Author(s): Ellis Penning; Koen Berends; John Lenssen; Rosanne Reitsema And Jonas Schoelynck
Linked Author(s): Ellis Penning
Keywords: Vegetated flows nature-based solutions maintenance streams field validation
Abstract: Regulated lowland streams in the Netherlands often experience significant aquatic vegetation growth during the summer period. This vegetation limits flow conveyance, causing waterlogged soils and an increased flood risk. Traditionally this vegetation is removed by mowing the full stream width at a regular time interval during the growing season to guarantee sufficient conveyance capacity. This often has a negative impact on the ecological functioning of the system. Nature-based water level management using ecologically sensitive mowing only a subsection of the cross-section can help reducing this ecological impact and at the same time provide the needed conveyance capacity. In a three-kilometer stream transect a field experiment was carried out to create validation data for hydraulic and vegetation models and assessment of the water quality changes during the mowing event. Widths of mowed stretches were varied from 2 – 6 meter, and discharges of 1 m3/s were flushed through the system after each mowing event by lowering the upstream weir (base flow of 0.1 m3/s). Water levels were recorded along the transect, water quality parameters were collected before and during the mowing event, biomass was collected at the downstream weir and total weight was related to the overall cover of vegetation in the stream and percentage removed. Results show a decrease of water level for every meter width mowed until, but not more than 4 m width. The effect of mowing on water quality was negligible, although we note that this is conditional on the mowing techniques used in this experiment.
Year: 2025