efficiency E s . The hydraulic efficiency, defined by Equation Al, is the 

 ratio of the average velocity in the sampler nozzle V t (in units of distance 

 per time) to the average velocity for the same flow condition at the same 

 vertical and horizontal location without the sampler V (in units of dis- 

 tance per time): 



E h = (Al) 



The trapping efficiency, defined by Equation A2 , is the ratio of the trap- 

 measured sediment transport rate q t (weight per width and time or equivalent 

 units) to the actual sediment transport rate for the same flow condition at 

 the same vertical and horizontal location without the sampler q (weight per 

 width and time or equivalent units): 



qt 



E s - (A2) 



q 



An ideal sampler has hydraulic and sediment -trapping efficiencies equal to 

 1.0, or 100 percent. Both field and laboratory tests are necessary to fully 

 evaluate the hydraulic and sediment- trapping efficiencies of a sampler for 

 various flow conditions and sediment characteristics. 



7 . Most suspended load samplers yield the suspended load transport rate 

 q ss (weight of sediment per unit time and width) from the product of the 

 concentration of sediment C (parts of sediment per parts of water) in a 

 water -sediment sample and the water discharge q (volume per unit time and 

 width) : 



q ss = C q (A3) 



For this relationship to accurately predict the suspended load transport rate, 

 sediment must be moving at the same velocity (speed and direction) as the 

 flow, and both C and q must be steady in time. A time -averaging procedure 

 could also be used as these quantities vary with time. Because material near 

 the bed travels more slowly than the flow speed, Equation A3 is not valid near 



A3 



