The Impact of Shrubby Floodplain Vegetation Growth on the Discharge Capacity of River Valleys

Abstract

Willow bush growing in floodplains is a dominant form of vegetation in lowland river valleys due to the availability of water and light. Uncontrolled growth of this plant results in a lower capacity of floodplain areas. Vegetation can narrow the active width of water flow, as well as change water flow velocities at hydrometric verticals falling within the floodplain and the main channel. This paper analyses the impact of long-term growth of willow shrubs on flow resistance coefficient values. Both an increase in the average diameter and the density characterised by the average distance between branches have a significant impact on reducing the flow. The adopted research variants were based on data on the growth rate of the most popular species and forms of willow found in the floodplains of the Warta River above the Jeziorsko reservoir. Two research scenarios were analysed, including data from 12 years, on the development of floodplain vegetation. The first scenario included only the change in diameter (vegetation grew on a cultivation plot), whereas the density remained constant. The second scenario investigated the inverse model-vegetation growing in an uncontrolled manner. The analysis of the tests proved the impact of various bush development scenarios on flow conditions. The results, referred to in the available research papers, indicated the importance of the dynamics of shrub development to the local flow conditions. It was stated that reduction in the flow, depending on the analysed scenario, could reach 45% for scenarios in which the only considered factor was the increase in diameter (at a constant density), and up to 70% in the case of increase in the density of vegetation. Thorough knowledge of this phenomenon may help manage and maintain natural river valleys.

Untitled

“…Very important aspects of protection analyses are studies of riverbed and catchment capacity, which were conducted by Walczak et al (2018) and Laks et al Hämmerling, M., Walczak, N., Walczak, Z., Zawadzki, P. (2019). Assessment of technical conditions of bank protection of watercourses and reservoirs in the city of Poznań.…”

Morphological and functional diversity of floodplain water bodies and their classification according to the structure of the surrounding vegetation cover

“…Vegetation can reduce the active width of a watercourse and alter the velocity of water flow on hydrometric verticals within the floodplain and main channel. It is important to note that this effect is not always negative and can have both positive and negative impacts on the ecosystem (Walczak et al, 2018). The flood regime, in turn, affects the structure of the floodplain vegetation (Wu et al, 2022).…”

Hydraulic Effect of Vegetation Zones in Open Channels: An Experimental Study of the Distribution of Turbulence

“…The occurrence of plant communities, such as shrubs of purple willow (Salix purpurea L.) or rushes of common reed (Phragmites australis), influences the flow conditions in the riverbed, and affects, in particular, the spatial distribution of flow velocity and stream turbulence [1][2][3][4]. Such plant hydraulic interaction is not easy to determine as it depends on many variable factors, e.g., plant species and mechanical characteristics [5][6][7] and their stage of development including the density of the plant zone [3,4,7,8]. This interaction also depends on the spatial configuration of the vegetation zone (quasi-regular vegetation development, e.g., in the form of a triangle, circle, rectangle, etc., or the opposite, very irregular) and on the location of the plant community (at riverside (Figure 1), or directly in the river current (Figure 2)).…”