Background: In the early morning of 20 August 2014, a high-intensity/low-duration rainstorm occurred in Hiroshima City, in southwest Japan. Within 3 h, the rainfall exceeded 200 mm, which is more than twice the monthly-average for this area. This heavy rainfall triggered 107 debris flows and 59 shallow slides, which caused 44 injuries, and 74 deaths. 133 houses were destroyed and an additional 296 houses were severely damaged. Most of the debris flows occurred in heavily weathered granite slopes, while others occurred in weathered hornfels slopes. A field investigation on two of the gullies in which the debris flows occurred was conducted in order to better understand the characteristics of the debris flows. Results: The main purpose of this investigation was to understand the geomorphological and geological conditions, the soil properties, and the initiation/traveling mechanisms of the debris flows. The longitudinal and cross-sectional profiles along the two gullies were measured, beginning at the source areas and ending at the downstream limits of the deposition areas. For soil property determination, disturbed and undisturbed soil samples were collected for laboratory tests which included in-situ density measurement, grain size distribution analysis and triaxial compression tests. In the triaxial compression tests, consolidated-undrained compression tests under different confining stresses were conducted to measure the strength parameters of the strongly-weathered granite. Pore-water pressure controlled triaxial test was conducted to simulate the failure process of the slope given an increase of the pore-water pressure. Chemical analyses of the granite samples were also conducted in order to understand the degree of weathering of the granite in the debris flow gully. Conclusions: A high intensity, short duration, localized rainfall event initiated debris flows in very steep slopes. These were initiated as a thin sliding mass in weathered coarse-grained granite and hornfels, and became two different types of debris flow after traveling down the slopes. The slope angle and the cross section of the gully, and the grain size of the debris significantly controlled the motion behavior of the debris flows.
City green economy plays an important role in the development of low-carbon economy and the achievement of sustainable development of economy, society and ecological environment. From the perspective of economy, society, environment and resources, the evaluation of the green economy in urban areas tends to offer us a new insight into the green economy of cities. This paper is about the creation of a novel urban green economy evaluation model and its application. First of all, we established a city green economy evaluation index system based on R cluster analysis and coefficient of variation. Secondly, based on the nonlinear weighted utilizing entropy weight method, a city green economy evaluation model is established based on inferior constraints. Thirdly, by comparing the differences between evaluation rankings under inferior constraints and non-inferior constraints, the advantageous factors and the disadvantageous ones in urban green economy development are obtained. The proposed model has been verified with the data on 15 sub-provincial cities in China. Empirical analysis results show that: (1) The proposed approach can accurately find out the advantageous and disadvantageous factors for each sub-provincial city; (2) In the evaluation of green economy development, the order of importance of the three criterion layers is X 1 Economy development > X 2 Social livelihood of the people > X 3 Resources and environment; (3) Local governments should implement differential, reasonable policies in order to improve their green economy development. Moreover, our research is not only significant for developing green economy in China's sub-provincial cities, but also serves as a reference for the development of green economy in other cities in the world.
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