STEP BY STEP BUILDING A FLEXIBLY LINED POOL
This sequence shows the construction of a retention basin. The outlet weir controls the normal water level, and the volume above that performs a temporary storage function for surfacewater drainage during storms. The weir regulates the rate of outflow and spreads the outflow over a number of hours so that the drainage system downstream is not overloaded. In short, the pool is designed to flood. It was planned as a simple, flexible butyl-lined pool, but one problem was the fluctuating groundwater table, which lifted the butyl liner. The solution was to install a one-way valve in the bottom of the pool.