The evolution of single and twin oblique particle clouds in stagnant water was investigated using a series of laboratory experiments and the effects of controlling parameters such as sand mass and nozzle spacing were studied. The time variations of particle cloud properties such as frontal position, horizontal and vertical centroids, cloud width, and frontal velocity were measured using image analysis and particle image velocimetry (PIV) techniques. The entrainment coefficients were extracted from the measurements. It was found that the main vortex motion of the frontal heads altered after the collision and a new integrated frontal head was formed. The effects of release angle and particle interactions were studied by comparing the time histories of maximum centerline velocities. It was found that the centerline velocity of twin oblique particle clouds in comparison with twin vertical particle clouds increased with increasing nozzle spacing. The time history of the ratio of horizontal to vertical centroids in oblique particle clouds determined the potential location of sand particles and a practical model was developed to determine the size and location of particle clouds with time. The time histories of normalized cloud width indicated a significant change after the frontal head collision. The particle interactions due to frontal head collision in twin oblique particle clouds significantly increased the cloud width until particle clouds reached the swarm phase. The time at which twin oblique particle clouds reached the swarm phase was recorded and a linear model was proposed to link the time to reach the swarm phase with the cloud aspect ratio and nozzle spacing.