The pond level299.00 m AOD and the regulator’s crest level297.50 m
AOD. Therefore the head causing flow, H1.50 m (neglecting velocity of
approach).
Check whether the flow is modular or non-modular:
upstream head, H 1 299.00 297.501.50 m;
downstream head, H 2 296.00 297.50 1.50 m.
The crest height above the downstream bed level, P 2 297.50
293.504 m. Therefore the submergence ratio H 2 /H 1 1 and P 2 /H 1
2.67, suggesting free-flow conditions over the weir. Assuming a
broad-crested weir (Q1.7beH3/2), the minimum effective width,
be100/(1.71.53/2)32 m.
Providing four equal spans of 10 m with piers 1.5 m thick,
clear waterway provided 40 3 1.535.50 m,
end contractions2(30.010.1)1.50.39 m.
Therefore the beprovided35.50 0.3935.11 m, which is satisfactory.
Worked Example 9.2
The figure below (Fig. 9.15) is a proposed weir floor with three vertical
pilings. Examine the uplift pressure distribution under the floor of the weir
and compare the result with Bligh’s creep flow theory.
Pressure distributions at key points:
(A) UPSTREAM PILING 1
Figure 9.6 gives the pressures (from DandEcurves) at DandEof the
extreme downstream pile– see the definition sketch on this figure – as a
first estimate which are then corrected for the floor thickness.
388 DIVERSION WORKS
Fig. 9.14 Filter construction with nylon fabric
