Impact of increased instream heterogeneity by deflectors on the removal of hydrogen sulfide of regulated urban waterways—A laboratory study

Laboratory experiments were conducted to test the hypothesis that increase in physical heterogeneity by deflectors would improve the water quality of urban regulated (straight and prismatic) waterways. Deflectors changed the near-uniform flow to a rapidly varied flow, as such the depth, velocity, and Froude number (Fr) variations were four, 10, and 14 times more than the without deflector scenario, respectively. Removal of hydrogen sulfide (H₂S), the main focus of the study, was significantly high when deflectors were placed in the laboratory urban waterway. Introduction of a sediment bed further improved H₂S removal; however, in this case turbidity and color were significantly high too. These observations endorse the fact that attenuation induced by deflectors and assimilation promoted by the sediment bed aids the H₂S removal. These facts were further strengthened by the significant strong negative correlations H₂S made with DO and pH for all experiments. Further studies are recommended for different deflector orientations and modified sediment beds (e.g., mixture of sediment and gravel), identification of localized water quality hot spots to capture spatial variation of water quality, and impact of increased heterogeneity on flood safety. Practitioner points: Increase in physical heterogeneity (by deflectors) on water quality improvement was studied in a laboratory set up. Deflectors changed the near-uniform flow to rapidly varied flow with several mesoscale physical habitats. Hydrogen sulfide (H₂S) removal was greatest with deflectors and the sediment bed, but was characterized by high turbidity. H₂S removal showed strong negative correlations with dissolved oxygen and pH.