## 1 Introduction  
Sediment erosion and deposition are key factors affecting the performance of water transport facilities, commonly found in water transport facilities such as port terminals, ship locks, and canal hubs, and they have become the main issues hindering their operation. This problem leads to the blockage of navigation due to the sediment deposition, erosion, and instability of the embankment, as well as environmental issues such as soil erosion and sediment entering the sea [1].  
Many scholars have conducted extensive research and surveys on the issues of sediment erosion and deposition. These studies mainly focus on two directions: One is the mechanism of erosion and deposition, such as the formation and development of erosion and deposition, the scope of erosion and deposition, and analytical or numerical models of scour development [2; 3; 4; 5]; the other is the analysis of the mechanical response of structures to changes in sediment erosion [6; 7; 8; 9]. These studies provide valuable references for the construction of engineering facilities in areas with complex sediment erosion and deposition changes, but they do not explain how to directly address the problem of bank slope erosion and deposition. The phenomenon of erosion and deposition on wharf slopes is a slow and continuous process that is difficult to detect before causing structural damage. Without an effective monitoring and alarm system, repairing only after damage occurs not only affects the normal operation of ports, docks, and navigation locks but also requires a significant investment of human and material resources. Therefore, it is extremely important to scientifically and effectively monitor the sediment erosion and deposition conditions on wharf slopes. Developing an efficient and low-cost device capable of identifying the water-soil interface is key to solving this problem.  
Due to the differences in thermodynamic parameters between water and soil, such as density, specific heat capacity, and thermal conductivity, identifying these differences has become the focus of developing related equipment. In the water medium, heat transfer primarily occurs through thermal convection [10]. In contrast, heat transfer in the soil medium occurs primarily through thermal conduction. Due to the low specific heat capacity and thermal conductivity of soil, heat transfer from the heat source is significantly slower [11]. Therefore, through the heating of hot and specific power sources in water and soil media, it can be observed that the two kinds of media have obvious temperature differences, and thus the dynamic capture and monitoring of the water-soil interface of the side slope of the bank slope is imperative.  
However, in theoretical research, the heat transfer law of linear heat sources is only derived in a single medium, due to the idealization of theoretical assumptions and the complexity of practical engineering, while disregarding the radial temperature variation in the soil-water coupling region during the heat transfer process involving a linear heat source [12]. At the same time, it was assumed that the linear heat source was located within a semi-infinite medium, resulting in discrepancies between experimental verification results and theoretical outcomes. In addition, physical experiments under excessive conditions have a long time and high cost, and the results are affected by multiple factors such as linear heat source model making, model slot size, and soil configuration accuracy [13]. Based on the accuracy and reliability of the numerical simulation with laboratory test results, this paper summarizes the rules governing temperature attenuation and propagation range for iron- and PVC-based linear heat sources across eight types of viscous soils as well as six types of non-viscous soils using finite element model analysis results. These findings provide a foundation for designing subsequent monitoring equipment.