ASSESSMENT OF OPERATION RULES IN RESERVOIR SYSTEMS: A CASE STUDY OF TARBELA & MANGLA

Operation rules curves of a reservoir are logical mathematical expressions that help in deciding releases at an instant using inflows, storages & system variables. This study has been carried out to assess the performance of rule curves of two of the largest reservoirs in Pakistan; i.e., Tarbela at River Indus & Mangla at River Jhelum. Three vital indicators; reliability, resiliency & vulnerability, delineating several facets of operational performance, were computed using 44 years of daily time-step dataset from 1976 to 2019. Rationale and impacts on account of assessed performance were evaluated. Intra and inter annual analyses were carried out for both reservoirs for the determination of performance indices, coefficient of variation (CV) for maximum and minimum rule curves, lag-time & frequency to attain Maximum Conservation Level (MCL). The status of Mangla was considered as per actual before and after raising. The results indicated that historic reliability & resiliency of Mangla were 12% & 29% respectively higher and a vulnerability of 39% lower than Tarbela. As a consequence, an average annual shortage of 85 Mm3 was encountered by Tarbela & 3.86 Mm3 by Mangla with adverse impact on the hydro-power generation. Further, based on evaluation of the scatter-plot of maximum and minimum rule curves of both reservoirs, it was observed that maximum (CV) values were encountered in the month of April leading to decrease in the reliability and minimum variation in the months of August & September. It was concluded that improved operational rules are essential for a reservoir system to effectively reduce its water shortages. Therefore, optimization of the existing rules is recommended for future work by considering more reservoir details so as to maximize the performance indicators.