1. Esri UC2013 .
2013 Esri International User Conference
July 8–12, 2013 | San Diego, California
Restoring the Chesapeake Bay
with ArcGIS
Tools for Planning Stormwater Treatment
Thomas Williams, EIT, LEED AP
AMEC Environment & Infrastructure

2. Esri UC2013 .
The Chesapeake Bay
• Largest Estuary in the US
• Drains over 64,000 mi2
- 6 States, plus Washington, DC
• 2009 Executive Order:
- Declared the Bay a National
Treasure
- Called for a renewed effort to
restore and protect the Bay
- Paved the way for the
Chesapeake Bay TMDL
Restoring the Chesapeake Bay with ArcGIS

3. Esri UC2013 .
The Chesapeake Bay TMDL
• What is a TMDL?
- Total Maximum Daily Load
- EPA-established “pollution diet.”
- Maximum amount of pollution a
water body can receive and still
remain healthy.
• The Chesapeake Bay TMDL
focuses on three pollutants:
- Nitrogen
- Phosphorus
- Sediment
Restoring the Chesapeake Bay with ArcGIS
Image Credit: 1

4. Esri UC2013 .
Urban Stormwater in the Bay Watershed
Restoring the Chesapeake Bay with ArcGIS
• Urban stormwater pollution is a major aspect
of the Chesapeake Bay TMDL.
• The Bay TMDL is affecting Municipal
Separate Storm Sewer System (MS4)
operators throughout the Bay Watershed.
• There are many existing tools for stormwater
planning, but most are non-spatial.
• How can we use GIS to…
• evaluate stormwater treatment options?
• track TMDL compliance?
• make watershed planning easier?
Image Credit: 2

5. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
ALERT
• AMEC developed a set of Python tools for ArcGIS, called
ALERT
• AMEC Load Estimation and Reduction Tracking
• Initially designed around Virginia’s draft regulations to
implement the Chesapeake Bay TMDL.
• ALERT framework has since been updated and expanded to
apply outside of Virginia and the Chesapeake Bay.
• Built to help communities:
• plan stormwater projects
• quickly evaluate different scenarios
• estimate the cost of compliance
!

6. Esri UC2013 .
ALERT Process Diagram
Restoring the Chesapeake Bay with ArcGIS
Water Quality Plan
Start / Finish
ArcGIS
Silverlight
Analyze
water
quality
scenarios
in ArcGIS
Estimate total
remaining effort
required to
achieve water
quality goals
Non-Spatial results
guide further GIS
analysis
Landuse Data
Calculate
Baseline Load
Develop
Projects
Calculate
Reduced Load
Non-Spatial
Analysis

7. Esri UC2013 .
ALERT Process: Calculate Baseline Loads
Restoring the Chesapeake Bay with ArcGIS
Calculate
Baseline Loads
Landuse Data
• Polygon layer attributed
with pollutant loading
and runoff information.
• lbs/ac/yr
(Loading Rates)
• mg/L
(Event Mean
Concentrations)
Baseline Loads
• Total annual pollutant
loads (lbs/yr) are
calculated.
• Simple Method
calculations consider:
• Impervious area
• Runoff coefficients
• Annual precipitation
either

8. Esri UC2013 .
ALERT Process: Develop Project Database
Restoring the Chesapeake Bay with ArcGIS
Project
Database
etc…
Water Quality Projects:
Pond Retrofit, 65 acres
Nitrogen Efficiency: 15%
Runoff Reduction: 0%
Cost: $275,000
Bioretention, 5 acres
Nitrogen Efficiency: 45%
Runoff Reduction: 20%
Cost: $110,000
Redevelopment, 10 acres
Nitrogen Efficiency: 50%
Runoff Reduction: 10%
Cost: Undetermined
Stormwater
BMPs
Landuse
Changes
• Treatment area
polygons
• Pollutant removal
and runoff reduction
efficiencies
• Other relevant
information

9. Esri UC2013 .
ALERT Process: Calculate Load Reductions
Restoring the Chesapeake Bay with ArcGIS
Iterates through
project database,
calculating and
tracking pollutant
and runoff
reductions.
Baseline Loads
Reduced Loads
(new polygon layer)
Detailed Results
(pollutant reductions
from each project)
Project
Database
Calculate
Load Reductions

10. Esri UC2013 .
ALERT Process: Calculate Load Reductions
Restoring the Chesapeake Bay with ArcGIS
Baseline Loads

11. Esri UC2013 .
ALERT Process: Calculate Load Reductions
Restoring the Chesapeake Bay with ArcGIS
Reduced Loads
Treatment
Area

12. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
Landuse
City of Alexandria, VA
Potomac River Basin
15.4 square miles
Population: 144,301 (2011)

13. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
Landuse (MS4)
Identified areas draining to the
City’s Municipal Separate Storm
Sewer System (MS4).

14. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
Baseline Loads

15. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
Baseline Loads BMPs
Proposed BMPs included pond
retrofits, new ponds, bioretention,
and projected redevelopment.

16. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
Reduced Loads BMPs

17. Esri UC2013 . Restoring the Chesapeake Bay with ArcGIS
Reduced Loads

18. Esri UC2013 .
ALERT Process: Non-Spatial Analysis
Restoring the Chesapeake Bay with ArcGIS
Baseline Loads
Reduced Loads Reductions
Non-Spatial
Analysis
• Results from GIS analysis
can feed into a non-spatial
component.
• Non-spatial ALERT tools are
used to roughly estimate the
remaining effort needed to
meet water quality goals.
• Project needs
(acres of treatment)
• Capital and annual
maintenance costs
• Total area of required
additional treatment is back-
calculated based on pollutant
reduction targets.

19. Esri UC2013 .
ALERT Process: Non-Spatial Analysis
Restoring the Chesapeake Bay with ArcGIS
1. Project Mix % by Area
Bioretention 10%
Filtration 10%
New Ponds 30%
Pond Retrofits 50%
2. Target
Pollutant
Phosphorus
3. Results
Treatment Area 145 acres
Initial Cost $3.5 m
Annual Maint. $81,000
Baseline
Target
Reduced
Phosphorus
Baseline
Target
Reduced
Nitrogen
Baseline
Target
Reduced
Sediment
Pollutant Loads (lbs/yr)
Results are used to guide further GIS analysis.

20. Esri UC2013 .
Closing Thoughts
1. GIS tools make planning
stormwater treatment:
• Easier
• More cost-effective
• More reality-based
2. Non-spatial analysis can be
informative, but requires
verification.
• Results should be regarded
as approximations.
• Ouputs guide further GIS-
based planning.

21. Esri UC2013 .
Thomas Williams, EIT, LEED AP
Water Resources Engineer
AMEC Environment & Infrastructure
thomas.williams@amec.com
More Information:
Image Credits
1. http://www.flickr.com/photos/particlem/
3733639670/sizes/o/in/photostream/
2. http://www.flickr.com/photos/thirteenofclubs/
3383558429/sizes/o/in/photostream
…