The effect of obstructions above the flat- and circular-stepped spillway on energy dissipation

Stepped spillways are significant water structures that aerate rivers, disperse energy, and lower the cost of the downstream pool. Energy dissipators are means made to lower flow velocity to manageable levels, preventing erosion in downstream areas. A study was conducted to assess the effect of obstructions above the stepped spillway using a wooden physical model of 50 cm height, 100 cm length, 80 cm width. A total of 24 laboratory experiments were carried out using two shapes of steps (flat and circular), three cases of obstruction (no obstruction, an obstruction at the middle of the step, and an obstruction at the end of the step), and four discharges. The results showed that the energy dissipation using flat stepped spillway is higher than that for circular stepped spillway of about 3 %. The relation is inverse between Delta & IEcy;/Eo (difference between upstream and downstream energy of stepped spillway/upstream energy) and E1/Eo (downstream energy/upstream energy), for all cases, whether flat or circular steeped spillway, with or without use of obstruction. In general, using a middle obstruction led to dissipate more energy than an end obstruction. For flat stepped spillway, the percentage of energy dissipation was 5 % when comparing a middle obstruction with no obstruction, while it was 4 % when comparing an end obstruction with no obstruction. For circular stepped spillway, the corresponding percentages of energy dissipation were 6 % and 5 %, respectively. The relation is direct between Delta & IEcy;/Eo and l/Eo, and the largest water path is in the case of using the middle obstruction for flat and circular steeped spillway. One empirical relation was proposed to compute Delta & IEcy;/Eo in terms of dimensionless variables using dimensional analysis.