This article examines the effectiveness of the manual system for distributing agricultural water among waterholders situated along the irrigation canals within the NekoAbad Irrigation District. Additionally, it investigates the spatial analysis of the dependability index under various water scarcity scenarios. To achieve the intended objectives, a model known as the integral-delay (ID) model was developed to replicate the hydraulic conditions within the conveyance, distribution, and delivery systems. The boundary conditions for the simulation model were established following an analysis of historical data regarding the surface water supply system at the diversion dam's location. Seven scenarios ranged from normal conditions to mild and severe water scarcity. The operational system's dependability index analysis comprises two principal components: calculating the daily average dependability index for water distribution and delivery at 162 secondary and tertiary off-takes and representing the dependability index distribution through regionalization maps. The findings indicate that applying a dominant and repetitive pattern enhanced the average dependability index for water distribution from the source to the downstream locations, affecting the main and all thirteen secondary canals. The study further analyzed the range of daily-average fluctuations in the dependability index of surface water distribution across various scenarios, including normal conditions, water shortages exceeding 10%, within the ranges of 10-15%, 15-20%, 20-30%, 30-40%, and below 40%. The results demonstrated fluctuations ranging from -16.2% to 26.61%. The spatial zoning maps revealed inefficiencies within the operational system's sustainable distribution of surface water during periods of scarcity and identified areas within the network that are particularly vulnerable.