Yeah fair points but I thought quite a lot about it when I was doing it (no designers, was just left to do what I saw fit

) The left hand side is lower anyway and although hard to make out is pretty much bedrock all the way under the bridge on that side. The right hand side which I rock faced is still the original line and height so don't think I've actually altered the flow too drastically if at all. My idea was that if in spate it floods over to the left well then it will actually be aligned better to go under the bridge rather than hitting the undermined abutment as it had been
Will definitely go up there in winter when it's in spate and see how it's fairing.
I did mention on the quote that the bridge was badly sited as it sits right on the dog leg of the river.