It is common for engineers to use countermeasures to protect hydraulic structures against scour. This study aims to explore the effect of jet injection through the pier body and a combined system of jet injection and bed suction as a pier-scour countermeasure around a circular pier in a laboratory flume. Laboratory experiments were conducted in two different flow depths (10.5 and 28 cm) using 1-jet and 3-jet injections, different jet locations and angles between the jets with bed suction rate Q s /Q 0 = 2%, in turbulence flow and clear water scouring conditions. The experimental data showed that the most optimal case in terms of pier-scour depth reduction occurred for lower flow depth, higher jet flow rate and angle between the jets equal to 90°. Also, the bed suction modifies the effect of jet scouring and reduces the local scour and sediment traort at the pier. The results of velocity profiles showed that jet(s) reduces the turbulent characteristics and vertical component of velocity, causing a decrease in the strength of the down flow. A quadrant analysis for the Reynolds stresses values revealed that the sweeps and ejections are the main contributions on the Reynolds shear stress production in the near-bed flow. Keywords : Jet, pier scour, bed suction, turbulence, quadrant analysis, flow-altering countermeasure.
