While it is desirable for a flume to have free, unimpeded discharge, it can be difficult to guarantee this under all flow conditions.  H Flumes have particularly low resistance to submergence, with submergence transitions of only 25-30%. The submergence transition of an H flume is 1/2 (or less) of other flumes capable of carrying comparable flows.  

When a sufficient elevation drop cannot be obtained, it may be necessary to correct an indicated head for the effects of submergence.  This can be done by:

Keep in mind that this correction is to approximate the free-flow head in the H flume – it is NOT a direct correction to the indicated flow rate.  With the corrected head determined above, the appropriate flow tables / equations can then be used.

Due to the added instrumentation costs, operational complexity of operating, and low submergence transition ratios, Openchannelflow recommends operating H Type flumes only under free-flow conditions.