The role of the HYPOrheic zone on the transporter-transformer functions of River corridors.

Introduction

Reactive substances transported in river corridors undergo several transformations having important implications for the fate of toxic chemicals and the health of fluvial ecosystems. Delivery of substances into the slow and geochemically-microbially rich hyporheic zone delays their downstream transport and promotes opportunities for biogeochemical reactions.

Environmental Factors

The resulting delay and reactivity at larger scales are shaped by the ubiquitous heterogeneity of environmental porous media and the temporal fluctuations that typify river corridors. These factors control transport and mixing limitations in the reactive regions of the hyporheic zone.

Current Limitations

However, the most widespread upscaling pictures neglect these fundamental aspects, assuming either:

• A transient storage in a well-mixed hyporheic zone
• Pure advective transport along non-interacting hyporheic streamlines

The paradigm of oversimplification leads to severe shortcomings, such as limited transferability of findings and great uncertainty in large-scale predictions.

Project Goals

HYPOR pursues a paradigm shift: ground the upscaling of reactive-transport in river corridors on the mechanistic knowledge of the hyporheic dynamics.

Objectives

1. Understanding Heterogeneity: First, we will improve the understanding of heterogeneity and temporal fluctuations controls through comprehensive numerical investigations at small scales.
2. Quantifying Stochasticity: Second, this will allow us to quantify, on a physical basis, the stochasticity in the transport and mixing limitations of point-injections (Green functions) as they encounter reactive regions. The stochastic evolutions of Green functions will be the building block of a novel reactive-transport upscaled model to overcome current shortcomings.
3. Uncertainty Analysis: Yet, the hidden nature of the hyporheic zone leads to uncertainty. Third, HYPOR will exploit the link between small-scale uncertain properties and physics-based upscaling elements in a new uncertainty analysis framework that propagates uncertainty at small scales onto large-scale predictions, quantifying their reliability.