104 



1987). Graf (1984), Middleton and Southard (1984), and Vanoni (1975) 

 review general concepts of sediment transport and fluid-particle interactions in 

 rivers, and 15 excellent papers on hydraulic processes and primary sedi- 

 mentary structures are reprinted in Middleton (1977). Deltaic and estuarine 

 sedimentation and structures are reviewed in Boggs (1987), Nichols and Biggs 

 (1985), and Wright (1985). 



River discharge data are available for many coastal rivers. A cursory 

 examination of the annual hydrograph will reveal the seasonal extremes. 

 Because of the episodic nature of coastal flooding, annual disharge figures 

 may be misleading. A useful parameter to estimate river influence on the 

 coast is the hydrographic ratio (H R ), which compares tidal prism volume with 

 fluvial discharge volume (Peterson et al. 1984). 



Oceanic currents 



Major oceanic currents intrude onto some continental shelves with enough 

 bottom velocity to transport sandy sediments. The currents operate most 

 effectively on the outer shelf, where they may transport significant volumes of 

 fine-grained sediments but presumably contribute little if any new sediment 

 (Boggs 1987). Along most coastlines, ocean currents have little direct effect 

 on shoreline sedimentation or erosion. Even off southeast Florida, where the 

 continental shelf is narrow, the western edge of the Gulf Stream flows at least 

 1/2 km offshore. However, in some locations where currents approach the 

 coastal zone, sediment discharged from rivers is transported and dispersed 

 along the adjacent coastline. This process may arrest the seaward prograda- 

 tion of the delta front while causing extensive accumulations of riverine- 

 derived elastics downdrift of the river mouth (Wright 1985). The most 

 prominent example of this phenomenon is the Amazon River mouth, where 

 the Guiana current carries Amazon sediments hundreds of kilometres to the 

 northwest (Wright 1985). The same current also disperses sediment from the 

 Rio Orinoco. 



In shallow carbonate environments, reefs thrive where currents supply 

 clean, fresh ocean water. Reefs stabilize the bottom, provide habitat for 

 marine life, produce carbonate sediments, and sometimes protect the adjoining 

 shore from direct wave attack (i.e, the Great Barrier Reef of Australia). In 

 the United States, live reefs are found in the Gulf of Mexico off Texas and 

 west Florida and in the Atlantic off Florida. Coral islands are found in the 

 Pacific in the United States Trust Territories. For geologic or engineering 

 studies in these environments, there may be occasional need to monitor 

 currents. Procedures of deep water current measurement are presented in 

 Appell and Curtin (1990) and McCullough (1980). 



In summary, the effect of tide or wave-induced currents is likely to be 

 much more important to most coastal processes than ocean currents. 

 Measurement of ocean currents may occasionally be necessary for geologic 

 studies in deltaic or carbonate environments. 



Chapter 5 Analysis and Interpretation of Coastal Data 



