curve number developed by automated methods as an approximate upper limit, and the curve number developed by TxDOT as an approximate lower limit, gave a coefficient of variation of 3.08%, and a mean value of 89. This number is used to reflect a reasonable error one might encounter in determining SCS curve number.
SIGNIFICANCE OF ERRORS
Following hydrologic parameter extraction, ranging from traditional methods using paper maps to advanced methods using TINs, a sensitivity analysis based on the concept of elasticity was conducted for Area 2.
Quantifying discharge elasticity with respect to parameter variation is a two-step process. The first step involves determining the variation in SCS lag time with slope, longest flow path, and curve number. Variations in parameter values using the four levels of parameter extraction were plotted against resulting
parameter value, resulting SCS lag
was used to describe the times, divided by the mean
parameter variation. The range of SCS lag time, was used to quantify
the lag time variation. The lag describes the lag time elasticity
variation, respect to
divided by the the parameter.
parameter variation, In other words, this
describes the percent increase that will occur in lag time parameter. If this number is less than 1, then lag time is
by a 1% increase in the “inelastic” with respect
to the parameter. If this respect to the parameter. time.
number is greater than 1, then lag time An elastic parameter will cause larger
is “elastic” with variations in lag