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.
Highlights
Riverbeds of large lowland rivers are characterised by a great diversity of flow conditions, and their cross-sections predominantly consist of a main channel and relatively extensive floodplains
The adopted research scenarios 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. of the Research Area and Field Measurement
The intensive technical inspection of dams),(willow the Jeziorsko reservoir the Warta the secondand largest storage growth of shrubby vegetation shrubs) in theon upper part river of theis reservoir its floodplains reservoir in terms of flooding area, and the fourth largest in terms of capacity among large storage within the embankments above it has been observed since regulatory works were completed in 1985
Summary
Riverbeds of large lowland rivers are characterised by a great diversity of flow conditions, and their cross-sections predominantly consist of a main channel and relatively extensive floodplains. Trees (i.e., goat willow, white willow)—this form of vegetation has a main trunk and foliage begins at a certain height It does not significantly affect the conditions of high water flow. In Sweden and the UK, shrub willow yields are similar to those in Poland, with a value of 8–12 t·ha−1 ·year−1 (up to 20 t·ha−1 ·year−1 in favorable conditions and with high mineral fertilization) fresh mass on production plantations [37,38,39] This means that the production of willow biomass is four to six times greater than the annual growth of wood in forests. For the purpose of this work, the impact of long-term growth of willow shrubs on the values of flow
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