Colloid generation during water flow transients

In quasi-stagnant groundwater aquifer colloids are found to have constant concentration and size distribution under constant flow conditions. In transient conditions induced by water flow rate variations, increases of colloid concentration and size distribution are observed. The present study focuses on colloids from water of a well instrumented short bore hole in the water bearing fissure around the migration zone of the laboratory tunnel at the Grimsel Test Site, Switzerland. The low ionic strength groundwater makes the colloid suspension stable. In this system, increases in concentration and size distribution by factors of 1.5–30, according to the colloid size (50–2000 nm), are observed when the flow rate increases, as a pulse, by factors of 20–40 in 6–10 s. Colloid generation by flow transient requires a minimum impulse (threshold) that is colloid size dependant.