Comparative hydraulic modeling for water hammer mitigation at the Al Razzaza pumping station in Karbala City, Iraq

Water hammer is a critical hydraulic phenomenon that can cause severe structural damage in pumping stations, particularly when systems are unprotected against sudden power failures. This paper provides an overview and evaluates risk reduction of a disastrous case of a water hammer that happened at the New Razzaza Pumping Station in Karbala, Iraq, soon after it was commissioned in 2022.The station pumping 20 m³/s Lake Razzaza using two parallel 2200 mm diameter carbon steel pipes, the pumps were displaced from their foundations due to a sudden power failure. A calibrated hydraulic transient model was constructed using the Bentley HAMMER software, which is based on the Method of Characteristics (MOC). The transient analysis baseline was calibrated to the design discharge of 20 m³/s; while direct transient measurements were unavailable, the model’s predictions were consistent with the observed structural failure. Three conditions were tested: the unprotected system; the Protection 1 (surge tank, air vessel, check valves, and air valve) ; and the proposed integrated Protection 2 which adds hydropneumatic tanks (1500 mm diameter and 5 m height) with a compressor to protection 1. The unprotected system yielded high transient pressures of about 420 kPa (187% above the normal operating pressure), and a dangerous 600-L vapor cavity at 200 m upstream. Protection 1 obtained a 45% downstream decrease in upstream peak pressures and annihilated vapor cavities, although it progressively lost its ability beyond 950 m downstream. Protection 2 also showed better and spatially uniform performance throughout all the pipeline zones, to within 10–20% of normal operating values in the mid-pipe pressures (300–700 m), an improvement of 20–30% over Protection 1. These results demonstrate the need for integrated, spatially distributed surge protection measures in large-scale pumping infrastructure.