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Hydraulic geometry influences some water quality parameters in a tropical headwater basin in southwestern Nigeria

Obateru Rotimi Oluseyi, Fashae Olutoyin Adeola, Osakunih Oluwatobiloba Isioma, Olusola Adeyemi Oludapo

Acta Geophysica

2023

Vol. 71, no. 4

1857--1866

Hydraulic geometry characteristics can influence stream ecosystem and biogeochemical processes at different spatial scales. Globally, studies are emerging on the relationship between channel geometry and water quality. However, these studies are few and far between most humid tropical basins. In this study, we assessed the relationship between hydraulic geometry and some water quality parameters [temperature, salinity, pH, electrical conductivity (EC), total dissolved solids (TDS) and total suspended solids (TSS)] across stream orders of a tropical headwater basin in southwestern Nigeria. Bankfull width, depth, velocity and discharge were measured at twenty-six (26) reaches across first-, second- and third-stream orders within the basin. Water samples were collected from these reaches and were analyzed. Bankfull width, velocity and discharge showed significant variation across stream orders, while the water quality parameters vary slightly in response to fluvial and geogenic interactions. We obtained r = − 0.417, p < 0.05 for TDS and discharge, r = − 0.399, p < 0.05 for depth and TDS, r = − 0.39, p < 0.05 for width and EC, and r = − 0.42, p < 0.05 for width and pH. The headwater basin is underdeveloped and it is still undergoing fluvial adjustment. We recommend the need for future studies to investigate the intrinsic interaction between channel geometry and stream water contamination for natural and disturbed headwater basins.

Depositional styles and adjustment of channel cross sections in a seasonal deltaic system: a large scale physical experiment

Luo You, Zhang Hongbin, Zhu Senlin

Acta Geophysica

2021

Vol. 69, no. 6

2443--2452

Small scale experiments provide limited mechanistic insight on the evolution of the cross-sections of the channel in a deltaic system. Here, we report the results of a large-scale tank experiment on the deltaic processes in a new river course into the Qinglan Lake. The depositional body occurred from upstream to downstream in the new river course in the depositional processes. Three depositional styles have been observed in the delta building: levee, stable-bar, and wandering-bar. Single thread and braided channels have been formed with deposits of levee style and stable-bar style. Wandering-bar style, which is an autogenic process, refers to the switching in the location of the main silting zones at different spatial–temporal scales and is frequently accompanied by avulsion, river braiding, and mainstream migration. The elevation of levees and bars increased to the bankfull elevation in the blocked river reach in the first 30~40 years and impacted the main channel flow. Comparing to the blocked river reach, the evolution of the bankfull elevation and geomorphic coefficient B0.5/H (B is width, H is water depth) of the cross-sections in the new reach indicates that the evolution pathways of the cross-sections could be divided into two stages: convergent stage and autogenic feedback stage. The convergent stage refers to a positive feedback loop, while the autogenic feedback stage is dominated by autogenic process. The present study shows the diversity of landforms, complex feedbacks and internal thresholds of a seasonal deltaic system, and the results provide another view on hydraulic geometry.