Drops or free overfall are the most common hydraulic structure used in irrigation channels, water distribution and wastewater collection networks, and in recent years in stepped spillways. To reduce earth fill expenses in locations where channel slopes are less than the ground slopes, drops are provided. A vertical drop is a structure where the flow passes over a vertical fall and descends into the, downstream of the drop (Fig. 1). Energy loss is achieved through turbulent mixing in the pool created downstream of the drop (Fig 2). The flow upstream a drop can be either subcritical or supercritical. For subcritical flow, the flow passes through the critical depth in the channel just upstream of the drop and then overflows the drop brink. For supercritical flow, the upstream depth is less the critical depth and is a function of the Froude number and discharge. Drops are generally categorized to be inclined or vertical. Vertical drops are also divided into four types according to their geometrical shapes, as shown in Fig. 3.
Recent researches on drops are focused in increasing the drop energy loss; e.g., providing additional step in the downstream channel (Fig. 3b), converging the brink section, using a netting drop-type dissipater at brink section (Fig. 4), etc. The most recent area is to study the characteristics of the falling jet. These may include the impact force on the downstream channel and controlling the vibration characteristics by using dampers (Fig. 5).
Author Papers on Drop Structure
Rajaratnam, N., and Chamani, M. R. (1995), “Energy loss at drops”, Journal of Hydraulic Research, 33(3), 373-384. More details…
Chamani, M. R., and Beirami, M. K. (2002), “Flow characteristics at drops”, Journal of Hydraulic Engineering, 128(8), 788-791. More details…
Chamani, M. R., Dehghani, A. A., and Beirami, M. K. (2005), “Characteristics of drops with sloping inverts”, 17th Canadian Hydrotechnical Conference, Edmonton, Canada, August 17-19, 865-870.More details…
Beirami, M.K., Nabavi, S.V., and Chamani, M.R. (2006), “Free overfall in channels with different cross sections and sub-critical flow”, Iranian Journal of Science and Technology, 30(B1), 97-105.More details…
Chamani, M.R., Rajaratnam, N., and Beirami, M.K. (2008), “Turbulent jet energy dissipation at vertical drops”, Journal of Hydraulic Engineering, 134(10), 1532-1535. More details…
Chamani, M.R., Beirami, M.K., Rajaratnam, N., and Dehghani, A.A. (2008), “Characteristics of subcritical flow over vertical drops with sloping aprons”, Iranian Journal of Science and Technology, 32(B5), 531-542. More details…
Nabavi, S.V., Beirami, M.K., Chamani, M.R., and Sterling, M. (2011), “Free overfalls in flat-based circular and U-shaped channels”, Flow Measurement and Instrumentation, 22(1), 17-24. More details…