... slightly each year as a result of continuous land reclamation and drainage...
↑_ _ _ _ _ _↑ AS A RESULT OF => DUE TO, BECAUSE OF
AS A RESULT OF => anything that is due to something already done.
AS A RESULT OF + NOUN
Common Errors:
As a result of he was disobedient, his boss fired him.
X AS A RESULT OF cannot be followed by a verb!
As a result of his disobedience, his boss fired him.
V AS A RESULT OF must be followed by a noun!