Response analysis of valley settlements to the evolution of debris flow fans under different topographic conditions: a case study of the upper reaches of Min River, China

The upper reaches of Minjiang (Min) River were selected to research the relationship between debris flow fan formation and topography. Combining the historical statistical data of settlement and debris flow events, there are 3 years (1994, 2004, and 2014) for which comparable data are available. With the support of remote sensing (RS) and geographic information system (GIS) technology, the distribution characteristics and evolution of valley settlements and debris flow fans in terrain conditions with varying elevation, slope, and slope aspect are analyzed. The coupled relationship between valley settlement and debris flow accumulation fan evolution is analyzed by regression analysis. The results show that the distribution characteristics of valley settlements and debris flow fans in the upper reaches of Min River show high consistency and convergence in different topographic conditions, and they have a response relationship with each other. With elevation, both settlements and debris flow fans increase linearly with each other, and, over time, the rate of change of the distribution of valley fans with debris flow accumulation increases then decreases. In regard to slope, both parameters conform to two polynomial function models, that is, the river valley settlement increases first and then decreases with the increase of debris flow accumulation fans. For the slope aspect, the number of valley settlements increases with the increase of the change rate of debris flow fans density. The study will provide some assistance for the countermeasures on valley settlements to the evolution of debris flow fans in the upper reaches of Min River.