It is imperative that groins extend 

 to the crest of the beach berm, or high 

 wave action will cause flanking (U.S. 

 Army Corps of Fngineers 1973b). If 

 the groin extends out from a seawall or 

 bulkhead, it should be solidly anchored 

 to that structure (Coen-Cagli 1932). 



Socioeconomic . The cost of groins 

 varies greatly, depending on construc- 

 tion materials, anticipated wave action, 

 tidal range, and whether additional 

 beach nourishment will be necessary 

 (U.S. Army Corps of Engineers 1971b). 

 A method of determining economic feasi- 

 bility of groin construction involves 

 comparison of construction and mainte- 

 nance costs with the cost of periodic 

 beach nourishment (Berg and Watts 

 1971). Prefabricated groins are often 

 economical to install. Timber groins and 

 low permeable structures are probably 

 the most economical for an individual 

 property owner (Horikawa and Sonu 

 1968, Pallet and Dobbie 1969), Cabion 

 groins (Figure 18) require extensive 

 maintenance. They are also unsightly 

 and vulnerable to damage by drifting 

 logs or other heavy debris. The aes- 

 thetic effects of groin placement should 

 not be neglected. A sandy beach is 

 more attractive than an eroded one. 

 However, the groins that protect it 

 should be as unobtrusive as possible 

 (Coastal Plains Center for Marine Devel- 

 opment Service 1973). Construction 

 activities should not interfere with re- 

 creational use of a beach. 



Biological . Very little information 

 is available concerning biological con- 

 straints on placement of groins. Carstea 

 et al. (1975a) recommended that restric- 

 tions be placed on the amount of sedi- 

 ment resuspended by construction activ- 

 ities. The effects of groin construction 

 and siting on wildlife propagation and 

 movement should be known and efforts 

 made to minimize adverse effects (Snow 

 1973). Construction should be planned 

 to avoid interference with fish spawning 

 areas or migratory routes (Persaud and 

 Wilkins 1976). Groins which capture all 

 littoral drift, thus encouraging or ag- 

 gravating downbeach erosion, should 

 not be constructed. Such erosion can 

 degrade aquatic resources. 



Construction Materials 



Groins can be built of almost any 

 material which will remain in place and 

 not deteriorate rapidly. Impermeable 

 groins are often constructed of sheet 

 piles supported by piles (U.S. Army 

 Corps of Engineers 1973b). The sheet 

 piles are wood, steel, or a combination. 

 Other materials for impermeable groins 

 include quarried stone, concrete, rub- 

 ble, and asphalt (Figure 19). Permeable 

 groins (Figure 20) are constructed of 

 similar materials, as well as of sand- 

 bags, sand-filled nylon tubes, wood, and 

 earth (Erchinger 1970). Stone groins 

 should have filter cloth under them to 

 prolong the life of the structure by de- 

 laying settling into the substrate. 



Expected Life Span 



Recorded life spans of groins vary 

 from 2 to 50 yr. Rubble or quarried 

 stone is reported as the longest lasting 

 construction material, followed by steel 

 (25 yr) , treated wood (20 yr), aluminum 

 (15 yr), and nylon bags (2 yr) (U.S. 

 Army Engineer District, Los Angeles 

 1974a, Chabreck 1968). All materials 

 vary in permanence, depending on salin- 

 ity, wave climate, and water tempera- 

 ture. 



Summary of Physical and Biological 

 Impacts 



Construction effects . Turbidity is 

 a major impact of groin construction 

 (U.S. Army Engineer District, St. Paul 

 1976b). Resuspension of toxic materials 

 can also occur, as can some noise, air, 

 and water pollution. Compared to jetties 

 and breakwaters, these physical effects 

 should be less because groins are rela- 

 tively small structures. 



Chron i c effects . Groins are intend- 

 ed to prevent erosion or to build the 

 beaches. However, in some cases they 

 contribute to erosion and to beach loss 

 elsewhere that is at least as serious as 

 what they were designed to prevent. A 

 number of cases have been reported where 

 downdrift beach erosion was aggravated. 

 An example of this is described by 

 Pallet and Dobbie (1969) where downdrift 

 cliff erosion was increased by the pre- 

 sence of a groin system. In spite of 

 this problem," groins serve their intend- 

 ed functions. Beaches are stabilized, 



38 



