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Effects of vegetation distribution along river transects on the morphology of a gravel bed braided river

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Zhu R. , Tsubaki R. , Toda Y.

tom Vol. 72, no. 2

1097--1112

The interaction between vegetation, sediment, and water flow creates various fluvial landscapes. Hydrological conditions and flood disturbances, as well as the habitat preference of vegetation, regulate its spatial distribution. To describe the spatial distribution of vegetation cover, here, we focus on vegetation distributions along river transverse transects that define vertical and horizontal distances from water areas during low flow periods. As one of the most dynamic river types, braided rivers can be significantly influenced by vegetation encroachment. However, the effects of vegetation distributions along river transects on braided river morphology remain unknown. To study the potential influence of vegetation distribution along river transects, a depth-averaged, hydro-morphodynamic model was employed. Using the model, we investigated a medium-sized, braided river with a gravel bed affected by riparian vegetation. The following scenarios of vegetation transect distributions were examined: (1) vegetation established near or covering the low water channel, and (2) vegetation established on bar tops and kept at a distance from the low water channel. The model successfully reproduced a reduction in the braiding index for a vegetated braided river. Depending on the transect distribution scenarios employed, significantly different effects for river morphology were obtained. For example, compared to vegetation on bar tops, vegetation located near the low water channel played a more critical role for changing river morphology, redirecting water flow, and changing the statistical characteristics of the riverbed elevation distribution. Vegetation near the low water channel not only concentrated water flow to low water channels but also redirected flow to the high elevation area by reducing low water channel flow capacity. The revealed effects of the vegetation transect distribution on river morphology development helped to determine effective management protocols for reducing the negative impact of vegetation encroachment.

Estimation of morphological changes of the Odra River valley in meandering sector between Chałupki and the Olza River mouth after 1997 flood

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Głowski R. , Kasperek R. , Parzonka W. , Wiatkowski M.

tom Vol. 33, no. 1

67-74

On the Polish-Czech Odra river section between Chałupki (Poland) and the Olza river mouth there are unique in European scale meanders (km 21.3 - 26.8). In the 20"1 century the break-up of two meanders caused by floods in 1967 and 1997 occurred. The total length of meandering section has become shorter and the hydraulic gradient increased. The sediments eroded and transported by the stream have settled in different zones of the meandering section. In 1997 the inlet to the meander I was blocked by settled sediments causing the break-up of this meander. The paper presents the preliminary estimation of morphological changes of the river bed and the physical and rheological characteristics for settled sediments.

Na polsko-czeskim odcinku rzeki Odry pomiędzy Chałupkami (Polska) i ujściem rzeki Olzy (Czechy) występują unikalne w europejskiej skali meandry (km 21,3 - 26,8). W XX wieku wystąpiło przerwanie dwóch meandrów podczas powodzi w 1977 i 1997 roku. Nastąpiło skrócenie długości rzeki na tym odcinku oraz wzrost spadku podłużnego. Erodowane i transportowane przez strumień rzeczny rumowisko osadzało się w różnych strefach odcinka meandrującego. Podczas powodzi w 1997 r. osadzające się rumowisko spowodowało zablokowanie wlotu do meandra nr I co spowodowało jego przerwanie. Artykuł prezentuje wstępną ocenę morfologicznych zmian koryta rzeki Odry oraz charakterystykę cech fizycznych i Teologicznych osadzonego rumowiska.