Effects of Hyporheic Exchange and Settlement on the Particle Size Distribution of Colloids

Colloid particle size plays an important role in contaminant adsorption and clogging in the hyporheic zone, but it remains unclear how the particle size changes during the transport of colloids. This study investigated the variation of the particle size of colloids in the overlying water and the effects of settlement and hyporheic exchange via laboratory experiments and numerical simulations with two main factors settlement and hyporheic exchange being considered. The results show that the particle size distribution varies when colloids transport in hyporheic zone, and both settlement and hyporheic exchange are involved in the exchange of colloids between stream and streambed. Large-sized particles are mainly controlled by settlement and advection and thus their concentration in the overlying water decreases more quickly; but small-sized particles are mainly controlled by hyporheic exchange and thus their concentration decreases more slowly, and some particles can be resuspended. The increase of retention coefficient and settling velocity will accelerate the transfer of colloids into the streambed. This study may provide important insights into the variation of the particle size of colloids in the overlying water and the effects of settlement and hyporheic exchange.