Providing an upstream glacis of 2 in 1, 5 m of horizontal apron (safety
factor for additional creep length), a downstream glacis of 3 in 1, and an
18 m long stilling basin (USBR type III basin – Chapter 5, Fig. 5.6 –
length3 times sequent depth), the total floor length,
b42.45 m37.32 m(Fig. 9.10). The total creep length (Bligh) 2 3 42.45 2 6 60.45 m.
Therefore the rate of head loss (gradient)H/L6/60.450.0992. The
head loss in the upstream cut-off0.0992 6 0.595 m, and in the down-
stream cut-off0.0992 12 1.19 m. The total head loss to the gate (point
1)0.5950.099212.881.87 m. The total head loss up to end of
the downstream glacis (point 2)0.5950.099224.453.02 m. The
total head loss up to the mid-point of the stilling basin (point
3)0.5950.099233.453.91 m. The RL of the HGL at
point 1299.00 1.87297.13 m AOD,point 2299.00 3.02295.98 m AOD,point 3299.00 3.91295.01 m AOD.The uplift pressure head above the top surface of the structure at
point 1, h297.13 296.690.44 m,point 2, h295.98 293.002.98m,point 3, h295.01 293.002.01 m.The thickness of the concrete at
point 1 (crest)1.2h0.5 m,point 2 (upstream of stilling basin floor) 1.2h3.5 m,point 3 (centre of stilling basin floor) 1.2h2.5 m.Adopt a stepped floor thickness downstream of the downstream glacis as
shown in Fig. 9.10 and a nominal thickness of 0.3 m for the upstream glacis
and the horizontal floor slab (uplift pressures are less than the weight of
water above).