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BMP Design Aids w w w. t r a n s p o r t a t i o n . o h i o . g o v 1 Equations / Programs Rational Method Mannings Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

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BMP Design Aids

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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Training Intent

Introduction and overview of various design aids (equations and programs) Not a detailed training on how to use each one

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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Rational Method

For peak flow rate only Q = CiA Q: flow rate (cfs) C: coefficient of runoff i: rainfall intensity (in/hr)

Based on time of concentration Sheet flow, shallow concentrated flow, and open channel or pipe flow

A: tributary area (ac)

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Rational Method

Q = CiA C:

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Rational Method

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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Manning’s Equation

(0.15 for Vegetated Biofilter)

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Manning’s Equation

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Manning’s Equation

Program or Spreadsheet Calculation

Use bisection method (trial and error)

Inputs:

Channel geometry and slope Manning’s roughness coefficient Flow rate

Results:

Normal depth Velocity

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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Discharge Equations

Orifice flow Weir flow

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Orifices

Orifices

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Weir Orifice

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Orifice Flow

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Weir Flow

L&D Vol. 2, 1102.3.4

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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ODOT CDSS

CDSS is a hydraulic design software developed by ODOT C – Culvert Design D – Ditch Design SS – Storm Sewer Design

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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SCS Curve Number

Technical Release 55 (TR-55) Technical Release 20 (TR-20) Urban Hydrology for Small Watersheds Determines runoff depth (inches) Combines with unit hydrograph theory Produces runoff hydrographs

Peak flow and total volume

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SCS Curve Number

CN: depth of runoff abstracted Total P – Abstracted P = Runoff Depth Runoff Depth * Area = Runoff Volume NRCS unit hydrograph gives runoff volume a shape (distribution over time) Produces a full runoff hydrograph

Time Runoff Flow Rate

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SCS Curve Number

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SCS Curve Number

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SCS Curve Number

Analyses that require a full hydrograph

Pre vs. post volumes (CSO areas) Routing a design storm through a detention basin, bioretention cell, or infiltration trench

Still gives peak flow rate, but will likely be slightly different from Rational Method

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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Hydrograph and Pond Routing Programs

Many different programs

Different inputs Different calculations Different limitations

Know your tool before you use it

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  • Basic Pipe or Open

Channel Capacity Calcs.

  • Basin Inlet/Outlet
  • Peak Flow and HGL
  • Steady/Unsteady Flow
  • Open Channels
  • Some Sediment

Transport/Quality

  • Often used in FEMA Floodplains
  • Normal Gravity Sewer, Detention Pond Design
  • Hydrology and Hydraulics Combined
  • Rational/TR-55/SCS Hydrology
  • Manning’s/Orifice/Weir Hydraulic Calcs.
  • Some Quality Calculations Available
  • Complex Drainage Systems that have:
  • tail water, reverse flow, pump stations, surface flooding
  • Horton/Green-Ampt Hydrology
  • Hydrodynamic and Kinematic Wave Hydraulic Calcs.
  • Detailed Quality Calculations Available

Common Hydraulics and Hydrology Software Options

Design Calculations

  • Hydraflow Express
  • Bentley CulvertMaster
  • Bentley FlowMaster
  • Urban Drainage HY22
  • HY-8, ODOT CDSS

HEC

  • HEC-1
  • HEC-HMS
  • HEC-2
  • HEC-RAS
  • GEO-RAS

Simple Stormwater Routing Models

  • HydraFlow Hydrographs
  • HydraFlow Storm Sewers
  • Bentley StormCAD
  • Bentley PondPack
  • HydroCAD

Robust Stormwater Routing Models

  • EPA SWMM
  • Bentley CivilStorm
  • AutoDesk SSA
  • PCSWMM
  • XP SWMM
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PondPack and HydroCAD

Inputs for runoff hydrograph

Area Curve number, land use, or runoff coefficient Time of concentration Design storm frequency

Produces runoff hydrograph Then route that hydrograph into your BMP

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PondPack and HydroCAD

Inputs for BMP

Stage vs storage curve (elevation vs. volume)

Inputs for BMP discharge

Stage vs. depth curve Each outlet

WQ orifices Weirs, catch basin grates Overflow weirs Discharge pipe

Downstream constraints (tailwater)

793 794 795 796 797 798 799 800 0 0.10.20.30.40.50.60.70.80.9 1 1.11.21.3 Elevation (ft) Volume (ac-ft)

Elevation vs. Volume

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PondPack and HydroCAD

Two types of analyses

Hydrograph routing Drawdown analysis

Split event into many short pieces and calculate:

Volume entering Volume leaving Volume and depth in basin

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PondPack and HydroCAD

Make sure you have all of the potential discharge conveyances Make sure the BMP storage information in the model matches the design sheets Make sure the modeled discharge conveyance characteristics match the design sheets and site, including tailwater Make sure the results make sense

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Rational Method Manning’s Equation Outlet Discharge Equations ODOT CDSS SCS Curve Number Hydrograph and Pond Routing Programs USGS StreamStats

Equations / Programs

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Rational Method

Peak flow rate only

Manning’s Equation

Flow conditions (velocity and depth) at a given flow rate

Outlet Discharge Equations

Flow rate at a given outlet shape and hydraulic head

ODOT CDSS

Hydraulic design of culverts, ditches, and storm sewers

SCS Curve Number

Full runoff hydrograph (flow rate over time and full storm volume)

Hydrograph and Pond Routing Programs

Full hydrograph, detention, peak flow rate, and draw down analyses

USGS StreamStats

Peak design storm flow rates as well as other stream statistics

Equations / Programs

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Questions ?

Jon Prier, P.E. jonathan.prier@dot.ohio.gov 614-644-1876