Downstream Control
Flow control facilities located at the downstream end of a conduit, when closed, subject the entire conduit to the full reservoir head and the possibility of high pressure leaks, piping along the conduit, and subsequent failure of the embankment. Special design considerations are necessary for dams with downstream control. A common recommendation is to house the conduit in a concrete-lined tunnel or to encase the conduit in concrete. Outlet facilities with downstream control should also have an emergency gate upstream of the conduit.
Considering Downstream Control? Considerations and Questions to Ask
Is there any chance of leakage through joints?
- Fusion welded HDPE, steel, and iron pipe provide adequate joints when pressurized.
- Bell and Spigot PVC pipe is generally not recommended because leakage is possible.
- Corrugated metal is not recommended because leakage at banding is highly probable.
Is the current upstream control subject to ice and operational damage?
- Downstream control is an option for problematic upstream control systems (For example, where ice damage is common). Center control should also be considered, noting that adding center control where it doesn’t already exist can involve significant excavation into the embankment. Downstream control can be added with minimal impact to embankment.
Is an alternate means to inspect the conduit available?
- Access for conduit inspection is limited. Providing an alternate way to access the conduit is important.
Energy Dissipation Structure Types
Cautions
Note: The content on this page was originally created as part of DamOutletWorks.org (DOWL, 2018). It has subsequently been updated and reformatted as part of the Dam Safety Toolbox.
Revision ID: 4731
Revision Date: 12/02/2022