TREES to OFFSET STORMWATER Charlestoncase Study 04: Charleston, South Carolina
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TREES TO OFFSET STORMWATER CharlestonCase Study 04: Charleston, South Carolina August 2018 Case Study 04: Charleston, South Carolina Charleston All other images in the report are credited to the Green Infrastructure Center Inc. (GIC) unless otherwise indicated. The work upon which this publication is based was funded, in whole, through a sub-recipient grant awarded by the USDA Forest Service through the South Carolina Forestry Commission to the Green Infrastructure Center and Charleston. The GIC is the project partner and technical services consultant. The contents do not necessarily reflect the views or policies of the USDA Forest Service or Charleston government, nor does mention of trade names, commercial productions, services or organizations imply endorsement by the U.S. Government. Publication Date: August 2018 August 2018 Project Overview CONTENTS This project, called Trees to Offset Stormwater, is a study of the City of Charleston’s forest canopy and the role that trees play in up taking, storing and releasing water. This study was undertaken to assist the City of Charleston in evaluating how to better integrate trees into their Project Overview ................................................................................... 1 stormwater management programs. More specifically, the study covers the role that trees play in stormwater management and shows ways in which the city can benefit from tree conservation Project Funders and Partners ..................................................................................... 1 and replanting. It also evaluated ways for the city to improve forest management as the city Outcomes ......................................................................................................... 1 develops. Community Engagement ......................................................................................... 2 PROJECT FUNDERS AND PARTNERS OUTCOMES Summary of Findings .............................................................................. 3 This is a pilot project for a new approach to estimate the role of This report includes those findings and recommendations trees in stormwater uptake. South Carolina is one of six southern that are based on tree canopy cover mapping and analysis, the states that received funding from the USDA Forest Service to modeling of stormwater uptake by trees, a review of relevant city Why Protect Our Urban Forests? ................................................................... 6 study how trees can be utilized to meet municipal goals for codes and ordinances, and citizen input and recommendations Additional Urban Forest Benefits ................................................................................. 9 stormwater management. The project was developed by the for the future of the City of Charleston’s urban forest. More specifically, the following deliverables were included in the pilot Quality of Life Benefits. 9 nonprofit Green Infrastructure Center Inc. (GIC) in partnership with the states of South Carolina, North Carolina, Alabama, study: Economic Benefits ............................................................................................. 11 Georgia, Florida and Virginia. The South Carolina Forestry Meeting Regulatory Requirements ............................................................................ 11 Commission is administering the pilot study in South Carolina. • Analysis of the current extent of the urban forest through Charleston was selected as the test case for South Carolina. high resolution tree canopy mapping, • Possible Planting Area analysis to determine where additional Natural Ecology in Urban Conditions – Changing Landscapes ................................... 12 The GIC created the data and analysis for the project. The trees could be planted, • A method to calculate stormwater uptake by the city’s tree Historic Land Cover ............................................................................................... 12 project was spurred by the on-going decline in forest cover throughout the southern United States. Causes for this decline canopy, Charleston Growth and Development Challenges. 13 arise from multiple sources including land conversion for • A review of existing codes, ordinances, guidance Sea Level Rise ..................................................................................................... 14 development, storm damages and lack of tree replacement as documents, programs and staff capabilities related to trees older trees die. Many localities have not evaluated their current and stormwater management, and recommendations for Charleston’s Green Future ........................................................................................ 16 tree canopy, which makes it difficult to track trends, assess losses improvement, or set goals to retain or restore canopy. As a result of this project, • Two community forums to provide outreach and education, Analysis Performed ................................................................................ 16 the City of Charleston now has baseline data against which to • Presentation of the results of the pilot studies as a case study monitor canopy protection progress, measures of the stormwater at the National Partners in Community Forestry Conference, Method to Determine Water Interception, Uptake and Infiltration .............................................. 17 uptake by its trees and water quality benefits provided by the and Land Cover, Possible Planting Area, Possible Canopy Area Analysis ............................................. 19 urban forest, as well as a way to prioritize restoration of canopy • A case booklet and PowerPoint presentation detailing the where it is needed. pilot study methodology, as well as lessons learned and best practices. Codes, Ordinances and Practice Review ........................................................... 29 The project began in October 2016 and the City of Charleston Evaluation and Recommendations ............................................................................... 29 staff members have participated in project review, analysis Best Practices for Conserving Trees During Development ...................................................... 32 and evaluation. The following city departments and divisions Tree Planting ...................................................................................................... 33 were involved in the project review committee: Information Technology and Geographic Information Services; Parks and Conclusion ........................................................................................................ 34 Urban Forestry; Planning, Preservation and Sustainability, and Zoning; and Public Service and Stormwater. Staff advised the Appendixes ......................................................................................... 36 GIC and coordinated Charleston community engagement events. Appendix A: Methods Appendix – Technical Documentation .................................................... 36 Appendix B: Community Comments ............................................................................. 38 Appendix C: Bibliography ......................................................................................... 40 The Angel Oak is one of the city’s oldest trees. 1 COMMUNITY ENGAGEMENT The City of Charleston can use this report and its associated products to: Two community meetings were held. The first meeting held in June 2017 provided an overview of n Set goals and develop a management plan for retaining or expanding its tree canopy by watershed. the project and an opportunity to gather community n Improve management practices so trees will be well-planted and well-managed. input and concerns regarding tree conservation and to review the canopy cover maps. The second meeting, n Educate developers about the importance of tree retention and replacement. held in November 2017, provided recommendations n Motivate private landowners (residential, commercial, and institutional) to protect their trees. for the city (see the list following) and elicited n Support grant applications for tree conservation projects. feedback on priorities for selected actions. All individual comments from both meetings were provided to the city and are listed in Appendix B. Residents asked that pine trees (Pinus sp.) and Summary of Findings The goal of this study was to identify ways in which water sweetgum trees (Liquidambar styraciflua) be included entering the city’s municipal separate storm sewer system (MS4) Satellite imagery was used to classify the types of land cover in tree preservation requirements. They suggested could be reduced by using trees. Tree canopy serves as ‘green in the City of Charleston (for more on methods see Appendix the city incentivize preservation of groups of trees infrastructure’ that can provide more capacity for the city to A). This shows the locations for areas with vegetative cover that over individual specimens and felt that 10-foot tree support ‘grey infrastructure’ (i.e. stormwater drainage systems) allow for the uptake of water and areas that are impervious buffers were inadequate in size for achieving tree in the future. It also can be used to show how the city can reduce and more likely to have stormwater runoff. High-resolution tree preservation. They also wanted more proactive city potential pollution of its surface waters, which can have an canopy mapping provides a baseline of tree canopy