Two tanks were fabricated from metal sheets, each with
30 cm diameter and 100 cm height and were fitted with a
half-inch outlet pipe, a drain valve and an outlet tap.
One of the tanks was filled in this manner: 10 cm stone at
bottom (pebbles); 8 cm filter gravel provided in two layers
of different sizes of 4 cm deep each (size ranges 0.8–1.5 mm)
and a layer at the top of 40 cm deep filter sand (with a par-
ticle size of 0.2–0.8 mm). This tank was used as control
tank for the experiment (HMF1). The other tank was also
filled in the same way except that a 10 cm crushed brick
(grain size ranging from 0.25 to 0.5 mm) was added in