Ever subject to'i p rtant hanges in their regimen, as tiie re-
gions by which 1 y e f e 1 are cleared of tiieir forests and
Drought under cul a on o e entury sees them deep, flowing
with an equable cu en a d 1 able only to a gradual increase iu
rolume during the a a ns f f hets ; while the next finds their
beds a prey to sudden and great fresliets, which leave them, after
their violent passage, obstructed by ever shifting bars and elbows.
Besides these revolutions brought about in the course of j'ears,
every obstruction temporarily placed in the way of the current
every attempt to guard one point from its action by any artificial



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means, inevi:ablv pioduces some coiresponding change at another,
which can ssldom lie foreseen, and for which ihe rcmody applied
may prove but a new cause of harm. Thus, a bar remOTed fiom
one point is foiirid gradually to form lower down ; one bank pro-
tected from the current's force transfers its action to the opposite
one, on any increase of volume from freshets, widening the bed
and frequently giving a new direction to the channel. OwJng te
these ever varying causes of change, the best weighed plans of
river improvement sometimes result in complete failure.
741. In forming a plan for a river improvement, the principal
objects to be considered by the engmeer, are, Ist, The means to
be taken to protect the banks from the action of the current.
2(i, Those to prevent inundations of the surrounding country.
