Sediment control from a diversion headworks system with special reference to Teesta Barrage

Abstract

The present study is mainly devoted to the evolvement of a methodology to design a silt excluder, considering not only the hydraulic parameters but also the sediment discharge including bed and suspended load. The study also includes the estimation procedure of the sediment entrainment through the canal head regulator into the main canal. In developing the design procedure of sediment excluder, a mbdification over Garde and Pande Method (1976) was carried out. The study also contains the best size, shape and location of different component structures of a barrage situated in alluvial plains. A literature survey of the existing barrages particularly in the Indo-Pak'subcontinent together with the available scale models has been also reviewed. Considering above, the design of the Teesta Barrage Silt Excluder has been evaluated and modifications suggested. It has been observed that the present sediment excluder containing discharge of 88.75% of canal discharge will have difficulty in efficient functioning due to nonavailability of hydraulic head for various flow conditions. Teesta River carries 31 million tons of bed material load yearly for 75% dependable flow, of which 75% is from suspended load and 28% is from bedload. Teesta River carries sediment particle range 0.074 to o.15mm, 0.15 to 0.30mm, 0.30 to 0.60mm and >0.60mrn of 42, 42, 14, 2 and 17, 46, 33 and 4 percent respectively from ,suspended load and bed mat~rial. A procedure to estimate bed and sdspended sediment load to be entrain~d into the main canal through the Canal Head Regulator of, the Teestsa B,ar'ragehas also been given. Quantitative values of bed and suspended sediment load with their various grain-size ranges are also estimated. Suggested rectification measures are also advised to incorporate in the Tecata Barrage during the construction phase of the project. Particularly a corrective measure was suggested for no entrainment of bed load and a reduction of 52% of the suspended load entrainment per year for lO-day average 75% dependable flow of the Teesta River based on the analysis of 33 . years data. The possibility of the installation of a sediment ejector in the Teesta Main Canal was also studied arid found to be suitably arranged provided some modifications in the crest level of CHR, FSL and canal bed of main canal are considered.