Impact of river morphology on water self-purification capacity

ABSTRACT The diversity of river morphology is a critical factor in promoting the sustainable development of aquatic ecosystems. However, rapid development in China has led to a simplification of river morphology, resulting in significant water environmental challenges. This study developed a multi-morphology mobile bed river experimental apparatus and designed four sets of comparative simulation experiments based on typical natural river morphology types: ‘mild slope – drop structure,’ ‘high-permeability – low-permeability,’ ‘high-velocity river – low-velocity shallow lake,’ and ‘obstructed – unobstructed.’ Pollutant reduction experiments were conducted, monitoring the concentrations of TN, NH3-N, NO3-N, and TP during a 96-h water circulation test. The experimental results revealed that the drop structure river, permeable slope river, high-velocity river, and rivers with certain obstructions exhibited average pollutant reduction rates that were 10.5%, 5.4%, 16.8%, and 4.7% higher than their respective control groups. Their steady-state reduction intensities were also higher, by 0.6%/h, 1.5%/h, 2.7%/h, and 1.5%/h, respectively, indicating more sufficient hyporheic exchange and significantly stronger pollutant reduction capacity. The reason is that these morphological elements provide conditions for turbulence and diffusion in water flow. This study provides references for river ecological restoration and sustainable utilization of water resources.