Measuring Water Surface Elevations (Stages) 



Water surface elevations should be measured for each cross-section at three 

 different flows. If cross-sections are established prior to runoff, then you 

 must return to the study area at least three more times, when runoff is 

 receding (high flow), near the end of runoff (intermediate flow) and during 

 late summer or early fall (low flow). 



It should be noted that it is unnecessary to collect surface elevation 

 measurements for all of the cross-sections within a study area at the same 

 flows. For example, if another cross-section is added to the study area at a 

 later date, the calibration flows for this new cross-section do not have to 

 match those for the remaining cross-sections. It is also unnecessary to have 

 the same number of calibration flows for all of the cross-sections within a 

 study area. 



Water surface elevations are measured at the water's edge directly opposite 

 the stake marking the cross-section on each bank. The stretching of a tape 

 across the cross-section is unnecesary, since the horizontal distances from 

 the headstake to the WEL and WER are not needed. Measure water surface 

 elevations to the nearest 0.01 ft. The mechanics of this measurement are 

 discussed in Bovee and Milhous (1978). Once water surface elevations are 

 calculated, repeat the measurements and check for surveying errors. If a 

 single bench mark is used, then water surface elevations should increase with 

 the upstream progression of cross-sections. 



As previously discussed, the WETP model assumes that the water surface 

 elevations at WEL and WER are always equal at a selected flow of interest. In 

 a stream channel, the surface elevations at the WEL and WER of a cross-section 

 should remain fairly equal as the flow varies, provided the elevations at WEL 

 and WER were matched when the cross-section was established. Consequently, it 

 is necessary to measure the water surface elevations at both WEL and WER 

 during all return trips to verify this assumption. These two measurements 

 should always be within approximately 0.1 ft of one another. For the larger 

 waterways, a greater difference is allowable. Average these two measurements 

 to obtain the water surface elevation that Is entered on the coding sheets. 



Measuring Stream Discharges 



The flow through the study area must be measured each time water surface 

 elevations are determined. On the larger waterways, it is best to locate 

 study areas near USCS gage stations to eliminate a discharge measurement. 



Use standard USGS methods when measuring discharges. Publications of Bovee 

 and Milhous (1978), Buchanan and Somers (1969), and Smoot and Novak (196R) 

 describe these methods and provide information on the maintenance of current 

 meters. Read these publications before attempting any discharge measurements. 

 Field training is also mandatory. 



5-4 



