Experimental investigation of the effect of opening of single mitergate on the volume of river bed scouring (case study: Bahmanshir navigational gate)

The opening and closing of the miter gates in the river direction have a special complexity that makes it necessary to study its effect on the bed scouring pattern. The present study was performed on miter gate gates (in the single gate opening position) and investigated the effect of a single miter gate opening on the scouring volume of the river bed (case study; Bahmanshir shipping gate). Timothy Loved (2012) used a physical model to investigate the condition of the upstream scour of the Dam of Mississippi River. The results showed that several holes were formed, the deepest of which is about 1.22 meters deep.

Based on the available laboratory facilities and conditions and the principle of similarity, a physical model with a scale of 20 (LR = 20) was constructed. The present study tests were performed on the experimental flume in the hydraulic laboratory of Khuzestan Water and Power Industry Research Institute. In this study, the physical model of the miter gate was placed inside a rectangular flume 6 m long, 1.30 m wide, and 0.5 m deep. The depth of sediment from the half-flume to the end (approximately 3 m in length) was 20 cm and no sediment was considered upstream of the miter gate. Sediment particles used in the present study were supplied from Bahmanshir River, their average diameter (D50) was 0.25 mm (D50 = 0.25 mm) and determined by the Geotechnical Laboratory; Sedimentary particles were silt. In the direction of flow conveyance, the volume and amount of discharge were controlled by a valve and a digital flow meter. The flow slowly and with low discharge entered the flume and the desired hydraulic head was checked and recorded on both sides of the miter gate (upstream and downstream of the miter gate) and finally, the flow enters the pumping tank through the downstream channel after passing through the miter gate and the navigation lock area and returns to the cycle. The Miter gate was tested with different discharge ratios as well as different opening speeds when one of the miter gate gates was opened. The miter gate in this study was made of Teflon; Using a laser meter, the data of the flume bed elevation (erosion and sedimentation) were read, the values of which were calculated by volume.

According to the results of Buckingham's dimensional analysis, several experiments were performed to determine the effect of parameters such as miter gate opening velocity ratio (2, 2.4, 3) and different discharge ratios (0.5, 0.75, and 1) on the scouring volume was done along the flume.

The results of the study of the effect of miter gate opening rate ratio on volume and scour depth showed that in general, with increasing valve opening speed, scour volume increased and decreased, which was due to flow concentration for a longer time at lower opening speed and caused erosion. The depth was greater than the opening speed of the valve. The results showed that with increasing the opening speed of the valve, the erosion volume increased up to 17.3%, and also with increasing the opening speed of the valve, the erosion depth decreased to 23%. It should be noted that with increasing flow, both the depth and the volume of the erosion hole increased, the depth of erosion increased to 18% and the volume of the hole increased to 17%. Regarding the hydraulic head, the results showed that with increasing the hydraulic head, the erosion depth increased to 42% and the scour volume increased to 85%.