The attached presentation was prepared by Pennoni Associates and Michael Baker Corporation to the Pittsburgh Parks Conservancy and members of the Pennsylvania Environmental Council Green Infrastructure Network. The presentation discussed various watershed modeling techniques for regional, watershed and local projects, as well as an overview of the different tools that engineers use to create these models.

1. Modeling Workshop
Prepared by:
Erin Copeland
Chad Davis, PE
Damon Weiss, PE
November 12, 2010

2. What is a Model?
Engineers tend to think of everything
as a model.
 Concepts
 Equations
 Processes and Workflows
 Software Packages
In fact, many engineering models are made up of smaller
models, which increases modeling variability and
complexity.

3. Application of Models to Water Resources
 Determining Water Balance of a Region
 Stream and Riparian Restoration Projects
 Predicting / Mitigating Flood, Landslide
or Drought Risk
 Distribution and Collection System Design
 Design of Bridges, Dams, and Urban Drainage Systems
 Predicting / Mitigating Erosion and Sedimentation
 Assessing Water Quality and Contaminant Transport Risk

4. Modeling the Water Cycle
 The Water
Cycle
includes
many
complex
processes
 Result
Many
different
models to
choose from

5. Modeling the Water Cycle…
Through the Eyes of an Engineer
 In reality, rainfall and routing are continuous processes.
 Models, however, can be linear or non-linear, statistical
or deterministic, single-event or continuous.
Hydrology
Hydraulics
Water Quality

6. Hydrology, Hydraulics and Water Quality
General Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Note: Models do not
always have to be this
detailed to be useful.
 Always tailor modeling to
your specific goals.
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

7. Hydrologic Modeling
Precipitation and Rainfall Distribution

8. Hydrologic Modeling
Precipitation – Synthetic Rainfall Distributions
 SCS Synthetic rainfall distributions are
used in lieu of actual storm events
 Type IA are the least intense storms
 Type II (Pittsburgh) are the most intense
 Represent fractional 24-hour rainfall,
which translates well to any storm
Actual Rainfall Data
(Hurricane Ivan)
Formulation of
Synthetic Rainfall

9. Hydrologic Modeling
Precipitation – Gridded Rainfall
 Only a few modeling
software programs
(ie: SWMM, HEC-HMS) can
handle gridded rainfall data.
 Benefits include increased
accuracy and calibration of
model to historic storm
events.
 Tradeoff: Higher costs and
steeper learning curve
 Used primarily for real-time
flood forecasting

10. Hydrologic Modeling
Surface Runoff

11. Hydrologic Modeling
Surface Runoff
 Rational Method
Runoff Coefficient, C
 Land Cover
 Soil Type
 SCS Method
Curve Number, CN

12. Hydrologic Modeling
Infiltration and Evapotranspiration

13. Hydrologic Modeling
Infiltration and Evapotranspiration
 Infiltration can be modeled on a
watershed scale, based on soil
maps, soils samples, and spot
infiltration tests
 Evapotranspiration can similarly
be modeled, based on
temperature variation, land
cover and soils data.
 For site-specific design, it is
preferable to measure
infiltration directly.

14. Hydrologic Modeling Software
Selecting the Right Model for Your Project
Rational
Method
TR-55
Modified
Rational
Method
HEC-HMS
SWMM
Project Cost
Breakpoint
Cost
Model Complexity and Accuracy

15. Hydrologic Modeling Software
Rational and Modified Rational Methods
Rational Method
 Q = C x I x A
 Return peak runoff rate,
but not volume
 Applies to very small basins
Modified Rational Method
 Model assumes peak
intensity is sustained
 Area under curve is runoff
volume

16. Hydrologic Modeling Software
Rational Method – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Rational Method requires
minimal inputs, but is
limited in output
 Only Modified Rational
Method outputs volume
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

17. Hydrologic Modeling Software
TR-55 Method
 Commonly used for a wide
range of applications
 Produces hydrographs suitable
for routing; therefore, often
used in stormwater
management design software

18. Hydrologic Modeling Software
TR-55 Method – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Ease of implement and
useful output make it an
attractive choice for site-
specific design
 Not for regional modeling
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

19. Hydrologic Modeling Software
HEC-HMS
 Offers complete hydrologic
modeling capabilities, including
input of GIS terrain, soils and
land cover data, gridded
precipitation, infiltration rates
and snow/ice melt parameters.
 Does not model hydraulics or
water quality. Intended to
be used in conjunction with
HEC-RAS for hydraulic
modeling.

20. Hydrologic Modeling Software
HEC-HMS – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Good for regional
modeling
 Very flexible. Easy to
define sub-watersheds for
later study.
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

21. Hydrologic Modeling Software
SWMM
 Offers complete
modeling for
hydrology, hydraulics
and water quality
 Steep learning curve
due to complexity
 Free through EPA, but
third-party graphical
versions exist too.

22. Hydrologic Modeling Software
SWMM – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Complete modeling
solution
 Tradeoff in model
complexity and
implementation costs
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

23. Hydraulic Modeling
Open Channels, Collection and Stormwater Management

24. Hydraulic Modeling
Open Channel and Collection Systems – Manning’s Equation
 Small channel
and collection
system modeling
is typically based
on Manning’s
Equation
 Applicable
to channels,
pipes,
ditches, etc.

25. Hydraulic Modeling Software
Open Channel and Collection Models – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Hydraulics based on
Manning’s equation are
used for swale design and
closed drainage systems
 Used for uniform flow only
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

26. Hydraulic Modeling Software
Open Channel (Streams) – HEC-RAS
 HEC-RAS (Army Corp)
Based on Energy Equation

27. Hydraulic Modeling Software
HEC-RAS – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Can be used for steady and
unsteady flow conditions
 Backwater, bridges, culverts,
levees, split flow, spillways,
weirs, drop structures, ice and ice
jams, sediment transport, etc.
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

28. Hydraulic Modeling Software
Stormwater Management
Bentley StormCAD
Bentley CivilStorm
Haesteds PondPack

29. Hydraulic Modeling Software
Stormwater Management – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Note: Models do not
always have to be this
detailed to be useful.
 Always tailor modeling to
your specific goals.
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

30. Hydraulic Modeling Software
Open Channel, Collection and Stormwater - SWMM
 SWMM
Robust closed system
modeling (piped)
 Hydrologic and hydraulic
functions in one model

31. Hydraulic Modeling Software
SWMM – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Complete modeling
solution
 Tradeoff in model
complexity and
implementation costs
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

32. Water Quality Modeling

33. Water Quality Modeling Methods
Simple Method
Other Models
 AQUATOX
 BASINS
 CORMIX for Mixing
Zones
 WASP7
 QUAL2K

34. Water Quality Modeling Methods: GIS Application
Nitrates / Nitrites
Total
Suspended
Solids
ArcGIS ModelBuilder

35. Hydrologic Modeling Software
Water Quality – Inputs and Outputs
Hydraulic
Outputs
- Velocity
- Flow Area
- Water Surface
Elevations
Water
Quality
Outputs
- Pollutant
Loading
Hydrologic
Model
Water
Quality
Model
WQ Inputs
- Event Rainfall
- Land Use
- Target Pollutants
- Pollutant
Concentration
- Calibration Data
Hydrologic Inputs
- Storm Return Periods
- Storm Durations
- Gridded Rainfall
- Terrain (DEM)
- Slopes
- Sub-watersheds
- Stream Connectivity
- Land Cover
- Soils
- Ice / Snow Melt
- Infiltration Assumptions
- Calibration Data
Hydraulic Inputs
- Channel Geometry
- Manning’s Coefficient
- Reach Lengths
- Modeling Approach
- Inline Structures
- Storage Areas
- Calibration Data
 Models vary considerably in
complexity
 More robust models may
include additional inputs not
listed here
Hydraulic
Model
Hydrologic
Outputs
- Peak Flow
- Runoff Volume

36. Groundwater and Snow/Ice Melt Modeling

37. Groundwater and Snow/Ice Melt Modeling
 Used primarily in advanced
modeling efforts
 Groundwater model
applications include
seasonal baseflow
determination, plume
analysis, evaluation of
aquifer resources, etc.
 Snow/ice melt models are
often used for winter flood
prediction

38.  Government/University Supported (freeware)
 Vender Options
HDS-5……………………………………….
HEC-HMS, HEC-1, HEC-2, SWMM,TR-55,
USGS Regressions, Bulletin 17B, WRIR 00-4189, PSU-IV,
SCS Method, Rational Method, VTPUSHM, HY-8, HY-22,
Summary of Available Modeling Software
HEC-RAS,

39.  What is the scale of my project?
 Regional, watershed, site specific…
 What am I hoping to determine (aka GOAL)?
 Flow rate, volume, reductions…
 What questions do I want to answer?
 CSO activated, flooding, infiltration…
 What accuracy do I need?
 Close enough, closer, really close…
 Do I need a “fancy” model and do I have the budget???
 Desired functions, user friendliness, standard of practice…
Some Questions to Address Before Starting…

40.  Complex Regional System…
 300 square miles
 265 regional CSOs
 52 regional SSOs
 4,000 miles of sewers
 Planning…
 Break into planning basins
 Develop model to evaluate basins and develop options
for a Regional Long Term Wet Weather Control Plan
Regional Example – ALCOSAN Planning Basins

41.  Data collection
 System as-builts, CCTV, manhole
inspections
 Flow monitoring
 Calibration and verification
 SWMM model of system
 Specific Solutions
 Large modeling effort equals
large costs
 Needs to be defensible given
future capital investments
Regional Example – ALCOSAN Planning Basins

42.  Relatively simplistic and cost effective
Regional Example – Act 167 Watershed Planning
 Data collection
 GIS based analysis
 Water quality samples
 Municipal input
 General solutions
 Range of solutions that can
be applied to certain areas
 Stormwater and
development planning tool

43.  Flooding due to interior flooding
 Significant emphasis placed on model selection
 Extensive public outreach and participation
Watershed Example – Hicks Creek

44.  Model selection: HEC-RAS vs. SWMM
Watershed Example – Hicks Creek
Table 1: Steady vs. Unsteady Modeling
Modeling Variable Steady Unsteady
Flood Volume
Representation No Yes
Flood Gate
Operation
Fixed
Condition Variable
Pump Stations No Yes
Pressure Conduits
Fixed
Condition Variable
Influence of
Susquehanna
Tailwater
Fixed
Condition Variable
Flow Reversal No Yes
Reservoir Routing No Yes
Channel Routing No Yes
Cost (considers cost
to complete project) Moderate
Moderately
High
Table 2: Modeling Software Program Evaluation
Factor HEC-RAS SWMM*
Bridge Routine Strong Neutral
Open Channel/Floodplain
Representation Strong Neutral
Floodplain Mapping Strong Neutral
Pump Representation Strong Strong
Groundwater
Representation Strong Strong
Pipe/Conduit System
Representation Neutral Strong
Pressure Conduit Neutral Strong
Cost of Program** $0 $4,400 to $6,400
Annual License and/or
Maintenance Fee (15%)** $0 $660 to $960
* SWMM5 software is free, but has less functionality and output options
**Cost shown is for commercial vender versions of SWMM

45.  Data collection
 LiDAR, few as-builts
 Groundwater wells
 Local input
 Historical photos
 Specific solutions
 Pump station, new culvert, levee modifications,
buyouts, etc.
 Significant modeling effort = moderate costs
 Needs to be defensible given future capital investments
Watershed Example – Hicks Creek

46.  Stream daylighting project
 Remove as much stormwater
from combined system to
create a stream
 Data collection
 As-builts, flow monitoring,
low flow estimates, CCTV
Watershed Example – Sheraden Park

47.  Modeling
 Combination of “Mouse”
and spreadsheet
representations
 Flowrates, volume,
separation, detention
Watershed Example – Sheraden Park
0
2500
5000
7500
10000
12500
15000
17500
20000
22500
25000
27500
30000
32500
35000
37500
40000
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Required
Storage
(ft
3
)
Time (hr)
Detention Volume Required 7/18/2002 Event
Required Volume = 34560 ft3
7/18/2002 Required Detention
Time
(hr)
Precip.
(in)
Runoff
(cfs)
I&I
Separated
(cfs)
Net
Runoff
(cfs)
Comb.
Runoff
(cfs)
Septic
Capacity
(cfs)
Required
Detention
(ft3
)
15:00:00 0.000 0.695 0.512 0.183 0.247 1.2 0
15:15:00 0.000 0.749 0.512 0.237 0.320 1.2 0
15:30:00 0.008 0.818 0.512 0.306 0.414 1.2 0
15:45:00 0.000 2.394 0.512 1.882 2.540 1.2 1206
16:00:00 0.048 0.778 0.512 0.266 0.359 1.2 450
16:15:00 0.017 3.303 0.512 2.791 3.768 1.2 2761
16:30:00 0.032 4.191 0.512 3.679 4.967 1.2 6152
16:45:00 0.015 2.675 0.512 2.163 2.920 1.2 7700
17:00:00 0.079 2.174 0.512 1.662 2.244 1.2 8639
17:15:00 0.327 3.783 0.512 3.271 4.416 1.2 11533
17:30:00 0.339 1.840 0.512 1.328 1.792 1.2 12066
17:45:00 0.155 3.641 0.512 3.129 4.224 1.2 14788
18:00:00 0.010 2.621 0.512 2.109 2.847 1.2 16270
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
3 4 5 6 7 8 9 10 11
Rainfall
(in)
Time
7/18/02 Hyetograph

48. Watershed Example – Sheraden Park
 Specific solutions
 Parallel systems
 New combined
 New storm
 New sanitary
 Limits of separation
 Existing and future
 Anticipated daylighted flow
 Significant modeling effort = moderate costs
 Needs to be defensible given future capital investments
 New combined selected
 Existing converted to
stormwater (groundwater)

49.  Redevelopment of two
city blocks
 Utilize green
infrastructure to reduce
CSO contributions
 Simplistic modeling
 Hydrologic based on
Rational equation
 Spreadsheet based
tools to determine
CSO reductions
Site Specific Example – Broad Street

50.  Used to support modeling efforts
 Determination of how a system responds
 Trouble shooting complex areas
 Model calibration
 Model verification
Flow Monitoring
 Allows for validation of
pilot projects
 Pre-construction to
establish baseline
 Post-construction to
establish results

51. Final Recommendations for Model Selection
 Determine what questions you want to answer. Fit the
model to the problem – not the other way around.
 Use the simplest method that can provide an answer to
your questions.
 Use the simplest model that will yield adequate accuracy.
 Question whether increased accuracy is worth the
increased effort. Essentially don’t over model.
 Be aware of the assumptions inherent to the model.
 Engage those that have the technical expertise. Anyone
can push a button, but not everyone knows what the
button truly does…

52. Erin Copeland
Restoration Ecologist
Pittsburgh Parks Conservancy
2000 Technology Drive, Suite 300
Pittsburgh, PA 15219
(p) 412-682-7275 x218
(m) 412-512-9639
(e) ecopeland@pittsburghparks.org
www.pittsburghparks.org
Contact Information
M. Damon Weiss, P.E.
Project Engineer
Pennoni Associates Inc.
701 Seco Road
Monroeville, PA 15146
(p) 412-521-3000 x3828
(m) 412-266-2492
(e) mweiss@pennoni.com
http://www.pennoni.com |
Chad R. Davis, P.E.
Water Resources Engineer
Michael Baker Jr., Inc.
Airside Business Park
100 Airside Drive
Moon Township, PA 15108
(p) 412.375.3077
(m) 412.523.9354
(e) cdavis@mbakercorp.com
www.mbakercorp.com