Barrage Regulators are considered one of the most important hydraulic structures that used to
control the released discharge and upstream and downstream water levels. New barrages are
constructed on the River Nile instead of the oldest ones, which are not able to resist the
requirements of increasing head difference upon their gates. The present study was focused on
investigating experimentally the effect of sill over stilling basin of Nagaa Hammadi regulator on the
length of reverse flow behind sill, velocity at the end of stilling basin, energy dissipation, length of
submerged hydraulic jump and scour formation downstream regulator apron. Experimental work
was carried out on a re-circulating flume with 1.0 m wide, 26.0 m long and 1.2 m deep, with
discharges range from 40 to 190 l/s. It is found that the sill over stilling basin has great effect on
flow characteristic and local scour depth formed downstream regulator especially for sill with right
and slopped faces at the upstream and downstream, respectively. The present study shows that, the
reverse flow length downstream sill decreases as the submergence ratio and Froude number
increase. In addition, using sill with right upstream and slopped face at downstream with Ls/L=0.6,
reduces the length of submerged hydraulic jump by 59% in average and thus leads to decrease
stilling basin length. Local scour depth downstream hydraulic structures were reduced by 43%.
Moreover, the energy dissipation was increased by 30% compared to the no sill case. Finally,
Empirical equations are developed using multiple linear regressions analysis.