M. M. MELLAT - Instructor, Civil Eng. Dept., Shiraz Azad University

The use of labyrinth weirs especially in narrow channels may be beneficial as these types of weirs increase the effective length of the spillway in a given space; therefore, in a given width and for a low effective head, such arrangement can pass larger discharges in comparison with the ordinary ones. For this reason, these weirs may be employed as a substituted for the gated spillways; in other words, using such technology eliminates necessity of using gates for accurate control of water level. The present study which is based on the results of experiments on scaled model, aims to clarify the effect of the slope of downstream apron in a labyrinth weir on its hydraulic performance. Observations indicate that: 1. In all cases of triangular or trapezoidal plan form, with increasing discharge, the discharge coefficient decreases. 2. For triangular labyrinth weirs, when the hydraulic head is medium or low, the discharge coefficient decreases with an increase in downstream slope; though for high hydraulic heads, the results are vice versa. 3. For trapezoidal labyrinth weirs, no relationship between discharge coefficient and downstream slope of the weir was observed, which may be due to the complicated hydraulic conditions in comparison with the triangular labyrinth weirs; therefore, further experiments are required using accurate and proper measuring techniques. 4. Qualitative observations on the hydraulic behavior of the flow over the labyrinth weirs in the present study, implies the major effect of downstream aeration under the nappes

Labyrinth weir, Discharge coefficient, Downstream slope