Measuring Cross-sectional Profiles 



The channel profile has to be determined for each cross-section. Unlike the 

 measuroinent of water surface elevations, this has to be done only once. It is 

 best to measure profiles at the lowest calibration flow when _ wading is 

 easiest. For the unwadable, larger waterways that require the use of a boat, 

 profiles are best measured at an intermediate calibration flow. 



For wadable streams, a measuring tape is stretched across the cross-section 

 with the zero point set on top of the headstake. Setting the headstake at 

 zero, while not mandatory, is a good practice that provides consistency in 

 your field technique. Never attach the tape directly to the headstake. The 

 tape is attached with a vise grip to a stake that is driven behind the 

 headstake. A vise grip can be attached directly to the stake on the opposite 

 bank to stretch and hold the tape in place. 



Elevations are now measured betweeen the headstake and water's edge using the 

 level rod. Elevations are measured at major breaks in the contour. The 

 horizonatal distance of each elevation measurement from the headstake (zero 

 point) is also recorded. Elevations are also measured between the water's 

 edge at the opposite bank and the opposite stake and the horizontal distance 

 from the headstake recorded for each measurement. Elevations of the exposed 

 portions of instream rocks and boulders are also measured in this manner. 

 Measure elevations to the nearest 0.01 ft and horizontal distances to the 

 nearest 0.1 ft. 



Be sure to collect profile measurements for points well above the water's 

 edge. It is a good practice, although not mandatory, to begin at the 

 headstake (0.0 distance) and end at the stake on the opposite bank. Remember, 

 the highest elevations on both banks of the cross-sectional profile must be 

 substantially higher than the stage at the highest calibration flow, if 

 predictions are to be made for flows of interest that exceed the highest 

 calibration flow. 



For the segment of the cross-section containing water, a different approach 

 involving the measurement of water depth is used. Water depth is measured 

 using a current meter rod or a rod fitted with a porcelain, enameled, iron 

 Rage. Do not use your level rod. Measure depths at all major breaks in the 

 bottom contour. Generally, 10-30 depth measurements are needed for streams 

 and creeks. Measure depths to the nearest 0.05 ft (current meter rod) or 0.01 

 it (rod fitted with gage). For each depth measurement, record the horizontal 

 distance from the headstake (zero point). The bottom elevation at each 

 distance from the headstake is determined by subtracting the water depth from 

 the water surface elevation (average for WEL and WER) . For example, if the 

 average water surface elevation is 9.26 ft and at 10.2 ft from the headstake 

 the water depth is 0.90 ft, then the bottom elevation at this distance is 8.36 

 ft (9.26 ft minus 0.90 ft). The elevations for all points covered by water 

 are calculated in this manner. 



5-5 



