Plunge Pool Research Articles

Assessing the pressure variation in the plunge pool of Yusufeli dam

In dam engineering, plunge pools are critical terminal structures, often causing substantial scour that poses risks at the foot of the dam. Scouring near dams is a nationwide concern, as it has led to more dam failures than any other cause. Thus, evaluating hydrodynamic pressures from impinging jets is crucial for pool floor stability design. This study utilised physical models, experimental facilities and computational fluid dynamics models to assess hydrodynamic pressures at Yusufeli dam. Results indicate that Flow-3D analysis and empirical equations yield similar pressure readings on the bottom of the plunge pool, one-third of the free fall pressures of the physical model. The physical studies using Froude similitude revealed drastically lower Reynolds numbers compared to prototype flows, affecting turbulence and air entrance simulation. Consequently, model-scale resistance issues dominate physical model calculations, introducing uncertainty. This study underscores the importance of carefully assessing hydrodynamic pressures on plunge pool floors, as modelling approaches significantly impact results. Findings from this study can enhance plunge pool design and stability in dam engineering, promoting safer structures.

Digital Flow in a Pool Induced by a Vertical Jet

Turbulent water jets remain a critical study area, particularly the relation of the water flow with air entrainment and its role in energy dissipation at different hydraulic structures. Plunge pools, formed by the impact of jets on water cushions, play a pivotal role in energy dissipation. Understanding the complex flow dynamics within these pools is essential for designing efficient hydraulic structures. In this research, we present a comprehensive investigation of different numerical simulations, defining two-phase (air-water) in different ways, and them compare with experimental measurements. The primary objective is to analyze the pressure distribution at the bottom of a plunge pool induced by a vertical jet and understand the importance of accurately defining air-water flow in the dynamics of the jet into the pool. Our study bridges the gap between empirical data and computational modeling, shedding light on the intricate behavior of such flows with different method-based solvers: VOF, sub-grid, and multi-phase Euler. Various computational domains, mesh configurations, and analyses spanning different time periods, frequencies, and scales were considered.

Jet impingement and the circular hydraulic jump on adverse-sloped beds

Hydraulic jump type stilling basins are the most common hydraulic structures for decreasing the excess kinetic energy of flow and are divided into three types: classical, radial and circular basins. Previous studies have reported that the hydraulic characteristics of flow are more favourable in circular basins than in the other types. Therefore, theoretical/experimental modelling was applied to examine the characteristics of circular hydraulic jumps on adverse-sloped beds in circular stilling basins. The present theoretical model applies the momentum and energy equations to derive equations for the sequent depth ratio and relative energy loss of circular hydraulic jumps and classical hydraulic jumps (CHJs). Analysing the effectiveness of the dominant independent parameters showed that increasing the sequent radius ratio up to 2 and the bed slope up to −5% decrease the sequent depth ratio and length of the circular hydraulic jumps by about 30% and 60%, respectively, whereas the relative energy loss increases by about 30%. In addition to the correlation coefficient, different error functions were determined to analyse the precision of the derived semi-theoretical equations. The present circular stilling basin acts like a plunge pool, having a small water depth for low discharges to have a submerged jet condition, downstream of large dams.

Formulating Dynamic Pressure Characteristics at Flat Plunge Pool Bottom and Inside Rock Joints

Formulating Dynamic Pressure Characteristics at Flat Plunge Pool Bottom and Inside Rock Joints

Determining the Relevance of Commonly Used Hydraulic Parameters for Representing the Water Erosive Force in Rock Mass Erosion within Dam Spillways

Spillways are essential control structures in hydroelectric dams for evacuating excess water during periods of high-water flow. These structures are generally excavated within a rock mass, without lining, and they take the form of a flow channel or a plunge pool. Rock mass erosion is an important issue facing engineers when designing unlined spillways. Methods commonly used to analyze this phenomenon are based on the threshold line concept, i.e., the correlation between rock mass resistance and its destruction against the erosive force of water. Multiple indices have been proposed for both rock mass quality and water energy (or erosive force) to assess rock mass erosion. The selection of appropriate indices is critical when evaluating hydraulic erosion. The erosive force of water is often represented by energy dissipation; however, other parameters, including average flow velocity and shear stress at the bottom of the flow channel, may also be relevant. Thus, a critical question is framed: which index best represents the erosive force of water? Here, we develop an approach to assess the applicability of the various indices used to represent the erosive force of water by relying on erosional events at more than 100 study sites. We determine that the most relevant parameters are linked to water pressure, as pressure head and flow velocity better explain the erosive force of the water than shear stress and water dissipation energy.

A salty snapshot: extreme variations in basal erosion patterns preserved in a submarine channel

The bases of active submarine channels are marked by large erosional features, such as knickpoints and plunge pools. However, their presence in ancient channel-fills has rarely been documented, so their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features hundreds of metres long and tens of metres deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base, inhibiting both the upstream migration of scours and smoothing of the channel base. The formation and preservation of these scours record the responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface and long-term channel evolution are both dominated by far more gradual processes.

Enhanced Physically Based Models for Pressure Characteristics at Plunge Pool Bottoms

Enhanced Physically Based Models for Pressure Characteristics at Plunge Pool Bottoms

A two-dimensional model for jet splashing rainfall intensity distribution in dam discharge based on laboratory experiments

Flood discharge atomization is a phenomenon of water droplets and mist diffusion caused by dam discharge, which brings heavy rainfall around the dam. The unnatural rainfall is harmful to the safe operation of hydropower stations and the stability of slopes. Jet splashing is the most important factor in the formation of flood discharge atomization. The splashing rainfall intensity and diffusion region are highly dependent on the jet impingement conditions. In this study, a two-dimensional splashing model is derived that describes the splashing rainfall distribution when a jet impinges on a plunge pool surface in terms of the jet impingement conditions. Given the close relationship between the splashing rainfall intensity distribution and the motion trajectories of droplets, it is hypothesized that certain droplet trajectories can accurately represent the distribution of rainfall intensity. The characteristic ejection angle of splashing droplets and the splashing diffusion coefficient are introduced to estimate the characteristic trajectories of droplets. Experimental data from laboratory tests are used to estimate the parameters of the splashing model. The current predictions are compared with the data from laboratory tests and prototype observations. The results suggest that the model accurately predicts the relative rainfall intensity at the upper region of the predicted curves, which corresponds to approximately 1/10 of the total height of the ideal parabola.

The study on morphological evolution process of gully headcut erosion in granite red soil hilly area based on an in situ scouring experiment

Gully headcut erosion (GHE) is a key process of gully erosion. However, there is a lack of effective monitoring of the spatiotemporal changes in gully head morphological characteristics that occur during the continuous GHE process. Through a continuous scouring experiment in the field, GHE morphological evolution characteristics were examined for different exposed soil layers (laterite layer and sandy layer), headcut heights (25, 50, 75, 100 and 125 cm) and flow discharge levels (60 and 120 L/min) in typical granite red soil hilly area. The results indicated that the width–depth ratio (WDR) of the erosion gullies decreased in the slope direction and that erosion gullies violently developed on the downslope when stable runoff was generated across the upstream surface. The GHE could be divided into three periods, namely, the gully formation period, active headcut period and stable erosion period, which were mainly reflected in the gully head (GH) and plunge pool erosion (PPE) below the gully bed. The gully headcut retreat (GHR) distance and headwall collapse (HC) range increased with increasing headcut height and flow discharge. PPE exhibited a disordered downward cutting pattern, and the degree of development fluctuated. The GHE degree was jointly affected by GHR, HC and PPE, and these three processes interacted. The gully headcut erosion amount (GHEA) of the laterite layer was smaller than that in the sandy layer, but the average headcut erosion contribution rate (HECR) was 58.51 %, which was higher than that of the sandy layer (48.53 %). The GHE was the main erosion path in the two soil layers, and the HECR was not affected by a single erosion process. The sandy layer was easily eroded, and the GH morphology changed markedly during scouring, while the gully erosion amount (GEA) ranged from 0.02 m3 to 0.21 m3. This was mainly affected by GH and PPE. In this study, niche-like caves may form in the sandy layer to intensify gully erosion. When the headcut height and flow discharge reached a certain degree, the GEA of the laterite layer with strong anti-erodibility will also reach a higher level, and the GEA varied between 0.01 and 0.17 m3. GHR and HC were the dominant gully erosion factors. GHE prevention should focus on the laterite layer, as an effective protective layer in granite red soil areas.

Effect of 3D submerged jet shape on maximum pressure of plunge pool bottom

Effect of 3D submerged jet shape on maximum pressure of plunge pool bottom

Morphology, seismic stratigraphy, and tectonic control of the Yitong submarine canyons – fan apron system in the northern South China Sea

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high, YCFS receives limited supply of the shallow-water sediments.

Waterfall height sets the mechanism and rate of upstream retreat

Abstract Waterfalls are among the fastest-eroding parts of river networks, but predicting natural waterfall retreat rates is difficult due to multiple processes that can drive waterfall erosion. We lack data on how waterfall height influences the mechanism and rate of upstream waterfall retreat. We addressed this knowledge gap with experiments testing the influence of drop height on waterfall retreat. Our experiments showed that shorter waterfalls retreat up to five times faster than taller waterfalls, when bedrock strength, sediment supply, and water discharge are constant. This retreat rate difference is due to a change in the erosion mechanism. Short waterfalls retreat by the formation of several small, rapidly eroding bedrock steps (i.e., cyclic steps), whereas tall waterfalls tend to form large bedrock plunge pools where lateral plunge pool erosion allows headwall undercutting and subsequent waterfall retreat. Because waterfall height can be partially set by the waterfall formation mechanism, our results highlight that the rate of waterfall retreat and subsequent landscape evolution can be modulated by the processes that form waterfalls.

Evaluation of basin-scale hydrogeological changes induced by reservoir operation at the Xiluodu dam site

Impoundment of large-capacity reservoirs has a great impact on groundwater flow in aquifer-aquitard systems. This impact occurs not only at the local scale in the dam area, but also at the regional scale under particular site conditions, causing unexpected geohazards and deformation phenomena. In this study, basin-scale hydrogeological changes induced by reservoir filling and operation at the Xiluodu dam site in southwest China are investigated by hierarchical numerical simulations. Hierarchical groundwater flow models consisting of a basin-scale model (34 km in horizontal dimension) and a site-scale model (4 km) are developed and solved with MODFLOW and a finite element code, respectively, by applying the output of the basin-scale model on the lateral boundaries of the site-scale model. The groundwater level changes in and the groundwater exchange between the confined and unconfined aquifer systems are evaluated. The groundwater level in the confined aquifer has significantly increased by about 96 m beneath the dam site since reservoir filling, and the dimension of the influence zone with an increase over 10 m in groundwater level reaches about 7–9 km in the basin. The rate of vertical leakage from the confined to unconfined aquifer first decreases during the initial filling, and then increases gradually as the pressure propagates into the confined aquifer. It is predicted that the dynamically equilibrated state will be reached in 2027. The local vertical leakage occurring in the plunge pool area along the unplugged boreholes drilled during site investigation is confirmed by a calculation based on the Theis formula. The results are useful for decision-making related to the reservoir operation and safety assessment of the dam.

Application of soft computing techniques to estimate the scouring depth formed by crossing jets.

The scouring depth caused by the water jet outputs from a dam is one of the crucial parameters for design purposes. Due to the importance of the subject, several laboratory studies have been conducted to understand this subject. Nevertheless, using soft computing techniques is a new attitude for modeling and predicting the natural process parameters. Herein, the types of soft computing techniques for estimating the scouring depth of a plunge pool caused by the symmetrical crossing jets have been explored. The parameters involved in the scouring phenomenon are densimetric Froude number, tailwater depth, vertical jet angle, horizontal crossing angles, and the distance between the crossing points of two jets and the water level. The prediction results show that the Multi-Layer Perceptron (MLP) model gives the best performance among the other models tested here. The Pearson correlation coefficient, root mean square error, and normalized root mean square error for the MLP model were 0.9527, 0.9039, and 19.36% for the test phase, respectively. Furthermore, based on the sensitivity analysis, the parameters, for instance, tailwater depth and vertical jet angle have the highest and lowest effects for predicting the scouring depth of a plunge pool, respectively.

3D numerical modeling of flows on a reduced model of a ski jump spillway with an erosion pit using a coupled SPH–FEM-DEM approach

Plunge pools are an economical means for discharging energy flows downstream of dams. However, the high energy discharge usually falls down from a considerable height, which leads to the phenomenon of erosion. The understanding of this risk is of paramount importance. In this study, a numerical modeling using a coupled SPH-FEM-DEM method was developed to simulate the hydraulic behavior of a physical model Ski-Jump Spillway. Several examples of validation demonstrate the precision of developed models.

Detection of leakage in the plunge pool area at Xiluodu arch dam with an integrated approach

The Xiluodu arch dam is one of the highest dams in the world. A noticeable leakage having a maximum rate of 192 L/s and accounting for 46 ∼ 75 % of the total discharge at the site has been observed in the plunge pool area since impoundment. For long-term safety of the dam, an integrated approach of groundwater temperature analysis, hydrochemical data clustering, cross-correlation function and inverse modelling is presented to detect the sources and flow paths of the leakage. It is found that the leakage is originated from three major sources, i.e., the confined limestone aquifer (underlain by the unconfined basalt aquifer), the reservoir and the downstream river. The vertical leakage from the limestone aquifer occurs through unplugged boreholes drilled during site investigation. Inverse modelling shows that induced by particle filling, clogging and rock deformation, the effective permeability of the unplugged boreholes follows the same exponential decay with the near-field basalt rocks upstream the impervious system. Consequently, the amount of the vertical leakage decreases annually, which leads to an annual decrease of the discharge in the plunge pool area. The leakage from the reservoir and the downstream river is dynamically stable in magnitude, which occurs through the basalt aquifer by bypassing the grout curtains in the dam and subsidiary dam foundations, respectively. During the past seven years of operation, the proportions of leakage from the above three sources account for, on average, 44 %, 31 % and 25 %, respectively.

Spatial distribution characteristics of splashing rainfall caused by nappe flow impingement on a plunge pool

Splashing is the main atomization source for a jet impinging on a liquid layer. Increased understanding of splashing rainfall characteristics can help to reduce the hazard of flood discharge atomization in hydraulic engineering. In this study, the spatial distribution of splashing rainfall caused by a nappe flow impinging on a downstream water cushion was experimentally investigated. Effects of the main hydraulic factors of impingement velocity, unit discharge, and water-cushion depth on splashing were investigated. The shape of splashing rainfall contours was approximately elliptical in horizontal planes. Maximum rainfall intensity was in the surrounding impingement region, and rainfall intensity decreased with an increase in the distance between the impingement center point and measurement points. Splashing rainfall intensity increased with increases in impingement velocity and unit discharge, whereas the opposite was observed with an increase in plunge pool depth. A gamma distribution described rainfall intensity distribution in the longitudinal and vertical direction, whereas a Gaussian distribution described intensity in the transverse direction. A series of empirical relations were proposed.

대심도 빗물저류배수시설 감세지 유무에 따른 바닥면 압력변화에 대한 실험 연구

To prevent against urban floods, deep rainwater storage and drainage system have emerged as the ultimate solution for urban floods. In this study, we analyzed the changes in floor pressure depending on the with or without of the plunge pool and the depth through hydraulic experiments. The hydraulic experiment was conducted on a total of 28 types which 4 plunge pool depths and 7 inflow conditions. The experimental results show that the deeper the ground plunge pool depth, the lower the standard deviation and variance of the bottom pressure and the more the pressure stabilizes, but the effect of the hydrostatic pressure on the plunge pool depth increases the overall pressure. In addition, when hydrostatic pressure is included, the bottom pressure is 2.0 to 1.4 times the hydrostatic pressure, and when hydrostatic pressure is excluded, it is analyzed to be 1.0 to 0.4 times the hydrostatic pressure. If further research is conducted on changes in bottom pressure according to the depth of the vertical shaft - depth of the plunge pool, it is believed that economic and safety design guidelines for deep rainwater storage and drainage system can be presented.

Vegetation affects gully headcut erosion processes by regulating runoff hydrodynamics in the Loess tableland region

Vegetation plays an important role in gully headcut erosion processes. However, it is still unclear how vegetation in the upstream area affects gully headcut erosion processes by changing the hydraulics. A series of in situ inflow scouring experiments were conducted on bare land plots and vegetation plots (including the upstream area, headwall, and gully bed) planted with Bothriochloa ischaemum (BI), Agropyron cristatum (AC), and Medicago sativa (MS) with clustered stems and Artemisia gmelinii (AG) with erect stems to investigate the influence of vegetation on the hydrodynamic parameters involved in gully headcut erosion processes. The results showed that, compared with bare land, vegetation increased the Manning roughness coefficient (n) and Darcy–Weisbach friction factor (f) in the upstream area by 0.2–2.5 times and 0.9–9.6 times, respectively, but reduced the runoff velocity in the upstream area and gully brink. However, the jet flow velocity at entry into the plunge pool increased rapidly after passing through the gully head. The influence of vegetation with clustered stems on roughness and runoff velocity was greater than that of vegetation with branched stems. At 3.6 m3/h inflow discharge, vegetation can increase the runoff shear stress of the upstream area. The energy consumption of the gully head, upstream area, and gully bed accounted for 74 to 76 %, 19 to 21 %, and 4 to 7 % of the total energy consumption, respectively. The four vegetation treatments reduced the gully headcut soil loss by 31 to 81 %, among which MS exhibited the highest reduction. The soil loss rate was positively correlated with the jet flow velocity and its kinetic energy, and the correlation was the best (R2 of 0.934 and 0.935, respectively, P < 0.01), presenting a logarithmic trend. These results are helpful to deepen the understanding of the roles of vegetation in regulating runoff hydraulic action during gully headcut erosion.

Flow Over the Spillway of AlAdhiam Dam Under Gated Condition

The AlAdhaim Dam is located 133 kilometers northeast of Baghdad. It is a multipurpose dam and joints the Iraqi dam system in 2000. It has a storage capacity of 1.5 billion m3. The dam has an ogee spillway with a length of 562 m, a crest level of 131.5 m.a.m.s.l. and a maximum discharge capacity of 1150 m3/s at its maximum storage height of 143 m.a.m.s.l. This research aimed to investigate the hydrodynamics performance of the spillway and the stilling basin of AlAdhiam Dam by using numerical simulation models under gated situations. It was suggested to modify the dam capacity by increasing the dam's storage capacity by installing gates on the crest of the dam spillway. The FLUENT program was used to simulate the flow over the spillway. The free surface was calculated using the volume of fluid (VOF) method. To deal with turbulence, the SST k-ω turbulence model was used. The study showed that the spillway is capable of carrying the designed flood discharge and the modified conditions with negative pressure behind the gate and at some points along the spillway. Hydraulic jumps occur at various distances throughout the plunge pool depending on the incoming velocity in the flip bucket.