Assessment of Sediment Hazard and Associated Measurement

Abstract

The uncontrolled excess sediment transport into farm fields and river reaches can have disastrous effects leading to hazards and mitigation of these serious issues need extensive study. Sediment hazards, a threat to different biotic and abiotic factors of the ecosystem take place due to either the transportation of sediment or its deposition. Various causes, effects, and mitigation strategies for the sediment hazard along with respective case studies are presented in this article. A natural physical phenomenon like rainfall, melting of glaciers as well as human activities like mining, construction of roads, and railway tracks can increase the availability of sediment and its transport results in landslides. The sediment carrying trace metals and harmful chemicals, when enters the river, can disturb the aquatic life and society dependent on the river. The sediment transport is also responsible for the hydro-abrasive erosion of the hydraulic components. In addition to sediment transport, sediment deposition is also a big issue as it reduces the reservoir capacity affecting various factors like irrigation, hydropower generation, etc. depending on it. From analyzing various case studies, it is inferred that the chance of sediment hazard is more where other natural hazards like floods, earthquakes, and volcanic eruptions are frequent as in the Himalayan regions, Japan, Colorado, etc. Various sediment measurement techniques are also discussed in the article, which includes the measurement of suspended sediment and bed load. In various mitigation measures, the reinforced synthetic fiber-based river bank stabilization is found to be the most durable method due to its high strength and non-biodegradable nature. Furthermore, the laser diffraction-based instrument is found to be the best method at the moment for measuring suspended sediments continuously as it can provide both size and concentration information with good accuracy. For bed load measurement, the radioactive tracer method is found to be the most flexible option as it can be used for in situ measurements and can also measure fine sediment particles. Knowing the sediment discharge and suspended sediment concentration (SSC) with a proper mitigation technique to tackle the sediment hazard can be selected or developed effectively and this will improve the living condition of flora, fauna, society, etc. during hazardous situations in addition to enhancing the efficiency of hydraulic structures and machinery. A land slide early warning system (LEWS) based on the rainfall forecast model is found effective in determining the threshold limit for evacuations in different national systems. In the future, the number of computational software to predict the flow pattern and intensity of sediment transport will increase.