If the erosion has been caused by the landward movement of waves and general landward migration of the front beach and wet beach area, the fixed position of the back beach will result in a narrowing of the useable beach.
(the erosion; has been caused; by the landward movement of waves and general landward migration of the front beach and wet beach area) (the fixed position of the back beach; will result; in a narrowing of the useable beach)
the erosion the fixed position of the back beach
has been caused will result
by the landward movement of waves and general landward migration of the front beach and wet beach area
in a narrowing of the useable beach