OPTIMAL UTILIZATION OF WATER RESOURCES OF MAHANADI RIVER BASIN IN ORISSA

Abstract

Integrated planning of a river basin as a single entity with multiple purposes and objectives is of primary concern for sustainable water resources development. Planning of reservoir systems, which is having a multifaceted complexity with economical, environmental, social and political dimensions and its planning at river basin level comprising numerous water resources projects makes it exceedinglycomplex. In this context, screening models provide a means for suggesting the promising alternatives by screening out several feasible alternatives as far as the integrated planning of a complex water resources system is considered. Large geographical extent of a river basin involving several number of reservoir systems considering their different stream flows characteristics makes it difficult to adopt an explicitly stochastic formulation which is relevant in modeling the real world basins. Thus, despite the development of various new techniques, implicit stochastic optimization models based on linear programming still remain one of the most readily applicable tool in the analysis of complex systems. Difficulties in explicit stochastic formulations have led the modelers of large integrated systems to rely on implicit stochastic optimization models (Labadie 1997). Apart from type of model suitable for any specific purpose, all most all the model formulations are having the following two majorshortcomings: Generally, the reservoirs are being planned to provide a pre-specified dependability of yield on annual basis. Although the aforesaid consideration satisfies the prescribed project dependability in terms of meeting the target demand, the extent of failure in annual yield during the failure years is not taken into account. This may result in a severe shortage of unknown magnitudes in meeting the demand during critical periods. Secondly, most of the modeling approaches, whether it is an optimization or simulation model, determines the system yield for a pre-defined within-year time period distribution derived from the percentage fraction of annual irrigation target of a proposed crop plan. By such an approach, re-crop planning has become essential since in most of the cases there is a mismatch between the annual yield and the annual irrigation target for the proposed crop planning. However, in that case it is all most difficult to achieve a crop plan satisfying the stipulated constraints that will fully utilize the reservoir releases of each time period. The above two inherent attributes limit the appropriateness of modeling approaches to a greater extent. This thesis presents the development and application of a screening model, based on implicit stochastic optimization scheme, named as Integrated Reservoir Yield Model in (IRYM) that overcomes the aforesaid shortcomings. It assesses the optimal annual yields from a system of reservoirs based onpre-specified annual release reliabilities depending upon different water uses with allowable percentage yield during failure years by simultaneously optimizing the crop plan for all the projects at the same time. Also it maximizes the benefits from all the water uses. Further, the model output provides information regarding the total nutritional production ofthe entire system. An attempt is made to enhance the applicability of the proposed model in the real world problems by overcoming the major limitations of existing yield model, viz., adoption of a single value of allowable percentage yield and a common set of failure years for all the reservoirs under the river basin for assessing the optimal system yield. Another major hindrance in employing any optimization technique to a river basin as a whole is the presence ofbarrages in the system configuration, predominantly in series with upstream reservoirs. For this type ofconfiguration setup, a combined optimization-simulation (OPT-SIM) technique isproposed, where optimization is done through IRYM. The proposed model is demonstrated by employing it to a portion of the transboundary Mahanadi river basin lying in Orissa State, India. The perspective planning made for this basin by Government of Orissa comprises of56 number ofsingle as well as multipurpose projects with barrages in series with upstream reservoir(s) and also without any upstream reservoir. The objective function is to maximize the total annual yield at each project for attaining the maximum value of allowable percentage yield which may satisfy at least the project specific target demands as far as possible during successful years under diverse hydrological conditions; and to check whether the system is self reliant in meeting the nutritional requirements of the projected population by the end of the planning horizon 2050 A. D. Aseparate model based on linear programming is formulated to obtain the optimal crop planning for abarrage in successful years and to assess the gross income from crop produces, and quantity of nutritional production for the optimal yield obtained through optimizationsimulation technique. The results of IRYM for reservoirs are then added to the above respective quantities to get the annual gross income from crop produces and nutritional production of the entire integrated system. Further, in order to ascertain the extent of sustainability of the system during failure years, above model is also used for crop planning in case of reservoirs for the allowable percentage yield that would be available during such years to assess the nutritional production and gross economic return from crop produces. Whereas crop planning for barrage during failure years is not done since, inflows in these years are not assured. IV IRYM requires the gross irrigation requirements of each crop for every within year time period at each project for optimal crop planning. These are, therefore, estimated for the crop plan proposed by the Government of Orissa (2001) by using FAO Penman-Monteith method. For such a large size problem, in order to ease the Herculean and time consuming task of input data preparation in the format prescribed for Extended LINDO/PC software, two computer programs written in 'FROTRAN' and 'C programming language are used for creating various equations representing reservoir related system constraints of IRYM. Validation of IRYM is done by comparing its results with the output obtained through simulation of the entire system by maintaining the IRYM operating policy (IRYMOP) at each reservoir in terms of annual release reliability, sequence of occurrences of the failure years, allowable percentage yield for the pre-specified failure years, and within year time period wise distribution of irrigation requirements as per the optimal cropping pattern of each project and the same is termed in this study as IRYM operating policy simulation (IRYMOP SIM). It is also tried to see the system performance by simulating the system using the standard operating policy termed as, SOP SIM, as normally done in case of reservoir planning and operation. This is carried out by simulating the entire system with-out prespecifying the failure years and allowable percentage yield during such years. However, within year time period wise distribution of irrigation requirements as per the optimal crop plan of each project obtained by the IRYMis used. Results of the OPT-SIM show that, the basin can produce optimal integrated annual system yield for an average annual release of 56.76 percent of the total target annual demand or 64.97 percent of the above annual system yield during failure years. The deficit is mainly in meeting the demand towards releases for checking the saline ingression in deltaic plane. Optimal yield obtained through SOP SIM approach is higher, but the deficits in failure years are severe and the quantum of release in these years is not ascertained. The OPT-SIM produces an integrated annual system yield almost equal to the yield produced by IRYMOP simulation. It differs only by 0.83 percent from IRYMOP simulation and 4.19 percent from SOP simulation with the simulated yields remaining on the higher side. Overall efficiency of OPT-SIM using two indices namely Index of agreement (d) and Nash-Sutclijfe efficiency function shows that, the efficiency of the proposed IRYM is 99.69 percent and 98.79 percent, respectively. Although simulation is considered as the basis for assessing the performance of IRYM, the superiority ofIRYM is that itmay provide initial inputs to simulation model runs. The optimal integrated system yield may not increase due to receiving of more contributions than what is being assessed from the upper portion of Mahanadi river basin lying in the state of Chhattisgarh (i.e., 64.22 percent of the virgin flow) because of inadequate reservoir capacity to accommodate and/or regulate the excess contribution. However, there would be an impact on Hirakud dam project and Manibhadra irrigation project, if less than the present contribution is received. The basin is self reliant in meeting the nutritional requirements of the projected population during the successful as well as failure years. Hydropower potential of the basin is found to be 1870 Gwhr. Annual gross return from water utilization for all purposes would be 39860 million rupees. No surplus water may be available as per the within-year time period demands at the importing basin for other exports (i.e., other than the stipulation made in the perspective planning). The study also reveals that, Out of the forty six reservoir projects, two major projects and five medium projects do not require any reservoir capacity for over year storage. It is demonstrated that, the IRYM can act as a better screening tool with an added advantage ofassessing the optimal system yield by simultaneously determining optimal crop plans at each project, considering system specific demands and hydrological diversity in a large river basin. The proposed model also provides better insight into the reservoir capacity requirements depending on the within-year distributions of inflows to the reservoir and releases from it by providing the within-year and over-year carry over reservoir storage capacities.