Heat transport in hyporheic zones due to bedforms: An experimental study

Abstract

Heat transport in hyporheic zones is critical for many temperature- sensitive physical, chemical, and biological processes. It also plays a role in the energy balance of rivers. To complement previous theoretical studies, we investigated the effects of hyporheic flow due to bed topography on hyporheic thermal dynamics through flume experiments. Diel temperature cycles were imposed in the channel and propagation of temperature signals into the sediment was examined for three different bed morphologies (flat bed, pool-riffle-pool, and rippled bed), three-channel flow rates, and two sediment grain sizes. Results show that the downwelling upstream and downstream of the bedforms and upwelling focused near the crest caused substantial advective heat transport and distinct thermal patterns in the sediment, with downwelling zones reflecting most of the surface water diel thermal range whereas upwelling zones were more buffered. Increasing permeability and channel flow rates increased advective transport. The results corroborate previous theoretical models further showing that hyporheic flow distinctly affects thermal patchiness in sediment. The results also have implications for heat tracing using analytical models which work well for flow fields without pronounced divergence and convergence and minimal dispersion, features atypical of hyporheic flow. © 2014. American Geophysical Union. All Rights Reserved.