In some locations the Environment Agency and Highways Agency want any structures to blend in with the local surroundings. To accommodate this we cast in Stainless Steel Dovetail Slots to the face of the backwall and Wingwalls and then any stone or brickwork can be tied in.  If a Flap Valve or Penstock is to be fitted we box out the backwall to the thickness of the facing work so that the required seal between the Headwall and Flap Valve/Penstock can be achieved.