Biogenic Nest Structures Modulate Hyporheic Exchange: Field Observations and Turbulence-Resolving Simulations of Flow and Oxygen Transport in Streams

Presenter: Huan Yang, Civil and Environmental Engineering

Authors: H. Yang, K. Strom, E. Frimpong, H. Foroutan

Abstract: Bluehead chub build gravel nests that temporarily reshape near-bed hydraulics and sediment–water exchange in streams. We ask whether nests enhance dissolved oxygen (DO) delivery to embryos within the nest, and whether fish behavior in choosing where to lay eggs aligns with hydraulically “optimal” incubation conditions. We combined field data with CFD to characterize flow structure and DO transport. We measured 26 nests in Tom’s Creek, Virginia, collecting velocity profiles, bed and nest geometry, and DO concentrations in both ambient flow and nest pore spaces. These data were used to develop a Detached-Eddy Simulation model representing a generalized nest–bed configuration. The model is parameterized by field-measured geometry and driven by measured upstream velocity profiles, resolving three-dimensional flow and DO transport within and around the nest. Results show localized intensification of hyporheic exchange and near-bed turbulence, supporting the hypothesis that the nest modulates flow and DO conditions critical for embryo development. By bridging turbulent flow physics with ecological function, this work provides a hydraulic perspective on fish behavior and offers insights for incorporating organism-driven roughness and exchange processes into reach-scale transport models.