Hydraulic modelling approach to optimize the irrigation channel flow in an arid zone of Pakistan

Abstract

Water is becoming progressively scarce and effective usage of accessible supplies is of major concern. Globally, 15% ~ 21% of the water allocated for irrigation is lost due to poor management and non-optimized conveyance practices. Pakistan is an agricultural country which hosts one of the world’s largest irrigation networks, Indus Basin Irrigation System (IBIS). The system has been found to operate with an irrigation efficiency of a mere 35% ~ 50% which is abysmally low. It is thus vital to oversee the proper management of this scarce resource while limiting the losses. The aim of the present study is to optimize the available irrigation channel flows based on Crop Water Requirement (CWR) and water balance approach, utilizing a suitable hydraulic model. The selected Hakra study canal covers an irrigated area of 2031 km2 with a 92 km length and lies in the semi-arid region in Punjab, Pakistan. For the detailed water balance study and hydraulic modelling of the system using HEC-RAS, daily channel flow data and climatic parameters were obtained for the period of 2011~2017 while monthly rainfall data from 1978~2017 were used for longterm trend analysis. The CWR was estimated and the irrigation scheme was formulated to define actual water surface profiles. A holistic modelling approach was followed incorporating channel inflows, evaporation/evapotranspiration, and seepage losses while alternate crop patterns and channel parameter optimization were considered for improving overall system efficiency. Application of Mann-Kendall test and the Sen's slope estimates for trend detection depicted an increasing trend of rainfall from 1978~2017. Further analysis of data revealed a slight decrease in depth to groundwater table in the study area and an increasing trend in the maximum and minimum temperature values as well. The better understanding of meteorological, hydrological and topographical conditions of the study area helped proper investigation and imitation of the actual hydraulic conditions in the area, enabling overall system optimization based on HEC-RAS model runs.