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Scale Effect on Zone Settling for Flocculent Suspensions with Clear Interface

Author(s): Shaohua Marko Hsu; Cheng Chieh Lin; Chao Qin Wang

Linked Author(s): Shaohua Marko Hsu

Keywords: Muddy lake; Settling velocity; Cohesive sediment; Reservoir

Abstract: Settling of cohesive sediment can be classified into four categories including single particle settling, floc settling, framework settling, and consolidation settling. In most reservoirs, suspended sediment is mainly composed of cohesive sediment. After a storm event, inflow with high concentration sediment provides sufficient sediment source and form a framework settling in a muddy lake near a dam location. Logical and technical difficulty has revealed that repeatable settling tests on the scales of realistic sizes are intractable. To perform sensitivity analyses for key parameters in settling procedures, conceptually simplified column tests are generally the feasible tools to understand such settling behaviors. However, the scale effects become an important issue if one applies results of column tests to the scales on sites. In this study, we used four different settling equipments with different sizes and three different types of cohesive sediments to conduct settling tests. Our test results showed that the clear interface may not be associated with floc settling. There are criteria for sediment concentration to create the framework settling with constant settling velocity. For cohesive material collected in Shihmem reservoir in northern Taiwan, the incipient concentration level for zone settling and for constant settling velocity are 25 g/L and 60 g/L, respectively. The scale effect on the horizontal scales does not exist for our columns and tank tests. In addition, the vertical scales only affect time lags for constant settling periods. The time dimensionless plot showed similar trends for each vertical scale.


Year: 2007

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