Water Surface Profiles Research Articles

Initial Experimental Investigation of Hydraulic Characteristics at Right-Angle Diversion in a Combined Canal and Pipe Water Conveyance System

To enhance the efficiency of irrigation water utilisation, China is progressively converting irrigation ditches into pipelines. The water distribution outlets in irrigation zones are predominantly right-angled, and there are typically occurrences of erosion, sedimentation, and structural deterioration in the surrounding areas. This article employs a synthesis of indoor physical model experiments and theoretical analysis to examine the distribution of channel flow velocity and variations in water surface profile, pipeline flow rate, diversion ratio, circulation intensity, and turbulence energy across different relative water depths. The experimental results indicate that the water surface adjacent to the main canal wall demonstrates a pattern of initial decline, followed by an increase and subsequently another decline; furthermore, as the water level in the main channel rises, the magnitude of this fluctuation progressively diminishes. In some sections of the canal, the water surface elevation progressively increases, albeit with minimal amplitude. With a constant relative water depth, an increase in main channel flow results in a corresponding increase in pipeline flow; however, the diversion ratio is inversely related to the main channel flow. Conversely, when the main channel flow rate is constant, the diversion ratio increases as relative water depth rises. The vertical flow velocity near the water diversion outlet has a negative value, signifying the existence of a backflow zone, while the horizontal flow velocity varies considerably, facilitating the formation of circulation and resulting in localised deposition and erosion. The water flow near the pipe inlet downstream of the lower lip of 0.5 times the pipe diameter is impacted by the return zone, which has a higher turbulence energy and circulation strength and is more susceptible to siltation. The turbulence energy of the water flow is higher in the range of 0.5 times the pipe diameter upstream and downstream of the pipe inlet. This research is highly significant in facilitating the conversion of irrigation channels into pipelines.

Flood Mapping using HEC-RAS and GIS: A Case Study of Palembang Watersheds

Flooding is a significant issue in Palembang City, affecting areas such as Gandus, Lambidaro, Boang, Sekanak, Bendung, Kidul, Buah, Juaro, Selinca, Nyiur, Aur, Sriguna, Kedukan, Keramasan, Kertapati and Jakabaring watershed. This research contributes to flood control measures by providing flood mapping and modelling for decision-makers and local authorities. The main objective of this paper is to perform a steady flow analysis to study the hydraulic characteristics of flow; velocity and water surface profile of the adjacent research areas. There are three processes involved in the data analysis: hydrological, hydraulic and spatial. The calculation of average rainfall is performed using the Isohyet method with the assistance of the IDW 3D Analyst tool in ArcGIS and the design discharge is calculated using the HSS Nakayasu method. The hydraulic analyses involve river morphology extraction using RAS Mapper tools in HEC-RAS. Steady flow simulations are conducted for normal water depth conditions and the highest tidal conditions. The simulation result is then reclassified and the flood location points are verified with observed data. For normal water depth conditions, the maximum water level in the Lambidaro watershed reaches 2,09 meters, which covers a flood area of 721,53 ha. Meanwhile, based on the highest tidal simulations, the maximum water level in the Selinca watershed reaches 3,21 meters, covering a flood area of 209,36 ha.

Hydraulic assessment of different types of piano key weirs

ABSTRACT Piano Key Weir (PKW) is a non-linear weir with a small foundation footprint that allows large discharges through a narrow channel. The presence of overhangs classifies it into A, B, C, and D. For different PKW types, this study aims to assess the discharge, hydraulic characteristics (flow regimes, water surface profile, and nappes interference), and energy dispersion. This study employs the FLOW-3D software and validated by comparing experimental types A and D PKW with numerical simulations. Experimental and simulation results agreed well, with lower MAPE values for both types. After that, eight simulations for each PKW type were run, with headwater ratios (H t /P) from 0.13 to 0.85 (H t : total upstream head above crest, P: PKW height). Regarding discharge performance, type-B was superior to all other PKW types at lower heads (H t /P ≤0.40) due to longer upstream overhangs. While at higher heads (H t /P > 0.40), type-A became the highest PKW type. Since PKWs disperse energy more effectively than linear weirs, they acquire new performance as energy dissipators. Type-C had the highest energy dispersion rate, followed by type-A, type-D, and type-B. Finally, an empirical equation was provided to predict energy dispersion rates over PKW types as a function of discharge coefficient.

Drag coefficients and water surface profiles in channels with arrays of linear rigid emergent vegetation

Although vegetation in watercourses has an important ecological function, from a hydraulic point of view, it increases flow resistance, determinates higher water levels and generates a greater risk of flooding. In engineering practice, to determine water levels, the drag coefficient must be known, whose experimental values, in literature, are provided for uniform or quasi-uniform flow. In this paper, the expression of a drag coefficient, previously proposed by the authors for the case of emergent rigid vegetation arranged in a linear manner, was used to simulate experimental water surface profiles, employing the effective width for the first time. The formula was validated by simulating 26 experimental profiles observed at the University of Calabria, over 1100 points in total, plus 8 published in literature. In some of these applications, the vegetation density was much higher than that for which the drag coefficient expression was derived. For this reason, it is possible to consider a new, wider field of validity for it. The proposed equation is independent of the Reynolds stem number, so that it can be used in natural streams and rivers, provided that viscosity effects can be considered negligible. Finally, some comments are offered on the application of a new formula proposed in literature regarding the computation of the profile when downstream depth is taken as a boundary condition.

Numerical modeling and validation of dike-induced water flow dynamics using OpenFOAM

ABSTRACT The basic purpose of the present research is to numerically elucidate the flow around a single dike in four different geometric configurations (CN: no cylinders, C5: 5 cylinders, C10: 10 cylinders, C15: 15 cylinders), under conditions of a constant flow rate and subcritical flow. This involved substituting the impermeable dike with varying numbers of piles to validate the observed experimental flow patterns, particularly the conditions leading to reverse flow formation. OpenFOAM, an open-source algorithm, was utilized for the simulation, incorporating the volume of fluid (VOF) method. Accurately depicting the reverse flow formation with minimal numerical diffusion, a strategy involving multizone meshing and the application of mesh refinement zones was utilized. These refinements were particularly focused on the section between 1.8 m and 2.2 m within the numerical domain. The water surface profile in front section of the dike and the averaged velocity at five different locations, which were then compared with the numerical results. The numerically predicted streamwise velocity showed a percentage error ranging between 0.5% and 4.5%. The numerical results from this study are pivotal in dike design, aiming to mitigate accelerated wear during flood events and to protect both the dike head and the adjacent bank from high energy flow failures.

Review paper on applications of the HEC-RAS model for flooding, agriculture, and water quality simulation

ABSTRACT The Hydrologic Engineering Center (HEC) of the United States Army Corps of Engineers (USACE) has developed the HEC-River Analysis System (RAS) hydraulic channel flow model as part of its portfolio of hydrologic and hydraulic modeling tools. HEC-RAS is a new version with capabilities to model flooding, modeling for agriculture production computations for water quality, and many more related to hydraulic modeling. The analysis components of the HEC-RAS system include one-dimensional steady flow water surface profile computations, one-dimensional and or two-dimensional unsteady flow simulation, one-dimensional and two-dimensional computations of quasi-unsteady or fully unsteady flow movable boundary sediment transport, and one-dimensional water quality analysis. The main objective of this paper is to review the use of HEC-RAS on flooding, agriculture, and water quality. The three primary components of the data input are plan data, geometry data, and flow data. Three of these scenarios applied to HEC-RAS and were proven by previous reviewers.

Evaluating the comprehensive flood impact assessment on the head reach of the Chiniot dam project

The major sources of surface water available to Pakistan are perennial flows of the River Indus and its tributaries i.e. Jhelum and Chenab Rivers. The creation of a reservoir of 0.9 MAF Capacity will cause the water level to rise and reduction in flow velocity on the Chenab River upstream of Chiniot Bridge. Consequently, it will cause sediment deposition which would further increase the water level due to the raised river bed level by deposited sediments. To study this storage, the reservoir has been modelled in HEC-RAS software to assess pre-dam and post-dam scenarios to simulate different conditions of river flow for water surface profile and sediment delta modelling of the reservoir reach, using historical daily water and sediment flows (1985–2022). The results of flood routing showed that the reservoir has attenuated the peak flood volume with safe releases at downstream side with proper operation of spillway gates. The average sediment inflow in the reservoir is worked out to be 38.4 metric tons. The results of sediment modelling and reservoir flood management indicated that after every 05 years of normal reservoir operation, reservoir flushing is recommended. Without sediment flushing, the river bed would be further raised beyond 189.0 m due to incoming sediment, resulting in further rise of water level up to 192.8 m which is the existing crest level of upstream training works of Talibwala Motorway Bridge.

Experimental and numerical investigations of the water surface profile and wave extrema of supercritical flows in a narrow channel bend

Supercritical flows in channel bends, e.g., in steep streams, chute spillways, and flood and sediment bypass tunnels (SBTs), experience cross-waves, which undulate the free surface. The designs of these hydraulic structures and flood protection retaining structures in streams necessitate computing the locations and water depths of the wave extrema. This study numerically and experimentally investigates the water surface profiles along the sidewalls, the wave extrema flow depths, and their angular locations in a narrow channel bend model of the Solis SBT in Switzerland. The 0.2 m wide and 16.75 m long channel has a bend of 6.59 m radius and 46.5° angle of deviation. The tested flow conditions produced Froude numbers ≈ 2 and aspect ratios ranging from 1.14 to 1.83. Two-phase flow simulations were performed in OpenFOAM using the RNG k–ε turbulence closure model and the volume-of-fluid method. The simulated angular locations of the first wave extrema and the corresponding flow depths deviate marginally, within ± 6.3% and ± 2.1%, respectively, from the experimental observations, which signifies good predictions using the numerical model. Larger deviations, especially for the angular locations of the wave extrema, are observed for the existing analytical and empirical approaches. Therefore, the presented numerical approach is a suitable tool in designing the height of the hydraulic structures with bends and conveying supercritical flows. In the future, the model’s application shall be extended to the design of the height and location of retaining walls, embankments, and levees in steep natural streams with bends.

Hydraulic-based optimization algorithm for the design of stormwater drainage networks

Stormwater drainage networks are designed to reduce the risk of rainwater damage to the served area. The purpose of optimizing a stormwater drainage system is to reduce overall construction costs and to meet hydraulic design requirements. Currently, designs that rely on software or manual calculations are limited by the available time and the designer’s capabilities. In fact, manual optimization for large networks consumes a lot of time and effort, and there is no guarantee that the optimal design is reached, also it is subject to human errors. In recent years, several researchers have focused on creating optimization design algorithms specifically for sewer and storm networks, such as genetic algorithm (GA), linear programming (LP), heuristic programming (HP),…etc. However, these studies were limited to covering one or two design parameters and constraints. Additionally, in some studies, the hydraulic performance of the designed network was not treated in a proper way, especially the water surface profile effects. So, the main objective of the study is to develop an effective hydraulic-based optimization algorithm (HBOA) that can dynamically get the optimal design with minimum total cost for a given storm network layout and meet all hydraulic requirements. To achieve this, a MATLAB code is created and coupled with SewerGEMS software that automatically simulates all expected optimization scenarios based on network hydraulic performance. The HBOA is validated economically and hydraulically using two benchmark examples from the literature. According to the economic validation, the total network cost generated by HBOA was the lowest when compared to the optimization methods found in the literature. During the hydraulic evaluation, it was observed that the optimization algorithm (GA-HP) used in the literature for the benchmark examples does not meet the hydraulic requirements where the networks are flooded, whereas HBOA meets the hydraulic requirements with minimal overall network cost. Also, the HBOA is applied to four real stormwater drainage networks that were already designed, constructed, and optimized manually. The four redesigned real cases using HBOA revealed a cost reduction of about 15% compared to the original designs, while consuming a few hours for the design and optimization processes. Finally, the developed HBOA is a robust, time-efficient, and cost-effective optimization and hydraulic design tool which could be used in the design of stormwater drainage networks with different design constraints with minimal human interference.

Steady free-surface flow in vegetation debris pad clogging trash racks

ABSTRACT We consider a steady water flow in a channel where a vertical grid is clogged by a rectangular patch of aquatic vegetation. Laboratory experiments are conducted to observe the decrease in the water table within the patch, as well as the subsequent head loss, as a function of the patch length, the flowrate and the upstream water height. Various models of porous media are used to produce theoretical formulae describing the water surface profile within the patch, among which the Barree–Conway model proves to perform reasonably well. However, for large enough Froude numbers a seepage face or water chute appears past the vegetation patch while non-hydrostatic effects become important. Under the latter condition, the accuracy of our analytic solution is less satisfactory, while remaining accurate enough for practical purposes. As confirmed by numerical simulations, with the specific aquatic plants used in our experiments the porous flow is not Darcian, so that the seepage and head loss could not be explained by the exact Polubarinova–Kochina theory.

Experimental and numerical study of the gated and ungated ogee spillway

This study was carried out by combining numerical modeling and experimental measurements to investigate the hydraulic characteristics of ungated and gated ogee spillways with high head ratios. The primary objective was to validate the use of a numerical model as a complementary approach to the experimental model for simulating the hydraulic behavior of these spillways, providing a more comprehensive understanding of their hydraulic properties under varying conditions of head ratios and relative gate openings. An Acoustic Doppler Velocimeter (ADV) was used to measure the vertical flow velocity distributions, and ultrasonic sensor wave gauges were used to obtain the time history of the water level. The results of the measurements were compared with the simulation results using a model fitted with three different turbulence models (realizable k-ε, RNG k-ε, k-ω SST). The numerical model was developed using OpenFOAM. With respect to the ungated spillway, three different head ratios ranging from 1.4 to 4.6, which correspond to high head ratios, were investigated. Similarly, three different relative gate openings ranging from 0.5 to 2 were investigated for the gated spillway. The results of water surface profiles and velocity profiles suggest that the numerical and experimental models achieve a good agreement for sections located further away from the spillway. For the ungated spillway, the simulation results for the near-spillway sections are enhanced when the head ratio increases. Considering the velocity profiles and error analysis, the realizable k–ε model was found to best predict the results of the experimental model. A discussion about the discharge equation, velocity fields, pressure fields, and the corner separation zone is also included in this study.

Discharge Formula and Hydraulics of Rectangular Side Weirs in the Small Channel and Field Inlet

In this study, experimental investigations were conducted on rectangular side weirs with different widths and heights. Corresponding simulations were also performed to analyze hydraulic characteristics including the water surface profile, flow velocity, and pressure. The relationship between the discharge coefficient and the Froude number, as well as the ratios of the side weir height and width to upstream water depth, was determined. A discharge formula was derived based on a dimensional analysis. The results demonstrated good agreement between simulated and experimental data, indicating the reliability of numerical simulations using FLOW-3D software (version 11.1). Notably, significant fluctuations in water surface profiles near the side weir were observed compared to those along the center line or away from the side weir in the main channel, suggesting that the entrance effect of the side weir did not propagate towards the center line of the main channel. The proposed discharge formula exhibited relative errors within 10%, thereby satisfying the flow measurement requirements for small channels and field inlets.

Pre-processing data and window function testing on wave spectrum analysis

Pre-processing data in oceanographic data research is an important step in processing data into the required information. This phase often takes longer and more rigorous time to present the correct data. Data pre-processing involves the selection of data, and the modification of data so that it can be readable in a computational algorithm. The data selection process includes selection of sample numbers, correction and filling of data gaps.The data used in spectrum analysis is the recording of the water surface profile of the wave in the data resolution of 1 second. The data needs to be corrected by the process of detrending against the tidal height which become the still water level. The spectral analysis is processed using the pwelch function on MATLAB. The frequency spectrum curve of the measurement is obtained from the calculation of the power spectral density value. In order to obtain a stable power spectral density curve, the Hann window function is used with the number of window elements, nfft/16.

Impact of Levee-Breach Width on the Channel–Levee–Floodplain: A Case Study in the Huaihe River Basin, China

Breach geometry is one essential feature for flood modelling in the channel–levee–floodplain system. It is hard to accurately predict the breach geometry because of its high uncertainty. However, due to the fact that breach geometry direct impacts the flow through the breach, the water surface profile in the channel and the flood hazard factors within the floodplain are changed with the breach geometry. To explore the impacts of breach width (one feature of the breach geometry) on the channel–levee–floodplain system, we took the Cinan Feiyou Flood Control Protection Area (CNFY-FCPA) in the middle reach of the Huaihe River Basin as the study area. We constructed a coupled 1D-2D hydrodynamic model to simulate the flooding with a series of breach-width scenarios. According to the simulation results of the models, we quantitatively analyzed the impacts of breach width on the inflow through the breach, fluvial flood process, and flood hazard factors in the CNFY-FCPA. The results indicate that (i) the relationship between the peak discharge (and inflow volume) and breach width was approximate to an S-shaped curve, while the peak discharge, inflow volume, and duration per unit width decreased with the wider breach; (ii) the breach caused a decrease in the water surface profile along the entire river sections; and (iii) while the breach width exceeded a certain width, the inundation area was nearly stable without changing with wider breach. The certain width was not the same in different rivers of 300 m in the Yinghe River and of 500 m in the Huaihe River. The research results can provide a scientific basis for flood-control and disaster-reduction decision making.

How hydraulic jumps form downstream of a negative step with channel expansion: experimental and numerical investigations of the transitions between wave jumps and submerged jets

AbstractWeirs and sills, particularly negative steps, play a pivotal role in modulating water flow, inducing hydraulic jumps that efficiently dissipate downstream energy. Beyond their aesthetic appeal, these features hold crucial engineering significance. This study combines physical experiments and numerical simulations downstream of a negative step featuring an abrupt width expansion. The spontaneous alteration of water flow conditions upstream and downstream of the step results in distinct flow regimes. By considering the critical Froude number to sustain an undular jump without wave breaking on a flatbed, we establish a framework for evaluating energy loss. Our analysis successfully delineates the transition limit between wave jumps and submerged jets downstream of a negative step. The co-existence regime of both jumps is explained by the analysis showing that the additional energy loss induced by the negative step is larger for the wave jump compared to the submerged jet. The abrupt width expansion at the negative step significantly reduces the transition depth between the submerged jet and wave jump, attributed to energy loss with intricate three-dimensional vortex motions—exceeding losses incurred by the negative step alone. We delve into the detailed mechanisms of these transitions through a three-dimensional numerical simulation of the energy-loss process and water surface profiles downstream of the step with expansion. The maximum energy loss by the undular jump and the minimum energy loss by the submerged jet are defined by the wave steepness at the limit of maintaining the undular jump and the jet plunging angle capable of sustaining the submerged jet, respectively.

Ressalto hidráulico submergido: uma análise em diferentes escalas

ABSTRACT Advancements in computational capabilities have enabled engineers and scientists to numerically model complex turbulent phenomena such as hydraulic jumps. This research assesses the capability of numerically simulating a hydraulic jump that occurs in the UHE Porto Colômbia's stilling basin at a flow rate of 4,000 m3/s. To achieve this, simulation results were compared with data from three hydraulic physical models (scales 1:32, 1:50, and 1:100) and full-scale measurements. The simulations employed the Ansys CFX solver, utilizing a Reynolds-Averaged Navier-Stokes (RANS) approach, the RNG κ-ε turbulence model, and the Volume of Fluid (VOF) method for air-water interactions. Various variables were analyzed, with satisfactory results for mean pressures, conjugated depths, roller length, water profile in less aerated areas, and mean velocity at the submerged hydraulic jump upstream section, with errors below 10%. However, the submerged hydraulic jump's start position and the representation of the water surface profile in the region near the jump toe yielded more disparate results. In conclusion, the methods and conditions applied in the simulations are apt for representing variables less impacted by aeration phenomena, establishing CFD simulations as a valuable tool for hydraulic jump analysis.

Experimental study on the inundation characteristics of flooding in a long straight subway tunnel

In recent years, the increase in extreme urban flooding events has caused severe property damage and safety problems. Subway tunnels are particularly vulnerable to underground space flooding. There have been traditional hydraulic experiments conducted to investigate unsteady turbulence properties of free surface flow in open channels. However, most experiments in flumes and pipes do not focus on the early formation process of inundation considering the unique structural configurations of subway tunnels. In this study, the general pattern that floodwater intrudes into a subway tunnel was studied by a scaled model experiment. Under different conditions of tunnel slope and inlet water discharge, the flood flow pattern, the water elevation, and flow velocity were investigated and analyzed. The results show that the flooding domain could be divided into three regions, including a Forming Region, a Uniform Region, and a Front Region. The unsteady Front Region performs an exponential rise in water elevation, and the velocity of flood propagation along the tunnel is nearly constant. The shape of the water surface profile is mainly influenced by tunnel slope, and the effect has a transition at the critical tunnel slope which was measured to be around 3‰. The classifications of flooding behavior under different conditions are described in detail. An empirical nondimensionalized formula for the tunnel inundation process in both unsteady and steady stages was proposed. This model enables rapid calculation of water depths with time in a subway tunnel. This research could provide an understanding of flood propagation in subway tunnels and facilitate the study of flooding detection and warnings in underground space. It also provides reference for evacuation decisions and subway flood control design.

Flood Estimation and Control in a Micro-Watershed Using GIS-Based Integrated Approach

Flood analyses when using a GIS-based integrated approach have been successfully applied around the world in large-sized watersheds. This study employed hydrological-hydraulic modeling to analyze flash floods by integrating HEC-HMS, HEC-RAS, and ArcGIS software for flood evaluation and control in a micro-watershed in the Samaru River, Nigeria. The watershed boundaries, its characteristics (soil and land use), the topographical survey, and the intensity duration frequency curve (IDF) of the study area were produced using data-driven techniques. The HEC-HMS model was used to derive the peak discharges for 2-, 5-, 10-, 25-, 50-, 100-, and 200-year return periods with the frequency storm method. Afterward, the water surface profiles for the respective return periods were estimated using the HEC-RAS hydrodynamic model. The simulated design flood for the 2-, 5-, 10-, 25-, 50-, 100-, and 200-year return periods at the reference location (the NUGA gate culvert) were 3.5, 6.8, 9.1, 12.1, 14.3, 16.6, and 19.0 m3/s, respectively, while those at the watershed outlet for the respective return periods were 7.5, 14.9, 20.3, 27.3, 32.6, 38.0, and 43.5 m3/s, respectively (with a water height of 0.9 m, 1.1 m, 1.3 m, 1.33 m, 1.38 m, 1.5 3m, and 1.8 m, respectively), at the NUGA gate culvert cross-section. The maximum water depths of about 0.9 m and 1.0 m were recorded in the right and left overbanks, which were similar to the simulated water depth for the 2- and 5-year return periods. Hence, for the smart control of floods passing through the river and major hydraulic structures, a minimum design height of 1.50 m is recommended. For the most economic trapezoidal channel section, a normal depth of 1.50 m, a bottom width of 1.73 m, a top width of 3.50 m, and a free board of 0.30 m is proposed to curb the overtopping of floods along the channel sub-sections. The findings of this study could help hydraulic engineers minimize flooding in streams and rivers overbanks in a micro-watershed.

Flow resistance at lowland and mountainous rivers

Abstract This study initially examines the various sources of flow resistance in sand-bed (lowland) and gravel-bed (mountainous) rivers along with the limitations of traditional estimation methods. The nondimensional hydraulic geometry approach, relating dimensionless flow discharge (q *) to the Darcy-Weisbach friction factor (f), has demonstrated good performance for both river types, covering shallow to moderately deep flows. However, accuracy in estimating f is affected by simplifications like assuming uniform and deep flow, neglecting bed load transport and vegetation effects, which require further evaluation. To address these issues, the proposed method is evaluated using data from four sand-bed rivers in Slovakia (with vegetation), and three gravel-bed rivers in Iran (dominated by cobbles and boulders). Bedforms prove to be significant resistance sources in all studied rivers. The approach yields separate predictors for each river type, showing a satisfactory agreement between observed and calculated values within a maximum deviation of ±20% error bands. These predictors are further validated using field data and established equations from rivers with similar physiographic characteristics. Results indicate the method performs well in predicting flow resistance in sand-bed rivers, slightly overestimating overall (+40%). It effectively captures riverbed features and vegetation influence under small-scale roughness conditions. However, the predictor’s validity for gravel-bed rivers is somewhat limited due to high variability in water-surface profiles, making it challenging to accurately capture flow dynamics under large-scale roughness conditions. Addressing complex characteristics of gravel-bed riverbeds, including boulders and local energy extraction, is crucial for improving the estimation of water-surface profile variations and flow resistance using the hydraulic geometry approach.

Impacts of Channel‐Spanning Log Jams on Hyporheic Flow

AbstractIn‐stream wood structures, such as single logs, river steps, and debris dams, are known to drive hyporheic flow, defined as the flow that goes into the subsurface region and then back to the free‐flowing surface water. The hyporheic flow plays an important role in regulating water quality and biogeochemical cycles in rivers. Here, we investigated the impact of a channel‐spanning porous log jam, representing piles of wood logs, on hyporheic flow through a combination of direct visualization and theories. Specifically, we developed a method using refractive index‐matched sediment to directly visualize the hyporheic flow around and below a porous log jam, formed by piles of cylindrical rods, in a laboratory flume. We tracked the velocity of a fluorescent dye moving through the transparent sediment underneath the log jam. In addition, we measured the water surface profile and the spatially varying flow velocity near the log jam. Our results show that the normalized log jam‐induced hyporheic flux remained smaller than 10% at Froude numbers () below 0.06 and increased by a factor of five with increasing at . We combined the mass and momentum conservation equations of surface flow with Darcy's equation to explain the dependency of the log jam‐induced hyporheic flux on . Further, we observed that at , the water surface dropped noticeably and the turbulent kinetic energy increased immediately on the downstream side of the log jam. These findings will facilitate future quantification of hyporheic flow caused by channel‐spanning porous log jams.