Abstract

Local scouring immediately downstream of stilling basin is unavoidable local velocity exceeds incipient motion velocity. This phenomenon causes a difference level between concrete floor of basin and river bed. In such circumstances a riprap is normally used to prevent the development of scouring hole. In this study, hydraulic model of Namrood dam is used to estimate stone size that is able to resist scouring as result of basin turbulent outlet flow. Tail water (y_t), the difference in level between basin floor and river bed (Z) and critical depth of flow in stilling basin (y_c) are required to be measured in order to develop a mathematical model for estimation of scouring. Results confirm considerable reduction of the stone size with increase of (Z) and (y_t) for same flow discharges, while stone size increases with flow discharge.

Key words: Riprap protection, stilling basin, hydraulic jump, stability number.