MIDSCALE PHYSICAL MODEL VALIDATION FOR SCOUR 

 AT COASTAL STRUCTURES 



PART I: INTRODUCTION 



1. Scouring of noncohesive sediments in the coastal region has been a problem for engineers since the 

 first coastal improvements were undertaken in ancient times. Modern coastal engineering recognizes the 

 seriousness of scour at coastal structures, and measures are taken to reduce the scour potential, based 

 largely on previous remedies that have shown some degree of success. There remains, however, a large gap 

 between present knowledge of scour and the knowledge necessary to develop engineering tools for the 

 prediction of scour evolution under specified environmental conditions. This gap in knowledge is not due to 

 failure to recognize the benefits to be gained by understanding the causes of scour and developing the 

 means for preventing it. On the contrary, much research has been directed at various aspects of the scour 

 problem (Powell 1987). However, researchers are faced with the problem of understanding the immense 

 complexity of the scouring mechanisms, such as waves and currents interacting with structures and 

 resulting turbulent water motions suspending and transporting sediment away from the toe of the 

 structure. Developing mathematical representations for this complex interaction is a formidable task 

 indeed, and only limited progress has been made in this area. 



Physical Models 



2. Physical models constructed and operated at reduced scale offer an alternative for examining coastal 

 phenomena that are presently beyond analytical skills. Dalrymple (1985) points out two distinct 

 advantages gained by using physical models to replicate nearshore processes: (a) the physical model 

 integrates the appropriate equations (unknown to mortals) governing the processes without simplifying 

 assumptions that have to be made for analytical or numerical models, and (b) the small size of the model 

 permits easier data collection throughout the regime, whereas field data collection is much more expensive 

 and difficult, and simultaneous field measurements are hard to achieve (Gourlay 1980). A third advantage 

 of physical models is the degree of experimental control that allows simulation of varied environmental 

 conditions at the convenience of the researcher. 



3. Of course there are also disadvantages to using physical models, most notably: 



