project 0 4193 regional characteristics of unit hydrographs
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Project 0-4193 Regional Characteristics of Unit Hydrographs. David B. Thompson, Texas Tech, RS George R. Herrmann, TxDOT, PD William H. Asquith, U.S. Geological Survey, Co-PI Xing Fang, Lamar University, Co-PI Theodore G. Cleveland, University of Houston, Co-PI. Background.

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project 0 4193 regional characteristics of unit hydrographs

Project 0-4193Regional Characteristics of Unit Hydrographs

David B. Thompson, Texas Tech, RS

George R. Herrmann, TxDOT, PD

William H. Asquith, U.S. Geological Survey, Co-PI

Xing Fang, Lamar University, Co-PI

Theodore G. Cleveland, University of Houston, Co-PI

background
Background
  • Substantial progress on the “Texas” hydrograph method has been made over the past 7 years or so ...
    • Design storm depth and temporal distribution--DONE
    • Weakness in Curve Number method documented--DONE
    • Unit hydrographs--almost DONE
    • Time parameters--almost DONE
  • What is left? A temporal loss rate model=excess rainfall
    • Complete the loop: Rainfall --> Excess Rainfall --> Runoff
    • Motivation for 2-year extension request . . .
primary 0 4193 objectives
Primary 0-4193 Objectives
  • Is the NRCS dimensionless unit hydrograph representative of Texas hydrology? SORT OF (at times)
  • If not, can alternative methods be developed? certainly YES
  • Can an alternative loss model to NRCS curve number method be developed from the existing database and resulting UH? Can a loss model “tuned” to the UH procedures that will result from 0-4193 to date? (Requested modification)
0 4193 approach
0-4193 Approach
  • Common database (93 watersheds and 1,600 events)
  • Joint but INDEPENDENT data processing . . .
    • Assumption of differing LOSS-MODELS--A necessary step
  • Unit Hydrograph Computations
    • Gamma UH fit to Qp and Tp (USGS): Shape and Tp parameters
    • Rayleigh IUH fit by error minimization (Univ. of Houston)
    • Linear programming fit by error minimization (Lamar Univ.)
    • Traditional method (Texas Tech Univ.)
time to peak
Time to Peak
  • Equation to estimate time to peak from main channel length, main channel slope, and development classification has been developed.
  • Measure of equation applicability
  • Measure of equation prediction accuracy.
  • Handy nomograph

UNDEVELOPED WATERSHEDS

0 4193 implications
0-4193 Implications
  • Watershed development influences UH shape and time scale.
  • GUH of same order of NRCS GUH.
  • GUH shape can be predicted and uncertainty computed.
    • K = function(L,D)
  • GUH Time-to-Peak (Tp) can be predicted without Time-of-Concentration (Tc) and uncertainty computed.
    • Tp = function(L,S,D)
  • GUH Tp can be predicted with Tc and uncertainty computed.
    • Tp= function(Tc, D)
  • THE TWO TpMETHODS COMPLIMENT EACH OTHER!
temporal loss rate functions
Temporal Loss-Rate Functions
  • Potential candidate models
    • Initial loss, constant loss-rate, runoff coefficients
    • Green-Ampt, and other phenomenological models

Work to Do

  • Modify existing analytical tools to accommodate search for optimal loss-rate function given a UH.
  • Apply to database to estimate parameters
  • Analyze results from parameter estimation
  • Synthesize and regionalize
unit hydrographs
Unit Hydrographs
  • A unit hydrograph (UH) is the hydrograph of runoff that results from a unit pulse of effective precipitation (runoff) distributed evenly over a watershed over a specific duration of time.
  • UHs are used for drainage designs for watersheds with drainage areas with a wide range of sizes.
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