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At the time that the study described in the
monograph commenced, all of the published research on
submerged thin plate weirs assumed that the upstream
and downstream beds were at the same level. In
practice downstream beds may be eroded by the flow
over the weir leading to unequal bed levels.
Using laboratory models, this study examined the
discharge over submerged weirs with unequal beds. The
resulting flow pattern was shown to be different to
that of the equal bed case. The approach channel
Froude Number differs from that of the equivalent
equal bed case. The standard formulas derived for
submerged equally bedded weirs were shown to give
incorrect values.
The existing standard formulas for calculating
discharge over submerged thin plate weirs treat
submerged flow as a variation of the free modular
flow. The later part of the study treats flow over a
submerged thin plate weir as a separate flow
condition and proposes an initial form of a new
discharge formula.

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