Headwalls are provided with gratings for one of two reasons, either to prevent persons or wildlife entering the culvert or to provide a barrier against debris entering the pipe/culvert and causing a blockage.  Three different configurations of standard grating are available and they can be manufactured in Mild Steel, fully welded and then galvanised or in Stainless Steel.  Where screens are included they need to be sized and designed to reduce the risks of blocking, make provision for adequate cleansing and maintenance, and be sized to permit the passage of fish and other fauna (for example bats) where appropriate.

Where used as a security screen the bar spacing must not exceed 150mm centres, where used as a debris/trash screen the bar spacing should not exceed 75mm centres.  Individual bars are 10 x 40mm Flat and the maximum bar length before bracing is necessary is 1.5m.  Any bracing is on the inside face of the screen for ease of raking.

The Cranked or Sloped Grating are the preferred type on inlets as when the water rises it pushes any debris up the grating rather than blocking it.  In both cases the screen where possible should be inclined close to  45 deg to the horizontal, however in circumstances where available space is limited, 60 deg should be considered as the maximum.  The horizontal section on the cranked grating, between the inclined face and the headwall allows additional flow capacity when the inclined section becomes blocked.  This also enables debris to be raked up over the screen during maintenance.  The maximum length of the sloped section should be no more than 2000mm, this allows the operative to rake it without having to overreach.  The horizontal section (platform) of the grating should have enough room for the operative to rake and store any debris from the sloped section if it cannot be accessed from above the headwall.  Therefore the depth of platform should be of similar dimensions to the rake reach required. Fencing on the platform can cause difficulties when raking debris so it is recommended that any fencing is removable.

Screens large enough to permit man entry should have an access panel secured with a heavy duty padlock.  A sliding bar with padlock may afford greater security than the use of chains.

Where you have a trash screen on an inlet you should always have a security screen on the outlet.  You can use a straight close coupled grating on the outlet as there should be no debris in the culvert itself due to the trash screen on the inlet.  Where you have a Flap Valve or Penstock on the outlet you will need to install either a sloped or cranked grating so the Flap Valve or Penstock can operate without restriction.

Bespoke gratings can be manufactured to suit customer requirements, please contact the Althon Sales Office for further details.