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The spatio-temporal evolution law of beach morphological features: taking Qujiang River in Longyou County as an example

The beach is an important barrier to maintain the health of the river. The shape of the beach affects the environmental capacity of the river, the attractiveness of the river’s landscape and the degree of ecological fragility to a certain extent. This paper took the Qujiang River in Longyou County, Zhejiang Province as the research object, and used BigMap software to obtain the geometric characteristic parameters of the beach in different years, calculated the landscape pattern index and disturbance degree, and analyzed the spatio-temporal evolution of the beach. The results show that: (1) From 1985 to 2020, the pattern of the beach has changed obviously. The total area of the beach has been reduced by 16.83%, and the number of beach has been reduced by 77.85%. (2) From an overall point of view, the disturbance degree of the beach from 1985 to 2020 is 0.024, and the change is not obvious; From the perspective of the river section, the disturbance degree from upstream to downstream is 0.102 (upstream)> 0.088 ( downstream)> 0.020 (midstream). (3) The construction of water conservancy projects, ship ripples and sand mining have affected the lateral sand transport conditions of the river and the hydraulic shear stress, which accelerated the evolution of beach and showed different distribution patterns.