Understanding Submergence
When the flow conditions are such that the downstream channel retards flow through the flume by more than 1%, a flume is defined as being submerged. As the downstream channel retards flow, the depth in the channel increases.
What is transition submergence?
The submergence transition is the ratio of the secondary point of measurement depth (Hb – located in the Parshall Flume's throat) to the depth at the primary point of measurement (Ha – located in the converging section of the flume). For Parshall Flumes, the submergence transition increases as the flume size increases.
What is the effect of submergence on the flow?
By increasing submergence ratio, upward flow starts from 70% of flow depth up to around 30% of flow depth from the bed and weakens downward flow.
