DF.SCRTPTTON OF THE WETP PROGRAM 



The WKT1' program uses ? to 10 sets of stage (water surface elevation) 

 measurements taken .it different known discharges (flows) to establish a rating 

 curve. Tliis curve has the equation, = p(S - zf) n where: 



= discharge 



S = stage height 



zf = stage height at zero flow 



p = a constant 



n = a constant exponent. 



The relationship of measured points, if perfect, would plot as a straight line 

 on log - log paper with r equal to the slope of the line and p equal to the 

 discharge when (S - zf) 1. The actual line is determined by least squares 

 regression using the measured points. Once the stage-discharge rating curve 

 for each cross-section is determined, the stage at a flow of interest can be 

 predicted. This rating curve, when coupled with the cross-sectional profile, 

 is all that is needed to predict the wetted perimeter at most flows of 

 interest . 



The stage height at y.oro Flow (zf) may be taken as the lowest elevation on the 

 cross-sectional prolile for riffles but is more diffic.lt to determine for 

 non-ntflesi, particularly pools, in which case the procedures of Rantz (1982) 

 should be consulted. The applicable portions of that paper are included in 

 Appendix A. 



The zf value for a non-riffle cross-section can also be measured in the field 

 II is the highest elevation of the thalweg (as referenced to the bench mark 

 elevation) at the downstream control, which is typically the head of a riffle 

 The control is a channel feature which causes water to backup in an upstream 



di reel ion. 



The value of zf is controlled by use of an option record (OPTS) in the input 

 uata. M the option is set to one, zf is either set to a value supplied bv 

 the us,., or in the absence of a supplied value, zf is automatically set to 

 the lowest elevation in the cross-sectional profile. If the user does not want 

 zf to equal the lowest elevation in the cross-sectional profile, the values 

 t"< zf are entered on the XSEC records. The option record must be the first 

 entry in the data file and is illustrated in Appendices B and C. 



rhe option of setting zf to zero by setting the option record to zero is also 

 available. Prior to this program revision, all results were obtained with zf 

 automatically set to zero. Option zero is included solely for the purpose of 

 comparing results. Because the program now incorporates zf into the 

 calculations, the accuracy of the hydraulic predictions for those flows of 



3-1 



