access to beaches and may result in 

 erosion of existing beaches. 



The ecological effects of a bulk- 

 head or seawall may be considerable. 

 Shorelines are often inherently unstable 

 and the structure of their biological 

 communities reflects this instability. 

 The erosion which bulkheads are de- 

 signed to halt is a natural process to 

 which the communities are adapted. 

 Halting the erosion will alter the natural 

 communities. Alternative structures, 

 such as revetments of riprap, will also 

 alter natural communities by providing a 

 different type of substrate. However, 

 riprap has several advantages over sea 

 walls. Erosion of areas on the borders 

 of the riprap may not be as severe as 

 with bulkheads or seawalls. The major 

 advantage of a vertical structure over a 

 properly installed revetment is the pro- 

 vision of mooring facilities or cosmetic 

 treatment of the shoreline. 



When the bulkheads or seawalls are 

 proposed in this coastal region, adequate 

 consideration must be given to a num- 

 ber of important factors. First of all, 

 given the existing littoral processes, 

 determine where erosion and accretion 

 will occur after installation of the struc- 

 ture. If erosion or accretion in an im- 

 portant habitat or navigable waters will 

 result, then one can anticipate additional 

 maintenance needs, such as beach nour- 

 ishment or dredging, or the construction 

 of additional structures. Secondly, bas- 

 ed on the expected physical impacts of 

 the structure, determine which aspects 

 of the biotic community will be affected 

 and the extent of the impact. For in- 

 stance, if an area containing the marsh 

 grass is to be bulkheaded and filled, 

 many biotic effects can be predicted - 

 such as reduction in the amount of pri- 

 mary productivity by marsh grasses 

 and, consequently, a reduced crop of 

 living and dead plant tissue for con- 

 sumption by other organisms. Valuable 

 spawning or rearing areas might also be 

 removed. Each situation is unique and 

 must be considered separately. 



CASE HISTORY - SMALL CRAFT HAR- 

 BORS IN COASTAL REGION 2 - 

 SOUTHERN CALIFORNIA 



A considerable amount of informa- 

 tion is available in literature on small 

 craft harbors in Coastal Region 2. Ben- 

 thic studies were conducted by Reish 

 (1961, 1962, 1963) from May 1956 to 

 April 1962, regarding the benthic fauna 

 and fouling communities in Alamitos Bay 

 Marina following construction. These 

 studies will be used as a base for a 

 case history of Alamitos Bay Marina. 



Alamitos Bay Marina is located in 

 Alamitos Bay in Long Beach, California. 

 The first marina basin was dredged 

 from land beginning in late 1955. The 

 basin was dredged to a depth of -12 ft 

 (-3.7 m) mean low water and had a sur- 

 face area of 12.5 acres (5 ha). In early 

 1956, after bulkheads had been con- 

 structed, the basin was filled with 

 water. Further dredging was conducted 

 in the central part of the basin. Boat 

 mooring began in early 1957. Reish 

 (1961) reported results of benthic sam- 

 pling from May 1956 to August 1959. 



The substrate of the first basin 

 was originally gray clay containing bits 

 of mica. In late 1957, black sulfide mud 

 was discovered at one of the sampling 

 stations. By summer of 1958, all sample 

 stations had a layer of black mud con- 

 taining a sulfide odor. This may be at- 

 tributed to poor circulation causing a 

 decreased oxygen supply. The number 

 of benthic specimens collected varied 

 quite noticeably during the first 2.5 yr 

 of study with an increase after the ba- 

 sin filled with water followed by a pre- 

 cipitous decline. The lack of water cir- 

 culation may have been the cause of the 

 decrease in population that occurred in 

 the spring of 1957. Low oxygen levels 

 were discovered above the basin floor. 

 Another possible cause of the benthos 

 reduction is pollution caused by the 

 boats in the basin. Benthic species com- 

 position within the basin was relatively 

 constant over the rest of the study pe- 

 riod and there was no indication of suc- 

 cession. Sixty percent of the species 

 and 87% of the specimens collected were 

 polychaetes (Reish 1961). 



In 1959, the dredging of three 

 more basins and the main channel be- 

 gan. Basins were dredged to -12 ft 



113 



