Ralph Budwig

Salmon spawning activities alter streambed morphology, forming a dune‐shaped egg nest called a redd. The spawning process increases redd sediment hydraulic conductivity, K_D, by removing fines, creating an egg pocket with larger sediment grains such that egg pocket hydraulic conductivity, K_EP, may be higher than K_D. Salmon females may create one or more egg pockets within a single redd. Although the impact of redd shape and K_D on redd‐induced hyporheic fluxes has been studied, the effects of streambed roughness, R, egg pocket permeability, and egg pocket location on egg pocket hyporheic fluxes, , (downwelling flows from the stoss side of the redd which may enter egg pockets) have not yet been quantified. This study investigates this knowledge gap with a set of numerical simulations supported by flume experiments. We simulated hyporheic flows for five egg pocket locations, five K_EP values from 0.0025 to 0.02 m/s, and 12 rough streambed surfaces. Surface roughness was scaled from a measured streambed surface in two ways—only vertically (R₁) and both vertically and horizontally (R₂)—with scaling coefficients ranging from 0.5 to 3. The measured streambed surface had a median diameter, D_50, of 1 cm and a standard deviation (σ_D) of 0.77 cm. The results indicate that the dimensionless flux into the egg pocket, increases noticeably with the downstream distance of egg pockets from the redd pit, and less strongly with . The near‐surface downwelling fluxes significantly increase with R₁, but only negligibly with R₂, and for deeper egg pockets, is minimally impacted by surface roughness. Our results suggest that the typical simplification of a smooth redd surface with a single redd hydraulic conductivity provides a good representation of the interstitial flow within the redd, and the effects of surface roughness and egg pocket hydraulic conductivity on fall within the uncertainty of the egg pocket location.

Porous media flows are common in both natural and anthropogenic systems. Mapping these flows in a laboratory setting is challenging and often requires non-intrusive measurement techniques, such as particle image velocimetry (PIV) coupled with refractive index matching (RIM). RIM-coupled PIV allows the mapping of velocity fields around transparent solids by analyzing the movement of neutrally buoyant micron-sized seeding particles. The use of this technique in a porous medium can be problematic because seeding particles adhere to grains, which causes the grain bed to lose transparency and can obstruct pore flows. Another non-intrusive optical technique, planar laser-induced fluorescence (PLIF), can be paired with RIM and does not have this limitation because fluorescent dye is used instead of particles, but it has been chiefly used for qualitative flow visualization. Here, we propose a quantitative PLIF-based methodology to map both porous media flow fields and porous media architecture. Velocity fields are obtained by tracking the advection-dominated movement of the fluorescent dye plume front within a porous medium. We also propose an automatic tracking algorithm that quantifies 2D velocity components as the plume moves through space in both an Eulerian and a Lagrangian framework. We apply this algorithm to three data sets: a synthetic data set and two laboratory experiments. Performance of this algorithm is reported by the mean (bias error, B) and standard deviation (random error, SD) of the residuals between its results and the reference data. For the synthetic data, the algorithm produces maximum errors of B & SD = 32% & 23% in the Eulerian framework, respectively, and B & SD = −0.04% & 3.9% in the Lagrangian framework. The small-scale laboratory experimental data requires the Eulerian framework and produce errors of B & SD = −0.5% & 33%. The Lagrangian framework is used on the large-scale laboratory experimental data and produces errors of B & SD = 5% & 44%. Mapping the porous media architecture shows negligible error for reconstructing calibration grains of known dimensions.

Salmon spawning activities alter streambed morphology, forming a dune-shaped egg nest called a redd. The spawning process increases redd sediment hydraulic conductivity, K _D , and congregates large sediment grains to form an egg pocket, such that egg pocket hydraulic conductivity, K _EP , may be higher than K _D . Salmon females may create one or more egg pockets within a single redd. Although the impact of redd shape and K _D on redd-induced hyporheic fluxes has been studied, the effects of streambed roughness, R , egg pocket permeability, and egg pocket location on egg pocket hyporheic fluxes have not yet been quantified. This study investigates this knowledge gap with a set of numerical simulations supported by flume experiments. We simulated hyporheic flows for five egg pocket locations, five K _EP values from 0.0025 to 0.02 m/s, and 12 rough streambed surfaces. Surface roughness was scaled from a measured streambed surface in two ways - only vertically ( R ₁ ) and both vertically and horizontally ( R ₂ ) - with scaling coefficients ranging from 0.5 to 3. The measured streambed surface had a median diameter, D ₅₀ , of 1 cm and a standard deviation of 0.77 cm. The results indicated that the dimensionless flux into the egg pocket increases noticeably with the downstream distance of egg pockets from the redd pit, and less strongly with K _EP *= K _EP / K _D . The near-surface downwelling fluxes significantly increase with R ₁ , but only negligibly with R ₂ , and for deeper egg pockets, flux into the egg pocket is minimally impacted by surface roughness.

Salmonids create an egg nest, called a redd, in hyporheic streambed gravel to bury their eggs, characterized by a pit and a hump topography, resembling a dune. Embryos' survival depends on downwelling oxygen‐rich stream water fluxes, influenced by the redd shape, stream hydraulics, and the hydraulic conductivity of the redd sediment, K. We hypothesize that downwelling fluxes increase with stream discharge and redd aspect ratio (A_R = A/L, with A, the redd amplitude and L, its length), and they can be predicted using a set of dimensionless numbers, which include the stream flow Reynolds (Re) and Froude (Fr) numbers, A_R, and the redd relative submergence (A/Y₀, with Y₀, the water depth). We address our goal by simulating the surface and subsurface flows with numerical hydraulic models linked through the near‐bed pressure distribution quantified with a two‐phase (air‐water) two‐dimensional surface water computational fluid dynamics model, validated with experiments. We apply the modeling approach to five redd sizes, which span the field observed range (from ∼1 to ∼4 m long), and by increasing discharge from shallow (0.1 m) and slow (0.15 m/s) to deep (8 m) and fast (3.3 m/s). Results confirm that downwelling fluxes increase with discharge and redd aspect ratio due to the increased near‐bed head gradient over the redd. Averaged downwelling fluxes are a function of Re, Fr, A_R, and hydraulic conductivity of the redd and not of the undisturbed streambed material. The derived regression equation may help evaluate regulated and unregulated flow impacts on hyporheic flows during embryo incubation.

Data for Mapping porous media velocity fields and grain bed architecture with PLIF

Salmonids bury their eggs in hyporheic streambed gravel, forming an egg nest, called a redd, characterized by a pit and a hump topography resembling a dune. Embryos’ survival depends on downwelling oxygen-rich stream water fluxes, whose magnitudes are expected to depend on the interactions among redd shape, stream hydraulics, and the hydraulic conductivity of the streambed sediment. Here, we hypothesize that downwelling fluxes increase with stream discharge and redd aspect ratio, and such fluxes can be predicted using a set of dimensionless numbers, which include the stream flow Reynolds and Froude numbers, the redd aspect ratio, and the redd relative submergence. We address our goal by simulating the surface and subsurface flows with numerical hydraulic models linked through the near-bed pressure distribution quantified with a two-phase (air-water) two-dimensional surface water computational fluid dynamics model, validated with flume experiments. We apply the modeling approach to three redd sizes, which span the observed range in the field (from ~1 to ~4 m long), and by increasing discharge from shallow (0.1 m) and slow (0.15 m/s) to deep (8m) and fast (3.3 m/s). Results support our hypothesis of downwelling fluxes increasing with discharge and redd aspect ratio due to the increased near-bed head gradient over the redd. The derived equation may help evaluate the effect of regulated flow (e.g., hydroelectric and flood control dams) on redd-induced hyporheic flows.

Quantification of velocity and pressure fields over streambeds is important for predicting sediment mobility, benthic and hyporheic habitat qualities, and hyporheic exchange. Here, we report the first experimental investigation of reconstructed water surface elevations and three‐dimensional time‐averaged velocity and pressure fields quantified with non‐invasive image techniques for a three‐dimensional free surface flow around a barely submerged vertical cylinder over a plane bed of coarse granular sediment in a full‐scale flume experiment. Stereo particle image velocimetry coupled with a refractive index‐matched fluid measured velocity data at multiple closely‐spaced parallel and aligned planes. The time‐averaged pressure field was reconstructed using the Rotating Parallel Ray Omni‐Directional integration method to integrate the pressure gradient terms obtained by the balance of all the Reynolds‐Averaged Navier‐Stokes equation terms, which were evaluated with stereo particle image velocimetry. The detailed pressure field allows deriving the water surface profile deformed by the cylinder and hyporheic flows induced by the cylinder.

Porous media are ubiquitous, a key component of the water cycle and locus of many biogeochemical transformations. Mapping media architecture and interstitial flows have been challenging because of the inherent difficulty of seeing through solids. Previous works used particle image velocimetry (PIV) coupled with refractive index‐matching (RIM) to quantify interstitial flows, but they were limited to specialized and often toxic fluids that precluded investigating biological processes. To address this limitation, we present a low‐cost and scalable method based on RIM coupled PIV (RIM‐PIV) and planar laser induced fluorescence (RIM‐PLIF) to simultaneously map both media architecture and interstitial velocities. Our method uses irregularly shaped grains made of a fluorocarbon plastic with refractive index of 1.36 and specific gravity of 1.93. This allows using a water–glycerin solution for the RIM fluid. By using RIM‐PIV, we mapped media structure with 2% accuracy, which improved to 0.2% with RIM‐PLIF because of improved image contrast.

Typically, fish passage design is informed by a critical velocity model whereby fish are assumed to fail passage if the water velocity is higher than the critical swim speed, an assumption that may not be met when locomoting fish are partially submerged. We applied a drag force model (DFM) approach for use in design of Pacific Lamprey (Entosphenus tridentatus) Passage Structures (LPS) where lamprey may be partially or fully submerged. Our investigation assessed the dead-drag forces at four levels of static submergence: fully submerged (120 mm), equally submerged (40 mm), partially submerged (15 mm), and skin-flow (5 mm) for a Pacific Lamprey physical model by varying simulated LPS slope and discharge conditions. We then used the results to establish drag force thresholds corresponding to the known critical velocity thresholds of Pacific Lamprey to predict passage success under partial and full submergence conditions. Consideration of drag force in fish passage could be used to improve or create species-specific design recommendations for fishways, or to inform the design of barriers to prevent invasive species passage. The results suggest consideration of drag force in addition to velocity is beneficial to predict Pacific Lamprey passage success under partial submergence conditions.