Utilizing StormTech Chambers for Stream Crossings technical note provides various design guidance with a chamber dimension figure for reference.

StormTech chambers offer the distinct advantage and versatility that allow them to be designed as open bottom stream crossings for low flow applications.

The design engineer can design the appropriate scour prevention measures or determine if an open bottom stream crossing is a viable option for the specific project. Culvert design software can be used to determine flow, velocity and flow depth inside the chamber.

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. The technical note goes in depth on each of these design considerations.

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.

Figure 2 shows four possible foundation/footing designs.

Figure 3 shows the anchor bolt placement in footings. Figure 4 shows contraction scour. Permissible shear velocities table is provided with material, clear water and water transporting colloidal silts sub headings.

References, formulas, sample designs, appendix are at the end of this technical note.