Biological impacts resulting from 

 the presence of a bulkhead include some 

 reduction in littoral zone productivity. 

 Foreshore habitat is likely to be elimi- 

 nated by construction of a bulkhead. 

 In rivers,bulkhead construction reduces 

 cover along the banks ( Bobersch midt et 

 al. 1976). Dredging may cause increases 

 in suspended solids, reduction in dis- 

 solved oxygen and increased concentra- 

 tion of hydrogen sulfide, and release of 

 pollutants which may be trapped in the 

 sediments (Morton 1976). These factors 

 can be detrimental to fish and other or- 

 ganisms in the vicinity of the dredging 

 operation. 



Bulkheading may protect certain 

 areas from erosion, at least temporarily. 

 Bulkheads may also provide mooring fac- 

 ilities. However, recreational activities 

 requiring unaltered habitat will be re- 

 stricted by bulkhead construction. 



Because bulkheads may result in 

 an increased energy environment and 

 erosion of adjacent beach areas, riprap 

 revetments may be preferred as an al- 

 ternative. If the bulkhead is needed, 

 riprap revetment may be placed in front 

 of the bulkhead to reduce scour and 

 biological damages. Exchange of subsur- 

 face water is facilitated through riprap; 

 wave energy is somewhat reduced be- 

 cause of its increased roughness. Both 

 revetments and bulkheads may limit ac- 

 cess to beaches. Groins and breakwa- 

 ters can also be considered as alterna- 

 tives to preserve a beach by altering 

 shoreline processes. 



CASE HISTORY - GROINS IN COASTAL 

 REGION 8 - GREAT LAKES 



The Michigan Demonstration Ero- 

 sion Control Program is involved in an 

 ongoing research program to test the 

 effectiveness of various shore protection 

 devices. The physical environment at 

 each test site is known; but, unfortu- 

 nately, no information is collected con- 

 cerning the biological environment. The 

 other sources of information concerned 

 with groins in the Great Lakes do not 

 include biological impact data either. 

 Biological effects must be inferred from 

 general information. 



Four Mile Park on the Lake Huron 

 shore in Sanilac County, Michigan, was 

 chosen as a test site for the six groin 

 types (Table 3). The bottom is clay 

 derived from the high clay bluffs along 

 the shore. Erosion has long been a 

 problem and homes have been destroyed 

 as the bluffs eroded (Brater et al. 

 1974). All six groins have had some 

 success in trapping sand at the base of 

 the bluffs (Figures 56 to 59); however, 

 the bluff is continuing to recede (Brat- 

 er et al. 1977). 



No information on construction im- 

 pacts was given. However, they can be 

 assumed to vary from mild turbidity and 

 beach disturbance for the sandbags to 

 somewhat more turbidity and beach dis- 

 turbance plus air and water pollution 

 for rock mastic structure. These were 

 constructed by pushing the rocks pre- 

 viously dumped on the beach into place 

 with bladed tractors and pouring hot 

 asphalt mastic over them (Brater et al. 

 1974). The effects of construction activ- 

 ities on the biota is not known. Since 

 the shoreline was actively eroding, with 

 little or no beach, any organisms pres- 

 ent should be adapted to a disturbed 

 environment. 



The success of the groins in trap- 

 ping sand resulted in a change from a 

 clay to a sand substrate. This may 

 have resulted in a change in species 

 composition of bottom dwelling organ- 

 isms. When a beach accumulates enough 

 sediment to prevent storm waves from 

 striking the bluffs and continuing the 

 erosion, loss of upland vegetation and 

 man-made structures along the bluff 

 should stop. 



128 



