Experimental Investigation of Flow Separation Zone in River Confluence in Subcritical Flow Conditions

In recent years, many hydraulic, sediment, and environmental researchers focused their studies on river junction hydrodynamics. River junction is an important morphological element of river systems. The incoming flow from a minor branch causes extensive variation of flow velocity, flow discharge, and sediment discharge which results in flow turbulence in the main channel. The main characteristic of river confluence is the dimensions of flow separation zone. This zone is developed from the downstream edge where the minor branch enters and extends to some distance downstream into the main channel. There are few parameters affecting the separation zone extension including the discharge ratio (Qr) the width ratio (Br) and the downstream Froude number (Frd). The effect of these parameters have been investigated on the separation zone length (L) and width (H). Experimental tests have been conducted in a 90 degree junction. The results show that as Qr increase L and H increases and as Frd increases the value of L and H decreases. In this study relations were developed which can be used for prediction of separation zone dimensions. The mean value of separation zone shape index also has been determined.