• The length of the cross sections should include the entire active 

 floodplain width and should continue to an elevation on both ends 

 equivalent to at least the highest point in the material site or the 

 buffer, whichever is greater. 



• Cross sections should be aligned perpendicular to the direction of flow 

 during flood events. 



• The distances between and direction of the cross sections should also 

 be surveyed. 



The surveys should be performed using standard surveying techniques. A descrip- 

 tion of these techniques and the desired accuracy is given in Bovee and 

 Mi Ihous ( 1978) . 



Temporary Bench Marks: Temporary bench marks (TBMs) should be placed at 

 one end of each of the cross sections and one near the active channel where 

 the discharge measurements are taken (Figure B- I ) . The TBM elevations should 

 be tied into a common datum (often arbitrary datum at the upstream cross 

 section) as described in Bovee and Mi Ihous (1978). 



Stage and Discharge: The stage (water surface elevation) should be re- 

 corded at the time the discharge measurements are taken. Discharge measure- 

 ments should not be taken while the discharge is rapidly changing. Discharge 

 measurements should be taken at a cross section in a relatively uniform chan- 

 nel reach; that is, the water surface slope and bottom slope should be similar 

 and the depth, area, velocity, and discharge should not change significantly 

 through the reach. Discharge measurements are taken by measuring the total 

 depth and the velocity at specified depths at 25 to 30 stations across the 

 ctiannel. The station (distance from a TBM) should also be recorded. Velocity 

 measurements should be taken at the following recommended depths below the 

 water surface relative to the total depth (d): 



- 0.2d, 0.6d, and 0.8d is most preferred 



no 



