3. Width of the Responding Profile, X . 



The width of the responding profile refers to the horizontal distance 

 between the landwardmost point of profile adjustment and the offshore closure 

 depth. The width along many shore-normal profiles in the region of interest 

 should be measured and averaged to obtain a representative value (Fig. 1). 



4. Overfill Ratio, R^. 



The percent of eroded material by volume to be carried as suspended load 

 beyond the closure depth should be estimated; additional erosion must compen- 

 sate for the loss from the active profile. Hobson (1977) explains how to 

 compute R^, based on textural parameters of "native beach" and "borrow" 

 materials. The same procedures can be applied here except that the parameters 

 for the borrow materials must be based on a composite sample of the eroding 

 section of shore; i.e. , the upper beach, in the case of an increase in lake 

 level, because this is the zone which supplies sediment to rebuild the profile 

 (Fig. 1). If lake levels decline, then erosion below the lever point supplies 

 material to prograde the upper part of the profile (Fig. 1). In this case, 

 the lower profile (between lever and closure points) corresponds to the 

 "borrow area." In either case "native" characteristics must be based on a 

 composite sample of the entire responding profile, from the upper limit of 

 profile adjustment to the point of profile closure. The lever point is useful 

 in describing the sediment balance concept. In practice it is an ill-defined 

 transition zone separating areas of predominant • erosion and deposition. For 

 long-term adjustments this transition may occur in the vicinity of the outer 

 bar, but its exact location is not critical for the application of present 

 procedures. 



If adequate data for calculating R^ are not available and the lake level 

 is rising, R. can be assigned a value of 1, provided that (a) there is less 

 silt and clay in the beach and backshore than there is offshore, and (b) the 

 mean grain size across the beach and backshore is greater than the mean size 

 offshore. A value of Ra = 1 indicates that all eroded material is expected to 

 remain in the zone of profile adjustment; if only P percent remains, then 

 R^ = 100/P. 



IV. EXAMPLE PROBLEMS 



The following problems are evaluated on the basis of limited available 

 survey data. They provide examples of the basic steps in applying the pro- 

 posed method of profile prediction. If these predictions were intended to 

 support actual design or management decisions, a more careful evaluation of 

 field conditions would be required. 



*************** EXAI4PLE PROBLEM 1*************** 



GIVEN : A contemplated change in the regulation plan controlling the water 

 supply to Lake Ontario would raise the long-term surface elevation 0.3 



FIND : The effect the higher stages would have at the eastern end of Lake 

 Ontario. 



