new garden major drainage problem

We have just built a new house and need to now think about the garden. the site is about an acre and has an open drain running through it. (coming all the way down from fields behind )There is water collecting at the front of the garden fronting the road and has nowhere to drain to.It resembles a small river and is very swampy around it.I think we would have to open up the road and let it drain through to the other side.Its in a rural area with fields at other side of the road.Do the council allow you to do this after all they passed the planning on the site.The builders have already put a large pipe in for drainage where it runs past the house.(and filled it all in).