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Parameter Sensitivity in Hydrologic Modeling - page 143 / 163

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Results show that although errors associated with parameter extraction methods may cause significant changes in lag time values, the errors become less significant once entered into a model to calculate discharge. Table 6.1 shows that lag time is inelastic with respect to longest flow path (LFP), as the elasticity of lag time with respect to this parameter is 0.8. Discharge is also inelastic with respect to longest flow path, with an elasticity of –0.22. This last number, discharge elasticity with respect to longest flow path, was determined by multiplying the lag time elasticity with respect to longest flow path by the discharge elasticity with

respect to lag time calculated using the value of 0.14.

(-0.28). The same method as

discharge elasticity with with longest flow path, is

respect to slope, also inelastic at a

Flow path and slope values were originally thought to be large contributors to lag time variations. This analysis shows that this is not necessarily

the case. both slope

Table 6.1 shows that SCS lag time acts and longest flow path (-0.50% and 0.80%

inelastically with respect to respectively). Once entered

into a hydrologic model, discharge, with discharge

variations in these parameters have minimal effect on elasticities of 0.14% and –0.22% respectively. Thus, a

1% variation in slope will cause a variation in longest flow path will

minimal 0.14% increase in discharge, cause a 0.22% decrease in discharge.

and

a

1%

Table 6.1 shows that curve number, unlike slope and longest flow path, has an elastic effect on lag time. The lag time elasticity with respect to curve number is -3.52. Discharge is also elastic with respect to curve number (at an

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