V-5-Effect of Two Hydroelectric Projects in Series on the Low Flow Characteristics of Satluj River.

Abstract

A large number of hydropower schemes on the Satluj River are in different stages of development. These river valley schemes will cause flow related impacts due to storage, flow diversion, tunnelling, muck disposal etc. There may be critical reaches in which altered flows are not able to sustain the riverbed ecology and riparian environment existing prior to implementation of the storage and diversion schemes. In this context, the effect of two hydropower projects in series on low flow characteristics of Satluj river has been evaluated in the present study. As an improvement over the previous hydrological studies of Satluj basin, the methodology proposed in this study is based on correlation between discharges of tributaries having similar catchment characteristics. Distinction has been made on the basis of (i) rainfed and snowfed catchments; (ii) durations with and without snowmelt contribution. Specific discharge (discharge per unit catchment area) duration curves of Sholding, Gaanvi, Shaba and Baspa streams are quite similar and hence discharge data of these streams can be used to estimate discharges of other streams on per unit catchment area basis. Difference in the values of Q90/Q50 for tributaries on right bank (Gaanvi, Bhaba) and left bank (Sholding, Baspa) indicate different normalized basetlow contributions from these catchments and it might be attributed to the amount of precipitation varying with the location of these catchments, whether in forward or leeward zones. Therefore, tributaries in the study area are divided into (i) Left bank tributaries having snow melt contribution, (ii) Right bank tributaries having snow melt contribution and (iii) Tributaries having no snow melt contribution. Estimated tributary discharges have been used in lean season flow mapping of Satluj river from Nathpa to Jhakri. Further, low flow characteristics of Satluj river at three locations i.e. (i) Nathpa, (ii) d/s of confluence of Sholding stream and (iii) Rampur have been analyzed. Flow variability (represented by ratio Q20/Q90) has significantly increased in post-NJHEP condition. The ground water contribution to Satluj flow (represented by ratio Q90/ Q50) is relatively higher in post-NJHEP condition compared to pre-NJHEP condition.