This technical note introduces the StormTech chambers advantage and versatility that allow them to be designed as open bottom stream crossings for low flow applications. Open bottom culverts using chambers are best suited for natural stream beds in low velocity water ways that support local wildlife crossings.

StormTech chambers come in 5 sizes with outside widths ranging from 25” to 100” with corresponding open spans of 15 to 85 inches, allowing the design engineer a wide variety of choices for their project.

There are four basic design considerations: structural design and cover depth, design of footings or foundation, design of clear opening and alignment and design of scour prevention. Supporting figures, equations and appendix are included.

StormTech chambers require stone above and on the sides of the chambers. When footings are used under the feet of the chamber, it is important that the footing width extend beyond the chamber feet at least the width of the normally specified perimeter stone column which is 12” for all chambers. Since the structural performance of the chamber is dependent upon stiffer materials surrounding the chamber relative to the flexible chamber, it is important to establish a proper load path to the stiff footing.

StormTech chambers require a stable foundation to support the feet of the chamber and to spread load to the subgrade soils. When chambers are used for stormwater storage applications, the foundation consists of compacted, crushed stone and the required depth of foundation stone is dependent upon cover height and bearing capacity of the underlying soils. For open bottom culvert applications, typical foundation stone might be erodible or in other cases, a natural stream bottom may be required. Therefore, the foundations for chambers in open bottom culvert applications are often special footing designs. The footing design should ensure a non-erodible base and should distribute the load from the feet of the chamber and the surrounding stone columns to the underlying soils based on the bearing capacity of the underlying soils.

Design for clear rise, span and corresponding openings for each StormTech chamber are provided in this document. These values are representative of the bare chamber or chamber based on a flat foundation. By placing the feet of the chambers on footings

nearly the entire inside width of the chambers can be left as an open bottom crossing.