Simulation of the sedimentation process in settling basins by using Delft 3-D model

Sediment transported by natural stream has often faced the designers of the irrigation system andhydropower plant with major problems when withdrawing water from these streams. Severalmeasures for solving the sediment problems at intakes have been proposed since ancient times.Most of the proposed sediment exclusion measures have been developed based on the practicalexperience and on empirical formulae derived from this experience.Sedimentation in canals is also a familiar problem to the operators and users of irrigation systems.Reductions in supplies, declining service areas and severe maintenance requirements can allresult from sediment deposition in the canals of an irrigation system. In extreme circumstances,sedimentation can compromise the viability of an entire system.Settling basin consists of two or more chambers which are much wider than the diversionsystems. The inlet and outlet chambers are locked by the hoisted gates. When the water passesthrough it the water rapidly looses it's velocity and the suspended particle have enough time tosettle down. As the particle move to chambers it descends due to self weight. The settling rate ofsuspended particle is also call fall velocity which depends on shape, size, viscosity andtemperature of waterTraditionally, settling basins were built based on retention time. The settling basins weredesigned to retain water for a specified period of time. However, most settling basins built thisway were oversized and inefficient because critical design criteria were not considered orinadequate. The settling basin consists of an oversized section of the canal or other arrangementin which the velocity is low enough to permit the suspended particles to settle out. Only clearwater will then enter the canal and the sediment is removed from the settling basin by sluicing ormechanical means.This present study provides an overview on the sedimentation process occurring in a settlingbasin and recommendations for a correct design of the basin based on a comparative study byapplying the classical methods and use of the modern simulation techniques, following athorough study of the available literature. The objective of the study is to describe in details theprocess of sedimentation and review on the prediction and design methods of the processes withspecial emphasis on the use of mathematical models.A case study to justify the significance of mathematical modelling approach in the design of thesettling basin using one, two and three dimensional model developed by DELFT HYDRAULICSis also presented