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EPA Region 6 Stormwater Conference: P. Erwin (Arkansas Forestry Commission)/E. Kuehler Presentation Addressing the Role of the Urban Forest in Stormwater Treatment

November 09, 2015

By: Walter G. Wright

Category: Arkansas Environmental, Energy, and Water Law

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Patti Erwin, Urban and Community Forestry Coordinator, Arkansas Forestry Commission and Eric Kuehler, Technology Transfer Specialist, United States Department of Agriculture and Forest Service undertook a presentation at the United States Environmental Protection Agency (“EPA”) Region 6 Stormwater Conference titled Managed or Not, Your Urban Forest is the Initial BMP in a Green Stormwater Infrastructure Treatment Train (“Presentation”).

The Region 6 Office of EPA in partnership with Hot Springs, Arkansas, along with the Municipal Separate Storm Sewer Systems and States in Region 6 hosted the Conference, which discussed the management of municipal stormwater (including new/upcoming regulations).

The Presentation addressed the important role that forests play in the water cycle including the management of stormwater.    Such management can include mitigation of stormwater by urban forests mitigate stormwater runoff in cities, towns or developed areas.

The presenters note that the term forest is not limited to rural or undeveloped areas. 

The components of the Presentation included:

  • Municipal stormwater runoff issues
  • Trees in the water cycle
  • Scientific evidence for trees and stormwater mitigation
  • Urban forest management strategies to maximize stormwater runoff mitigation
  • Municipal forest management assistance from state forestry agencies
  • Modeling case studies

In addressing these topics, Ms. Erwin and Mr. Kuehler noted some of the problems associated with stormwater runoff such as:

  • Increased quantity (flooding)
  • Increased velocity (erosion)
  • Increased water quality (pollution)
  • Decreased quality of life (drinking water/recreation)

Some of the factors contributing to stormwater runoff were identified:

  • Removing tree canopy cover
  • Removing understory and ground cover (vegetative/detritus)
  • Removing permeable top soil (leaving dense subsoil)
  • Compacting and paving over soil
  • Grass sod over subsoil

After addressing some of the measures used to address stormwater runoff, the presenters asked the question:

  • Can our urban forest be a Best Management Practices to help mitigate stormwater runoff?

To address this issue, they discussed the forest and the water cycle and note some of the research into trees and stormwater mitigation.  One 2006 study involved an Arkansas area of forest watersheds involving Jack Creek and Jones Creek and urban watersheds in Fayetteville and Little Rock.  The results of the Arkansas stormwater study included:

In 2006, for every one percent tree canopy increase, one could expect a decrease in annual discharge of 1.2 million gallons of water.

The presenters conclude from such research that:

  • Impervious surface cover drives stormwater runoff in urban areas
  • Reducing soil permeability increases runoff
  • Urban tree canopy cover will not solve all our problems
  • Forest systems can still play a role in mitigation
  • Perhaps it is time to start thinking about systems as we develop our cities

Ms. Erwin and Mr. Kuehler undertook a description of an urban forest system.  They also addressed urban forest management strategies including urban tree canopy assessments in Fayetteville, North Little Rock, Little Rock, West Memphis, and Bentonville, Arkansas.  The “major findings for Fayetteville” are stated to include:

  • Fayetteville has 36% urban tree canopy cover based on 2010 imagery
  • Stormwater savings (at 36% UTC, Fayetteville’s tree canopy is valued at an estimated $64 million based on avoided stormwater facility construction costs)
  • There are 50,000 potential tree planting locations near residential buildings

An example of a tree planting over imperious surfaces is found at the Beaver Water District Administration Center.  Other facilities in Northwest Arkansas were described.

Various ordinances and other municipal requirements found in some cities in Arkansas addressing this issue such as Fayetteville and Hot Springs were reviewed.  For example, ordinance amendments described as landscaping, screening and buffering considered by the Bentonville City Council in 2013 are discussed.  Also described is a landscape ordinance in Rogers and the development of the Rock Creek neighborhood in western Little Rock, along with the Little Rock Central High School neighborhood program. 

A particular focus was the information derived from the Rock Creek watershed urban forest management modeling project such as:

  • Stream flow for the entire watershed incorporating a variety of relevant inputs/data

The project addressed model runoff from various tree cover scenarios.  The Presentation reviewed the pollutant loading results under various scenarios.  With the modeling project summary concluding:

  • Increasing tree canopy cover and encouraging growth over impervious surfaces
    • Reduce annual flow and pollutant loading by up to 2.5%
    • Through rainfall retention by leaves
  • Increasing canopy cover in conjunction with reduced DCIA
    • Reduced pollutant loading by up to an additional 6.3% over DCIA reduction loan

The presenters conclude by noting the various stormwater runoff benefits trees provide and state that “the urban forest can regulate stormwater flow so that BMPs can work effectively.”  They also note that the urban forest can provide other co-benefits such as:

  • Increased energy conservation/reduced urban heat island effect
  • Decrease air pollutants
  • Increase property values
  • Increase business traffic
  • Increase personal health

They conclude with the following questions:

  • Are trees considered in your stormwater planning?
  • What barriers prevent the use of trees as green infrastructure?
  • What information is needed to help you consider trees/urban forest in your stormwater management plans?

Click here to download a copy of the Presentation.

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