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In the pre-TGD period, the sediment budget shows that the Shashi Reach was subjected to significant erosion (Table 2). The sediment eroded from the reach amounted to 0.7 × 108 m3 from 1981 to 2002. Erosion mainly occurred in the low-flow channel and reached 0.77 × 108 m3, while in the bars, accretion took place, reaching 0.07 × 108 m3 (the value is the amount of bank-full flow channel minus low-flow channel). After the TGD began to operate, the mean SSD decreased noticeably. The average annual sediment load decreased by 80% post-TGD. This change generally matched the changes in erosion/accretion on the riverbed in the reach. The erosion that occurred pre-TGD continued. Table 2 shows that during the initial stage (c. 2003–2006), transitional stage (c. 2006–2008), and normal stage of the TGD project, the eroded sediment in the flood channel of the reach reached 0.48 × 108, 0.14 × 108, and 0.64 × 108 m3, respectively. Erosion still occurred predominantly in the low-flow channel. Over all three stages of the TGD project, the ratio of the amount of erosion in the low-flow channel to the amount in the bank-full channel was about 90%.

Table 2

Quantification of the erosion and the deposition in the river channel (×108 m3)

1980–20022003–20062006–20082008–2013
Bank-full flow channel −0.70 −0.48 −0.14 −0.64 
Low flow channel −0.77 −0.45 −0.13 −0.57 
1980–20022003–20062006–20082008–2013
Bank-full flow channel −0.70 −0.48 −0.14 −0.64 
Low flow channel −0.77 −0.45 −0.13 −0.57 

Negative values indicate erosion.

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