Hydraulic Performance of I-Head and T-Head Groynes in Series.

Groynes are river training structures which are constructed across the river extending outwards from the channel bank towards the mainstream to channelize the stream, protect banks from erosion and improve navigability of the channel. When constructed in series, in addition to local effect, groyne fields, formed between two consecutive groynes, contributes significantly to the scour and flow conditions. In this study, experiments on two simple cases of a series of three I-head and T-head groynes were conducted to compare the scour and flow characteristics under similar hydraulic and geometric setups under clear water scour conditions. The experimental setup consists of a 20 m long, 1 m wide, and 0.30 m deep fixed bed masonry flume with a longitudinal bed slope of 0.0006. A test section filled uniformly with sediment of mean diameter d_50= 1.05 mm begins from a distance of 10 m and ends at 13 m from the flume inlet. A series of three transparent Perspex sheet groyne models were installed in the test section ensuring a fully developed flow, with a spacing of three times the groyne length between them. Results show that there is a noticeable difference between the performance of the I-head and T-head groyne series. It was observed that in the case of T-head groynes, the magnitude of velocity vectors inside the groyne fields are considerably smaller than the similar areas in the I-head groyne fields. While the presence of wing of the T-head groyne resulted in greater scour at the upstream tip of the first groyne on the upstream with respect to I-head groyne, very less scour was observed near tips of second and third groynes in both cases. The existence of wing resulted in moving the high-stress detached shear layer away from the body, thereby increasing the zone of influence of the groynes.