RHEOLOGICAL RELATIONSHIP TO SEDIMENT DEPOSITION RATE IN MACAN WEIR SEDIMENT TRAPS

Abstract

Irrigation canals require a sediment trap to control not-allowable sediment deposits in the primary irrigation canals to maintain the highest paddy yield. The not-allowable sediment deposit for Cimacan River, not only non-cohesive sediment (dia>0.07mm) as for regular river, but also cohesive sediments (dia<0.07mm) that could be cemented rapidly under the laminar flow condition and then potentially decrease the performance of irrigation canals. This paper presents the resulting study of the rheologic characteristic of the cemented bed sediments and the threshold velocity related to the sediment cementing process of irrigation canals in the Cimacan River. The study was conducted based on field and secondary data. The geological investigation had been carried out and tested to obtain grain-size distribution, sediment stratification, and water temperature in the Cimacan river tested in 2017 and 2019. Secondary data is taken to support the comparison study. Based on this study, it is found that the cemented sediment could be flushed only when the average velocity of the lower layer of the flow is greater than the threshold velocity of cementing occurrence. In this case, the μ movement curve as a function of viscosity Iv that could reach beyond the range of 3×10-5<Iv<2 had shown the validation of local rheology models. Meanwhile, the range of Iv<3×10-5 could be described as transitions flow where μ→μs could be expected for flushing the sediment layer. Numerical models can easily calculate this rheology regime. However, to achieve maximum results, it is necessary to develop a physical model supported by a binocular microscope.