Monitoring of the flow velocities and directions of fissure water in bedrock： based on colloidal particle motion, south-central China

Abstract The colloidal borescope, using colloidal particle motion, is used to monitor the flow velocities and directions of groundwater. It integrates advanced techniques such as microscopy, high-speed photography, and big data computing and enjoys high sensitivity at the micron level. Data analyses have revealed that colloidal borescope monitoring results are significantly higher than conventional hydrogeological monitoring results and calculations. This study analyzed the monitoring data of the flow velocities and directions of bedrock fissure groundwater from five wells in the mountains, hills, inland plains and coastal plains of south-central China and plotted the motion trajectories of colloidal particles in the groundwater. Based on these results, it proposed a concept of cumulative flow velocity, before summarizing four types of cumulative flow velocity vs. monitoring time curves. Using curve-fitting equations, the limits of cumulative flow velocities as the monitoring time tends to infinity were then calculated as the actual flow velocities of the groundwater. This procedure is referred to as the limit equation method. The results of this study were as follows: (1) the fissure water in bedrock in south-central China has an instantaneous velocity of 415.42‒635.17 µm/s, a mean 10 min velocity of 339.25‒432.16 µm/s, a cumulative flow velocity of 188.30‒412.92 µm/s, and an actual flow velocity of 186.82‒412.95 µm/s; (2) the flow velocity of the bedrock fissure groundwater is related to factors such as aquifer lithology, fracturing degree, the filling conditions of fractures, and the homogeneity of structural surfaces; and (3) overall, the actual and cumulative flow velocities of the groundwater in aquifers of different lithologies can be sequenced as: fissure water in vesicular basalts > fissure water in the solution-enlarged fractures in limestones > fissure water in schists > fissure water in granites.