Deflectors to introduce heterogeneity to canals

Abstract

Canals are manmade lotic water systems constructed for flood control, navigation, irrigation, etc. In general, canals are eco-hydrologically homogeneous. As such, a canal might have the same prismatic cross section and an even bed profile along its course. Such characteristics do not support rich biota, something a sustainable society expects. Several past studies have attributed heterogeneity to be an important factor for a healthy stream. In this study the deflectors were used to introduce the heterogeneity in canals. In tandem studying flow complexity by deflectors, their role with respect to sediment (sand) and seed transport, and fisheries were also studied. The model canal's (laboratory flume) homogenous velocity of 0.4 m/s changed to a range of values from 0.1 to 0.7 m/s after placing deflectors. Similarly, water depth changed from a uniform 30 mm to a range from 20 mm to 70 mm. This resulted in formation of flow patches similar to flow patches formed by meso-scale physical habitats such as pools and riffles. Sediment deposition was patchy and seemed to be stable as only a minor bedload movement was observed for prolonged durations. This meant it is possible to achieve a quasi-equilibrium state in field canals where upstream brings sediments. Seed trapping was weak for floating type seeds, whereas non-floating seeds managed to get deposited with sediment. Fishes quickly migrated to the pool like areas that resulted from deflectors. The results suggested the role of deflectors in transforming a homogenous channel to heterogeneous channel that has the potential to have rich biota which is essential in ecological rehabilitation works.