Experimental Study of Site-Specific Soil Water Content and Rainfall Inducing Shallow Landslides: Case of Gakenke District, Rwanda

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.

Experimental Study on Runoff and Sediment Production of the Fully Weathered Granite Backfill Slope under Heavy Rain in Longling, Yunnan Province

“…Regarding the mechanisms of slope flow and sand production, under specific rainfall intensity and catchment area conditions, the production of slope flow primarily hinges on the soil's infiltration characteristics [55,56]. In contrast, the sand production on slopes predominantly results from gully wall collapse and runoff scouring [57][58][59].…”

Nghiên Cứu, Đánh Giá Tiềm Năng Ứng Dụng Cảm Biến Gia Tốc Trong Quan Trắc Và Cảnh Báo Sạt Lở

“…Theo nghiên cứu của HWANG và các cộng sự [7], khi thể tích nước trong đất đạt đến giá trị bão hòa do mưa, có thể gây ra sạt lở mái dốc do sự suy giảm cả cường độ chống cắt và lực dính của đất. Tuy nhiên, theo nghiên cứu của Martin Kuradusenge và các cộng sự tại Rwanda [9], giá trị ngưỡng để cảnh báo dựa vào lượng mưa hoặc hàm lượng nước trong đất cho các khu vực và vị trí khác nhau là không cố định. Bởi vì nó còn phụ thuộc nhiều vào thành phần hạt, địa chất nền đất, hệ số mái dốc, tính chất thảm thực vật.…”

Developmental characteristics of rainfall-induced landslides from 1999 to 2016 in Wenzhou City of China

“…This fits well with the field survey results: the Baofeng debris flow in Wencheng County occurred ~10 min after typhoon Megi in 2016 and the Cangjiang landslide occurred only 5 min after typhoon Soudelor in August 2015. This association occurs because heavy rainfall can make the soil layer saturated for a short time (Kuradusenge et al, 2021), then the continuing rainfall generates large runoff that provides enough excitation energy to cause the movement of rock-soil masses.…”