Page - 181 - in Book of Full Papers - Symposium Hydro Engineering

utilities and their settlement in different parts of the transmission network which will cause many problems. Sediment particles in water at high speeds cause irreparable damages to hydro mechanical parts of the hydroelectric structure such as pumps and turbines. In plants in India, irreparable damage to turbine blades due to sand in water (After two to three thousand hours of operation of turbines) (Ranga Raju et al. 1999). In water transmission, especially in networks where the water is transmitted by gravity, water flow cannot hold sediment particles in the suspended mode because water speed is low and this leads to settlement and accumulation of sediment particles in the channel bed over time. This causes problems such as: A) Accumulation of sediments in the channel and a decrease in the channel free depth and capacity; B) High cost of dredging irrigation canals; C) Erosion of channel walls and aquatic structures; D) Creation of favorable conditions at the floor of canals for growth of plants, and changes in roughness coefficient. These kinds of problems have encouraged many aquatic structure experts to take on appropriate and effective measures from the beginning and avoid the entry of sediments into water transmission and distribution networks as much as possible. One way is to separate sediments using vortex settling basins. In this type of settlings, vortex flow is used to separate sediment from water flow. This method is a solution for separating solids from liquids at high speeds, unlike classical settling basins in which settling occurs at lower speeds using the gravity force. The vortex created in these basins is generally a Rankine-type vortex consists of a forced vortex in the center of the basin and around the central orifice and a free vortex in the outer section of the central vortex of the basin (Athar et al. 2002). In this type of settlings, flow is directed within the basin completely tangentially and exits from the top weir while rotating around the basin. The settling phenomenon and sediment movement towards the washing orifice are occurring by secondary flows. Sediment particles are separated from water with the loss of only a small amount of discharge. Sediment particles entering the basin move along a spiral path towards the basin center (Ziaei 2000). Therefore, in such systems, the extension of the settling path of sediments is several times larger than the basin size. Among the advantages of this sediment control method compared to other conventional methods like classic settling basin, one can point to reduce water losses, cost- effectiveness, its permanence unlike other settlings, no need for short-term dredging and smaller size (Paul 1991). Extensive research has been conducted on a vortex settling basin by Vokes and Jenkines (1943), Velioglu (1972), Salakhov (1975), Cecen and Bayazit (1975), Sulivan et al. (1978), Curi et al. (1979), Mashuri (1981,1986), Svarovski (1981), Ogihara and Sakagouchi (1984), Sanmogantan (1985), Esen (1989), Zhou et al. (1989, 1997), Paul et al. (1991), Ziaei (2000), Athar et al. (2002, 2003) , Keshavarzi and Gheisi (2006) and Niknia et al. (2011). By 181