We are looking into taking down a conservatory and replacing with an extension but our property has a stream cutting across the back garden and underneath part of the bungalow. This continues under our road and beyond. I doubt we would be allowed to close it up / block off our section of the stream. Can anyone advise us as to how difficult / additional cost this would incur with laying foundations ? The road has no history of flooding and there are no visible signs of subsidence, leaks, cracks, damp etc.