Side-Channel Spillways

---

These types of control structures are suited for service and auxiliary spillways. Bathtub and side-channel control structures should be considered where there is limited space (insufficient space to accommodate a straight or curved ogee crest control structure) and there is adequate rock foundation. Also, these types of spillways are applicable to concrete, embankment, and composite dams, and they can be gated or ungated. These types of control structures have the potential for large discharge capacity and can be used with conveyance features including chutes, conduits, and tunnels. However, larger discharges than design levels can result in suppression and/or submergence of the crest and a reduction in the effective crest length. As the effective crest length is reduced, the spillway becomes less efficient (i.e., higher hydraulic heads may not significantly increase the discharge). Larger discharges could lead to downstream “throat” hydraulic control and adverse hydraulics, such as overtopping chute walls or pressurizing conduits or tunnels. A typical consideration is that a hydraulic jump occurs in the control structure before the flow enters the downstream conveyance feature (chute, conduit, or tunnel). This is done to establish a hydraulic control just downstream of the control structure, which facilitates the flow path down the conveyance feature (i.e., minimizes unstable flow in the conveyance features such as standing or cross waves). Examples of bathtub spillways include the service spillways at Reclamation’s Island Park Dam (embankment) and Fontenelle Dam (embankment). Examples of side-channel spillways include the service spillways at Reclamation’s Big Sandy Dam (embankment) and Paonia Dam (embankment).

Best Practices Resources

Design Standards No. 14: Appurtenant Structures for Dams (Ch. 3: General Spillway Design Considerations), USBR

Citations:

Revision ID: 7128
Revision Date: 07/11/2023