A headwall is a retaining wall which is designed to support a structure such as a bridge or to provide retention for a culvert or drainage ditch. On bridges, headwalls can be found at the bridge abutment where the bridge meets the earth. Headwalls on culverts and other drainage projects are usually found around the outlet and similar structures may also provide support at the inlet.
Concrete is a classic choice of material for a headwall because it is strong, durable, and very sturdy. Some headwalls may be cast in place so that they conform with the landscape while other projects may utilize precast headwalls made in a standard shape and size. In either case, the headwall holds back soil, rock, and other materials so that they will not erode over time and compromise the integrity of the project the headwall is designed to support.
Masonry headwalls made from brick, rock, and similar materials are also an option. Before the widespread use of concrete, masonry had to be utilized for retaining walls, and some older structures have headwalls made from masonry for this reason. In other cases, people may think that masonry is more aesthetically pleasing and they can build a headwall from masonry or face a concrete headwall with masonry.
Without a headwall, the dirt and rock around the structure could wear away with time. In the case of a bridge, this could lead to a bridge failure which might be catastrophic in nature. For drainage projects such as culverts, the erosion of dirt and rock around the outlet could block the culvert, preventing it from draining properly. This could lead to flooding at the other end of the culvert which could contribute to the development of additional erosion problems.
Periodically headwalls may need to be repaired or replaced. They can crack or split as a result of seismic activity, for example. When a headwall requires replacement a retrofitting crew can assess the situation and determine the best course of action to take. Regular maintenance including keeping weeds free of the headwall, checking for cracks, and making sure that the headwall remains properly sealed is important as it will allow people to prevent problems and to identify issues at the start, when they will be much easier to address.
This term is also used in geology to refer to a specific part of a glacial formation. In this case, headwalls are high and steep cliffs.
