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Desertification and Land Degradation Processes
Published in Ajai, Rimjhim Bhatnagar, Desertification and Land Degradation, 2022
As the process of erosion progresses, rills give rise to gullies, and with further erosion, a network of gullies is formed. The intricate network of gullies is called ravines. Ravine is a small narrow steep-sided valley that is larger than a gully and smaller than a canyon and that is usually formed by running water. The word ‘ravine' denotes gullied land containing a system of gullies running almost parallel to each other and entering a river flowing much lower than the surrounding land. Sharma (1968) has defined a ravine as a channel of ephemeral flow, denuded and guided essentially by the presence of rejuvenated streams and having steep sides and head scarps with a width and depth always larger than a gully. Ravines begin along the riversides and encroach upon the catchment area by head-ward growth. Therefore, ravines are said to be the forms produced by river action and gullies are the function of catchment area (Sharma 1980). In simple terms, ravines are defined as a system of gullies formed along the course of the river system. In this case, gully formation begins along the riverside and encroaches upon the catchment area with the flow of river water during the rains. Usually, ravines develop in unconsolidated materials due to changing land use patterns and the associated change in catchment hydrology. In the field, ravines are recognized as very deep and wide channels, greater than 2 m in depth and width along the course of rivers (FAO 2011). Ravines and gullies have been found to occur in the alluvial valleys of both humid as well as dryland regions.
Bayesian learning of Gaussian mixture model for calculating debris flow exceedance probability
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2022
Qin-Xuan Deng, Jian He, Zi-Jun Cao, Iason Papaioannou, Dian-Qing Li, Kok-Kwang Phoon
In this section, the proposed method is applied to learning a BGMM of Qtotal and Pmax based on the data observed at Jiangjia Ravine, China, and to calculating their EPs based on the learned GMM. Jiangjia Ravine is located at Yunan province, China, and the main gully is 13.9 km with the catchment area of 48.6 km2. The Chinese Academy of Sciences set up Dongchuan Debris Flow Observation and Research Station (DDFORS) at Jiangjia Ravine. The DDFORS has been monitoring and recording debris flow events in the area since 1961 (Kang et al., 2006, 2007; Hong et al. 2015). In this study, the observational data of Qtotal and Pmax of 118 continuous debris flows, which last for a relatively long duration and produce a large amount of discharge, occurring from 1987 to 2000 are used for illustration. Details of the database of continuous debris flows adopted in this study are referred to Table A.2 by Hong et al. (2015), which are not provided here for conciseness.
Predictive modeling and analysis of runout distance of physical mudflows based on a discrete element method
Published in Journal of the Chinese Institute of Engineers, 2021
Jian Ye, Gordon G. D. Zhou, Jinfeng Liu
The physical mudflow flume tests focused on the morphology, maximum depositional width, and maximum depositional length, rather than the rheology, sedimentology, stratigraphy, and other physical characteristics of physical mudflows. The material for physical mudflow flume tests was derived from a gully near the entrance of the Jiangjiagou ravine, Yunnan Province, China. This material has wide variation in particle size, from clay to gravel, with a maximum size of 10 mm. According to the physical and mechanical properties and characteristics, mudflows can be divided into three types: diluent mudflows, viscous mudflows, and viscoplastic mudflows. When the bulk density is more than 1.85 g/cm3, the viscosity and shear force increase sharply with each increase of bulk density (Ma et al. 2005). The characteristics of the mudflow are as follows: viscous mudflow gradually transitions to plastic mudflow with the characteristics of plastic flow. Therefore, the physical characteristics of our physical mudflows should correspond to those of plastic mudflows. Physical mudflow flume tests comprised six groups, with a bulk density for each group of 2.0 g/cm3. The gradient of the physical mudflow flume (Figure 1(a) and Table 1) reached a maximum of 12°, with a constant gradient of 2° in the area of deposition, whereas the physical mudflow volume changed for each group. Table 1 shows the relevant test parameters for the physical mudflow flume tests.
Palestinians and donors playing with fire: 25 years of water projects in the West Bank
Published in International Journal of Water Resources Development, 2021
Julie Trottier, Anaïs Rondier, Jeanne Perrier
Until donor intervention, nearly all wastewater seeped into the aquifer through domestic cesspits or was channelled into a nearby wadi: a valley, ravine, or channel that is dry except in the rainy season. The many trajectories of these flows led simultaneously to recharge and contamination of the upper, unconfined aquifer. The wastewater eventually gathered in wadis and, in the western and north-eastern aquifers, flowed into Israel through the Green Line, mainly through the six entry points illustrated on Figure 2. In 2017, 21.4 million m3 of wastewater flowed into Israel, which billed the PA USD 31 million for treating it (World Bank Group, 2018). The PA counts on WWTPs and reuse projects to eliminate this outflow of surface wastewater into Israel and thereby eliminate this sizeable expense.