Distribution of clay‐sized sediments in streambeds and influence of fine sediment clogging on hyporheic exchange

Abstract

AbstractIn this work, the deposition of clay‐sized fine particles (d50 = 0.006 mm) and its subsequent influence on the dune‐induced hyporheic exchange are investigated. Fine sand (D50 = 0.28 mm), coarse sand (D50 = 1.7 mm), and gravel (D50 = 5.5 mm) grains were used to form homogenous model streambeds; one control ‐ no clay input, and two treatments ‐ increasing clay inputs for each grain type. The results indicate that the clogging profiles of clay‐sized sediments may not be predicted accurately using the previously proposed metric based on the relative sizes of infiltrating and substrate sediments. Further, the depositional patterns vary with the initial concentration of clay particles in the surface water. The assessment of clogging profiles in coarse‐grained model streambeds also reveals a preferential infiltration of the clay particles in the hyporheic downwelling regions. The results from the dye tracer test suggest that the accumulation of clay particles altered the exchange characteristics in the treatment flumes. For each grain size, the treatment flumes exhibit lower hyporheic flux and higher median residence times compared to their respective control flumes. The dye penetration depths were lower in treatment flumes with fine and coarse sand compared to their respective control flumes. Interestingly, higher penetration depths were observed in treatment flumes with gravel compared to their respective control flume potentially due to the generation of preferential flow paths in the partially clogged gravel beds. The clogging altered the hyporheic fluxes and residence times in the coarse‐grained model beds to a greater degree in comparison to the fine sand beds. Overall, our findings indicate that the properties of both fine and substrate sediments influence the clogging patterns in streambeds, and the subsequent influence of fine sediment clogging on hyporheic exchange and associated processes may vary across stream ecosystems.