Urban Forestry and Water Quality Assessment Tools

Vincent VerweijAMEC Earth & Infrastructure

Contact Ian Hanou at:ian.hanou@amec.com or303‐742‐5320

Tree Canopy and Water Quality

• Catches rainfall• Reduces peak flow of runoff

• Stores harmfulpollutants

• Reduces soil erosion, reducing sedimentpollution

Overview of Models

• CITYGreen

• i‐Tree Hydro

• EPA Stormwater Management Model

• Western Washington Hydrology Model

CITYGreen

• GIS and Excel‐based tool• Calculates the ecological and economic benefits provided by trees and other green space

• Analyzes replacement cost of urban canopy loss• Uses locally‐based reference data for benefitestimates

• Current Vs. Future condition comparison• Currently not supported for ArcGIS 10

CITYGreen Input

• Location• Land Use• Cost for replacement of tree function

CITYGreen Input

• Air Quality Reference City: Cincinnati

• Hydrologic Soil Type “C”

• Hamilton County Digital Elevation Model, resampled to 5-meter resolution

• Land cover raster configuration in CITYgreen and associated curve numbers (CN)

between 0 and 100 where a higher CN indicates higher imperviousness and runoff): Impervious Surfaces: Unpaved: Dirt (CN 87), Impervious Surfaces: Paved: Drain to sewer (CN 98), Cropland:

Row Crops (CN 82), Meadow: Continuous grass, generally mowed, not grazed (CN 71), Trees: Impervious

understory (CN 91), Trees: Grass/turf understory: Ground cover > 75% (CN 72), Trees: Forest litter

understory: No grazing, forest litter and brush adequately cover soil (CN 70), and Water (CN 100).

• Replacement land cover: Urban: Commercial/Business (CN 94)

• Construction cost: $3.00/cubic foot

CITYGreen Output

Water Runoff and Pollution

Air Pollution and Carbon Storage

i‐Tree Hydro

• Part of larger i‐Tree suite• Uses GIS and USGS elevation data to calculatehydrologic aspects of the study area

• Canopy‐oriented: Uses variety of canopycharacteristics in its calculations.

• Generates reports on Impervious flow, Sediment, heavy metal, nutrient runoff and oxygen content

i‐Tree Hydro

• Targeted by Cincinnati Parks for adoption of several strategies to reduce peak flow rates out of the basin.

• Study examines the expected impacts of reforestation of other land cover, and improvement of understory, on flow rates

i‐Tree Hydro Input

• Elevation Data (USGS)• Landcover Percentages• Study Area size• Percentage Evergreen Cover• Hydrologic Parameters of Study Area (optional)

i‐Tree Hydro Input

i‐Tree Hydro Input

Raw Data Inputs Location

WS. Area (square meters)

Percent Tree Cov. LAI

Percent Evergreen Start Date End Date

Cincinnati, Hamilton County, OH 11,002,648 47.6% 5 1.0% 2/3/2010 11/25/2010

Surface Cover Types Percent

Cover Types Beneath

Tree Cover PercentTree 47.6% Shrub 0.0%Shrub 0.5% Herbaceous 0.0%Herbaceous 21.1% Soil 90.0%Water 0.0% Impervious 10.0%Impervious 29.9% --Soil 0.9% --Total 100.0% Total 100.0%

Initial Data Inputs

i‐Tree Hydro Output

Runoff Flow

Pollution Increase

EPA Storm Water Management Model (SWMM) 

• Full‐fledged hydrologic analysis tool• Analyzes benefits of a variety of Best Management Practices

• Returns values on stormwater runoff and pollution

• Single‐event to long‐term (continuous)• Requires significant knowledge of hydrologic modeling 

• Not focused on tree canopy alone

SWMM Input

• Area• Slope• Landcover (Impervious)• Elevation Data• Stream gauges• Weather data• Stream Network

– Width– Depth– Base Flows

SWMM Interface

Coarse Scale - Bull Run Watershed, Fairfax, VA

SWMM Interface

Fine Scale – Street Project

SWMM Simulation Output

Western Washington HydrologyModel (WWHM)

• Hydrologic model specialized to King County, home to metropolitan Seattle and Puget Sound

• Similar to SWMM in complexity• Puts more emphasis on vegetation

– Takes into regard local forest makeup

• Uses Long‐term rainfall data 

WWHM Coverage

Seattle

WWHM Inputs

• Land Use:– Pervious: forest, pasture, lawn– Impervious: roads, roof tops, driveways, sidewalks, and parking lots

• Soil Type• Watershed• Local hydrologic parameters

WWHM Output

Renton, WA, hydrologic analysis

Summary

• CITYGreen– Direct dollar values, fairly minimal work

• i‐Tree Hydro– Quick simulation with runoff values with some GIS work

• SWMM– Full hydrologic analysis, requiring in‐depth expertise

• WWHM– Localized hydrologic model with focus on vegetation

Summary/Questions

• CITYGreen– Provides report in dollar values, for easy communication, requiring relatively little expertise

• i‐Tree Hydro– Quick simulation with runoff values with some GIS workrequired. Still in Beta production

• SWMM– Full hydrologic analysis, not necessarily focused on forestry, but very powerful analysis

• WWHM– Localized hydrologic model with focus on vegetation and forestry

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