Changes over flood season in turbidity maximum zone in a mountainous macrotidal estuary from 1986 to 2020

The construction of channel regulation projects, reservoirs, and other human activities have led to significant changes in channel geometry and hydrodynamic conditions in mountainous macrotidal estuaries. However, their impact on the long-term evolution of the turbidity maximum zone (TMZ) in these estuaries is still unclear. Therefore, the Minjiang Estuary (ME) was selected as the study area and using the Gabor filter and surface suspended sediment concentration (SSSC) data retrieved from GF PMS/WFV and Landsat-TM/ETM+/OLI images in the flood season from 1986 to 2020, the flow direction of Chuanshi Waterway, the spatiotemporal evolution characteristics of TMZ in the ME, and the influence of human activities on these were analyzed. The results indicate that during flood tides in the past 35 years, the TMZ was mainly distributed in sections from the Changmen to the Chuanshi and Meihua waterways. The construction of the Shuikou Reservoir caused the SSSC to decrease by 65 mg/L at the Chuanshi Tidal Gauge Station in the ME. The TMZ in the ME waterway channel notably migrated toward the sea due to the waterway regulation project, with the landward and seaward boundaries moving by 2.5 km and 3 km seaward, respectively. The main distribution area moved from Jinpaimen to the section from Chuanshi Waterway to the mouth of the ME. These variation characteristics were basically consistent with the annual average TMZ in the flood season. Through the interactions between nature and human interventions, the flow regime of the ME tended to converge in the flood season. Therefore, human activities have significantly impacted the long-term evolution of the TMZ in the ME.