Attenuation Capacity Research Articles

Lightweight and broadband 2D MoS2 nanosheets/3D carbon nanofibers hybrid aerogel for high-efficiency microwave absorption

Three-dimensional (3D) porous molybdenum disulfide nanosheets/carbon nanofibers (MoS2/CNF) hybrid aerogels were synthesized by using solvothermal method and following carbonization, where two-dimensional (2D) MoS2 nanosheets were homogenously in-situ grown on the interconnected CNF skeleton derived from bacterial cellulose, forming a hierarchical porous structure. This unique heterogeneous structure of the MoS2/CNF hybrid aerogels were conducive to electromagnetic loss, including conduction, polarization, multi-scatterings, and reflections, thus resulting in a balanced impedance matching and microwave attenuation capacity. It was found that the resulted MoS2/CNF hybrid aerogels demonstrate excellent microwave absorbing performance when the only 5.0 wt% fillers were loaded in paraffin. Particularly, MoS2/CNF-2–900 hybrid aerogel displayed an effective absorption bandwidth of 5.68 GHz and minimum reflection loss (RLmin) value of −36.19 dB at a thickness of 2.0 mm. As the thickness increases to 4.4 mm, the RLmin value of MoS2/CNF-2–900 hybrid aerogel reaches −48.53 dB. Electromagnetic loss mechanism analysis indicates that such improved microwave attenuation is attributed to proper component, multiple heterogenous interface and hierarchical porous structures. All the results in this work pave the avenue for the development of ultralight microwave absorber with high absorption capacity as well as broad effective absorption bandwidth.

Nitrous oxide hot moments and cold spots in a subtropical estuary: Floods and mangroves

Flood events can transport large nitrogen loads to the ocean in short periods with the potential to produce significant nitrous oxide (N2O) emissions along an estuarine gradient. Here, we evaluate temporal and spatial N2O air-water fluxes from both seasonal, and flood-event timescales in an urban subtropical estuary surrounded by mangroves (Coffs Creek, Australia). Overall, the estuary was a minor atmospheric source of N2O with emissions of 3.9 ± 1.2 μmol m−2 d−1. However, the mangrove-dominated lower estuary was a sink of N2O in the dry months (−5.4 ± 2.2 μmol m−2 d−1), then a source in the wet months (11.7 ± 1.6 μmol m−2 d−1) and also during an eight-day flood event (66.9 ± 9.8 μmol m−2 d−1). The flood event drove changes in estuary N2O dynamics, creating a ‘hot moment’ with the highest N2O emissions following the transport of nitrate + nitrite (NOX) from the modified catchment. The hot moment coincided with a 13-fold increase in mean daily N2O emissions and increased annual net emissions estimates to the atmosphere by 41%. In the mangrove-dominated creek sections, N2O was consumed in the dry conditions (cold spots). Seasonal variation was prominent in the attenuation and consumption of N2O in the mangrove dominated sections of the creek, while flood events potentially reduce natural creek NOX attenuation capacity and elevate N2O emissions. Without observation s in both seasonal and episodic rainfall timeframes, estuarine N2O studies in subtropical regions may underestimate N2O emissions and budgets.

The role of seasonal vegetation properties in determining the wave attenuation capacity of coastal marshes: Implications for building natural defenses

Coastal marsh vegetation plays an important role in coastal protection by attenuating waves and mitigating shoreline erosion. However, the different vegetations show wide variability in biophysical properties on seasonal and spatial scales, and the effectiveness of coastal vegetation on wave attenuation remains uncertain. In the spring, summer, and autumn seasons of 2019, we investigated the spatiotemporal variability in vegetation properties and wave attenuating ability of two dominant marsh species, Scirpus mariqueter (short and flexible Cyperaceae) and Phragmites australis (tall and stiff Poaceae), in a coastal wetland in the Yangtze Estuary. The wave parameters and water depth were measured at the two marshes and ranged from 25 to 100 m landward of the low mudflat edge. The results indicated that the aboveground biomass and height of vegetation are crucial properties determining the ability of wave attenuation, and the pioneer vegetation belt has the highest wave dissipation efficiency. Phragmites, with greater biomass and stem structure, were more effective in reducing wave height than Scirpus. This study further revealed the importance of seasonal variability in vegetation growth in species-specific wave attenuation. Most Scirpus stems senesced and broke up from autumn onwards, losing their wave attenuation ability. Although Phragmites could not colonize the low-lying flats such as Scirpus, most Phragmites stems remained stiff and high biomass at the later growing stage, maintaining wave attenuation ability and wave decay values consistent with those observed in summer. Moreover, Phragmites has a great capacity to capture sediments and raise flat elevations, which might enhance the wave attenuation efficiency with vegetation-sediment interactions. Information from this study is helpful in evaluating the dynamic effectiveness of wave attenuation in coastal marshes. Therefore, we suggest that a hierarchical mixed community of Scirpus and Phragmites be established as an effective natural defense to offset their individual biological limitations due to seasonality and spatial niches.

Excellent microwave absorption of Fe3O4/Ag composites attained by synergy of considerable magnetic loss and dielectric loss

Urgent demands to reduce the harmful electromagnetic radiation and improve weapons survivability made it necessary to develop high-efficiency microwave absorption materials, especially those operating in frequency range of 2–12 GHz. In this work, Fe3O4/Ag composites were synthesized by one-step hydrothermal method. Microwave absorbing performance can be flexibly tuned by varying Fe3O4/Ag molar ratio from 2:1, 3:1, to 4:1. An increase in Fe3O4/Ag molar ratio would lead to an enhanced permeability over the frequency region of 4–12 GHz. Meanwhile, real part of permittivity remains almost unchanged whereas the imaginary part drastically decreases, making impedance matching and attenuation capacity increase dramatically. In this way, splendid microwave absorption performance with broad absorption bandwidth within a range of 4.88–9.76 GHz and minimum reflection loss of −63.2 dB could be achieved at composite thickness of 3.6 mm.

Controllable heterogeneous interfaces of cobalt/carbon nanosheets/ rGO composite derived from metal-organic frameworks for high-efficiency microwave attenuation

Structural design and composition control are crucial in determining the EM wave attenuation of an absorber; however, the balancing of the EM parameters has always been a formidable challenge. Here, we successfully designed a 3D hierarchical Co/carbon nanosheets (CNS)/rGO magnetic-dielectric composite with controllable composition and microstructure as a high-efficiency absorber by using a three-step route. Benefiting from the synergetic effect and heterogeneous interfaces, the hierarchical Co/CNS/rGO composite displayed strong microwave attenuation and broad absorption frequency band. Furthermore, the nanocomposite with porous structure promoted multiple reflection and scattering, thereby improving the attenuation capacity. The hierarchical Co/CNS/rGO composite exhibited strong microwave absorption capabilities when the filler loading was 20 wt%. Specifically, the maximum reflection loss (RL) was up to −65.5 dB at 12.4 GHz with a matched thickness of 2.5 mm and the corresponding absorption bandwidth was 8 GHz. Such excellent results not only serve as an inspiration for the enhancement of interfacial polarization of an absorber, but they also provide a novel avenue to synthesize high-efficiency microwave absorber with controllable structural design and composition regulation.

Lightweight polyaniline coated fly ash magnetic beads/nickel powders composites with promising electromagnetic waves absorption performance

The utilization of fly ash (FA) and the treatment of electromagnetic pollution have become important contents of current environmental management. A new type of electromagnetic waves absorption material was obtained by using fly ash magnetic beads (FAB), nickel powders (Ni) and polyaniline (PANI) in this study. A novel core–shell PANI@FAB/Ni composite was successfully prepared by interfacial polymerization of PANI on the surfaces of FAB and Ni. The structure, composition, morphology, magnetic property and electromagnetic parameters of composites were investigated in detail. Due to the synergistic effect of several different loss mechanisms, which improved attenuation capacity and impedance matching, the optimal reflection loss of PANI@FAB/Ni at 5.52 GHz was −67.07 dB (thickness of 5.48 mm). Meanwhile, the effective absorption bandwidth of PANI@FAB/Ni is 4.24 GHz with a thin matching thickness of 1.98 mm. This novel electromagnetic waves absorption material made of FAB has potential commercial prospects.

Synthesis of hierarchical porous nitrogen-doped reduced graphene oxide/zinc ferrite composite foams as ultrathin and broadband microwave absorbers

Magnetic graphene foams with three-dimensional (3D) porous structure, low bulk density and multiple electromagnetic loss mechanisms have been widely recognized as the potential candidates for lightweight and high-efficiency microwave attenuation. Herein, zinc ferrite hollow microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/ZnFe2O4) composite foams were prepared via a solvothermal and hydrothermal two-step method. Results demonstrated that the attained magnetic composite foams possessed the ultralow bulk density (12.9–13.5 mg·cm−3) and 3D hierarchical porous netlike structure constructed through stacking of lamellar NRGO. Moreover, the microwave dissipation performance of binary composite foams could be notably improved through annealing treatment and further elaborately regulating the annealing temperature. Remarkably, the attained composite foam with the annealing temperature of 300.0 °C presented the integrated excellent microwave attenuation capacity, i.e. the strongest reflection loss reached −40.2 dB (larger than 99.99% absorption) and broadest bandwidth achieved 5.4 GHz (from 12.4 GHz to 17.8 GHz, covering 90.0% of Ku-band) under an ultrathin thickness of only 1.48 mm. Furthermore, the probable microwave dissipation mechanisms were illuminated, which derived from the optimized impedance matching, strengthened dipole polarization, interfacial polarization and multiple reflection, notable conduction loss, natural resonance and eddy current loss. Results of this work would pave the way for developing graphene-based 3D lightweight and high-efficiency microwave absorption composites.

Influence of the Droplet Velocity on the Attenuation of Overpressures in a Water Mist

Mist generator is a basic element of systems designed to protect from explosions. It is responsible for forming a suppression barrier between the place of explosion and the zone to be protected. The effectiveness of the system is determined by the capacity of the mist to suppress blast overpressure and impulse. The attenuation capacity, on its turn, depends on mist properties, such as droplet size, water concentration in mist and droplet velocity. The paper examines droplet velocity influence on overpressure and impulse attenuation in mist when the properties of the latter are in the following ranges: droplet size - 15-345 μm; droplet velocity - 5.5-35 m/s; shock wave velocity – 515-718 m/s, droplet impact angle - 900. The influence of drop velocity on blast attenuation has been assessed according to overpressure and impulse reduction factors.

Mangroves As Coastal Bio-Shield: A Review of Mangroves Performance in Wave Attenuation

Mangroves have been recognized as soft structures that provide coastline protection. The capability of dampening waves helps minimize destruction from catastrophic events including erosive wave attacks, torrential storms, and tsunamis. Mangroves act as the first line of coastal defense in natural tragedies such as during the Super Typhoon Haiyan 2013 and Indian Ocean Tsunami 2004, whereby the leeward mangrove area encountered less damage than the unprotected area. This has further brought the attention of researchers to study the attenuation performance of these coastal vegetations. Based on an extensive literature review, this paper discusses the attenuation mechanism of mangroves, the factors influencing the dissipation performance, studies on mangrove dissipation via different approaches, the dissipation efficiency, mangrove conservation and rehabilitation efforts in Malaysia and implementation of mangrove as coastal bio-shield in other countries. The study highlights that mangrove parameters (such as species, width, density etc.) and wave parameters (such as wave period and incident wave height) are among the contributing factors in mangroves-induced wave attenuation, with different efficiency rates performed by different mangroves and waves parameters. Towards that end, several improvements are proposed for future research such as to incorporate all influencing dissipation factors with specific analysis for each species of mangroves, to perform validation on the studied mangroves attenuation capacity in different settings and circumstances, as well as to address the extent of protection by the rehabilitated mangroves. A systematic and effective management strategy incorporating ecological, forestry, and coastal engineering knowledge should be considered to ensure a sustainable mangroves ecosystem and promising coastline protection by mangroves. Doi: 10.28991/cej-2021-03091772 Full Text: PDF

Synthesis of three-dimensional porous netlike nitrogen-doped reduced graphene oxide/cerium oxide composite aerogels towards high-efficiency microwave absorption

Three-dimensional (3D) graphene aerogels with porous structure and lightweight feature have been regarded as promising candidates for microwave attenuation. Herein, nitrogen-doped reduced graphene oxide/cerium oxide (NRGO/CeO2) composite aerogels were fabricated via a hydrothermal route. The obtained composite aerogels possessed low bulk density and unique 3D porous netlike structure constructed by the stacking of lamellar NRGO. Moreover, it was found that the microwave dissipation performance of NRGO aerogel could be notably improved through complexing with CeO2 nanoparticles and carefully regulating the contents of CeO2 in the composite aerogels. Remarkably, the attained NRGO/CeO2 composite aerogel with the content of CeO2 of 44.11 wt% presented the comprehensively excellent microwave attenuation capacity, i.e. the optimal reflection loss reached −50.0 dB (larger than 99.999% absorption) at a thickness of 4.0 mm and wide bandwidth achieved 5.7 GHz (from 12.3 GHz to 18.0 GHz, covering 95.0% of Ku-band) under an ultrathin thickness of only 1.9 mm. Furthermore, the probable microwave dissipation mechanisms of as-synthesized composite aerogels were clarified, which included the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, notable oxygen vacancy effect and enhanced conduction loss. This work could shed light on developing graphene-based 3D broadband microwave absorption composites.

Boosting dual-interfacial polarization by decorating hydrophobic graphene with high-crystalline core-shell FeCo@Fe3O4 nanoparticle for improved microwave absorption

Manufacturing heterostructure architectures with multiple interfaces and understanding the interfacial polarizations are important for exploring high-efficient microwave absorbents. Herein, high-crystalline core-shell FeCo@Fe3O4 nanoparticles were in-situ anchored on graphene. The FeCo@Fe3O4/graphene hybrids reveal boosting microwave absorption which can be adjusted by controlling the graphene component. The hybrids show an optimal reflection loss of −74.4 dB at 9.6 GHz with a thickness of 2.58 mm. The effective absorption bandwidth can reach 3.7–18 GHz when the thickness is 1.5–5.0 mm. The improved microwave absorption is attributed to better impedance matching, high attenuation capacity and boosting dielectric polarization. The specific heterostructures comprised of FeCo core, Fe3O4 shell and graphene nanosheet carrier can induce abundant multiple heterogeneous interfaces, which can generate lattice distortion for dipolar polarization and introduce space charge separation for interface polarization. Theoretical calculation demonstrates that electrons transfer among the multiple interfaces and generate charge redistribution, leading to dipole and interface polarizations. Besides, the hybrids are hydrophobic, which can improve the stability of electric devices in wet. This work not only provides a point of view to boost the microwave absorption through dielectric polarization, but also gives a new insight to design environmentally friendly microwave absorbents by hydrophobic treatment.

N-Doped Carbon Fibers with Embedded ZnFe and Fe3C Nanoparticles for Microwave Absorption

Microwave absorbing materials (MAMs) play a vital role in the field of electromagnetic wave pollution protection. Herein, multiple interfacial ZnFe/Fe3C@C porous nanofibers as a microwave absorber were prepared by electrospinning and subsequent thermal treatment. The elaborately designed ingredients and porous feature of the structure introduce good impedance matching. The multiple interfacial heterojunction structure and the self-doping of nitrogen atoms of the proposed carbon-based magnetic fibers promote dielectric polarization relaxation. Moreover, the attenuation capacity and impedance matching can be adjusted by the carbothermal temperature. The obtained composites exhibit excellent microwave absorption performance, which possess a minimum reflection loss of −33.57 dB at 13.92 GHz and an effective absorption bandwidth (RL < −10 dB) of 4.16 GHz. These favorable characteristics and excellent performance of ZnFe/Fe3C@C porous nanofibers can promote the development of an efficient, lightweight microwave absorber.

Impact mitigation performance of hybrid metamaterial with a low frequency bandgap

Elastic metamaterials exhibit a significant potential in wave attenuation and impact mitigation application owing to their unusual dynamic performance. This work is aimed at investigating the properties and impact mitigation performance of a novel hybrid metamaterial (HMM) fabricated using 3D printing based on a selective laser sintering (SLS) technology. This HMM consists of periodic mass inclusions integrated with a conventional reentrant frame, producing a local resonance mechanism and negative Poisson's ratio properties. Dispersion characteristics and vibration modes are numerically demonstrated, and the results indicate three wide bandgaps in low frequency ranges induced by the local resonance mechanism. The wave attenuation capacity of the HMM is explored numerically and experimentally, and it proves that the bandgap of the HMM can be flexibly tailored by adjusting geometrical configuations of HMM. A comprehensive comparison between the wave mitigation capacity of HMM and the base reentrant structure is established computationally under different modulated unit impact pulses. When the bandgap overlap ratio is 42.5%, HMM can reduce the transmitted peak force by a factor of 2.17 and the root mean square (RMS) value of the reaction force by a factor of 1.59, highlighting the role of bandgap overlap ratio in enhancing the impact mitigation performance of HMM. Furthermore, an impact test indicates that the HMM shows an approximately 22.6% better mitigation performance under the same impact energy than that of a conventional reentrant structure. These results confirm the potential application of the proposed hybrid metamaterial in impact mitigation and noise control.

Preparation of FeNi/C composite derived from metal-organic frameworks as high-efficiency microwave absorbers at ultrathin thickness

Developing metal–organic frameworks (MOFs) derived microwave absorbers with the merits of thin matching thickness, broad bandwidth and strong absorption still remains a big challenge in the electromagnetic absorption field. Herein, FeNi-MOFs derived magnetic-carbon composites were fabricated via a solvothermal and pyrolytic two-step strategy. It was found that the micromorphology of carbon frameworks could be regulated from the regular octahedron to spherical shape through facilely adjusting the molar ratios of Fe3+ to Ni2+ in the precursors. Furthermore, results revealed that the molar ratios of Fe3+ to Ni2+ had notable effects on the electromagnetic parameters and microwave attenuation capacity of attained composites. Significantly, the obtained FeNi/C composite with the molar ratio of Fe3+ to Ni2+ of 1:0.5 showed the comprehensively optimal electromagnetic attenuation performance, i.e. the reflection loss achieved −40.2 dB (larger than 99.99% absorption) and absorption frequency band was as high as 5.8 GHz (from 11.9 to 17.7 GHz, covering 96.7% of Ku-band) under an ultrathin thickness of 1.65 mm. Besides, the probable microwave dissipation mechanisms were clarified, which mainly derived from the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, enhanced conduction loss and natural resonance effect. Therefore, our results would be helpful for designing and developing high-performance microwave absorbing composites derived from MOFs.

Hydrodynamics of a dual-module pontoon-net floating breakwater system: Numerical simulations and prototype tests

Floating breakwaters with a mooring system have been widely applied to protect marine infrastructures (e.g., artificial beach or island, aquaculture farm or marine vessels in harbors) from being destroyed by severe waves. In this paper, an innovative cylindrical dual pontoon-net floating breakwater was developed to enhance the wave attenuation capacity. This dual-module floating breakwater system was constructed as the prototype for on-site testing. A fully nonlinear time-domain model based on the coupled iterative solutions of the fluid integral equation and the pontoon-net dynamic equations was proposed to simulate the interactions between waves and the floating breakwater system. The flow field around the nets was simulated by introducing a porous-media model with Darcy’s law, while the deformation of the flexible nets was solved by using the lumped mass model. The instantaneous free surface was captured using the mixed Eulerian-Lagrangian (MEL) approach which employs an improved moving-grid technique based on the spring analysis to re-mesh the instantaneous water surface and the body wetted surface. On-site tests were also conducted to evaluate wave transmission performance of the floating breakwater system and to validate the numerical model. The comparisons show that the numerical solutions are in good agreement with the measured data. The effects of incident wave direction, wave period, wave height, net height, net number and net porosity on the hydrodynamic performance of the floating breakwater system were emphatically examined.

Synthesis, gamma and neutron attenuation capacities of boron-tellurite glass system utilizing Phy-X/PSD database

Phy-X/PSD was applied to evaluate the properties of gamma and neutron attenuation of TeO2–B2O3–RnO (R = Mg, K, and Zn) glass systems which is fabricated successfully by high temperature melting method. The abilities of gamma ray shielding were investigated by the relative parameters effective atomic number (Zeff), half-value layer (HVL), tenth value layer (TVL), mean free path (MFP), and fast neutrons (ΣR) which are crucial gamma shielding parameters. Meanwhile, the parameter of ΣR plays an essential role for evaluating the abilities of the neutron shielding. The study results revealed a phenomenon that the improving of TeO2 fraction from 11 mol% to 61 mol% decreases the parameters of gamma shielding μ, μ/ρ, Zeff, and ΣR, and also increases HVL, TVL, and MFP parameters, which based on the high atomic number of tellurium. Furthermore, the prepared glasses were effective shielding material which can reduce fast neutrons as well as gamma rays, illustrating that prepared glass system possesses excellent properties of gamma shielding.

Regulating Percolation Threshold via Dual Conductive Phases for High-Efficiency Microwave Absorption Performance in C and X Bands.

The development of high-efficiency microwave absorbers for C and X bands still remains a challenge, limiting the settlement of corresponding electromagnetic pollution and radar stealth. In this work, a reduced graphene oxide (RGO)/Cu/Fe3O4 composite is successfully proposed by a one-step solvothermal method with a GO dispersion content of 5 mL, where Fe3O4 exhibits high magnetic loss from natural resonance at the C band, and Cu nanorods and RGO are introduced as dual conductive phases to produce suitable dielectric properties by regulating the percolation threshold. The results show that the existence of Cu nanorods significantly reduces the conductivity and dielectric loss of the composites, optimizing the coordination of attenuation capacity and impedance matching in the C and X bands. Consequently, the obtained RGO/Cu/Fe3O4 composite shows outstanding microwave absorption performance with the maximum effective absorption bandwidth (EAB) value of 5.2 GHz at a thin thickness of 3.1 mm, which covers 84% of the C band and 46% of the X band (4.64-9.84 GHz). The performance is superior to the vast majority of previous absorbers in the corresponding bands.

One-dimensional Ni@Co/C@PPy composites for superior electromagnetic wave absorption

The conductive networks for electron hopping and migration constructed by one-dimensional (1D) composite absorbers are highly desirable to improve the electromagnetic (EM) wave attenuation capacity. Herein, the Ni@Co/C@polypyrrole (PPy) composites integrating the advantages of component and microstructure were fabricated. The addition of Co/C and PPy effectively optimized the impedance matching and improved the EM attenuation. Under the comprehensive impacts of multiple reflections/scattering, conduction loss and interface polarization, the Ni@Co/C@PPy composites showed superior EM wave absorption with the reflection loss (RL) value of −48.76 dB and the effective absorption bandwidth (EAB) of 5.10 GHz at a corresponding thickness of 2.0 mm. The largest EAB could reach 5.54 GHz (7.24–12.78 GHz) at the thickness of 2.2 mm. This work provides a great reference for fabricating 1D novel EM wave absorption materials.

Investigation of novel 3D-printed diatomic and local resonant metamaterials with impact mitigation capacity

A novel dual local resonance metamaterial chain, at a low frequency regime (<200 Hz), is designed and fabricated using selective laser sintering technology for characterization of wave attenuation and impact mitigation, consisting of a main structure and cantilever-in-mass resonators as a periodic sub-structure. The dispersion characteristics and mode polarization of metamaterial chains with various resonators are studied using a mass-spring model and finite element modelling simulation. The results clearly demonstrate the bandgap of the dual resonance system is extended by both the local resonance and diatomic resonance mechanisms. A parametric study is established to optimize the bandgap ratio, revealing that the bandgap of the design can be shifted by changing the stiffness ratio between two resonators in the sub-structure. The wave attenuation in the frequency domain obtained from impact modal tests exhibits a good agreement with computational results. In particular, the dynamic load attenuation capacities of the metamaterial chains under different impact durations are studied using impact mitigation tests, which show that the dual resonance design has the best attenuation performance under impact force, where the transmission rate is driven down to 0.2, compared with 0.48 for the design without resonators.

How Do Fractures Influence Hyporheic Exchange in Sedimentary Rock Riverbeds?

AbstractBedrock rivers represent a hydrogeological environment in which surface water flows along an exposed bedrock surface. Studies of hyporheic exchange have exclusively involved rivers composed of unconsolidated fluvial sediments, leaving a critical knowledge gap. This study evaluates the conditions that could support bedform‐scale hyporheic exchange within a fractured sedimentary bedrock river based on field data collected near Guelph, Canada. Hyporheic exchange at the bedform‐scale was evaluated by numerically modeling the migration of a conservative solute tracer through a bedrock riverbed within a two‐dimensional vertical cross‐section along the flow direction. A stochastic discrete fracture‐matrix framework was developed to represent measured subsurface fractured bedrock properties, producing a probabilistic distribution of potential hyporheic exchange pathways. Flow and transport model results indicate that: (a) bedform‐scale hyporheic exchange within a bedrock river exists with high fluid flow velocities in fractures, yet long solute residence times due to diffusion across the fracture‐matrix boundary; (b) the coincidence of fractures and hydrodynamic head gradients across the riverbed controls the spatial extent of bedform‐scale hyporheic exchange; and (c) the potential variability in hyporheic exchange residence time is large (i.e., tens of years) due to the inherent variability in facture network properties. Our field‐based numerical study indicates that the average (median) residence time may not be a good proxy for the potential natural attenuation capacity of a fractured sedimentary bedrock riverbed and that hyporheic exchange has the potential to emplace surface water contaminants within the fractured porous rock matrix that could become a long‐term source of trace contaminants.