Multistep Planning Model for Conjunctive Use of Surface‐ and Ground‐Water Resources

Abstract

A three‐step modeling approach is presented for comprehensive analysis of the planning problem involving integrated use of surface and ground water in irrigation. Applicability of the approach is illustrated by a case study of the Bagmati River Basin in Nepal. In the first step, a stochastic dynamic programming model, which considers most of the interacting processes of the conjunctive‐use system, is used to derive the long‐term operation policy guidelines for alternative plans. Then, a lumped simulation model is used to evaluate the alternative plans and policies, considering a number of mutually related synthetic sequences of streamflow and rainfall. Various economic (cost and benefit) as well as risk‐related (reliability, vulnerability, and resiliency) performance measures and their tradeoffs are evaluated. Finally, a multiple‐criteria decision‐making method (compromise programming) is used to select the most satisfactory alternative plan for indicating the system design (pumping and diversion canal) capacities and water allocation policies, Important policy and management implications are drawn from sensitivity analyses with respect to unit pumping cost, irrigation system efficiency, and recharge coefficient.