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Spatial variability of sediment grain size across stream orders in the headwater catchment of Omi River Basin, southwestern Nigeria

Igbozurike Joy Chimemela, Adeyefa Adewale Oluwagbenga, Obateru Rotimi Oluseyi, Olusola Adeyemi Oludapo

Acta Geophysica

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2025

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Vol. 73, no. 4

3513--3529

EN

Sediment grain sizes vary with channel material and morphology, hydraulic processes and environmental controls in the basin and may influence basin ecological health. In this study, we assessed the variation in particle size distribution across stream orders and along the longitudinal profile of the Omi River basin in Ibadan, southwestern Nigeria. The basin was partitioned into upstream, midstream and downstream segments along the longitudinal profile. Forty (40) reaches were sampled across the first-, second-, and third-order streams. Sediments from the riverbed were collected at the reaches using a sediment grabber and analyzed for particie sizes using standard laboratory techniques. Fine-grained sediments (75-210 gm) exhibit dominance across the stream orders, although it is intermixed with silt and pebbles in the mid-stream and occasioned by silt downstream. We identified no significant difference in particle size distribution across stream orders (X2 (16) = 13.234, p > 0.05) and along the river longitudinal profile (X2 (16) = 21.963, p > 0.05) due to the dominance of fine sand. Further, a significant variation in the distribution of sand (F(2,37) = 8.981, p < 0.05) and clay (F(2,37) = 4.110, p < 0.05) particle size components along the longitudinal profile was obtained. The prevalence of fine-grained sediments suggests that the basin may be experiencing considerable soil erosion and sediment transport, impacting water quality, stream stability, and aquatic ecosystems. Therefore, we recommend further research on the sediment grain size dynamics relative to river water quality and channel geometry in the basement complex terrain of humid tropical environments.

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Modelling flow changes in potential climate change conditions - an example of the Kaczawa basin

Kuchar L., Iwański S., Jelonek L., Szalińska W.

Studia Geotechnica et Mechanica

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2012

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Vol. 34, nr 2

51-62

EN

Climate change, regardless of the causes shaping its rate and direction, can have far-reaching environmental, economic and social impact. A major aspect that might be transformed as a result of climate change are water resources of a catchment. The article presents a possible method of predicting water resource changes by using a meteorological data generator and classical hydrological models. The assessment of water resources in a catchment for a time horizon of 30-50 years is based on an analysis of changes in annual runoff that might occur in changing meteorological conditions. The model used for runoff analysis was the hydrological rainfall-runoff NAM model. Daily meteorological data essential for running the hydrological model were generated by means of SWGEN model. Meteorological data generated for selected climate change scenarios (GISS, CCCM and GFDL) for the years 2030 and 2050 enabled analysing different variants of climate change and their potential effects. The presented results refer to potential changes in water resources of the Kaczawa catchment. It should be emphasized that the obtained results do not say which of the climate change scenarios is more likely, but they present the consequences of climate change described by these scenarios.

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Application of Newtonian nudging data assimilation method in hydrodynamic model of flood flow in the Lower Biebrza Basin

Mirosław-Świątek D.

Studia Geotechnica et Mechanica

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2012

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Vol. 34, nr 2

91-105

EN

The paper presents a 1D hydrodynamic flood flow model employing a data assimilation procedure based on Newtonian nudging. Data assimilation was used to determine correctly the upstream boundary condition defined as a discharge hydrograph. In the model developed, "nudging to individual observations" method was used. The data chosen for assimilation were water table levels recorded by a D-Diver automatic sensor installed in the river channel c. 1.5 km below a computational cross-section opening the analysed stretch of the river and the adjacent valley. This hydrological model of flood flow containing the data assimilation procedure is based on a one-dimensional Saint-Venant system of equations (dynamic wave model). The calculations were performed for the 2010 spring flood event at a 20-km stretch of the river and the floodplain in the upper part of the Lower Biebrza Basin. Modifying the boundary condition by using data assimilation has dramatically improved the accuracy of water table predictions during floods in the area of the Lower Biebrza Basin.