Environmental and hydraulic study of novel limestone porous weir for river aquatic life protection and treating selected contaminants

Generally, porous weirs are considered as friendly environmental structures used to reduce the negative impact of flash floods. All previous studies used solid concrete weirs or gabion weirs that used gravels. Researches rarely deal with the performance of porous weirs hydraulically and environmentally together. In this study the hydraulic characteristic, flow types, and environment effect for porous weirs were studied experimentally and theoretically. Limestone was used instead of gravel as an adsorbent material for the porous weir to improve its efficiency for removing selected contaminants, including lead (Pb), turbidity and total suspended solids (TSS). The effect of limestone porous weir onto pH of the effluent water samples was also measured. The limestone permeable weir was investigated as an alternative to the solid concrete weir as it is cheaper, more environmentally friendly and also efficient in the removal of some river contaminants at the same. Two-dimensional numerical computational fluid dynamics (CFD) modeling for flow over and through porous weirs was performed using the volume of fluid method and shear stress transport k-omega model for turbulence through ANSYS 16.1. Many samples of water were collected before and after the porous weir for environmental analysis. The results showed a good convergence between the CFD model and experimental results. Moreover, the results showed that the CFD model gave root mean square error values equal to 0.877, 0.979, and 0.625 cm, respectively for the three discharges selected, 0.4, 1.85, and 2.75 m(3) h(-1), respectively selected for comparison between the CFD model and the experimental work. On the environmental side, the effects of flow rates were studied at an initial concentration equal to 1.5 mg L-1 of Pb ions and 50 mg L-1 for turbidity. The designed weir shows good removal efficiency for both lead and turbidity. The maximum removal efficiency was found to be 92.5%, 72% and 59% for lead, turbidity and TSS, respectively. The greater the time the lower the removal of pollutants, and lower discharge resulted in a greater percentage of removal.