UM-9 : Model parameter evaluation using catchment characteristics

Abstract

In view of growing development of water resources in many projects, it becomes necessary to estimate discharge values for ungauged watersheds or sites within a region. The simplest way is to transfer the information from catchments for which data are available to nearby ungauged catchments within a given region having similar hydrological characteristics. If loss rate parameters and unit hydrograph parameters of a rainfall-runoff model such as Nash Model are related to the catchment characteristics, then the relationships thus obtained can be used to estimate discharges for ungauged catchments.

In this User's manual the following form of non-linear equations have been adopted between Nash Model parameters and catchment characteristics.

NK = a ( LLc/ S )b , K = C (L)d,

where, N & K are the average parameters of the Nash Model for each gauged catchment, L is the length of the main channel, Lc is the length from the outflow point to a point on the main stream, a,b,c and d are the unknown coefficients.

The unknown coefficients a,b,c, and d in the above equations are obtained using multiple-linear regression programme MULTI.FOR after transforming the above equations into the linear form through logarithmic transformation. Knowing the coefficients a,b,c and d the parameters of Nash Model for ungauged catchments can be obtained after solving the above two equations. The computer programme MULTI.FOR takes the values of NK as a dependent variable and (LLc/i-§ ) as an independent variable for first equation and the values of K as dependent variable and L as an independent variable for second equation. The programme gives the regression coefficients, the standard error of estimate, standard error of regression coefficients, correlation coefficients, t-statistics and F-statistic etc. as the output. The computer programme MULTI.FOR has been implemented and tested on VAX-11/780 system. Input and output specifications for the programme have been described. The programme could be run on other computer system, having FORTRAN compiler, after making suitable modifications in the programme.