Sep 1, 2011

What is a Rubber Dam?

A rubber dam is a rubber membrane filled with water or air, attached to the concrete sill. In the upright – full position it serves as a barrier which impounds water. It functions as a barrier in the river where we want to use running water as a drive for a hydroelectric power plant or we want to use the river for field irrigation. Rubber dams are cylindrical rubber fabrics placed across channels, streams and weir or dam crests to raise the upstream water level when inflated. The membrane is a multi-layer fabric made of synthetic fiber (usually nylon)and rubberized on one or both sides. The fabric is quite flexible and yet exhibits good wear-resistance characteristics. A layer of stainless steel mesh or ceramic chips can be embedded in the surface layer to reduce or prevent vandal damage.
The inflatable flexible membrane dams (IFMD, or rubber dams) were developed in the early 1950s - Flexidam - Imbertson. They are installed in stream and river beds, generally being bolted into a concrete foundation. They are used to divert water for irrigation, temporarily raising existing dams, flood control, water retention for aquifer recharge, reducing water intrusion into fresh water areas, protect low-lying coastal areas from tidal flooding, enabling fish passage past diversion works, by deflation, and for sewage retention/separation during flood events.

Inflatable dams can be filled with water, air or both. They are low pressure - typically 4 to 10 psi. The present trend suggests an increased use of air-filled membranes because they can be deflated or inflated more rapidly, and they are little affected by freezing conditions. Characteristic dimensions cover typically lengths of about 100 m with specially-made membranes up to 200-m wide, dam heights usually less than 5-m but some special designs might be up to 10-m high. The membrane is usually deflated for large overflows. It is however common practice to allow small spillages over the inflated dam. During overflows greater than 20% over-topping, vibrations might result from fluid-structure interactions and the instabilities might damage or destroy the rubber membrane. Several failures were experienced (e.g. CHANSON 1996). In practice, a deflector (i.e. fin) is installed on the downstream face of the rubber dam to project the nappe away from the membrane, hence preventing rubber membrane vibrations.

There are more than 2000 inflatable rubber dams around the world. Durability can be excellent: recently, a 35 year old dam in eastern Ontario, Canada was replaced, and while still functional in both freezing winter conditions when it was air filled, and water filled in summer, it was deemed to have served its useful life, and was replaced.