2 Background 



Regional Coastal Processes and Geomorphology 



In general terms, this section of the southeastern Lake Michigan shore is 

 characterized by eroding bluffs which consist of glacial deposits with some 

 instances of relict dune formations. A detailed summary of the morphology 

 and related references for this section of the Lake Michigan coast is pro- 

 vided by Parson and Smith (1995). The general coastal morphology of 

 Lake Michigan is described by Hands (1970). 



The lake bed also consists of glacial sediments (with isolated outcroppings 

 of shale bedrock) covered with a veneer of sand and gravel of variable thick- 

 ness. The sand and gravel cover represents a recent (i.e., in a geological time 

 perspective) lag deposit that has been derived from the erosion of the lake bed 

 and bluff in this region. Near the mouth of the SL Joseph River, the presence 

 of an incised vaUey results in a very thick cover of sand over the underlying 

 glacial sediment. However, along most of the coast, the glacial sediment is 

 probably within to 4 m of the lake bed surface. A discussion of the pro- 

 cesses of shoreline recession on such "cohesive shores" is presented later in 

 this chapter. 



The 120-year bluff recession rate, averaged for Berrien County, was about 

 0.6 m/year (Hands 1976). Short-term and local rates can be much higher, 

 particularly during periods of high lake levels. Downcutting of the lake bed 

 between 3 and 4 m has been reported by Foster et al. (1992) for the period 

 between 1945 and 1991 south of St. Joseph Harbor. The net alongshore sedi- 

 ment transport direction is from north to south. The harbor jetties act as par- 

 tial to fuU littoral transport barriers. 



Site Conditions and Beacli Nourishment History 



This investigation will focus on a 12-km section of shoreline extending 

 3 km north of, and 9 km south of, the harbor jetties at St. Joseph (refer to 

 Figure 1). Immediately north of the harbor entrance, the fiUet beach influences 

 the shoreline morphology for approximately 1 km. The remaining 2 km of 



Chapter 2 Background 



