Document Type : Research Paper
Due to the problems of hydraulic structures at blocking bodies in debris flows this research has been carried out. Hence, in this study the effect of the trap drop bodies such as logs and branches of trees on piano key weirs at individual step was considered. The debris flows, decreasing in discharge capacity and raising the water level can be expected in the piano key weirs. The experiments of this research were performed on two piano key weirs with 10 and 30 cm in height on an experimental flume, 12 meters in length, 80 cm width and height of 70 cm. On these weirs three parapet walls with 2.5, 3.5 and 4.5cm height were installed. As a hydraulically criterion, Individual branches and logs in debris flow were studied. Individual experiments showed that the diameter and the upstream head of spillway affect the likelihood of blockage. However, both the increasing in diameter and head decreasing, increase the blockage. Therefore the probability blocking increases in D/H>1 and it decreases at D/H<0.3.