Read it through once

The levee is the crowning work of bank revetment, although not necessarily in immediate connection. It may be set back a short distance from the revetted bank; but it is, in effect, the requisite parapet. The flood river and the low river cannot be brought into register, and compelled to unite in the excavation of a single permanent channel, without a complete control of all the stages; and even the abnormal rise must be provided against, because this would endanger the levee, and once in force behind the works of revetment would tear them also away.