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

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.