Author(s): Dorota Miroslaw - Swiatek; Pawel Marcinkowski; Michal Dytkiewicz; Adam Kiczko

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Keywords: Flow resistance; River Narew; Vegetative blockage factor; Two-layer model

Abstract: The hydraulic resistance of natural channels is mainly due to vegetation. This study examines the hydraulic resistance of fully developed macrophyte vegetation. The vegetation effect on hydraulics is modeled using the simplified two-layer model with the vegetative blockage factor. This model links parameters characterizing vegetation physical features with the hydraulic resistance described using usually the Manning roughness coefficient. Research was carried out on a 25 m reach of the Upper River Narew. It is a lowland, low-gradient (0.0002 m/m) river situated in north-eastern Poland, characterized by temperate climate and precipitation amount ca. 600 mm per year resulting in an average flow of 15 m3/s. The channel is strongly vegetated with macrophytes growing on the bottom and banks. Blockage factors (the proportion of a cross-section blocked by vegetation) were determined for six cross-sections at analyzed river reach. The measurements performed in cross-sections verticals included: the species of macrophyte present; water depth and velocity; height of the top of the macrophyte above the bed; height of the underside of the macrophyte above the bed; and whether that macrophyte was present between that profile and the next. The velocity were measured using OTT MF Pro electromagnetic flow meter in 5-6 points in each vertical profile. For each measurement series a water slope was taken. As the outcome of the study Manning roughness coefficients and parameters of the two-layer were determined.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221442

Year: 2022