The Development and Application of Indus Basin Model Revised (IBMR)

The computer model used by WAPDA / Consultants in Master Planning Studies up to and including RAP, essentially routed surface water under different simulations. Therefore, in order to convert the water inputs to agricultural out puts, a more versatile and powerful analytical tool was needed. Consequently in 1976, soon after start of word on RAP, the World Bank initiated work on a large-scale mathematical model of the Indus Basin based on linear programming. WAPDA provided the necessary data to be used in the process of model development. The resulting Indus Basin Model (IBM) was completed in 1981-82, which could combine the standard agricultural modeling techniques, with surface water reservoirs and canal distribution network of the Indus Basin. The model also incorporated conjunctive use of surface and groundwater in the area s underlain by fresh groundwater. In essence, IBM links the hydrology of a conjunctive stream and aquifer system with an economic model of agricultural production. Termed as Farm Level Model (FLM), it can represent activities for each of 9 Agro-climatic Zones (ACZs) covering 45 canal commands of the Indus Basin as outlined in RAP.

IBM was a valuable research / planning tool but its large size with 8000 equations prevented obtaining solutions for more than a few alternatives. It was also recognized that partial analytical techniques, as conventionally employed for cost benefit analysis were inadequate for large multi-purpose project like Kalabagh Dam Project. A model, which could evaluate the benefits of additional water throughout ACZ’s and for all the major crops was required. Consequently in 1985, the World Bank undertook revising the model including its input data, structural modification and deleting a large number of constraints. The resulting model, called Indus Basin Model Revised (IBMR) was extensively used in 1986-87 by the World Bank for analysis of the proposed Kalabagh Dam and some other projects.

World Bank further updated and validated the model in 1989 for Water Sector Investment Planning Study (WSIPS) using the field data collected by WAPDA in 1988. This model was transferred to WAPDA in 1989 and was extensively used for evaluation of projects identified in the plan by year 2000 under maximum and minimum funding scenario.

The IBMR has been modified and upgraded as per recommendations of the World Bank in the context of National Drainage Programme (NDP) according to 2001 conditions.