Parameter Sensitivity in Hydrologic Modeling

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Parameter Sensitivity in Hydrologic Modeling

• Tanya Hoogerwerf
• March 7th, 2002

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Outline

• Flood discharge calculation overview
• Problem statement and research objectives
• Case studies
• Sensitivity analysis of hydrologic parameters
• Conclusions

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Flood Discharge Calculation
Watershed Parameters
Discharge
Lag Time
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Hydrologic Modeling Parameters
Slope
Longest Flow Path
Area
Soil Type and Land Use (CN)
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How Are Parameters Calculated?
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How Are Parameters Calculated?
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Lag Calculation
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Flood Discharge Calculation
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Problem Statement

• Differences encountered in lag results between
  traditional methods and automated methods

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Research Objectives

• For traditional and automated processes,
  determine
• Sources of error
• Range of errors
• Significance of errors

Use Automated or Traditional Methods?
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Outline

• Flood discharge calculation overview
• Problem statement and research objectives
• Case studies
• Sensitivity analysis of hydrologic parameters
• Conclusions

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What Was Used to Test?

• Set up the four levels of case studies
• 3 differently sized areas

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Determination of Parameter Sensitivity
Slope
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Case 1 Measurement From Paper Maps
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Case II On Screen From Raster Maps
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Case IIIA 10m and 30m Digital Elevation Models,
Using GIS/CRWR-PrePro
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Case IIIB 10m and 30m Digital Elevation Models
Using WMS
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Case IV Automated Methods Using WMS and a
Triangulated Irregular Network Model (TIN)
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Case Study Results
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Outline

• Flood discharge calculation overview
• Problem statement and research objectives
• Case studies
• Sensitivity analysis of hydrologic parameters
• Conclusions

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Elasticity As a Measure of Sensitivity

• Elasticity is dimensionless
• Provides measure of sensitivity
• lt1 is inelastic
• gt1 is elastic

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Analytical Calculation of Gradients

• As the longest flow path varies by 13.2, the lag
  varies by 10.6
• The elasticity is 10.6/13.2 0.80inelastic

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Numerical Calculation of Gradient
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Sensitivity Results
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Elasticity
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Elasticity
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Conclusions
Use Automated or Traditional Methods?

• Automated methods using grid-based DEMs are less
  time consuming than traditional methodsUSE
  AUTOMATED METHODS
• Slope and longest flow path measurements do not
  greatly influence discharge
• Measurements of area do not vary greatly, spend
  time/resources obtaining accurate soil and land
  use data for CN

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Thanks
Dr. Maidment David Stolpa Dr. Charbeneau Dr.
Barrett Dr. Nelson CRWR Group EWRE Friends
Environmental Modeling Systems, Inc.