Culverts, whether they are box culverts or pipe culverts, often require soil stabilization around the localized area of culvert placement, especially at the inlets and outlets. To stabilize soil conditions around culvert Inlets and Outlets gabion headwalls, wing walls, and scour aprons are often implemented.

Headwalls are designed to protect the slopes of an embankment against lateral scour as well as retain the embankment itself and to increase culvert efficiency by providing a flush inlet as opposed to a projecting one.  Gabion headwalls can be designed and constructed in a variety of configurations and typically include wing walls and scour aprons. The wing walls prevent scour, soil erosion, retain the embankment adjacent to the culvert, control grade elevations and direct water flow. The scour apron is placed at the base of the inlet our outlet and is designed specifically to prevent scour and erosion on the base.

Designing Gabion Headwalls and Wingwalls:

Terra Aqua offers multiple solutions for headwall and wing wall applications. Terra Aqua’s gravity wall systems and Stable Slope System are ideal for headwall and wing wall applications. The factors considered when choosing the appropriate solution for each application will be based on wall height, existing soil conditions, applied loads and other factors. The typical design parameters discussed in the gravity gabion wall, Stable Slope, and Earth Anchor Walls sections (in this web site) shall apply when designing gabion head walls and wing walls.

Designing Gabion Scour Aprons:

A scour apron is often required, on the base, at the inlets or outlets of culverts to inhibit scour, stabilize soil conditions, and reduce flow velocities to allow for a transition from culvert to native soil. Gabion and Reno mattresses are an ideal solution for scour apron applications and allow for a smooth consistent monolithic structure transition from Headwall to wingwall too scour apron. The gabion or reno mattress scour apron shall be designed according to the criteria presented in the Channel Lining Section of this web site. The table provided below offers a recommendation as to the appropriate thickness and length of the scour apron in relation to the flow velocity. An important consideration when designing the gabion or reno mattress scour apron is abrasion. If the outlet of the culvert is elevated above the gabion or reno mattress scour apron a concrete cap can be utilized to protect the gabion or reno mattress wire from abrasion extending the lifespan of the apron.   

Calculated outlet velocity Length of apron Thickness of apron
Less than 7 ft./second Gabion not required, based on existing soil conditions. Apron not required.
7 to 10 ft./second 9 ft. 9"-12"
10 to 15 ft./second 12 ft.-22 ft. 12"
Over 15 ft./second 22 ft.-34 ft. 18"