DEVELOPMENT OF RISK ASSESMENT FRAMEWORK FOR OPTIMIZING THE SYSTEM PERFORMANCE OF SPATE IRRIGATED AREAS IN PAKISTAN

Abstract

Hill-Torrent fed irrigation system / Spate irrigation system constitutes major portion of the Pakistan’s dry-land farming system and covers all four provinces with varying extents or magnitudes. It differs significantly from modern surface and groundwater irrigation systems. The hill torrents emerge from mountain ranges and farm a secondary network of natural surface drainage system. These hill torrents bring in uncertain flash floods of shorter duration and high peaks. Due to steep gradients, flood water flows with high velocities, which sometime result in damages to standing crops, irrigation system, earthen infrastructure etc, and some time risk to human lives as well. Flood flow spread both in transverse and longitudinal directions. As the flood flows move on the flatter terrain, its silt load also reduces the channel carrying capacity. Thus the fundamental issue henceforth is the assessment of inherent risk & uncertainty in torrent spate irrigation system, affecting the productivity of the command area. The study area was selected in piedmont plains of D.I.Khan division, KP which are surrounded by the mountains of Suleiman range on the north-west and by the Indus River towards the south-east. The branching and looping channels of the torrents make the diversion of flows a complex enterprise. During research the working methodology of Daraban Zam irrigation system was studied and noted that local farmers construct earthen dykes across the smaller branches of torrents that divert floodwater to their embanked fields. However, these channels remain functional only during low to medium intensities of incoming flows. Flash floods, especially in the Monsoon season, not only damage the diversion infrastructure in head reaches, but also proceed to tail reaches un-obstructed due to high velocities & sediment load. This factor have been of serious concern for low productivity even after a wet year and ample runoff availability. The aim of this research study was set as exploration of the potential risks involved in the spate irrigation system and identification of their ranking in optimizing the system performance. After collection and evaluation of last 15 years data, seven different kinds of risks have been delineated, this may affect the productivity. These were: availability (Floods); Non availability (drought); Siltation of channels; Sedimentation in the fields; Water quality; In-appropriate diversion/application and Non-observance of water rights. Risk matrix were developed while looking at the likelihood and consequence rating of the potential risks for different reaches i.e. head, middle & tail. Then on the basis of their ranking, risk registers were prepared for all three reaches and quantification of risks involved in the spate irrigation system was done to quantify, the effect of above risks on the performance of the system. Based on results of the study, it is thus recommended that risks identified in the risk register for different reaches need to be addressed in order of their preference in that particular reach. Finally a Risk Minimization Plan (RMP) is proposed firstly started from small scale i.e. tributary channel and its command area and then further extended to all command area based on initial results. It may include, Annual rehabilitation and de-siltation of existing channels, Establishment of a network of diversion and distribution structures at strategic locations to ensure equitable distribution of water, Enforcement of water rights as per division ratios and revision and up gradation in the areas where population growth has changed the land use, Community awareness and training programs for modern techniques dissemination and Government assistance in development of On-Farm water management systems in spate irrigated areas as well. Keywords: Spate Irrigation; Floods, Drought, Risk Analysis, Sedimentation