This study was initiated to introduce non-submerged spur dikes as training structures to reduce erosion at the opposite bank to diversion channel at Naga Hammadi barrage through minimizing the velocity values near the banks. The length of the bank to be protected is 450m. The width of diversion channel is 172m; however the average channel width at the region under study is 450m. A two dimensional mathematical model were used to simulate many cases. To assure model validity, experimental results were used for verification. The model simulated longitudinal and transverse velocities as well as the spur working length. A financial economic evaluation as a function of groin length is introduced to help in selecting the optimum group with minimum cost. Eighteen runs (18) were executed where three (3) effective parameters were tested. These parameters were the contraction ratio, which is defined as the spur length to the channel width (L/B), the spur orientation angle; and the spur spacing. The contraction ratio was varied between 0.1 and 0.2 while the used orientation angle are 60O, 90O and 120O and the spacing was 2, 4, and 7 times as much as the spur length. The measurements covered 60 grid points along four longitudinal lines (A, B, C, and D) crossed by 15 lateral cross sections. The study concluded that the maximum spur working length is occurred with repelling spurs of 120o with a 0.2 contraction ratio at 2L or 4L spacing. On the other hand, 7L spacing produced the minimum working length in addition to its discontinuity. It was also found that the working length is inversely proportional to the spur spacing but it is directly proportional to the spur length for a fixed orientation angle and spacing. The maximum and minimum values of longitudinal velocity occurred in the case of using a spur with an orientation angle of 900 with a contraction ratio of 0.2. It was also noticed that changing the spur length, spacing, and orientation angles did not affect the maximum transverse velocities. For the tested cases, the maximum and minimum transverse velocities are located at the middle third of the channel. There is a clear similarity between the longitudinal velocity in case of implementing repelling and straight spurs. For fixed spur length and spacing, using a group of spurs at any orientation angle, both longitudinal and transverse velocities decrease at the different cross sections in the vicinity of the bank by 50% and 20%, respectively. Using a group of 10% contraction ratio length presents more economic solution from the view of cost evaluation when compared to 20% contraction ratio length. The study recommended that 4 spur oriented at 60o with 10% contraction ratio length and spacing of 4 times spur length can be used to protect the attacked 450m at the bank facing the temporary diversion channel, while the repelling and straight types spur with 0.2 contraction ratio could be implemented to produce a deep channel. The scour associated to spurs existence is discussed in a separate paper.
Keywords
Oriented Spur dike, mathematical model, velocity components, and working length.
|
