or nylon materials are generally placed by hand directly on the model bed, 

 injected into the model as a slurry from a tank through a hose equipped 

 with a flared nozzle, or injected as a slurry through a perforated trough. 

 If an injection of the plastic or nylon material at a uniform rate over 

 an extended period of time is necessary, an injection system consisting 

 of a material reservoir, a rotating distribution wheel, and an electric 

 drive motor with a variable-ratio gearbox is used. At the correct injec- 

 tion time, the mechanism is activated by a cam on the tide generator and 

 operated imtil the injection period has been completed. Gilsonite is 

 injected into the model as a slurry from a circular tank through perfo- 

 rated pipes. The tank is equipped with motor-operated mixing blades to 

 maintain a uniform consistency of the slurry. The slurry is introduced 

 by gravity or pumped flow from the tank into the perforated pipes during 

 the injection period. 



(11) Shoaling Recovery Apparatus . The plastic or nylon materials 

 are recovered with a flared nozzle connected by a hose to an aspirator and 

 discharged into a tub for decontamination, or with a jet pump connected to 

 a hydrocyclone for separation of the water and material. Gilsonite is re- 

 covered with either the aspirator apparatus or the jet pump; however, sepa- 

 ration by the hydrocyclone is not very effective. 



(12) Dye Injection Apparatus . A given weight of powdered fluo- 

 rescent dye is thoroughly mixed with a known volume of water and stored 

 in a tank. The tanks are equipped with a system of valves, tubes, and 

 rotameters to control the desired inflow ratio at the injection location. 



(13) Salinity and Dye Samplers . Water samples are withdrawn 

 from the model by suction, either orally by model tec?inicians or by a 

 vacuum pump. In the first method, the samples are obtained in a small 

 pipette (typically 25 cubic centimeters) by suction applied to a short 

 piece of tubing attached to the pipette. For obtaining simultaneous, 

 multidepth samples, a multidepth sampler which consists of a number of 

 single samplers designed to withdraw simultaneous samples at various 

 depths at one position is used. Multidepth samples can be withdrawn 

 either by suction applied orally or from a vacuum pump connected to a 

 central manifold, which in turn is connected to tubes running to each 

 sampling location. This latter device enables simultaneous sampling 

 at all desired depths at all sampling stations throughout the model. 

 Samples can also be withdrawn continuously (or intermittently) over 



a complete cycle to obtain an integrated sample. The sampling system 

 is similar to the multidepth sampler described above, except that the 

 sample container must be larger. 



(14) Saltwater-Freshwater Mixing Simulators . Occasionally, the 

 proper degree of mixing of saltwater and freshwater cannot be achieved 

 through the use of roughness elements or model boundary roughness. This 

 is particularly true for models of broad, shallow estuaries with small 

 tidal ranges where wind action is the primary mixing agent. The use of 

 a simulator is then necessary to achieve the proper degree of mixing. 



