Experimental Study of Roughness Reduction of Large Aqueducts in the Middle Route of the South-to-North Water Diversion Project

The roughness of the aqueduct in the Middle Route of the South-to-North Water Diversion Project has increased due to factors such as the natural aging of concrete and biological attachment. To increase the flow capacity of the project, a roughness reduction test was carried out in April 2021 by installing a nano-rubber coating on the Fangshui River aqueduct, which consists of three aqueduct bodies arranged in parallel. Before and after the test, as well as two years after the test, three field observations were conducted. The analysis revealed that compared to aqueduct body 2, which was only cleaned of surface attachments, after excluding the difference in the background roughness, the nano-rubber coating reduced the roughness of aqueduct body 1 by 0.0013 (10.00%). After two years of operation, the roughness was 0.0010 (7.41%) lower, indicating that the nano-rubber coating had a good and lasting effect on the roughness reduction. The roughness field observation results are sensitive to flow rate and water level measurement errors. For aqueducts with a low head and a high flow rate similar to those of the Fangshui River aqueduct, non-contact measuring instruments should be preferentially utilized, and sufficiently accurate flow rate measurements should be ensured to improve the accuracy of the roughness calculation.