IMPROVEMENTS IN LONG TERM SIMULATION STUDY FOR RESERVOIR PLANNING

Abstract

Conventional procedures of reservoir planning were evolved considering limitations of data, computational facility and methods of analysis. With availability of computer technology and analytical tools, it is now possible to simulate long-term behaviour of reservoir under variety of conditions and make the reservoir planning more realistic as well as reliable. Even the preliminary reservoir design in prefeasibility stage can be made more realistic and informative. In this study, certain improvement for reservoir planning have been formulated and illustrated through a case study. Preliminary Design In the present study, Gould Gamma method and simulation procedure have been used for developing storage size-withdrawal-probability of failure relationship during preliminary design phase. Analysis of Sediment Distribution Standard type classification of a reservoir in the Area Reduction Method is not constant over entire project life. Due to change in standard type classification, seditnent distribution pattern will also change and vice versa. Even if standard type classification does not change during a period, elevation—area--capacity curve will still undergo revision due to new zero elevation and due to the updated elevation—area—capacity curve at the beginning of the period. Therefore, progressive change in elevation—area—capacity relationship and consequent change in available live storage capacity have been considered in long-term simulation study of Batutegi reservoir. Improvements in Hydropower Simulation Algorithm Linear regression equations have been developed between a). Initial and average elevation, and b). Initial area and average area for different power targets to find net head for power generation and net gain/loss of water due to rainfall and evaporation over reservoir area. Further, net gain/loss have been considered to vary over entire simulation period due to random rainfall. Similarly, variation in power plant efficiency with turbine discharge has been accounted for in the simulation study. Relationships between storage size, power generation (and annual energy generation) and dependability have been developed. Such studies provide useful information to work out trade off between storage capacity, power generation and reliability. iii Abstract Improvements in Irrigation Simulation Algorithm (i.) Alternate irrigation demand pattern related with different scenarios of target irrigation area and different cropping intensities have been considered. Irrigation release requirements at Batutegi reservoir vary from year to year also due to randomness of flow contribution from interim catchment between Batutegi reservoir and Argoguruh weir. (ii.) The concept of Golongan (Group) system of irrigation has been introduced and applied to reduce peak irrigation demand. In case of Batutegi project, peak demand has been reduces from 5003 m3/month/ha to 3686 m3/month/ha by staggering crop calendar over six groups of service area. (iii.) Storage capacity requirement have been worked out for different dependability levels of irrigation water utilization. Dependability has been analyzed on crop seasonal basis also, so as to give due to importance for planning irrigation in a particular season. (iv.) Trade off between irrigation water supply and power generation at different reliability levels provide flexibility to a planner to choose a combination of irrigation supply and power generation at desired reliability levels. Simulation algorithms : (i.) An algorithm for a multipurpose reservoir (hydropower and irrigation) incorporating various improvements has been prepared (Figure 5.2). (ii.) An algorithm for estimation of turbine flow and power generation with variable head loss and efficiency has been developed (Figure 4.4). (iii.) An algorithm depicting application of reservoir operation .rules for estimation of water release through power intake and through irrigation intake with irrigation priority has been developed (Figure 5.3). Conclusions from case study of Batutegi reservoir are : (i.) Installed Capacity greater than 16 MW is not necessary if only hydropower generatibn is considered. (ii.) With same gross storage size (580 MCM), Installed Capacity (24 MW) and target irrigation area (condition VIII) as in project report, annual irrigation reliability by present study is 88%, which is higher than reliability of 75`)/0 considered in project report. A storage of 460 MCM is adequate to meet 75% irrigation reliability criteria. (iii.) A cultivable area of 94,123 ha with 160% crop intensity (100% in wet season and 60% in dry season) can be served with 88% reliability in wet season, 96% reliability in dry season and 88% annual reliability. In addition, 96.5 GWh average annual energy (11 MW average power) will also be available.