Development of a physical model facility and investigation of flow pattern due to groyne on the right bank of Jamuna river near kazirhat-natibpur area

Abstract

A physical model facility has been developed near building for the dept of Water Resources Engineering, BUET, Dhaka. This was a long felt need of the department for hydraulic model studies. Previously this facility was available only at River Research Institute (RRI), Faridpur. The model studies at RRI concentrate on field problems and are not available for academic research. After developing the mode~ the aim was to prepare a physical be~ model of Jamuna river for the reach length between Kazirhat and Ganges-Jamuna confluence to study the morphological response of the river due to groyne. The secondary purpose of the study was also to get an insight about the suitable location for the ferry ghat at Natibpur, which is under constant threat of erosion and deposition. The sand bed in the physical model facility is 45.73m (150 feet) long and 10.67 m (35 feet) wide. It is filled up with 0.81m (2 feet 8 inch) depth of sand of Dso equal to 0.18mm. Two Rehbock weirs are incorporated as measuring devices in the system, one at the upstream end and the other at the re-circulating canal. Three gauge points on the western side to measure depth of water in the sand bed and one manually operated instrument carriage made of steel truss are also installed over the bed for data acquisition. The water supply in the system is developed with a storage pool capacity of 210 m3 with three centrifugal pumps (total capacity 150 lis) with control valves. After the completion of physical model facility, the braided channel of Kazirhat- Ganges Jamuna confluence area, which is about 16 km long and 4 km wide, was represented on this model. The horizontal and vertical scale ratios are 1:400 and 1:60 respectively. For this purpose the river charts were collected from BIWT A. Five representative discharges covering wide ranges of river flow were selected. By studying the flow lines and the morphological changes (mainly scour and siltation) the location of one groyne was identified around Natibpur. The model study showed that by providing a groyne at Natibpur the area dis of the ferry ghat upto 1.5 km could be protected at moderately high flow. The study also showed that the bank line from Natibpur upto the Ganges-Jamuna confluence near Aricha could be protected from scour by constructing four normal groynes in series with a gap of 800m c/c approximately.