rooster river watershed based plan technical memorandum #2

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  • Project No. 20090730.A20

    Technical Memorandum #2:Low Impact Development &

    Green Infrastructure Assessment

    Rooster River Watershed Based PlanSeptember 2013

    Prepared For:

    City of Bridgeport

    In Cooperation With:

    Connecticut Department ofEnergy & Environmental Protection

    Southwest Conservation District

  • Table of Contents

    Technical Memorandum #2:Low Impact Development & Green Infrastructure Assessment

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    1 Introduction ................................................................................... 11.1 What is LID and Green Infrastructure? ................................................................ 11.2 Objectives .............................................................................................................. 2

    2 Site-Specific Project Concepts ................................................... 22.1 Assumption School Parking Lot Retrofit .............................................................. 42.2 Blackham School LID Retrofit .............................................................................. 62.3 Former Handy & Harman Site Flood Storage and Tidal Wetland Restoration .. 112.4 Invasive Species Removal ....................................................................................132.5 Green Infrastructure Retrofit at Madison Middle School ....................................142.6 Green Infrastructure Retrofit at Bridgeport Public Library .................................162.7 Green Infrastructure at Owen Fish Park ..............................................................192.8 Pocket Park at Madison Avenue and Vincellette Street .......................................212.9 Green Streets Design for Ridgeview Avenue....................................................... 232.10 Green Infrastructure Retrofit at Post Road Traffic Circle ................................... 262.11 Woodside Circle Open Space Stream Restoration .............................................. 27

    3 Other Potential Green Infrastructure Retrofits ......................... 29

    4 References .................................................................................. 35

    Tables Page1 Other Potential Green Infrastructure Retrofits 29

    Figures Page1 Retrofit Concept Plan for Assumption School 52 Typical Pervious Parking Stalls with Vegetated Filter Strip 63 Typical Bioretention Design 64 Blackham School LID Retrofit Concept 85 Modular Green Roof System Installation 96 Typical Green Roof Design 97 Before and After Concept Design for a Bioretention Area for the Parking Lot 108 Diagrams of Selected Permeable Pavement Systems 119 Flood Storage and Tidal Wetland Restoration at the Former Handy & Harman Site 1210 Photos of Japanese knotweed in the Rooster River Watershed 1311 School Greening Concept 15

  • Table of Contents

    Technical Memorandum #2:Low Impact Development & Green Infrastructure Assessment

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    Figures Page12 Typical Subsurface Gravel Wetland Design 1613 North Branch Public Library LID Concept 1714 Typical Tree Box Filter (Source: Hydro International, Inc.) 1815 Existing and Proposed Bioretention Basin at the Bridgeport Public Library 1916 Green Infrastructure and Buffer Restoration at Concept at Owen Fish Park 2017 Existing Stream and Proposed Stream Restoration Concept 2118 Pocket Park at Madison Avenue and Vincellette Street Concept 2219 Ridgeview Avenue Green Street Retrofit Concept Visualization 2420 Typical Green Street Parking Bay 2521 Typical Bioretention Bulb-out 2522 Turney Creek Restoration Concept at the Traffic Circle 2723 Woodside Circle Open Space Stream Restoration Concept 2824 Higher-Priority Target Retrofit Areas 3325 Lower-Priority Target Retrofit Areas 34

    Appendices End of ReportA Site-Specific Project Cost Estimates

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    1 Introduction

    1.1 What is LID and GreenInfrastructure?

    Low Impact Development (LID) and green infrastructure are the preferred approaches for stormwatermanagement by CTDEEP and EPA, but are also relatively new and sometimes not well-understood bydesigners, municipalities, and the public.

    LID is an approach to land development (or re-development) that works with nature to managestormwater as close to its source as possible. LIDprinciples include preserving and restoring naturallandscape features, minimizing effective imperviouscover (i.e., the impervious cover that is directlyconnected to the storm drainage system and/orreceiving waters), and creating functional andappealing site drainage that treats stormwater as aresource. The goal of LID is to mimic a sites pre-development hydrology by using design techniquesthat infiltrate, filter, store, evaporate, and detainrunoff close to its source. LID addresses stormwaterthrough small, cost-effective landscape features located throughout a site. LID is a versatile approachthat can be applied equally well to new development, urban retrofits, and redevelopment projects.

    Green infrastructure is similar to LID and refersto systems and practices that use or mimic naturalprocesses to infiltrate, evapotranspire, or reusestormwater. Green infrastructure and LID includestormwater management practices such as raingardens, permeable pavement, green and blueroofs, green streets, infiltration planters, trees andtree boxes, and rainwater harvesting, for example.These practices capture, manage, and/or reuserainfall close to where it falls, thereby reducingstormwater runoff and keeping it out of receivingwaters.

    In addition to reducing polluted runoff and improving water quality, green infrastructure has beenshown to provide other social and economic benefits relative to reduced energy consumption, improvedair quality, carbon reduction and sequestration, improved property values, recreational opportunities,overall economic vitality, and adaptation to climate change. For these reasons, many communities areexploring the use of and are adopting green infrastructure within their municipal infrastructureprograms.

    Coventry Town Hall Annex, Coventry CT; Source: CTDEEP

    Evergreen Walk Mall Parking Lot, South Windsor, CT Source: CTNEMO

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    1.2 Objectives

    As documented in Technical Memorandum #1, State of the Rooster River Watershed (March 2013),stormwater runoff is a significant cause of water quality impairments and contributes to urban floodingin the Rooster River and Ash Creek watershed. Much of the watershed was developed prior to theadoption of stormwater quality regulatory requirements. Therefore, most of the existing drainageinfrastructure consists of traditional storm drains/catch basin and drainage pipes that discharge directlyto surface waters without treatment, other than detention to maintain peak rates of discharge.Uncontrolled stormwater runoff from impervious surfaces is a significant source of impacts to surfacewaters and water quality within the watershed. An important objective of this watershed plan is toreduce runoff volumes and pollutant loads through the use of LID and green infrastructure.

    A watershed assessment was performed to identify opportunities and develop concepts for site-specificLID and green infrastructure retrofits that could also be applied to other similar land uses and locationsin the watershed. This technical memorandum documents the methods and findings of this assessment.

    2 Site-Specific Project ConceptsSite-specific restoration or retrofit concepts were developed for selected sites using a two-step approach.First, a desktop screening-level review was performed to initially identify potential areas of the watershedwith the greatest feasibility for stormwater retrofits. This screening-level review considered watershedcharacteristics such as soils, land use, land ownership, and proximity to surface waters and identifiedimpairments. Field inventories were then conducted in May 2013 within areas identified by thescreening-level review, and retrofit concepts were developed for the most feasible sites.

    The site-specific project concepts presented in this section are intended to serve as potential on-the-ground projects for future implementation. The locations of the potential projects described in thissection are shown in the figure on the next page. They provide examples of the types of projects thatcould be implemented at similar sites throughout the watershed. It is important to note that the conceptspresented in this section are examples of potential opportunities, yet do not reflect site-specific projectdesigns. Property owners and other affected parties are responsible for evaluating the ultimate feasibilityof these and similar site-specific concepts.

    Preliminary, planning-level costs were estimated for the site-specific restoration concepts presented inthis section. These estimates are based upon unit costs derived from published sources and the proposedconcept designs. Capital (construction, design, permitting, and contingency) and operation andmaintenance costs were included in the estimates, and total annualized costs are presented in 2013dollars based on the anticipated design life of each restoration concept. A range of likely costs ispresented for each concept, reflecting the inherent uncertainty in these planning-level cost estimates. Amore detailed breakdown of the cost estimates is included in Appendix A.

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    Site-Specific Project Locations

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