90 



ANALYSIS OF FLOW PROBLEMS 



If the slope is steep, a hydraulic jump may form, followed by an Si 

 curve. For this curve to form as shown, the channel must extend out 

 past the end of the hydraulic jump, and the side walls must be high 

 enough to prevent water from flowing into the channel from the sur- 

 rounding pool. If the depth of flow is at the critical, flow at the outlet 

 is as shown for the critical slope, in Fig. 802, provided that the channel 

 extends far enough out into the pool to insure that velocities at the 

 end have been reduced enough to prevent any large-scale disturbance. 



Fig. 802. Long Uniform Channel with Lower End Submerged in Reservoir or Lake. 



Flow on the steep slope and on the critical slope in Fig. 802 is shown 

 as uniform flow at the normal depth. The results will be nearly the 

 same if there is a backwater curve on the slope which converges toward 

 the normal depth as it approaches the pool level. Since the flow is at 

 or below the critical depth, the discharge and flow down the slope are 

 determined entirely by upstream conditions, and are not affected by the 

 level of the water in the pool. 



The pool level does affect the curve upstream if the channel has a mild 

 slope. Two possibilities may be distinguished, as shown in Fig. 802. 

 If the water level in the pool is higher than the level of the normal 

 depth at the end of the channel, an Ml curve will form; if lower, an 

 M2 curve will form. Under either circumstance the pool elevation 

 affects the profile for some distance upstream, and thus may affect the 



