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Abstract
Small vegetated drainage ditches play an important role in water and nutrient removal, but may cause water blocking problems. The aim of this study was to investigate vegetated drainage ditches’ hydraulic and wetland hydraulic characters. Field experiment were carried out, small drainage ditches with Juncus, Zizania latifolia, and Acorus calamus were selected under different water flows, and a tracer experiment was also conducted. Research findings suggested that with increased water flow, vegetation roughness coefficient declined, vegetation resistance rose, and drag coefficient declined. Small drainage ditches with emergent vegetation showed a high roughness coefficient value, which was most significant in Juncus, followed by Zizania latifolia, and Acorus calamus. Plants each took on a unique eigenvalue k that was a relative coefficient between the drag coefficient and stem Reynolds number. As small ditches for drainage showed longer residence time and smaller surface hydraulic loading, they featured excellent wetland hydraulic characteristics that could be weakened rapidly as rainfall or flood intensified. This study indicates that the small vegetated drainage ditch shows favorable wetland hydraulic characteristics with good discharge capacity and can be extensively used in irrigated districts.
Highlights
In rice irrigation districts, there are a large number of natural drainage ditches that are mostly vegetated and play an important role in the ecosystem
The of results indicated that the roughness coefficient of different drainage ditchesEquation was 0.43~4.45, and that roughness coefficient declined as the flowwith rate increased
N Acorus calamus lati f olia drainage ditches was 0.43~4.45, and that roughness coefficient declined as the flow rate increased
Summary
There are a large number of natural drainage ditches that are mostly vegetated and play an important role in the ecosystem. Due to the fact that China faces serious non-point source pollution, such vegetated drainage ditches are used for non-point source pollution control, such as removal of nitrogen and phosphorus, and sediment blocking [1]. Farmers purposefully grow cash crops in those small drainage ditches for higher economic income. Discharge capacity of ditches can be impacted by plants. Quantitative analysis and evaluation of the comprehensive impact of plants on both aspects is of significance for drainage ditch design, operation, and management. Instead of focusing on the roughness coefficient and velocity distribution characteristics of hydraulic elements, as well as the mechanism that causes such a phenomenon, researchers of previous studies mainly investigated the resistance of vegetation to water flow from a ditch design perspective
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