Numerical Simulation of Tarbela Reservoir Sedimentation

Abstract

All lakes and reservoirs created on natural rivers are subject to sedimentation. This represents a great challenge to the dam engineers and reservoir managers to devise suitable ways and means to slow down this phenomenon significantly in order to improve sustainability and gain optimum benefits from the reservoir. Tarbela dam is one of the largest earth filled dam in the world used for power generation and irrigation purposes. Commissioned in mid-seventies, it has seen its usable storage capacity reduced from initial 9.68 Million Acre-Feet (MAF) in 1974 to 7.30 MAF in 2010/2011. The objective of the present research is to study the process of sedimentation in the reservoir-river system leading to the formation of the delta by numerically simulating the phenomenon using United States Bureau of Reclamation 1d river model. The model would require extensive data from the field for its setting up and later calibration. The data can be divided into three categories; Geometrical, Hydrological, and that related to sediments. The model used is United States Bureau of Reclamation’s (USBR) Sedimentation and River Hydraulics – one dimensional (SRH – 1d). It solves 1d Saint Venant equations along with the bed and suspended sediment continuity equation for determining the erosion and deposition volumes as well as the changed geometry of the bed. The model can be run for steady flow as well as for unsteady sediment routing taking into account the lag processes in sediment movement. The model is to be calibrated by a simulation period of eight years from 2000 to 2008. The observations of river-reservoir system bathymetry collected from the yearly field surveys would serve as the basis of calibration and validation of the model results. The objective of this research is to develop a model of the reservoir sedimentation using a 1d river hydraulic model. The 1d model despite its obvious limitations of being section-averaged remains a useful tool which can simulate sediment movement over long durations (typically years) for long river reaches (typically, 100 km) in a relatively quick time (typically hours) with modest computer resources. Such a model would serve as an operational tool for the Dam managers to estimate in advance the deposited volumes and its distribution along the river axis. It may serve to simulate different scenarios that can improve the optimum reservoir operation by furnishing a scientific response, albeit, limited.