also change to maintain continuity of flow. Generally speaking, if a channel 

 is widened, it often satisfies continuity by becoming shallower. Similarly, 

 if a channel slope, or gradient, is increased, thus increasing velocity, 

 continuity is commonly satisfied by a reduction in depth. Exponent values 

 for selected study sites and other rivers are given in Table 6. The ex- 

 ponents exhibit a wide range of variability for different rivers; Rundquist 

 (1975) found that the exponents and the coefficients can be expressed as 

 functions of the bank-full discharge. The coefficient c and exponent f in 

 the power relation for hydraulic depth were found in addition to be a func- 

 tion of the median bed material size. The exponents in the power relations 

 may change at a given site for discharges above bank-full because of the 

 typically abrupt change in bank slope at bank-full conditions. 



The slope of the water surface profile for a typical river generally 

 will parallel the bed slope at low f low, often producing a -sequence of r i f- 

 fles and pools. At flood flows, the pool-riffle sequence is not apparent 

 in the water surface profile (Figure 31). 



Flood Flow Water Surface Profile 



Low Flow Water Surface Profile 



m^^^}}^= 



Bed Profile 



Figure 31. Schematic diagram showing change in water surface slope in 

 response to a change in water discharge. 



Naturally occurring flow obstructions in rivers can include vegetation, 

 rock or snow avalanches, aufeis, and boulders. The effect of an obstruction 

 on the hydraulics is to cause a local increase in velocity which often 



105 



