Increased Riparian Vegetation Density and Its Effect on Flow Conditions

Abstract

The physical and biological structure of riparian vegetation fundamentally influences floodplain roughness, and thus the flood velocity and flood levels of a river. The study aims to provide detailed spatial data on the vegetation density of a floodplain, and to model the effect of the actual vegetation and various scenarios on flow conditions. LiDAR data were applied to evaluate the density and roughness of the submerged understory vegetation over the densely vegetated floodplain of Lower Tisza, Hungary. Then, HEC–RAS 2D modelling was applied to analyse the effect of the actual vegetation on flow conditions. Further scenarios were also created to predict the effect of (i) invasive plant control, (ii) no maintenance, and (iii) riparian vegetation restoration (meadows). According to the results, since the 19th Century, the increased vegetation density is responsible for a 17-cm flood level increase, and if the vegetation grows even denser, a further 7 cm could be expected. As the vegetation density increases, the overbank flow velocity decreases, and the crevasses and flood conveyance zones gradually lose their function. Simultaneously, the flow velocity increases in the channel (from 1 m/s to 1.4 m/s), resulting in an incision. Applying LiDAR-based 2D flow modelling makes it possible to plan sustainable riparian vegetation maintenance (e.g., forestry, invasive species clearance) from both ecology and flood control perspectives.

Development of Suspended Sediment Monitoring of the Tisza Using an Indirect Measurement Method

“…1) was constantly increasing, so the same discharge was conveyed by increasingly high water levels (Kiss et al, 2019). Based on previous studies, the factors affecting the increasing height of the flood waves are various, including the overbank accumulation of the floodplain, formation of natural levees and increasing density of riparian vegetation (Kiss and Fehérváry, 2023). These processes significantly limit the conveyance capacity of the floodplain; thus, the kinetic energy of the river decreases, and the transported suspended sediment is thereby deposited, accelerating the accumulation processes of riparian areas (Kiss and Sándor, 2009;Kiss et al, 2019).…”

Comparative Analysis of Riverine Plastic Pollution Combining Citizen Science, Remote Sensing and Water Quality Monitoring Techniques

“…During floods, the transport rate of plastic litter could be as much as 500 plastic bottles per minute [6]; thus, it is called the "plastic flood" [28]. When the overbank flood enters the floodplain, its flow velocity is drastically decreased by the dense riparian vegetation [29], so the drifting MaPs are trapped. Smaller flood waves are also important conveyors of MaPs.…”