situation usually results in more readily formed tombolos. Colonial Beach may 

 be an example of this process (Figure 13). 

 Local water level range 



33. Prediction of the exact effect of a large water level range on 

 shoreline response to detached breakwaters is extremely difficult. Generally 

 speaking, a range over 1.5m will tend to hinder permanent tombolo formation, 

 especially if the structure is significantly overtopped during high water, and 

 will certainly prevent the shoreline salient from attaining a smooth equilib- 

 rium shape. Winthrop Beach, with a tidal range of 2.7 m, is a good example of 

 large tide range effects on shoreline response (Figure 10). In this case, two 

 distinctive shoreline planforms developed, which were (a) a high-tide, low- 

 sinuosity salient, and (b) five individual, low-tide sinuous tombolos. On the 

 Great Lakes, variations in water level may cause seasonal or longer period 

 changes in the stable beach planform. Lakeview Park exhibits very distinctive 

 spring and fall shorelines which return each year (Figure 11), due, in part, 

 to the approximately 0.5-m seasonal variation in water level. Storm-induced 

 surges may cause significant, rapid changes in the beach planform which may 

 include the loss of beach material. 



Natural beach slope 



34. The natural slope of the preconstruction beach may be an important 

 consideration in selecting the appropriate distance offshore for the break- 

 water and in predicting its configuration. If the profile is gently sloping 

 and the structure is to be placed outside the surf zone, the breakwater may 

 have to be placed farther offshore and lengthened in order to be an effective 

 sediment trap. A difficult design problem is the combination of a gently 

 sloping beach and a large water level range. A large segment of the beach 

 profile may be active over the range of water level changes. Choosing an 

 optimum structure location under such conditions may be difficult. 

 Sediment supply 



35. The development of a stable beach planform is dependent on there 

 being sufficient sand to satisfy the equilibrium condition imposed by the 

 breakwater and local wave climate. If the required sediment is not available 

 from neighboring beaches (perhaps because of a reduced natural sediment supply 

 or the presence of groins, seawalls, or rock intrusions), the salient(s) may 

 develop very slowly, cause unacceptable levels of downdrift starvation, or may 

 never reach equilibrium. Winthrop Beach and East Harbor are examples of 



34 



