May 4, 2005

Stormwater Asset Management Using GIS

Vithal V. Deshpande,

Environmental Coordinator,

City of Somerville, Massachusetts,

and

Britta Roden,

M.S. Economics Candidate

Tufts UniversityMay 4, 2005

Environmental Expo & ConferenceSeaport World Trade Center

Boston, MA

May 4, 2005

Acknowledgement

• USEPA Region 1 for Funded this project under Water Quality Agreement Grant.

• Tufts University provided GIS computing resources.

• Denise Castronovo (Tufts Academic Technology Department) and Prof. Jeff Zabel (Economics Department) provided helpful comments.

May 4, 2005

About Somerville

• Located within the lower Mystic River basin and is surrounded by the Mystic River and Alewife Brook along its western and northern parts.

• Somerville is the most densely populated urban area in Massachusetts, with a population density of 18,868.1 people per square mile, [4.1 square miles] (Census2000).

• Given the relatively small space that is shared by the 77,478 Somerville residents, it is crucial to make pollution prevention a priority. Credit for

photographs on this slide: Jonas A. Kahn, © 2004

May 4, 2005

Where is Somerville?

BOSTON

MEDFORD

SAUGUS

MALDEN

CAMBRIDGE

BROOKLINE

WOBURN

REVERE

MELROSEWINCHESTER

ARLINGTON

STONEHAM

EVERETT

NEWTON

SOMERVILLEBELMONT

CHELSEA

WATERTOWN

WAKEFIELD

WINTHROP

LEXINGTON

BURLINGTON

QUINCY

LYNN

1 0 10.5 Miles

May 4, 2005

Stormwater Issues

• Environmental hazards in the Mystic River include:– chemicals leaching from

waste disposal sites,

– contaminated sediments, excessive inputs of plant nutrients,

– discharges of sewage containing pathogenic bacteria, and

– inputs of fuel hydrocarbons, road salt and toxic metals in stormwater runoff.

May 4, 2005

Approach

• Environmental Management System at its core but without formal adoption.

• Information Technology implementation for interactive database.

• Geographic Information System (GIS) utilization to mapping BMPs

• Analysis of “Green Cover” from Stormwater and Environmental Perspective

• Integration with Stormwater Management

May 4, 2005

Environmental Management System

• Continuous Improvement Process

Inventory Impact

Improvement

May 4, 2005

Stormwater Pollution Reduction Initiatives

• Elimination of combined sewer overflows (CSOs) and dry weather overflows – 9 out of 11 CSOs are eliminated

• Monitoring water quality – EMPACT Project – 2 years of real time monitoring

• www.mysticriveronline.org or www.epa.gov/empact

• Stormtreat Installation at Alewife Brook• Pollution Prevention• Hazardous Waste Collection• Street Sweeping• Public Awareness Campaign• Trees• Catch basin Cleanup

May 4, 2005

Inventory Analysis

• Best Management Practices– Structural – Non-Structural

• Departments• BMP Status

– Ongoing (Functioning)– Under Consideration

• Cost– Personnel– O&M– Budget

May 4, 2005

Database Development

• Microsoft Access Database

• Customized for Somerville Operation

May 4, 2005

Stormwater Asset Management System

• Customized Forms

• Customized Reports

• Easy for Management Review

May 4, 2005

Geo Information System (GIS)

• GIS overlays for structural BMPs

• Includes location and cost of BMPs.

• BMPs included for GIS Overlays– Catch Basin Maintenance – Combined Sewer Overflows (CSOs) – Stormdrains Street Sweeping – Stormtreat System

May 4, 2005

GIS – Storm Drains

0 0.5 10.25Miles

4Gravity Mains Sewage

Gravity Mains Sewage Critical

Streets

Separate Stormdrains

City Boundary

Surface Water

Somerville Stormdrain CostsStormdrains Cost

repairs 2003amount paid to contractorincludes repairs of catch basins $800,000

work hours amount paid to sewer division $350,000

MWRA sewer treatmentfor combined sewer system in all of Somerville and separate sewer system in critical areas (shaded orange) $11.5 million

Total $12.65 million

May 4, 2005

GIS - Catch Basins

0 0.5 10.25Miles

4plan

City Boundary

Surface Water

CatchBasins

Somerville Catch BasinsCatch Basin Cleaning Costs 2003

Quantity Marginal Cost Total Cost

In-House 500 CB $65/CB 32,500Contractor 2200 CB $25/CB 55,000

87,500Worst Case:In-House 1000 CB 115/CB 115,000Contractor 1700 CB $25/CB 42,500

157,500

Waste Disposal3 tons /CB8000 tons /year not available not available

Repairs100-150 CBs /yearrepaired by contractor not available

cost included in $800,000spending on storm drains

May 4, 2005

GIS – Combined Sewer Overflows (CSOs)

Tannery Brook

2 Penny Brook

0 0.5 10.25Miles

4

Streets

CSOs

Brooks

City Boundary

Surface Water

Somerville Combined Sewer Overflows (CSOs)

CSO 001ACDM study

to remove CSO

2 Penny Brook CSOMedford outflowowned by MWRA

MWRA CSOowned jointly by Somerville

and MWRA CSO 007Aowned by MWRA

Alewife Brook Mystic River001A CSO MWRA CSO

Maintenance 0 0Repairs 0 0Possible Improvements $3-5million no plans

May 4, 2005

GIS - Stormtreat

0 0.1 0.20.05Kilometers

4Streets

StormTreat System, C2M Grant

Stormwater Plant (future)

City Boundary

Alewife Brook

Somerville Stormtreat Costs

Stormtreat Cost

Installation $125,000

State Grant -($75,000)

cleaning quarterly4 days per year ($4000) $16,000

Total $66,000

May 4, 2005

GIS – Street Cleaning

0

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Monday

Thursday

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00

Sunday

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Satruday

Sunday

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Sunday

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Sunday

Sunday

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Tuesday Night0

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StreetCleaningSchedule

Weekdays

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

Sunday

Tuesday Night

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city_boundary

Somerville Street Cleaning Districts

May 4, 2005

Water QualityMystic River & Alewife Brook

• Lower Mystic River and Alewife Brook are surrounded by Somerville, Cambridge, Medford and Arlington

• Loss of recreational opportunities due to CSOs and wet weather discharges.

• Several test data available from governmental agencies, research institutions and non-profits.

• No uniformity in data was observed, hence no data was considered for inventory at this time.

Collecting and evaluating water quality data near BMPs will be considered in the next stage of the project

May 4, 2005

Tree Cover as BMP

Pervious versus Impervious Surfaces• Pervious: rainwater is filtered, recharges into groundwater • Impervious: surface runoff, pollutants wash into rivers

Why Trees? • intercept the rainwater• slow down flow and movement towards the drainage area • reduce volume of stormwater and peak flow rates • less surface runoff, less pollutants wash into rivers• AmericanForests tree canopy targets:

25% for urban residential zones15% for central business districts

May 4, 2005

Impact of Trees on Stormwater Runoff

Runoff Volume

Time

less treesmore trees

HYDROGRAPH

May 4, 2005

CITYGreen

• Software Developed by American Forests (www.americanforest.org)

• Estimates stormwater runoff, time of concentration, and peak flow during a rainstorm

Results:

1) volume of water that trees prevent from turning into runoff

2) Economic value of tree cover

3) Air Quality benefits of tree cover

May 4, 2005

Runoff volume is computed from:

- tree canopy coverage

- average rainfall

- soil type

- slope

- other land cover features

CITYGreen – Inputs

Computations based on TR-55 algorithm developed by the Natural Resource and Conservation Service at the Department of Agriculture

May 4, 2005

• Satellite imagery from Digital Globe (June 2004) with leaves

• Image classification using Erdas Imagine software

• CITYGreen uses classified satellite image to create a land cover file

• CITYGreen analysis: Somerville digital elevations model for slope, classified land cover image, and Boston rainfall average and soil composition

• Analysis for Somerville and individual neighborhoods

CITYGreen Methodology

May 4, 2005

Satellite Imagery

Somerville False Color Satellite Image

May 4, 2005

CITYGreen Landcover Classification

City Green Landcover Classificationbased on satellite image

City Boundary

Landcover Classification

City Green Feature

Impervious Surfaces: Buildings/ structures: All other buildings

Impervious Surfaces: Paved: Drain to sewer

Impervious Surfaces: Unpaved: Dirt

Open Space - Grass/Scattered Trees: Grass cover 50% - 75%

Trees: Grass/turf understory: Ground cover < 50%

Water Area

May 4, 2005

Tufts University Area

Detail of Powderhouse Circle, Tufts Football Field

False Color Image, red represents trees, grass, lawn

May 4, 2005

Tufts University Area Landcover Classification

Detail of Powderhouse Circle, Tufts Football Fieldafter City Green landcover classification

May 4, 2005

Somerville Neighborhoods

NORTH CAMBRIDGE

MID-CAMBRIDGE

AGASSIZ

NEIGHBORHOOD 9

Winter Hill

West Somerville

Ward Two / Cobble Hill

Tufts

Ten Hills

Spring Hill

Prospect Hill

Powder House

Magoun / Albion

East Somerville

Davis Square

Central Hill

Somerville Neighborhoods

Somerville Neighborhoodsand adjacent Cambridge Neighborhoods

CentralHill

DavisSquare

EastSomerville

MagounAlbion

PowderHouse

ProspectHill

SpringHill

TenHills

Tufts

WardTwo_CobbleHill

WestSomerville

WinterHill

Cambridge Neighborhood 9

Cambridge Agassiz

Mid-Cambridge

North Cambridge

May 4, 2005

CITYGreen Calculations - I

Curve Numbers:

• CN (weighted) = Total Product of (CN x Percent land cover area) / Total Percent Area or 100

Potential Maximum Retention after Runoff begins:

• S = ( (1000 / CN) - 10)

Runoff Equation:

• Q = [ P - 0.2 ((1000 / CN) - 10) ]2 / P + 0.8 ((1000 / CN) - 10)

Flow Length:

• F = (total study area acres0.6) * 209.0

Lag Time:• L = ((F0.8) *((S + 1.0) 0.7) /

(1900 * ((slope)0.5)))Time of Concentration:• Tc = 1.67 * LUnit Peak Discharge:• log(qu) = C0 + C1log(Tc) +

C2[log(Tc)]2Peak Flow:• Peak = (qu * Am * Q * Fp)Storage Volume:• Vs = Vr *(C0 + (C1(qo/qi)) + (C2

((qo/qi) (qo/qi))) + (C3 (qo/qi) * (qo/qi) *

• (qo/qi))) * study area acres * 43560.17 / 12

May 4, 2005

CITYGreen Calculations - II

Variable Definitions

• P = Average Rainfall for a 24 hour period (inches)

• Am = study area acres / 640 to determine square miles

• Fp = Swamp pond percentage adjustment factor

• qo =Existing peak flow condition with trees

• qi = Peak flow without trees

• C0..... = TR-55 Coefficients in accordance with rain type

Output Values• Peak = Peak Flow (cfs)• Vs = Storage volume (cubic feet)• Vr = Runoff Volume (in)• CN = Runoff Curve Number

(weighted)• Q = Runoff (inches)• F = Flow length (feet)• S = Potential Maximum Retention

after Runoff begins (in)• L = Lag Time (hours)• Tc = Time of Concentration

(hours)• qu = Unit Peak Discharge (csm /

in)

May 4, 2005

T

City Green Report for Air Pollution and Carbon Sequestration

May 4, 2005

City Green Report for Stormwater

May 4, 2005

City Green Analysis Neighborhoods Summary

Somerville Neighborhood Impervious Surfaces: Buildings

Impervious Surfaces: Paved

Impervious Surfaces: Unpaved

Impervious Total

Open Space: Grass

Trees Water Area

Central Hill 30.2 % 20.6 % 15.3 % 66.1 8.3 % 25.6 % 0.1 %

Davis Square 32.9 % 20.1 % 17.3 % 70.3 7.5 % 22.1 % 0.1 %

East Somerville 35.9 % 22.6 % 12.9 % 71.4 4.7 % 10.6 % 13.3 %

Magoun / Albion 36.2 % 20.7 % 14.2 % 71.1 6.9 % 21.3 % 0.7 %

Powderhouse 32.0 % 19.4 % 16.0 % 67.4 9.1 % 23.6 % 0 %

Prospect Hill 33.6 % 21.3 % 15.5 % 70.4 7.5 % 21.9 % 0.1 %

Spring Hill 31.1 % 20.4 % 16.5 % 68.0 8.2 % 23.7 % 0.1 %

Ten Hills 34.2 % 21.6 % 13.5 % 69.3 7.5 % 19.7 % 3.5 %

Tufts 25.1 % 18.2 % 17.0 % 55.0 9.2 % 30.5 % 0 %

Ward2/CobbleHill 46.0 % 28.0 % 11.7 % 85.7 4.5 % 9.6 % 0 %

West Somerville 30.7 % 20.3 % 15.4 % 66.4 8.2 % 25.3 % 0.3 %

Winter Hill 36.3 % 22.1 % 15.4 % 73.8 7.3 % 18.8 % 0.2 %

Somerville 35.9 % 22.5 % 14.3 % 72.7 6.6 % 18.0 % 2.8 %

May 4, 2005

CITYGreen Neighborhoods Stormwater Analysis

Somerville Neighborhood

Time of Concentration % change

Peak Flow % change

Infiltration % change

Runoff in inches w/ trees

Runoff in inches w/out trees

Storage volume needed cu.ft

Total Stormwater Savings

Central Hill -21.88 39.88 -38.95 3.76 4.26 95,170 $190,339

Davis Square -18.89 37.74 -35.25 3.76 4.17 307,916 $615,832

East Somerville -13.24 22.35 -33.49 3.61 3.84 652,545 $1,305,089

Magoun/Albion -22.63 44.27 -43.34 3.68 4.17 242,612 $485,224

Powderhouse -21.88 44.51 -38.95 3.76 4.26 194,161 $388,322

Prospect Hill -18.89 34.35 -35.25 3.76 4.17 188,718 $377,437

Spring Hill -21.88 44.60 -38.95 3.76 4.26 369,762 $739,524

Ten Hills -19.56 36.42 -39.47 3.68 4.09 367,307 $734,613

Tufts -27.32 62.57 -44.78 3.76 4.44 262,843 $525,687

Ward2/CobbleH -13.24 22.60 -33.49 3.61 3.84 790,565 $1,581,130

West Somerville -21.88 44.95 -38.95 3.76 4.26 367,983 $735,965

Winter Hill -15.67 27.93 -30.83 3.76 4.09 292,187 $584,374

Somerville -19.56 39.21 -39.47 3.68 4.09 4,315,039 $8,630,078

May 4, 2005

CITYGreen – Neighborhoods Summary Chart

Somerville Landcover

30,2%

32,9%

35,9%

36,2%

32,0%

33,6%

31,1%

34,2%

25,1%

46,0%

30,7%

36,3%

35,9%

20,6%

20,1%

22,6%

20,7%

19,4%

21,3%

20,4%

21,6%

18,2%

28,0%

20,3%

22,1%

22,5%

15,3%

17,3%

12,9%

14,2%

16,0%

15,5%

16,5%

13,5%

17,0%

11,7%

15,4%

15,4%

14,3%

8,3%

7,5%

4,7%

6,9%

9,1%

7,5%

8,2%

7,5%

9,2%

4,5%

8,2%

7,3%

6,6%

25,6%

22,1%

10,6%

21,3%

23,6%

21,9%

23,7%

19,7%

30,5%

9,6%

25,3%

18,8%

18,0%

0,1%

0,1%

13,3%

0,7%

0,0%

0,1%

0,1%

3,5%

0,0%

0,0%

0,3%

0,2%

2,8%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Central Hill

Davis Square

East Somerville

Magoun / Albion

Powderhouse

Prospect Hill

Spring Hill

Ten Hills

Tufts

Ward2/CobbleHill

West Somerville

Winter Hill

Somerville

Impervious Surfaces: Buildings

Impervious Surfaces: Paved

Impervious Surfaces: Unpaved

Open Space: Grass

Trees

Water Area

May 4, 2005

CITYGreenNeighborhoods Air Pollution Removal

Somerville Neighborhood

CO Ozone NO2 Particulate Matter SO2 Total

  lbs/yr Value lbs/yr Value lbs/yr Value lbs/yr Value lbs/yr Value lbs/yr Value

Central Hill 40 17 506 1554 280 859 373 765 146 110 1345 3305

Davis Square 119 51 1508 4634 834 2561 1111 2280 437 328 4009 9854

East Somerville 302 129 3827 11757 2115 6497 2820 5784 1108 831 10172 24998

Magoun, Albion 84 36 1066 3276 589 1810 786 1612 309 232 2834 6966

Powderhouse 75 32 949 2915 524 1611 699 1434 275 206 2522 6198

Prospect Hill 73 31 919 2823 508 1560 677 1389 266 200 2443 6003

Spring Hill 144 61 1821 5595 1006 3092 1342 2753 527 396 4840 11897

Ten Hills 144 61 1818 5586 1005 3087 134 2748 526 395 3627 11877

Tufts 117 50 1487 4568 822 2525 1096 2247 430 323 3952 9713

Ward2 CobbleH 150 64 1898 5832 1049 3223 1399 2869 549 412 5045 12400

West Som. 153 65 1943 5968 1074 3298 1431 2936 562 422 5163 12689

Winter Hill 105 45 133 4085 735 2257 980 2010 385 289 2338 8686

Somerville 1506 643 19071 58591 10539 32379 14052 28824 5521 4143 50689 124580

May 4, 2005

CITYGreen AnalysisCarbon Storage & Sequestration

Somerville Neighborhood Total Tons Stored Total Tons Sequestered (annually

Tree Cover in acres Percent Tree Cover

Central Hill 642.66 5.00 14.9 25.6 %

Davis Square 1,916.12 14.92 44.3 22.1 %

East Somerville 4,861.33 37.85 50.1 9.6 %

Magoun / Albion 1,354.55 10.55 30.5 21.3 %

Powderhouse 1,205.23 9.38 28.0 23.6 %

Prospect Hill 1,167.26 9.09 27.0 21.9 %

Spring Hill 2,313.62 18.01 53.5 23.7 %

Ten Hills 2,309.95 17.98 45.7 19.7 %

Tufts 1,888.98 14.71 43.9 30.5 %

Ward2/CobbleHill 2,411.33 18.77 54.7 9.6 %

West Somerville 2,467.84 19.21 56.8 25.3 %

Winter Hill 1,689.05 13.15 38.8 18.8 %

Somerville 24,227.09 188.61 488.1 18.0 %

May 4, 2005

Major Findings of CITYGreen Analysis

• Somerville has 18% tree cover on average (9.6 – 30.5%)

• Trees remove 4,315,039 cu. ft of stormwater• Stormwater savings from trees: $8,639,078 per year • Trees postpone time of concentration by 20% • Trees reduce peak flow by 40% • 40% of stormwater infiltrates • Trees remove 50,689 lbs of air pollutants per year• Benefits of air pollution removal $124,579 per year

May 4, 2005

Observations

• This project assisted to understand the importance of periodical and systematic water quality testing program.

• This system will assist to analyze potential benefits of future BMPs.

• The city could use the GIS layers as a decision-making tool once detailed water quality data is available. By using up-to-date water quality data from the critical locations in Somerville the city could identify which investments would yield the highest potential benefit in water quality improvements.

• Such program will assist to address the problem, define the solutions and in the process increase the potential of recreational use of the urban waterways.

May 4, 2005

Final Comment

• Developing a stormwater asset management system works like a hidden treasure, thus providing us with:

– A “Best Management Practice for our BMPs”.

– The system helps us understand the different perspectives of stormwater management:

– Engineering, Policy, Economics, Educational, and

– Provides directions for better urban environmental planning while satisfying the various regulatory needs.