Stormwater ponds

Improved sedimentation and characterization and risks of accumulated sediment.

Particulate matter transported by stormwater is considered to be one of the most important parameters with regard to stormwater quality. This is because on the surface of the particles, other pollutants are also carried with the stormwater to the receiving water body, which can be a lake or river. A common technique to reduce the particle content of stormwater for decades has been stormwater ponds.

Some ponds are poorly designed from the start and over time it is common for stormwater ponds to become undersized due to the growth of the catchment area by connecting more sub-areas to the sewer network and new construction of areas. The undersizing leads to impaired sedimentation and treatment. In addition, accumulated sediment will eventually need to be removed and disposed of, and the sediment may then contain high levels of pollutants.

The available surface area is a limiting factor in the design of stormwater ponds that will affect the sedimentation efficiency and the cost of collecting accumulated sediment. For this reason, a structure to improve the sedimentation process and reduce resuspension of already accumulated sediment has been tested - a so-called bottom grid. The bottom grid acts as a trap for accumulated sediment and is placed on the bottom at the inlet of the dam.

In cooperation with a technical university in Prague, the Czech Technical University, different geometric designs of the grid have been investigated with regard to sedimentation efficiency. Parameters analyzed include raster cell size, height and angle. A scaled physical model of the grid structure was constructed for the experiments performed in the Hydraulics Laboratory in Prague.