Hydrology - NCTCOG

1 ISWMTM Technical Manual Hydrology Hydrology : Hydrological Analysis Downstream Assessment Streambank Protection Water Balance Rainfall Tables Hydrologic Soils DataiSWMTM Technical Manual Hydrology Hydrology HO-i April 2010, Revised 9/2014 Table of Contents Hydrological Analysis .. HO-1 Estimating HO-1 Introduction to Hydrologic methods .. HO-1 Symbols and Definitions .. HO-4 Rainfall Estimation .. HO-5 rational Method .. HO-7 Introduction .. HO-7 Application .. HO-7 Equations .. HO-7 Time of Concentration .. HO-8 Rainfall Intensity (I).

2 HO-10 Runoff Coefficient (C) .. HO-10 Example Problem .. HO-10 SCS Hydrological Method .. HO-15 Introduction .. HO-15 Application .. HO-15 Equations and Concepts .. HO-15 Runoff Factor (CN) .. HO-17 Urban Modifications of the SCS Method .. HO-18 Travel Time Estimation .. HO-19 Simplified SCS Peak Runoff Rate Estimation .. HO-23 Example Problem 1 .. HO-25 Hydrograph Generation .. HO-28 Example Problem 2 .. HO-32 Hydrologic Stream Routing .. HO-33 Snyder s Unit Hydrograph Method .. HO-33 Introduction .. HO-33 Application.

3 HO-33 Urbanization Curves .. HO-34 Determination of Percent Urbanization and Percent Sand .. HO-35 Modified rational Method .. HO-38 Introduction .. HO-38 Design Equations .. HO-39 Example Problem .. HO-40 iSWMTM Technical Manual Hydrology Hydrology HO-ii April 2010, Revised 9/2014 USGS and TxDOT Regression methods .. HO-41 Introduction .. HO-41 USGS Equations for Urban Basins .. HO-41 Application of USGS Equations .. HO-42 Peak Discharge Limitations for Urban Basins .. HO-42 TxDOT Equations for Rural (or Undeveloped) Basins.

4 HO-43 Rural (or Undeveloped) Basin Application .. HO-43 Example Problem .. HO-46 References .. HO-47 Downstream Assessment .. HO-48 Introduction .. HO-48 Downstream Hydrologic Assessment .. HO-48 Reasons for Downstream Problems .. HO-49 methods for Downstream Evaluation .. HO-50 Example HO-51 Streambank Protection Volume Estimation .. HO-53 Streambank Protection Volume Calculation .. HO-53 Example HO-55 Water Balance .. HO-57 Introduction .. HO-57 Basic Equations .. HO-57 Example HO-61 References .. HO-63 Rainfall Tables.

5 HO-64 Methodology .. HO-64 References .. HO-64 Hydrologic Soils Data .. HO-82 Electronic Soil Maps .. HO-82 Online Web Soil Survey .. HO-82 Downloading Soil Surveys .. HO-82 iSWMTM Technical Manual Hydrology Hydrology HO-iii April 2010, Revised 9/2014 List of Tables Table Applications of the Recommended Hydrologic methods .. HO-2 Table Constraints on Using Recommended Hydrologic methods .. HO-3 Table Symbols and Definitions .. HO-4 Table Frequency Factors for rational Formula .. HO-8 Table Times of Concentration.

6 HO-9 Table Recommended Runoff Coefficient Values .. HO-11 Table Weighted Runoff Coefficient .. HO-12 Table Composite Curve Number Calculation Example .. HO-18 Table Runoff Curve Numbers1 .. HO-20 Table Roughness Coefficients (Manning's n) for Sheet HO-22 Table Ia Values for Runoff Curve Numbers .. HO-26 Table Dimensionless Unit Hydrograph With Peaking Factor of 484 .. HO-31 Table Example of Dimensionless Unit Hydrograph With Peaking Factor of 484 .. HO-32 Table Typical Values of Cp .. HO-34 Table Percent Urbanization and Imperviousness Summary with Associated Land Use Categories.

7 HO-36 Table Permeability Rating for the Determination of Percent Sand .. HO-37 Table Hydrologic Loss Rates .. HO-38 Table Rainfall Factors a and b for the Modified rational Method (1-year through 100-year return periods) .. HO-40 Table USGS Peak Flow Regression Equations for Dallas-Fort Worth Urban Areas .. HO-43 Table Regression Equations for Estimation of Peak-Streamflow Frequency for Hydrologic Regions of Texas1 .. HO-44 Table Monthly Precipitation Values .. HO-58 Table Saturated Hydraulic Conductivity .. HO-59 Table Evaporation Monthly Distribution Grapevine, Texas as a % of Annual Total.

8 HO-60 Table Summary Information for the North Dallas Site .. HO-61 Table Collin County Rainfall Data .. HO-66 Table Dallas County Rainfall Data .. HO-67 Table Denton County Rainfall Data .. HO-68 Table Ellis County Rainfall Data .. HO-69 Table Erath County Rainfall Data .. HO-70 Table Hood County Rainfall Data .. HO-71 Table Hunt County Rainfall Data .. HO-72 Table Johnson County Rainfall Data .. HO-73 iSWMTM Technical Manual Hydrology Hydrology HO-iv April 2010, Revised 9/2014 Table Kaufman County Rainfall Data.

9 HO-74 Table Navarro County Rainfall Data .. HO-75 Table Palo Pinto County Rainfall Data .. HO-76 Table Parker County Rainfall Data .. HO-77 Table Rockwall County Rainfall Data .. HO-78 Table Somervell County Rainfall Data .. HO-79 Table Tarrant County Rainfall Data .. HO-80 Table Wise County Rainfall Data .. HO-81 List of Figures Figure The 16 Counties Participating in NCTCOG .. HO-6 Figure Example IDF Curve (Dallas County, Texas) .. HO-6 Figure rational Formula - Overland Time of Flow Nomograph .. HO-13 Figure Manning s Equation Nomograph.

10 HO-14 Figure Approximate Geographic Boundaries for SCS Rainfall Distributions .. HO-16 Figure SCS Solution of the Runoff Equation .. HO-17 Figure Composite CN with Connected Impervious Areas .. HO-21 Figure Composite CN with Unconnected Impervious Areas .. HO-21 Figure Average Velocities - Shallow Concentrated Flow .. HO-24 Figure SCS Type II Unit Peak Discharge Graph .. HO-27 Figure Dimensionless Unit Hydrographs for Peaking Factors of 484 and 300 .. HO-30 Figure Modified rational Definitions .. HO-38 Figure Hydrologic Regions for Statewide Rural Regression Equations.