the potential is important to have a basic understanding of project’s effect on channel stability, ecological fluvial geomorphology. This section discusses the benefit, nutrient loading and fish passage. principles behind fluvial processes and how they Because of the interconnectivity of river systems, relate to stream habitat. Stable stream systems are
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