The wave climate and consequently the longshore transport rates at a site 

 can vary significantly from year to year. If data are available for other 

 time periods that represent extremes in transport climate, additional sediment 

 budgets should be constructed to provide further insight into the range of 

 conditions under which a weir-jetty system is expected to operate. 



The Beaufort Inlet example may be atypical since it describes an area 

 which has a net increase in sand accumulation. For example, the problem is 

 one of distributing excess sand in the overall system between updrift and 

 downdrift beaches. In other cases, allocating a sand deficit between updrift 

 and downdrift beaches at a reasonably stable condition appears to be necessary 

 for the successful performance of a weir jetty. Seasonal fluctuations in 

 transport conditions at a weir are discussed in Section VII which deals with 

 predicting the storage requirements of weir-jetty deposition basins. 



VII. UPDRIFT BEACH AND DEPOSITION BASIN STORAGE ANALYSIS 



In designing the updrift beach, an assessment must be made of the expected 

 equilibrium shoreline under various directions of wave attack, particularly if 

 seasonal reversals in transport are common at the site. At sites where rever- 

 sals are common, an optimum weir-jetty system will store sand in the updrift 

 beach to be transported by waves back up the beach, thus precluding erosion of 

 the updrift beach and the need for backpassing. This is considered "active" 

 storage (see Fig. 29). Sand will also be stored adjacent to the updrift jetty 

 where it is sheltered by the jetty and cannot be removed by normal wave 

 action. This sand, considered "dead" storage (Fig. 29) , accumulates after 

 construction of the jetty and once deposited tends to remain in place. The 

 amount of active storage needed in the updrift beach depends on the magnitude 

 and frequency of reversals in transport. If reversals are large in magnitude 

 and occur seasonally with long periods of transport in one direction followed 

 by long periods of transport in the other direction, the amount of active 

 storage required may be large. On the other hand, if reversals are frequent 

 with short periods of time between them, the amount of active storage required 

 will be small. 



Sondtight 

 "Dead" Storage' Vv\ Jetty Section £-;."Deod" Storage 



Figure 29. Sand storage on updrift and downdrift 

 beaches near a weir jetty. 



48 



