The suspended solids trap efficiency of the roadside gully pot

The roadside gully pot is a major component of many drainage systems used to protect the downstream sewers and receiving waters from excessive sediment deposits. This work aims to investigate the solids retention efficiency of a full size concrete pot by means of a laboratory test rig. Results from single-size quartz sand particles show that, for a given pot size, retention is influenced primarily by influent flow rate and particle diameter and to a lesser extent, retained sediment bed height. The major retention mechanism was postulated to be sedimentation within an hydraulically completely mixed environment. Transient re-erosion of the deposited bed was noted under extreme conditions with steady state concentrations never exceeding 10 mg/l. A model based on the proposed removal mechanisms was tested and shown to be in good agreement with the data.