Abstract
Shallow landslides are among the natural threats causing death and damage. They are mostly triggered by rainfall in mountainous areas where precipitation used to be abundant. The amount of rainfall inducing this natural threat differs from one site to another based on the geographical characteristics of that area. In addition to the rainfall depth, the determination of soil water content in a specific zone has a major contribution to the landslide prediction and early warning systems. Rwanda being a country with hilly terrains, some areas are susceptible to both rainfall and soil water content inducing landslides. But an analytical study of the physical threshold determination of both rainfall and soil water content inducing landslides is lacking. Therefore, this experimental study is conducted to determine the rainfall and soil water content threshold that can be fed in to the landslide early warning system (LEWS) for alert messages using the Internet of Things (IoT) technology. Various experiments have been conducted for the real-time monitoring of slope failure using the toolset composed of a rain gauge, soil moisture sensors, and a rainfall simulating tool. The results obtained show that the threshold for landslide occurrence does not solely correlate with the total rainfall amount (or intensity) or soil moisture, but also influenced by internal (geological, morphological) and environmental factors. Among the sampled sites, the sites covered by forest indicated no sign of slope failure, whereas sites with crops could slip. The experiments revealed that for a specific site, the minimum duration to induce slope failure was 8 hours, 41 minutes with the rainfall intensity of 8 mm/hour, and the soil moisture was above 90% for deeper sensors. These values are used as thresholds for LEWS for that specific site to improve predictions.
Highlights
Rainfall-induced shallow landslides are among the most natural disasters that causes deaths and substantial economic losses damaging infrastructure or plants in different mountainous regions around the world [1,2,3]
The study consisted of the measurement of rainfall and soil water content using a rain gauge and soil moisture sensors
Steep slopes are more susceptible to shallow landslide incidence compared to the very steep slopes
Summary
Rainfall-induced shallow landslides are among the most natural disasters that causes deaths and substantial economic losses damaging infrastructure or plants in different mountainous regions around the world [1,2,3]. Rainfall-induced landslides are mainly caused by intrinsic factors like geological and geomorphological parameters and extrinsic factors such as hydrological conditions, climatic conditions, earthquakes, and volcanic eruptions [9,10,11]. Hydrological factors such as rainfall and ground water table location influence the slope stability. The water content in the shallow soil is almost absent during the dry season When it rains, the rainwater starts penetrating into the earth characterized by different permeability properties, and the ground becomes moist. The matric suction ðψmÞ plays a crucial role in landslide occurrence and is defined as the difference between pore air pressure ðuaÞ and pore water pressure ðuwÞ [15,16,17,18]
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