REVIEW OF DESIGN ELEMENTS FOR BEACH-FILL EVALUATION 



by 

 R.D. Hobson 



I. INTRODUCTION 



Nourishment of eroding beaches and the building of beaches for storm 

 protection present important design problems to the coastal engineer. 

 Over 50 percent of recent Federal shore protection projects call for beach 

 fill and, in most cases, the fill material must be suitable for satisfying 

 recreational demands as well as for defense against storms. The major 

 expense of these projects is often in beach construction. 



Situations calling for beach fill are neither new nor unique and histor- 

 ically, the coastal engineer has used his experience and intuition to 

 select among the available fill materials. Intuition and experience cannot 

 be discounted and it is not that intention here but during the past 20 years 

 several "formalized" approaches to the beach-fill problem have been pub- 

 lished (e.g., Dean, 1974; James, 1974, 1975). This study summarizes these 

 approaches, explains their basic concepts, and shows, by example, their 

 use and interpretation. These formalized beach-fill schemes are, by 

 necessity, simplistic approaches to highly interactive systems in nature, 

 and it should be emphasized that the schemes are intended to serve the 

 engineer as additional tools rather than replacing existing tools. 



A general systematic approach to a beach-fill problem might be as 

 follows. An eroding beach requires nourishment, and to specify materials 

 appropriate to that system, it is assumed that information must be obtained 

 that characterizes the process-response relationships within the system; 

 i.e., the sediment textures and geometric features (responses) of the beach 

 reflect the waves and currents (processes) operative within that environ- 

 ment. Presumably, the study of one set of elements (process or response) 

 will reveal the characteristics of the other set. However, the beach 

 environment is highly complex and these process-response interactions are 

 not well understood. Therefore, beach-fill schemes are generally formu- 

 lated using a few response elements; namely, characteristics of the grain- 

 size distributions of sediments found on the beach. These grain-size 

 parameters are then used to compare beach sediments with available borrow 

 materials to assess their beach-fill potential. The major point to be 

 emphasized is that appropriate data must be obtained to characterize both 

 existing beach sediments {native composite grain-size distributions) and 

 potential borrow sediments {borrow composite) to effectively use any of 

 the existing design methods. 



This study reviews and summarizes the research in preparation and 

 published on the following subjects: (a) Analyzing and characterizing 

 sediments, (b) general aspects of sampling beaches and borrow sites, and 

 (c) the calculation and use of composite grain-size distributions (gsd) 

 within existing beach-fill schemes. The original referenced work should 

 be consulted for broad background information. 



