A three-dimensional model for analyzing the effects of salmon redds on hyporheic exchange and egg pocket habitat

A three-dimensional fluid dynamics model is developed to capture the spatial complexity of the effects of salmon redds on channel hydraulics, hyporheic exchange, and egg pocket habitat. We use the model to partition the relative influences of redd topography versus altered hydraulic Conductivity (winnowing of fines during spawning) oil egg pocket conditions for a simulated pool-riffle channel with a redd placed at the pool tail. Predictions show that altered hydraulic conductivity is the primary factor for enhancing hyporheic velocities and dissolved oxygen content within the egg pocket. Furthermore, the simulations indicate that redds induce hyporheic Circulation that is nested within that caused by pool-riffle topography and that spawning-related changes in hyporheic velocities and dissolved oxygen content Could create conditions Suitable for incubation in locations that otherwise Would be unfavorable (reinforcing the notion that salmonids actively modify their environment in ways that may be beneficial to their progeny).