height and direction. Immediately after a storm, waves begin to return 

 sediment to the eroded beach, either through the motion of bar-and-trough 

 (ridge-and-runnel) systems, or by berm building. The parameter F = 

 H^/(yft) , given by equation (4-29), determines whether the beach erodes or 

 accretes under given conditions. If F is above critical value between 1 

 and 2, the beach erodes. 



(4) The slope of the foreshore. There is a tendency for the foreshore to 

 become steeper as grain size increases, and to become flatter as mean wave 

 height increases. Data for this relation exhibit much scatter, and quan- 

 titative relationships are difficult to predict. 



c. Sediment Budget . Section VH,6 summarizes material on the sediment 

 budget. Table 4-16 tabulates the elements of the sediment budget and 

 indicates the importance of each element. Table 4-15 classifies the elements 

 of the sediment budget. 



A sediment budget carefully defines the littoral control volume, 

 identifies all elements transferring sediment to or from the littoral control 

 volume, ranks the elements by their magnitude, and provides an estimate of 

 unknown rates by the balancing of additions against losses (eq. 4-58). 



If prepared with sufficient data and experience, the budget permits an 

 estimate of how proposed improvements will affect neighboring segments of the 

 littoral zone. 



IX. TIDAL INLETS 



Some of the most important features of a sandy coastline from a standpoint 

 of littoral processes are those breaks in its continuity which may be broadly 

 classified as estuaries and inlets. 



An estuary may be the mouth of a large river; but it is usually char- 

 acterized by having a funnel shape and a wide opening to the sea (i.e., wide 

 in relation to the length of the tidal wave in shallow water) and by being 

 nonref lective to ocean long wave action (i.e., tidal waves can propagate up an 

 estuary) . 



An inlet, on the other hand, generally has banks that are roughly 

 parallel; it is usually small with respect to the interior basin and reflects 

 long wave activity (inlet currents originate hydraulically because of 

 hydraulic head difference between the ocean and bay, rather than due to tidal 

 wave propagation). 



This section will treat both of these shoreline continuity breaks under a 

 broader definition of "inlets" since the effects of both are generally similar 

 with respect to the littoral processes that occur in their vicinities. 



1. Geomorphology of Tidal Inlets . 



The bulge of sand formed just seaward of an inlet is called an ebb-tidal 

 delta. Commonly, the ebb-tidal delta is offset; i.e., the sand accumulation 

 protrudes farther seaward on the downdrift side than on the updrift side of 

 the inlet. In areas of low average wave activity ebb-tidal deltas can extend 



4-148 



