Morphological change and its response to human activities in the Estuary of Minjiang River, China since last early century

The evolution of subaqueous deltas in mountain rivers is highly sensitive to variations in sediment load and hydrodynamic conditions, and human activities can rapidly alter these parameters. To better understand the evolution of the subaqueous Minjiang River Delta (MRD) under human activities, we investigated the effects of construction of reservoirs, channel training walls, land reclamation activities, and sand mining from 1910 to 2010. Analysis of bathymetric and fluvial discharge data revealed that the MRD shoals generally experienced slight development during the study period, but with alternating stages of erosion and deposition that were related closely to sediment discharge and the role of human activities. The northern MRD was more strongly affected by decreasing sediment load, while the southern MRD was more influenced by land reclamation. Human activities in the MRD can be divided into five stages: Weak (before 1935), blockage (1935-1950), slight strong (1950-1970), strong (1970-2000), and stable (since 2000). Correspondingly, the geomorphic evolution of the MRD can also be divided into five stages: Natural evolution, channel blockage, southern channel erosion, divergence, and degradation. Furthermore, the morphodynamic response time of MRD to a decrease in riverine sediment was found to be less than 10 years, which is much faster than the morphodynamic changes observed in large-scale estuaries and deltas. These results provide further insight into interpreting morphodynamic changes in typical small/medium-sized estuaries and deltas under various human activities.