stormwater asset management using gis v5
TRANSCRIPT
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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Friday
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Tuesday
Monday
Thursday
Wednesday
0 0
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00
Sunday
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Monday
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Satruday
Sunday
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Sunday
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Sunday
Sunday
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Sunday
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Tuesday Night0
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Sunday
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StreetCleaningSchedule
Weekdays
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
Tuesday Night
0
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.