equal to the intake velocity. Reduction of the bias of the 

 flow either into or away from the sampler assures that a 

 representative sample can be collected. Point -integrating 

 samplers are held at a specified depth for a period of 

 time, thereby collecting a time- integrated sample. These 

 samplers can be lowered to the design depth and then 

 activated to begin sampling. Depth- integrating samplers 

 are lowered from the surface to the bed and returned at a 

 constant rate. The collected sample represents an average 

 concentration for the river depth. An example of a point - 

 integrating sampler is the Anderson- Einstein sampler shown 

 in Figure A5. The Anderson- Einstein sampler consists of a 

 pint milk bottle with water intake and air-exhaust tubes to 

 facilitate sampling. A point- integrating sampler that 

 measures the quantity of sediment entering the apparatus 

 rather than the sediment concentration is the Delft bottle 

 (Jarocki 1963, as referenced in Graf 1984). This sampler 

 consists of an entrance pipe, 0.022 m in diameter, that 

 expands to 0.31 mm in diameter; in the rear is a cover 

 plate with holes. As the water -sediment mixture enters the 

 sampler, the expanding pipe causes the mixture velocity to 

 decrease, and the sediment is expected to settle out in the 

 inner chamber while the fluid exits through the rear holes. 

 This sampler is illustrated in Figure A6 . 



(2) Pumping Sampler 



Pumping samplers pump a water -sediment mixture at a par- 

 ticular point through a pipe or hose. In principle, the 

 intake velocity can be adjusted to be equal to the fluid 

 velocity, and a representative sample of any volume can be 

 obtained. However, adjustment of the pump velocity to 

 equal the fluid velocity is very difficult. An average 

 concentration for a particular depth can be measured by 

 collecting a sample over a period of time. Several coastal 

 studies that have used pumping samplers are discussed in 

 the "Coastal Suspended Sediment Apparatus" section. 

 Disadvantages of pumping samplers include: the pumping 

 rate must be continually regulated as the flow velocity 

 varies; large suspended sediment particles tend to settle 

 in the pipe, necessitating higher pumping velocities; the 

 depths at which the sampler can be used are limited by 

 resistance of the hose/pipe to fluid currents and by vacuum 

 capability of the pump; and the bulkiness of the sampler 

 limits portability. 



c. Indirect-measuring (or continually recording) samplers. 



These samplers measure some phenomena occurring as a result of 

 sediment transport. Three types of such devices have been 

 identified by Graf (1984) and are described below. 



A9 



