6/9/2014. Hydrology Options for Dynamic Modeling at the Inlet Level. Agenda. Introduction. Introduction. Typical Questions.

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1 Hydrology Options for Modeling at the Inlet Level Matt Manges, PE, CFM LAN Saul Nuccitelli, PE, CFM City of Austin (former LAN employee during this project) Derek St. John, PE, CFM LAN /9/1 Agenda Introduction Typical Questions Example Project Hydrology Comparisons Recommendations Introduction modeling is growing in popularity Hydrology not well standardized Multiple ways of developing hydrologic inputs Watershed or inlet-level 3 1

2 Why Does the Hydrology Method Matter? Could influence analysis results hydrographs aren t often addressed in design manuals No single standard method Potential for thumbtack hydrographs Inlet level drainage areas may be smaller than the method s original assumptions Typical Questions for Inlet Hydrographs? What loss/routing method should be used? What hyetograph should be used? How do dynamic flows compare to static flows? Should peaks match? Should dynamic peaks be lower or higher? Are there any simplifying assumptions? How do inlet level areas compare to watershed level modeling? City of Austin Euclid-Wilson Storm Drain Improvements Historic flooding issues 19 s Era System Mixed land use.1 mi of storm sewer 3 Inlets Major systems with creek outfalls

3 City of Austin Euclid-Wilson Storm Drain Improvements Historic flooding issues 19 s Era System Mixed land use.1 mi of storm sewer 3 Inlets Major systems with creek outfalls 7 Euclid-Wilson Background Studied & designed in 1-11 with static methodology Second system was not constructed due to AT&T conflict City wanted to understand installed LOS, D model Analysis Summary Rational Method 1% AEP storm event StormCAD NRCS/SCS Type III Rainfall Distribution 1% AEP, -hour storm event NRCS/SCS Loss and Routing InfoWorks ICM 9 3

4 7 DA-Aa Mix of residential & street,. Ac, C= DA-Ac Mix of residential & street, 1.Ac, C= DA-A street,.ac, C=

5 3 DA-A17c Highly Impervious,.3 Ac, C= Storm Drain Hydrograph Comparisons SD-A1-1 Mid point of system Storm Drain Hydrograph Comparisons 3 SD-A1-1 Northern Outfall

6 Why the Differences? Rational Intensities based on IDF Constant intensity, average over a duration Hyetograph shape based on SCS Type III distribution Rainfall depth based on DDF NRCS/SCS method is more sophisticated Initial abstraction, losses, timing 1 Other Options Modified/Universal/Unified Rational Hydrograph Estimates of duration Small Watershed Method (Malcolm s) No hyetograph, realistic volume Clark Unit Hydrograph with R Adjustment Widely utilized in Houston region peak flow to match static flow 17 7 DA-Aa Mix of residential & street,. Ac, C= Modified Rational Clark 1

7 1 DA-Ac Mix of residential & street, 1.Ac, C= Modified Rational Clark 19 1 DA-A street,.ac, C= Modified Rational Clark 3 DA-A17c Highly Impervious,.3 Ac, C= Modified Rational Clark 1 7

8 Storm Drain Hydrograph Comparisons SD-A1-1 Mid point of system Modified Rational Clark Storm Drain Hydrograph Comparisons 3 SD-A1-1 Northern Outfall Modified Ratonal Clark 3 Ponded Area Comparisons NRCS/SCS Mod. Rational Clark

9 Ponded Area Comparisons NRCS/SCS Mod. Rational Clark Ponded Area Comparisons NRCS/SCS Mod. Rational Clark Recommendations Conform with Design Manuals (when possible) Standardize approaches with reviewing agencies Discuss & decide ahead of time Understand your assumptions 7 9

10 Other Considerations Reporting time step below minimum Tc Review the history of each method Look first to your criteria Open channel hydrology If peak flow matching is required Change non physical parameters Data is documented for the future Questions? Matt Manges, PE, CFM