302 



PATTERSON-SIMMONS. MODEL STUDIES 



[Ch. 17 



To illustrate the investigation of this type of problem by model analy- 

 sis, the study of Pryors Island Reach of the Ohio River has been se- 

 lected as an example. 



The low-water channel of Pryors Island Reach (Fig. 1) follows a 

 characteristic series of bends and crossings interrupted at points by 

 island or towhead formations. The maintenance of a 9-foot project 

 depth through this reach was seriously complicated by heavy shoaling 

 at three critical sections: from the head of Pryors Island to the foot 



Doe IsL 



Fig. 1. Location map, Pryors Island Reach model study. 



of Sisters Island; just above Stewarts Island; and at Old Maids Cross- 

 ing just above Dog Island. The purpose of the model study was to 

 develop plans for realignment and dike construction to make the 

 channel self-maintaining. 



The basic requirement of a model designed for such purposes is that 

 it reproduce accurately the bed-load movement of the prototype sys- 

 tem under similar hydraulic conditions. To achieve this end the bed 

 of the model is constructed of sand, crushed coal, haydite, or other 

 movable material, and hydraulic forces are adjusted until the model 

 will reproduce, within specific time intervals, the changes in bed con- 

 figuration that are known to have occurred in nature. 



The Pryors Island model reproduced a 15-mile length of river, as 

 shown by Fig. 1, to the linear scale ratios of 1:600 horizontally and 

 1 : 150 vertically. Banks and overbank areas were molded in concrete 

 to prototype configurations. The stream bed was of crushed coal, 

 molded to prototype contours by means of removable templets. Pro- 

 visions were made for reproducing any desired discharge hydrograph 



