It sounds as if you are working with water waves in
a shallow tray. If your straight line waves impinge directly on a ridge
that is parallel to the wave, then they really shouldn't change
direction at all, because of the symmetry of the situation. If they
turned to the right, then you could make the same argument that they
should have turned left.
If the ridge is not infinite in
length, however, the edges of the waves will curve around the ends of
the ridge and fill in the space behind the ridge. This is a phenomenon
If the ridge is not parallel to the
wave crests, then the wave will change in direction because the speed
of the wave in the shallow water will be less than it is in deep water.
for a description of the speed of water waves in different depths. This
phenomenon is pretty much the same thing that happens to light when it
changes direction upon entry into a material in which light travels at
a different speed (refraction).
Both of these processes are described in detail with illustrations on this page
(republished on 08/01/06)