# 4 | L-shaped cofferdam | Support on a bridge pile2020-10-20T13:41:51+01:00
# 4 | L-shaped cofferdam | Support on a bridge pile
This is the typical installation for structures with one or more piers.
Start from the bank and go around the pier upstream, ensuring that you have:
a long enough barrier to ensure a watertight seal against the bridge pier
an opening between the supports wide enough for the dam to pass through
Depending on the slope and the force of the current, it may be necessary to set up a second installation downstream of the bridge.
In this case, do not go past the chosen pier. Attach the dam to the pier facing the starting bank.