Workshop on Storm Water Modeling Approaches

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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.

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  • Hydrologic Engineering Centers River Analysis System (HEC- RAS)
    Hydrologic Engineering Centers Hydrologic Modeling System (HEC-HMS)
    Storm Water Management Model (SWMM)
    TR-55, Urban Hydrology for Small Watersheds
    Bulletin 17B – Flood Frequency from gage data
    Water-Resources Investigations Report 00-4189 TECHNIQUES FOR ESTIMATING MAGNITUDE AND FREQUENCY OF PEAK FLOWS FOR PENNSYLVANIA STREAMS
  • Workshop on Storm Water Modeling Approaches

    1. 1. Modeling Workshop Prepared by: Erin Copeland Chad Davis, PE Damon Weiss, PE November 12, 2010
    2. 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. 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. 4. Modeling the Water Cycle  The Water Cycle includes many complex processes  Result Many different models to choose from
    5. 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. 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. 7. Hydrologic Modeling Precipitation and Rainfall Distribution
    8. 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. 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. 10. Hydrologic Modeling Surface Runoff
    11. 11. Hydrologic Modeling Surface Runoff  Rational Method Runoff Coefficient, C  Land Cover  Soil Type  SCS Method Curve Number, CN
    12. 12. Hydrologic Modeling Infiltration and Evapotranspiration
    13. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 23. Hydraulic Modeling Open Channels, Collection and Stormwater Management
    24. 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. 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. 26. Hydraulic Modeling Software Open Channel (Streams) – HEC-RAS  HEC-RAS (Army Corp) Based on Energy Equation
    27. 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. 28. Hydraulic Modeling Software Stormwater Management Bentley StormCAD Bentley CivilStorm Haesteds PondPack
    29. 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. 30. Hydraulic Modeling Software Open Channel, Collection and Stormwater - SWMM  SWMM Robust closed system modeling (piped)  Hydrologic and hydraulic functions in one model
    31. 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. 32. Water Quality Modeling
    33. 33. Water Quality Modeling Methods Simple Method Other Models  AQUATOX  BASINS  CORMIX for Mixing Zones  WASP7  QUAL2K
    34. 34. Water Quality Modeling Methods: GIS Application Nitrates / Nitrites Total Suspended Solids ArcGIS ModelBuilder
    35. 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. 36. Groundwater and Snow/Ice Melt Modeling
    37. 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. 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. 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. 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. 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. 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. 43.  Flooding due to interior flooding  Significant emphasis placed on model selection  Extensive public outreach and participation Watershed Example – Hicks Creek
    44. 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. 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. 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. 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 RequiredStorage(ft3) 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. 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. 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. 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. 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. 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

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