A PRIMER OF BASIC CONCEPTS OF LAKESHORE PROCESSES 



by 

 David B. Duane, D. Lee Harris, Richard 0. Bruno, 

 and Edward B. Hands 



I. INTRODUCTION 



Waves and currents vary with, among other things, geography, water 

 level (stage of tide), season, and offshore slopes. The net effect of 

 wave and current forces impinging upon a shoreline is to change the 

 morphology of that coastline. Because these waves and currents act to 

 modify the present configuration of the coastline, they can collectively 

 be referred to as geologic agents, tjiowledge of the evolution of land- 

 forms (the response of the land to these forces) , and the rate and manner 

 of the modification of landforms are factors considered in coastal 

 engineering practice. 



In general, the model of sediment transport can be thought of as 

 movement of a sand grain from some source such as a headland, to a barrier 

 beach, to a dune, into an inlet or to an offshore sink. This process of 

 sediment transport has been active since the beginning of geologic time 

 and the record of such processes is preserved in the stratigraphic column. 

 This natural process becomes of concern to man when it interferes with or 

 affects what man wants to do. There is no complaint of coastal erosion 

 until structures are threatened with destruction. There is no complaint 

 of beach erosion until the sand beach a family enjoys is disappearing. 

 There is no harbor siltation problem until boats can not enter the harbor. 



Knowledge of the processes of erosion, transportation, and deposition 

 of sediment in the coastal zone is of value to the engineer and the 

 geologist. However, the time scale of interest in these processes 

 differs; the scale used by the coastal engineer is short (real time to a 

 few decades) while that of the marine geologist is longer (a few hundred 

 to a billion years). In both disciplines however, the knowledge satis- 

 fies an economic need, as well as an intellectual need. Problems, 

 analytical techniques, and ranges of precision differ because of the 

 differences in time scale. 



Design of engineering works in the coastal zone considers not only 

 the materials to be employed and the forces which they must withstand, 

 but also considers the modifications the works will introduce in the 

 natural processes operating on the coast and nearshore zone. The basic 

 concepts involve interactions of the atmosphere, hydrosphere, and 

 lithosphere such as: generation of water motion and directions of flow; 

 characteristics of the flow; water levels and their periodicity; bed form 

 generation and movement; and sediment entrainment and transport. A brief 

 discussion of these various concepts follows. 



