ANALYSIS OF CHANGES IN HYDRAULIC PARAMETERS IN A LOWLAND RIVER USING NUMERICAL MODELING

Abstract

Aim of the study: River channels are dynamic structures in which fluvial processes leading to equilibrium state between energy of flowing water and the stability of the bed material. The changes of river morphology is difficult to capture using the monitoring tools, however, physical or numerical modeling can be used instead to reflect these natural processes. Objective of the study is to analyze the variability of hydraulic parameters and their impact on morphological changes using numerical modeling of a regulated section of the Nida River. Material and methods: On the basis of field measurements, numerical model of the river was built. In this section, the channel has been strengthened, which enables the process of its restoration. Numerical modeling was carried out for a range of flows from low to an overbank one. Bankfull discharge was determined using the Riley method. Calculations based of modeled parameters made it possible to analyze their impact on the bed dynamics. Results and conclusions: The numerical modeling resutls (average velocity, shear stresses, and water depth) was used to calculate shear velocity, Reynolds Number, Grain Reynolds Number and settling velocity. The lack of clear trends of changes in individual parameters with increasing flows proves the existence of irregular connections between flowing water and riverbed. Changing discharge in the river affects not only the intensity of fluvial processes, but also their location. The bottom morphology created during low flows is completely changed at the passage of high water, as indicated by measurements and simulations of the examined section of the Nida River.