Displaying all posts in the Green Infrastructure category.

How One Contractor is Helping to Ensure Durham, North Carolina Stays Leafy

Veteran willow oaks shade streets in Durham, North Carolina. (Source: News Observer)

Veteran willow oaks shade streets in Durham, North Carolina. (Source: News Observer)

Nearly 40 percent of Durham’s 108 square miles are covered by trees. However, without proper maintenance of the existing inventory and systematic replanting efforts, this percent is at risk of decreasing. The city must plant an estimated 1,680 new trees every year for the next 20 years in order to maintain the current canopy coverage.

For many Durham residents, the fragile state of thousands of willow and water oaks planted in the 1930s is all too familiar. Not only are the willow and oak populations near the end of their natural lifespans, construction, vehicle exhaust, improper pruning, and cankerworms have have also weakened the trees’ health. By some estimates, Durham will lose an average of 650 of these large trees and 100 smaller trees per year over the next 20 years due to storm damage, accident and natural attrition. Currently, the city removes 750 or more dead and dying trees annually, a number that can rise due to natural disaster, disease, and pests.

The City of Durham hired Raleigh-based Leaf & Limb to inventory the aging willow and water oak populations in the city rights-of-way in order to create a digital map of the trees. Katie Rose Levin, an arborist consultant with Leaf & Limb and manager of the project with the City of Durham, has extensive experience helping clients collect and leverage tree inventory data for prioritizing maintenance, long-term planning, and regulatory compliance.

While inventories can be expensive and time-consuming to complete, they are essential for allowing organizations to plan for losses and gains and performing a cost-benefit analysis on maintenance activities. “You cannot manage something if you don’t know what you’re managing,” said Levin. With consistent tracking of data, a tree inventory becomes a living document that you can use to develop a master plan, make data-driven management decisions and track maintenance work. “Every city should have an inventory of all its infrastructure. Just as other infrastructure records need to be updated by technicians following maintenance, trees must be mapped and tracked, too,” said Levin.

 

Map of Durham, NC.

A map from the Environmental Affairs Board ‘Recommendations On Sustaining a Healthy Urban Forest In Durham, N.C.” shows the percentage of tree-canopy coverage in different parts of Durham. (Source: News Observer)

Leaf & Limb worked closely with the City of Durham to define a list of data collection fields and develop a set of guidelines for assessing the trees. “It’s important to understand how the data collected is being used. The goals of the tree inventory will dictate what information is being collected,” said Levin. Levin trained staff to recognize insects and diseases specific to willow and water oaks before going out in the field to collect data. Collecting extraneous data increases inventory costs and total time required.

According to Levin, it often makes sense for a contractor to complete an inventory for a city. Inventories are time intensive and require a specialized set of knowledge and tech savvy, which can make it difficult for municipalities to complete while also staying on top of their routine activities. Leaf & Limb chose to collect the data using OpenTreeMap as it was customizable, mobile-friendly and could be easily added to Durham’s existing tree map. Alex Johnson, the City of Durham’s Urban Forestry Manager, also noted that he did not want the data collected in a proprietary platform that would make it difficult to use later. He wanted a platform that did not require technical expertise and could use used to engage the community in stewardship activities.

The city also plans on completing a canopy analysis to establish a baseline, and set a goal of what percentage canopy coverage they want to maintain across the city. It is important that the city continues to calculate canopy coverage on the neighborhood-level. Studies have highlighted the lack of tree planting in poorer neighborhood. In recent years unequal distribution of canopy in cities can be exacerbated by the fact that cities tend to plant trees where trees have been recently removed. Canopy coverage data can help the city more effectively close the gap.

You can find more information on how technology can support the long-term monitoring of urban trees; assist with tree planting and maintenance data processes, and enable data to be organized and shared in a report prepared by Azavea for the Pennsylvania Horticultural Society and the USDA Forest Service Philadelphia Field Station.

How to Calculate the Environmental and Economic Benefits of your Bioswales and Rain Gardens

Cities are increasingly turning to green stormwater infrastructure (GSI) to reduce runoff.

Cities are increasingly turning to green stormwater infrastructure (GSI) to reduce runoff, which helps maintain water quality and reduce flooding and erosion.

Stormwater runoff is a major cause of water pollution in cities. When rain falls on roofs, streets and parking lots, the water is not all absorbed into the ground. Instead, stormwater drains through gutters, storm sewers and other collection systems, and is then released into nearby bodies of water. This water often contains pollutants like trash, bacteria, chemicals and heavy metals. And, the quantity of water and speed of flow can cause erosion and flooding, and damage habitat, property and infrastructure.

Cities worldwide are looking to improve water quality and invest in strategies to mitigate stormwater runoff. Historically, cities have managed stormwater through the use of expansive and capital-intensive underground storm sewer systems known as gray infrastructure. However, use of green infrastructure, an approach to water management that protects, restores or mimics the natural water cycle, has become increasingly popular. Unlike gray stormwater infrastructure which is designed to move stormwater away from the built environment as quickly as possible, green infrastructure reduces and treats stormwater at its source. Strategies for incorporating green infrastructure at the site-level include the use of permeable pavements, bioswales, rain gardens, vegetated or “green” roofs, rain barrels, and cisterns.

Bioswale in a parking lot.

The control of stormwater runoff is a major issue in urbanized areas. Bioswales and other green stormwater infrastructure helps reduce runoff. (Source: Rhyne Landscape)

Green infrastructure provides communities with economic, environmental and community benefits yet not all benefits are easily quantified. Understanding the benefits of green infrastructure, and comparing them to their gray infrastructure counterparts requires a common unit of analysis. While it is fairly straightforward to place a monetary value on gray infrastructure, it can be more difficult to do so for green infrastructure. However, looking only at construction and maintenance costs – planning, installation, operation and replacement – ignores the environmental, economic and social benefits green infrastructure provides. In fact, research has found that when you take into account the water quality, air quality, energy and community benefits provided by green infrastructure green approaches are shown to outperform single-purpose gray approaches.

A report from the Center for Neighborhood Technology (CNT) outlines the benefits of five different types of green infrastructure features. The environmental and social benefits accrue at varying scales based on local factors like climate and population.

This diagram outlines the benefits of five different types of green infrastructure features. The environmental and social benefits accrue at varying scales based on local factors like climate and population. (Source: Center for Neighborhood Technology)

With OpenTreeMap you can calculate ecosystem services for two different types of green infrastructure features: rain gardens and bioswales. Once you denote the area of your rain garden or bioswale on OpenTreeMap, the cloud-based platform automatically calculates the total amount of stormwater diverted. The equation used to calculate stormwater diverted was developed by San Francisco, California-based non-profit organization, Friends of the Urban Forest (FUF). OpenTreeMap then converts the amount of stormwater diverted into dollars saved based on the conversion rates used in the U.S. Forest Services’ iTree application.

Annual stormwater diverted = Annual rainfall x (area of polygon + (square footage of area that drains to the rain garden x runoff coefficient))

The runoff coefficient refers to the percentage of rainfall that hits the drainage area that makes it to the rain garden or bioswale. Some portion of rainwater may runoff too quickly to be absorbed by green infrastructure or may be diverted in some other way. In OpenTreeMap, the default coefficient is 0.85, meaning 85% of the rain that hits the area that drains to the rain garden or bioswale will actually make it to the rain garden or bioswale. This coefficient is an average estimate based on data from Ken Edwards, Ph.D., P.E., owner of LMNO Engineering, however, the exact percentage of runoff varies based largely on the type of material in the drainage area (asphalt, brick, cement etc).

To improve the accuracy of the calculation, map owners can customize the units and number of decimal places for annual rainfall, the area of the green infrastructure feature and the area of the adjacent drainage area.

OpenTreeMap software.

With OpenTreeMap, you can map and manage your green stormwater infrastructure along your trees.

Calculating the ecosystem benefits associated with green infrastructure helps planners calculate the savings green infrastructure provides in terms of stormwater filtration, floodwater storage, clean drinking water and carbon sequestration among other benefits. Shared metrics for quantifying ecosystem benefits are important for tracking the effectiveness of investment in green infrastructure and helps reposition the role of urban green space from an optional amenity to key ingredient for building more sustainable communities.

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