Lake Michigan water levels are also discussed by Parson, Morang, and Nairn 

 (1996). 



Shoreline Recession 



An investigation of long-term shoreline recession rates north and south of 

 the hartx)r jetties at St. Joseph was completed by the Land and Water Manage- 

 ment Division, Michigan Department of Natural Resources (MDNR). The 

 original study was completed in August 1978 to document change in shoreline 

 location over a 40-year period. With the addition of a series of April 1989 

 aerial photographs, the original study was updated to describe 51 years of 

 shoreline change. The length of the comparison masks the influence of such 

 factors as fluctuating water levels, storms, shore protection structures, and 

 other natural and human disturbances. Recession data for St. Joseph are sum- 

 marized in Figure 4. 



From the harbor jetties northward, the shoreline was accretional for 2.5 km, 

 with an average annual accretion rate of 0.96 m/year (see Figure 4). North of 

 the accretional zone, the remaining 13 km of shoreline assessed by the MDNR 

 had an average annual recession rate of 0.76 m/year. South of the harbor 

 jetties, only the first 0.8 km of the shoreline (corresponding to the zone of 

 influence from the fillet beach) had a long-term depositional trend, wliile the 

 remaining 13 km of shore has been eroding at varying rates. 



From the feeder beach at St. Joseph to the southern limits of the MDOT 

 Revetment, the shoreline recession rates range from 0.36 m/year to 1.16 m/ 

 year. There are two possible explanations for erosion along the protected 

 shore south of the harbor jetties: (a) the revetment was not present for the 

 entire period of the air photo comparison, and/or (b) the revetment was con- 

 structed at the base of the bluff and the beach in front of the revetment has 

 since eroded. When the results from the original investigation (August 1978) 

 are compared to the second assessment (April 1989), in general, the annual 

 rates of recession have decreased for the Railway and MDOT Revetment sec- 

 tions. This suggests that the shoreline recession rate has been reduced or 

 eliminated locally with the construction of the revetment. 



At Shoreham, where the shoreline is only partially protected, long-term 

 recession rates are higher than to the north, ranging from 0.88 to 1.83 m/year. 

 For the remaining 7 km of shoreline south of Shoreham, the average annual 

 recession rate was 0.69 m/year. 



14 



Chapter 3 Existing Data Sources 



