Folkard, Andrew Martin (2016) Variations in flow resistance in small agricultural streams due to idealized aquatic vegetation distributions. In: 11th International Symposium on Ecohydraulics, 2016-02-07 - 2016-02-12, Melbourne Cricket Ground.
Abstract
The work reported here considers flow resistance due to vegetation in the smallest of surface water drainage channels – streams and agricultural drainage ditches of the order of 1m wide and 10cm deep. The second investigation explored the way in which the spatial distribution of obstacles to the flow affected flow resistance in these small channels. In practice, such obstacles in these channels are usually patches of aquatic vegetation. However, vegetation has complex hydraulic properties. Therefore, to elucidate the specific effects of the spatial pattern of obstacles, we used arrays of hydraulically-simpler obstacles, namely sandbags. We found that the maximum efficiency of energy conversion from potential energy to kinetic energy in the flow occurred when the sandbags covered 50% of the total area they occupied. If they were more spread out than this, it allowed the creation of individual wakes, which between them increased energy dissipation; if they were more piled up, this caused plunging of the flow over them, which also increased energy dissipation, though to a much lesser extent that individual wake formation.