Stone absorber has been installed adjacent to the existing Port Huron Harbor 

 breakwater and, in addition, was used for some of the proposed improvement 

 plans. Based on past experience, 1 :60-scale model structures should not create 

 sufficient scale effects to warrant geometric distortion of stone sizes in order to 

 ensure proper transmission and reflection of wave energy. Therefore, rock-size 

 selection was based on linear scale relations and an assumed specific weight of 

 2,643 kgcm (165 pcf) for the prototype rock. 



Ideally, a quantitative, three-dimensional, movable-bed model investigation 

 would best determine the impacts of breakwater modifications with regard to 

 sediment deposition in the vicinity of the harbor. However, this type of model 

 investigation is difficult and expensive to conduct, and each area in which such an 

 investigation is contemplated must be carefully analyzed. In view of the com- 

 plexities involved in conducting movable-bed model studies and because of 

 limited funds and time for the Port Huron Harbor project, the model was molded 

 in cement mortar (fixed-bed), and a tracer material was obtained to qualitatively 

 determine sediment patterns and subsequent deposits in the harbor vicinity. 



Model and appurtenances 



The model was constructed of concrete mortar and reproduced the extreme 

 southern portion of Lake Huron and the entrance to the St. Clair River. Approxi- 

 mately 1.1 km (0.7 miles) of the United States shoreline was reproduced on the 

 west, which included Port Huron Harbor, as well as about 0.8 km (0.5 miles) of 

 the Canadian shoreline on the east. Detailed bathymetry was reproduced in 

 Lake Huron with a sloping transition to the wave generator pit elevation of -23 m 

 (-75 ft). The total area reproduced in the model was approximately 965 sq m 

 (10,400 sq ft), representing about 3.4 sq km (1.3 square miles) in the prototype. 

 Vertical control for model construction was based on low water datum (Iwd), and 

 horizontal control was referenced to a local prototype grid system. A general view 

 of the model is shown in Figure 16. 



Model waves were reproduced by an 18.3-m-long (60-ft-long), electro- 

 hydraulic, unidirectional spectral wave generator wdth a trapezoidal-shaped, 

 vertical motion plunger. The wave generator utilized a hydraulic power supply. 

 The vertical motion of the plunger was controlled by a computer-generated 

 command signal, and movement of the plunger caused a displacement of water 

 that generated the required experimental waves. The wave generator also was 

 mounted on retractable casters, which enabled it to be positioned to generate 

 waves from the required directions. 



An Automated Data Acquisition and Control System, designed and con- 

 structed at WES (Figure 17), was used to generate and transmit wave-generator 

 control signals, monitor wave-generator feedback, and secure and analyze wave 

 data at selected locations in the model. Through the use of a microvax computer, 

 the electrical output of parallel-wire, capacitance-type wave gauges, which varied 

 with the change in water-surface elevation with respect to time, were recorded on 

 magnetic disks. These data then were analyzed to obtain the parametric wave 

 data. 



32 Chapter 6 Physical Model 



