Channel thalweg position in Corson Inlet fluctuated between 1949 and 1974 

 with a general trend of moving from the south to the north side of the inlet. 

 Thus, as the inlet widened and migrated south, the thalweg lagged behind the 

 migration rate and changed its relative position to the north side of the 

 throat . 



Shifts in channel orientation at Corson Inlet were apparently gradual 

 (Fig. 59). The inlet changed direction from north to south between 1949 and 

 1960, then progressively began to shift to a more southerly direction. The 

 channel length (Fig. 60) is directly related to orientation. The channel is 

 shortest when oriented toward its northern extreme. When oriented toward the 

 south the channel length seaward of the throat may be 25 percent greater than 

 when oriented 50° farther north. The period of change in orientation and 

 channel length appears to be less than the period of inlet migration or per- 

 haps out of phase with the cycle of inlet migration to the south and with inlet 

 widening. 



b. Townsend Inlet . Historically, Townsend Inlet has migrated south at a 

 rate of 9 feet per year (periods 1842-1955 and 1949-74). For the past 25 years 

 the south shore of Townsend Inlet has been stabilized by groins and a bulkhead. 

 The southerly migration has thus been at the expense of inlet width which has 

 decreased at a near constant rate of 16 feet per year. The channel has remained 

 near or slightly south of the center of the inlet during the southerly migration. 

 There was no significant change in channel orientation from 1949 to 1974. 



c. Beaches Adjacent to Inlets . Inlet shoaling may result in erosion of 

 downdrift beaches; i.e., the inlet may be removing sand from the longshore 

 transport system. The removal or release from the inlets may be gradual or 

 abrupt. Although knowledge of the trapping and release mechanisms of inlets is 

 limited, it is known that inlets act as a type of filter for material moving 

 parallel to shore. Their removal and release period has a significant effect 

 on the stability of downdrift beach and groin systems. 



The changes in the plan area of visible bars (Fig. 61) and the change in 

 shoreline position near the inlets are the only evidence available concerning 

 volume changes in the inlet systems. Trends are not obvious in Figure 61. Note, 

 however, that the plan area of the shallow ebb tidal bars can vary by as much as 

 a factor of 8. The data in this report indicate no relationship between inlet 

 migration, inlet widening, or channel behavior, and the volume of sand stored in 

 ebb tidal shoals. 



Inlet movements frequently cause a loss of sediment from one side of the 

 inlet and a gain on the other side. Based on a simple regression analysis of 

 Figure 62, the shore north of Corson Inlet gained land area at the rate of 0.006 

 square mile per year (R = 0.90, where R = correlation coefficient) during the 

 1949-74 period. The shore south of the inlet, i.e., the Strathmere shore, lost 

 land area at a rate of 0.007 square mile per year (R = -0.81). The combined 

 north and south shore changes, also shown in Figure 62, varied widely with a 

 25-year average loss of -0.00086 square mile per year (R = -0.15). Assuming a 

 mean sand volume of 0.13 cubic yards above MSL per square foot of beach (Fig. 

 70) , the average yearly sand volume gain to beaches north of Corson Inlet was 

 22,300 cubic yards and the average yearly loss was 26,000 cubic yards. The 

 average yearly loss of sand from the inlet beaches was therefore 3,700 cubic 

 yards . 



88 



