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Laboratory experiments were performed to study the impact of the relative particle protrusion P/D (P is the protrusion height and D is the diameter of the target particle) on the mechanism of entra...

Knowledge of locomotion of fish near river confluences is important for prediction of fish distribution in a river network. The flow separation zone near the confluence of a river network is a favorite habitat and feeding place for silver carp, which is one of the four major species of Chinese carp and usually provides positive rheotaxis to water flow. In the current study, a series of laboratory experiments were done to determine the behavioral responses of juvenile silver carp to the hydrodynamic forces near the separation zone of a channel confluence. The locomotion and trajectory of juvenile silver carp were recorded by infrared thermal imaging, while the flow velocity field near the separation zone was measured by a Particle Image Velocimetry (PIV) system. A total of 60 juvenile silver carp were released near the separation zone among which 40 carp swam in the upstream direction. Amongst them, 24 carp swam to the tributary and the remaining 16 swam into the main channel. Almost all these 24 carp travelled initially along the boundary of the separation zone near the corner, where flow shear was strongest, and then swam to the tributary. Instead of avoiding zones of strong vorticity, they chose and followed a trajectory along which the flow vorticity was large. On encountering these vortical flows, they increased the tail-beat frequency and decreased the tail-beat amplitude to maintain body stability. These observations provide important knowledge on locomotion of fish near river confluences and are beneficial for the fish habitat protection.

Mixing processes downstream of river confluences impacts the ecology and the related environmental management of river networks. A clear understanding of such processes is challenging, especially for confluences having width-to-depth ratios larger than 100, due to the limited available field data. In this study, four field surveys based on hydro-acoustic and conductivity measurements were conducted near the confluence between the Yangtze River and the Poyang Lake, which are the largest river and freshwater lake in China, respectively. It was found that mixing dynamics at the confluence were controlled by a complex interaction among the momentum flux ratio, secondary flow and the lock-exchange flow associated to the density contrast between the two tributaries. Slow mixing was observed during high-flow conditions that generated dual counter-rotating secondary cells, with the downwelling flow acting as a barrier in the post-confluence channel. In contrast, more rapid mixing was observed during low-flow conditions when only a single channel-scale secondary flow was identified. The mixing processes were also affected by the lock-exchange flow associated to the density difference between the two confluent flows. Such lock-exchange enhanced mixing when the Yangtze River waters had higher temperature, that is, lower density than that of the Poyang Lake. In low flow condition, the penetration of the much larger momentum flux of Yangtze River created a “two-layers” structure with the contribution of the density difference, which further enhanced the curvature-induced helicity. The findings from the present study improve our current understanding of mixing dynamics in large river confluences.

Although infrequent, volcanic tsunamis have accounted for almost 20% of those killed by volcanic eruptions since 1000 A.D (Mastin and Witter in J Volcanol Geotherm Res 97(1–4):195–214. https://doi.org/10.1016/S0377-0273(99)00174-2 , 2000; Latter in Bull Volcanol 44(3):467–490. https://doi.org/10.1007/BF02600578 , 1981). The destructive potential and unpredictability of such waves highlight the need to improve our understanding of the phenomena. Underwater eruptions are one of the source mechanisms that can generate volcanic tsunamis. For example, the 1952 explosions of Myojinsho volcano which destroyed a surveying boat of the Japan Hydrographic Department, killing 31 people, also generated a series of tsunamis. Wave gauges at Hachijo Island, 130 km from the volcano, recorded waves of up to 92 cm, which provide us with one of the few wave gauge observations of a tsunami generated by a volcanic eruption. The present work is based on the mathematical model of Duffy (J Volcanol Geotherm Res 50(3):323–344. https://doi.org/10.1016/0377-0273(92)90100-R , 1992), who analysed surface waves generated by an instantaneous underwater point-source volcanic explosion. We extend this work by modifying the source model to include time dependence and compare the efficiency of wave generation of the following sources: the instantaneous source used by Duffy (1992), a source with exponentially decreasing intensity of the explosion, and two time-constrained sources—a source with a defined sharp end to the explosion, and a source that ceases with a cavity at the free surface. The shorter the characteristic time of the exponential explosion, the more like the original Duffy model the resulting waves are. Waves resulting from time-constrained explosions exhibit a beating behaviour. The duration of the explosion modulates the generated wave field while the average wave amplitudes remain the same. Conversely, the geometric parameters of the explosion affect the wave amplitudes. The beating behaviour of our second time-constrained model bears a strong resemblance to that observed in tsunami records from the 1952 Myojinsho explosions. Thus, we apply the model to these events. The predicted leading wave is absent in the recorded data, but the trailing waves were calculated accurately, particularly in terms of the wave phasing and the lengths of the wave groups. We infer that the absence of this leading wave could be due to the mathematical formulation of the problem and it reflects how gas-rich explosions produce sea-surface displacements. The results suggest that the beating behaviour observed in the wave gauges records could have been a consequence of time constraints on the duration of a volcanic explosion.

Local scour is an important design factor for submerged weirs. This study conducted a clear-water scour experiment at a submerged weir, using the particle tracking velocimetry technique to measure ...

The Australian Forum for Operational Oceanography (FOO), started in 2015, established a working group to focus on wind-waves. One of the aims of this working group was to identify the key priorities of wind-waves research. This undertaking has been driven by Australian needs, but Australia is just one part of the larger international waves community; results of this process are also relevant to other marine-focused nations. The process to identify research priorities engaged both researchers and stakeholders in a democratic, collaborative, and iterative process. The main steps were 1) soliciting possible research questions via an online survey, 2) reviewing and editing the questions at a face-to-face workshop, and 3) ranking the research questions. A total of 360 survey invitations were emailed to possible participants, with 69 respondents. Half of these were from research organizations, and the remainder from private industry, service providers, or government. The survey gathered a list of ideas that were consolidated to 155 suggestions, which were further reviewed by participants at a wind-waves research symposium and then ranked via a voting process. A second round of online voting was then undertaken that specifically targeted the industry and stakeholder community. The top five priorities were identified, and are referred to here as “tier 1” priorities. A further 10 priorities were identified, and are referred to here as “tier 2,” providing a total of 15 top-ranked priorities.

Owing to the interplay between the forward Stokes drift and the backward wave-induced Eulerian return flow, Lagrangian particles underneath surface gravity wave groups can follow different trajectories depending on their initial depth below the surface. The motion of particles near the free surface is dominated by the waves and their Stokes drift, whereas particles at large depths follow horseshoe-shaped trajectories dominated by the Eulerian return flow. For unidirectional wave groups, a small net displacement in the direction of travel of the group results near the surface, and is accompanied by a net particle displacement in the opposite direction at depth. For deep-water waves, we study these trajectories experimentally by means of particle tracking velocimetry in a two-dimensional flume. In doing so, we provide visual illustration of Lagrangian trajectories under groups, including the contributions of both the Stokes drift and the Eulerian return flow to both the horizontal and the vertical Lagrangian displacements. We compare our experimental results to leading-order solutions of the irrotational water wave equations, finding good agreement.

Theoretical source models of underwater explosions are often applied in studying tsunami hazards associated with submarine volcanism; however, their use in numerical codes based on the shallow water equations can neglect the significant dispersion of the generated wavefield. A non-hydrostatic multilayer method is validated against a laboratory-scale experiment of wave generation from instantaneous disturbances and at field-scale submarine explosions at Mono Lake, California, utilising the relevant theoretical models. The numerical method accurately reproduces the range of observed wave characteristics for positive disturbances and suggests a previously unreported relationship of extended initial troughs for negative disturbances at low dispersivity and high nonlinearity parameters. Satisfactory amplitudes and phase velocities within the initial wave group are found using underwater explosion models at Mono Lake. The scheme is then applied to modelling tsunamis generated by volcanic explosions at Lake Taupō, New Zealand, for a magnitude range representing ejecta volumes between 0.04–0.4 km3. Waves reach all shores within 15 minutes with maximum incident crest amplitudes around 4 m at shores near the source. This work shows that the multilayer scheme used is computationally efficient and able to capture a wide range of wave characteristics, including dispersive effects, which is necessary when investigating submarine explosions. This research therefore provides the foundation for future studies involving a rigorous probabilistic hazard assessment to quantify the risks and relative significance of this tsunami source mechanism.

Caldera lakes are prominent volcanic features that can pose an additional hazard due to water presence, such as tsunamis, lahars, or flooding by lake breakout. Many of these lakes are populated and occupied by infrastructure on their shore, such as hydroelectric facilities. Volcanogenic tsunamis are a lesser modelled hazard compared to their seismogenic relatives, and the understanding of wave-making potential from subaqueous explosive eruptions is poor due to practical limitations of volcanic observation. Prior studies utilised models of surface waves produced from analogous chemical and nuclear explosions; however, these are derived from dated naval research and require reassessment.This study verifies a non-hydrostatic, vertically-Lagrangian multilayer method from the open-source software Basilisk against a laboratory flume experiment to assess suitability for modelling waves produced by variable size disturbances. This is then used to evaluate free-surface initial condition models of shallow water explosions on a U.S. Army submerged explosive series on generating waves in Mono Lake, California. On establishing fitness of the underlying models, these are applied to simulate hypothetical scenarios of submarine eruptions at Lake Taupō, New Zealand. Event locations and disturbance sizes are chosen corresponding to vent sites and magnitudes of eruptions during the Holocene. The initial disturbance is fitted to a function of estimated eruption energy. Vulnerable areas include small settlements across the eastern shore, Taupō township and the lake outflow control gates. After the initial tsunami waves, a seiche of lower amplitude is established in the hour following the event. Such eruptions in lakes may pose multiple simultaneous hazards with minimal arrival times (< 15 minutes for tsunami waves at Taupō); therefore the modelling of eruptive scenarios is a primary approach to inform local area hazard maps of submarine volcanism and raise preparedness for surrounding facilities and communities.

Periodic water waves generate Stokes drift as manifest from the orbits of Lagrangian particles not fully closing. Stokes drift can contribute to the transport of floating marine litter, including plastic. Previously, marine litter objects have been considered to be perfect Lagrangian tracers, travelling with the Stokes drift of the waves. However, floating marine litter objects have large ranges of sizes and densities, which potentially result in different rates of transport by waves due to the non-Lagrangian behaviour of the objects. Through a combination of theory and experiments for idealised spherical objects in deep-water waves, we show that different objects are transported at different rates depending on their size and density, and that larger buoyant objects can have increased drift compared with Lagrangian tracers. We show that the mechanism for the increased drift observed in our experiments comprises the variable submergence and the corresponding dynamic buoyancy force components in a direction perpendicular to the local water surface. This leads to an amplification of the drift of these objects compared to the Stokes drift when averaged over the wave cycle. Using an expansion in wave steepness, we derive a closed-form approximation for this increased drift, which can be included in ocean-scale models of marine litter transport.

The modification and utilization of rivers in regions where small-bodied diadromous fish are prevalent has largely occurred without fully understanding the migration behaviour of these species. As ...

The Australian marine research, industry, and stakeholder community has recently undertaken an extensive collaborative process to identify the highest national priorities for wind-waves research. This was undertaken under the auspices of the Forum for Operational Oceanography Surface Waves Working Group. The main steps in the process were first, soliciting possible research questions from the community via an online survey; second, reviewing the questions at a face-to-face workshop; and third, online ranking of the research questions by individuals. This process resulted in 15 identified priorities, covering research activities and the development of infrastructure. The top five priorities are 1) enhanced and updated nearshore and coastal bathymetry; 2) improved understanding of extreme sea states; 3) maintain and enhance the in situ buoy network; 4) improved data access and sharing; and 5) ensemble and probabilistic wave modeling and forecasting. In this paper, each of the 15 priorities is discussed in detail, providing insight into why each priority is important, and the current state of the art, both nationally and internationally, where relevant. While this process has been driven by Australian needs, it is likely that the results will be relevant to other marine-focused nations.

The magnitude 7.8 Kaikoura earthquake on the north-eastern coast of South Island, New Zealand induced a tsunami, which affected many north-facing bays in Banks Peninsula. The V-shaped Little Pigeon Bay experienced pronounced inundation compared to adjacent bays, causing heavy damage to a cottage at the head of the bay. In order to investigate the characteristics of the tsunami flow in the bay, a numerical model based on nonlinear shallow water theory was established, using tidal levels from the neighbouring Sumner sea level gauge. Three incident wave angles were tested, ranging from due north to 30° east of north. The simulated maximum run-up heights were validated with surveyed results. For all the wave directions, a resonance with a period of 6.3 min was found from 50 to 100 min in the simulation. Based on the physical dimensions of Little Pigeon Bay, idealised models were set-up to analyse the influence of V-shaped embayment on maximum water level, maximum velocity and maximum momentum flux. Bays with sand bars of different crest heights were also investigated. A sand bar with a relatively low crest height (dw/d ≥ 0.5) did not significantly reduce the maximum velocity and the maximum momentum flux.

This paper describes 64 experiments conducted in a sand-recirculating flume using coarse sand (d50 = 0.85 mm), investigating the interference of local scour between a circular pier (diameter D = 48 mm) and a downstream submerged weir (weir height z = 30 mm) with different separation distances L. The experimental results show that, for clear-water scour, the scour depth at the pier can be reduced by up to 54% by the downstream submerged weir when L = 0. This reduction decreases with increasing L until it approximately vanishes at L = 6D. For live-bed scour, besides the upstream bed aggradation, the downstream submerged weir can affect the local scour at a pier through two mechanisms: (i) superposition of local scour areas; and (ii) altering flow patterns. The mechanism (i) can increase the scour depth at the pier significantly when the pier is located in the upstream scour area of the submerged weir. The mechanism (i) vanishes at a distance L1, where the pier is located out of the upstream scour area of the submerged weir. The mechanism (ii) is similar to that of the clear-water scour tests, and can reduce the scour depth at the pier. The reduction effectiveness of mechanism (ii) decreases with increasing L until it becomes zero at a distance L2. Based on the experimental data, L1 and L2 are found to be 2D and 12D, respectively. For safe design, L1

Our study used empirical modeling to predict the fate of microplastics (MPs) in natural and engineered water systems, focusing on the unplanned indirect potable reuse practiced in Auckland for water drawn from the Waikato River. The study estimated the contribution of wastewater treatment plants (WWTPs) and nonpoint sources (agricultural and urban runoffs) of MPs using a worst-case and a best-case scenario developed using the literature review. The contribution of nonpoint sources of MPs was integrated into WWTP discharges for simplifying calculations. The concentrations of MPs in WWTP influents were deduced from the corresponding population served by the WWTP and estimated per capita generation rates of MPs. Relevant removal efficiencies were applied for estimating effluent concentrations at different stages of wastewater treatment. The fate of MPs along the river was approximated using an empirical riverine transport model by classifying MPs in terms of particle sizes. Finally, the concentrations of MPs in drinking water were estimated by applying literature-based removal efficiencies at every stage of drinking water treatment. It was estimated that the smaller size MPs (10–50 μm) would be predominant in Auckland's drinking water. However, the total concentration of MPs in Auckland's drinking water was estimated to be

The 2016 M w 7.8 Kaikōura earthquake was one of the largest earthquakes in New Zealand’s historical record, and it generated the most significant local source tsunami to affect New Zealand since 1947. There are many unusual features of this earthquake from a tsunami perspective: the epicentre was well inland of the coast, multiple faults were involved in the rupture, and the greatest tsunami damage to residential property was far from the source. In this paper, we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast, then present tsunami tide gauge and runup field observations of the tsunami that followed the Kaikōura earthquake. For the size of the tsunami, as inferred from the measured heights, the impact of this event was relatively modest, and we discuss the reasons for this which include: the state of the tide at the time of the earthquake, the degree of co-seismic uplift, and the nature of the coastal environment in the tsunami source region.

This paper presents a study of the waves generated by a solid block landslide moving along a horizontal boundary. The landslide was controlled using a mechanical system in a series of physical experiments, and laser-induced fluorescence measurements resolved both spatial and temporal variations in the free surface elevation. During its constant-velocity motion, the landslide transferred energy into ‘trapped’ offshore-propagating waves within a narrow frequency band. The wave trapping is demonstrated by investigating the wave dispersion characteristics using a two-dimensional Fourier Transform. The first of the trailing waves broke at Froude numbers greater than or equal to 0.625. The parametric dependence of the largest-amplitude waves and the potential energy within the wave field are discussed. The experimental results were compared to the predictions of an incompressible Navier–Stokes solver with and without turbulence models. The numerical model under-predicted the measured wave amplitudes, although it accurately predicted the measured wave phasing. The turbulent model more accurately predicted the shapes of the trailing waves. Both experimental and numerical results confirmed that investigations into wave generation by submerged objects moving at constant velocity should also consider the initial acceleration of the object, as this affects the overall evolution of the wave field. The applicability of the horizontal-boundary results to more realistic field scenarios is discussed.

At 12:02:56 a.m. Monday, November 14 2016 NZDT (11:02:56 a.m., November 13 2016 UTC) a magnitude 7.8 earthquake struck near Kaikōura on the north-eastern coast of the South Island of New Zealand. This earthquake caused a tsunami along New Zealand’s east coast that was recorded on a number of sea level gauges. Outside of the Kaikōura region, north facing bays along Banks Peninsula were most affected by the tsunami. Of these, Little Pigeon Bay experienced extensive inundation and an unoccupied cottage was destroyed by the wave run-up. We report on the inundation extent and (inferred) flow directions at Little Pigeon Bay, including a study on temporal changes in the field evidence of this inundation. Preliminary modelling results indicate that the waves may have excited resonance in the bay. We also present results from inundation surveys of nearby, north-facing bays on Banks Peninsula. The excitation of resonance in Little Pigeon Bay provides an explanation for the more severe inundation and damage there in comparison to these nearby bays.

Equilibrium clear-water scour depths predicted by existing equations based on the peak flow rate of a flood hydrograph can be overly conservative for submerged weirs in mild-slope sandy riv...

New laboratory data of local scour at submerged weirs are presented. The dimensionless scour depth downstream of a submerged weir in a uniform sediment bed is expressed as a function of dim...

The net movement of Lagrangian particles under water waves comprises a Stokes drift in the direction of wave propagation and an Eulerian return flow in the opposing direction. Accurate prediction of the Eulerian return flow in the ocean is of importance in modelling the transport of plastic pollution, oil, wreckage, and sediment. Herein, we derive a multiple-scales solution for the Eulerian mean flow under wavepackets that is valid for all water depths, both relative to the length of the wave and the length of the wavepacket. To validate this solution, we carry out Particle Tracking Velocimetry experiments in a long flume to extract the mean motion from Lagrangian seeding particles under wavepackets, finding good agreement. The extraction technique is able to deal with small background motion and sub-harmonic error waves associated with wave generation by the paddle, the latter being relatively large in finite-depth flume experiments. In finite depth, the return flow is forced by both the divergence of the Stokes transport on the wavepacket scale and the formation of a non-negligible mean set-down underneath the packet, which acts like a bounding streamtube in the form of a convergent-divergent duct. The magnitude of the horizontal return flow is thus enhanced, with particular relevance to transport in the finite-depth coastal environment.

Sanitary and stormwater sewers are buried assets that play important roles in the prevention of diseases and the reduction of health risks for our societies. Due to their hidden nature, these assets are not frequently assessed and maintained to optimal conditions. The lack of maintenance can cause sewer blockages and overflows that result in the release of pathogens into the environment. For cities, monitoring sewer conditions on a large-scale can be costly, time-consuming, and labor-intensive if using current low-throughput technologies, such as dye testing or closed-circuit television. Alternatively, smart sensor systems can provide low-cost, high-throughput, and automatic data-driven features for real-time monitoring applications. In this study, we developed ultrahigh-frequency radio-frequency identification (UHF RFID)-based sensors that are flushable and suitable for sanitary and stormwater pipes quick surveys. 3D printed RFID sensors were designed to float at the water-air interface and minimize the water interference to RF signal communications. The optimal detection range was also determined to support the design and installation of the reader in various utility holes. Field trials demonstrated that the UHF RFID system is a low-cost, high-throughput, and robust solution for monitoring blockage, illicit-connection, and water flow in sewer networks.

Coastal bridges serve as lifelines connecting affected areas to the outside world after extreme events such as tsunamis. It is thus important to predict tsunami loads applied to bridges vulnerable to tsunami attack. Most previous studies have focused on the horizontal force on bridges due to tsunamis. However, the overturning moments applied to bridges also contribute to the flexural failure of the bridge and have not been thoroughly investigated. Continuing efforts should be made to quantify tsunami-induced loads (forces and overturning moments) on coastal bridges. This study presents a series of experiments undertaken to study the tsunami loads on slab bridges using tsunami bores. Apart from the average horizontal pressure (Ph) and the horizontal (Fx) and vertical (Fz) forces, the overturning moments about the base of the pier (Myb) and the pier-deck connection (Myp) were analysed, which are closely related to the flexural failure of bridges in tsunamis. Four different pier heights were tested, as well as seven tsunami bore cases for each bridge set-up. Results show the maximum “area-adjusted momentum flux” (the product of the flow velocity squared and the contact area of the bridge in the direction of the flow) provides a better predictor for the maximum horizontal force than the maximum momentum flux, which has been used to calculate horizontal forces on emergent structures with a uniform width in the vertical direction. When a bridge is fully submerged under a tsunami, the overturning moments Myb and Myp applied to the bridge are largest at a specific pier height. Empirical equations are proposed to calculate the maximum loads (Ph, Fx, Fz, Myb and Myp) at the initial impact stage. The threshold of jump inception when a tsunami impacts a bridge has been discussed.

Since tsunamis pose a threat to many coastal areas, the mitigation of tsunami forces is important in saving lives and reducing damage when a tsunami comes. Barriers are generally constructed to protect coasts from extreme waves including tsunamis. Although extensive research has been conducted to investigate tsunami forces on coastal structures, the effectiveness of defensive structures such as barriers, seawalls and embankments in mitigating these forces has not been studied thoroughly. This paper presents a series of physical experiments to investigate the effectiveness of barriers in reducing tsunami bore impact (and associated pressures) on a vertical wall. While horizontal forces and overturning moments on the wall can be significantly reduced if the barrier is high enough, low barriers can lead to larger horizontal forces and overturning moments than if the barrier were absent. Predictive equations are proposed for reduction ratios of horizontal forces and overturning moments, as well as other methods to estimate horizontal forces.

This paper presents an experimental study of local scour at submerged weirs with different downstream slopes. Thirty-three tests of coarse sand (d50=0.85 mm) and 24 tests of fine sand (d50...

The waves generated by a submarine landslide, of great concern to coastal communities, exhibit strong dependence on the landslide motion along the sea floor. A series of two-dimensional physical experiments investigate the waves generated by a solid block landslide moving along a horizontal boundary, allowing measurement of both onshore- and offshore-propagating waves using the laser-induced fluorescence technique. This technique provides high-quality free surface measurements over the entire length of the experimental flume, and hence a data set that can be used to validate numerical models for this idealised scenario. The landslide motion is provided by a mechanical system, allowing testing of a range of landslide accelerations and terminal velocities. The landslide Froude number governs the overall behaviour of the wave field. At lower Froude numbers, the waves are almost entirely generated by the landslide acceleration and deceleration, and the offshore- and onshore-propagating wave groups contain approximately equal energy. Interactions between the landslide and the offshore-propagating waves become more important as the Froude number increases. Two inviscid-irrotational models demonstrate the importance of dispersive effects for tsunamis generated by a submarine landslide, and correctly predict the behaviour of the entire wave field at low Froude numbers. The predictions in the vicinity of the landslide worsen with increasing Froude number, due to the linear free surface conditions used by the models. Lower Froude numbers appear to be more representative of previous sloping-boundary experimental geometries, although rigid block landslides still represent an idealisation of a field scenario.

Insight is provided into focused wave group runup on a plane beach by means of laboratory wave flume experiments and numerical simulations. A focused wave group is presented as an alternative to an empirical description of the wave conditions leading to extreme runup. Second-order correction to the laboratory wavemaker generation signal is observed to remove about 60% of the sub-harmonic error wave that would otherwise contaminate coastal response experiments. Laboratory measurements of the wave runup time history are obtained using inclined resistance-type wires and copper strips attached to the beach surface. The numerical wave runup model is based on hybrid Boussinesq-Nonlinear Shallow Water equations, empirical parameters for wave breaking and bed friction, and a wetting and drying algorithm. After calibration against experimental runup data, the numerical model reproduces satisfactorily the propagation, shoaling and runup of focused wave groups over the entire length of the wave flume. Results from a comprehensive parametric study show that both measured and predicted maximum runup elevations exhibit strong dependence on the linear focus amplitude of the wave group (linked to its probability of occurrence), the focus location, and the phase of the wave group at focus. The results also demonstrate that extreme runup events owing to focused wave incidence cannot be characterised using spectral parameters alone. The optimal band of focus locations shifts onshore as linear focus amplitude of the incident wave group increases. Optimisation of phase and focus location leads to a maximum runup elevation at each linear amplitude, and, when generated using second-order corrected paddle signals, the maximum runup appears to approach saturation at very large focused wave amplitudes. This study therefore moves beyond simple wave focusing, and presents a focused wave group as a tool for investigating the relationship between extremes within an incident wave field and extreme wave runup.

A new approach to obtaining oil and water flow rates in producing horizontal wells has been developed using a pulsedneutron tool. This approach uses separate measurements of oi I and water velocities in combination with separate holdup measurements to obtain the flow rates. The velocity measurement uses both water-soluble and oilsoluble chemical markers, each of which is insoluble in the other fluid phase for the measurement. The markers are injected into the borehole by a logging tool at one location and detected by a pulsed neutron tool at a second location. The transit time between injection and detection of the marker gives a measurement of the fluid velocity. Since the markers are soluble in only one phase, the velocity of each phase can be measured separately. This measurement has been made under both laboratory and field conditions to measure velocities from 10 to 500 ft/min at horizontal and several degrees deviation from horizontal. The results of these tests show good linearity and repeatability of the measurement. Tbe holdup measurement is performed using the inelastic data from a pulsed-neutron tool. With these data, it is possible to quantitatively obtain the holdup of all three phases by combining information from the inelastic near/far ratio with the near and far carbordoxygen ratio. This approach to the holdup measurement has been demonstrated using a combination of laboratory data, Monte Carlo modeling, and field data. The results of this study have demonstrated that the RMS accuracy of this measurement is about 6% on each of the three phases. Introduction As horizontal wells have become more prevalent, the ability to reliably evaluate the production performance of these wells has become increasingly important. Existing production logging techniques, such as spinners, that have been successfully used in vertical wells cannot always be applied to horizontal wells with full confidence due to the segregated flow in the borehole. For this reason, new techniques must be developed to evaluate oil and water flow rates in horizontal wells. To determine the flow rates of the oil and water phases in a horizontal well, one must either l) measure the individual oil and water flow rates directly, or 2) measure the individual oil and water velocities in addition to their holdups. (It should be noted, that for most production logging applications in horizontal wells, measuring only the holdup or only the velocity of the production fluids is usually insufficient to determine the source of production problem s.) This paper will address the second approach, the measurement of individual oil and water velocities and their holdups. Oil and Water Velocity Measurement Several currently ava[lable technologies make it possible to measure water velocity in horizontal wells. The oldest of these’ uses a radioactive tracer such as Iodine-131 with an 8day half-life. The iodine is placed in a water-soluble form. This material is iniected into the borehole and then measured .! as It passes a gamma-ray detector. The time between injection and detection enables the calculation of the flow velocity of the water. This method can also be applied with some success to oil velocity measurements by placing the iodine into an oilsoluble form. The limitation of this approach is that the oilsoluble form is usually an emulsion that can exhibit some unique problems due to the nature of emulsions. With the increased restrictions and risks associated with the use of radioactive tracers in the borehole, it is desirable to have a method of performing these velocity measurements without using radioactive tracers. This is one of the reasons that the WFL* Water Flow Log, was developed. This approach relies on the activation of oxygen in the water using a 14-MeV neutron generator and measures the transit time of the activated oxygen irr the borehole< thus giving a measure of the water velocity. Unfortunately, this method does not * Mark of Schlumberger

Conventional production log interpretation using a spinner assumes that the spinner responds to the holdup-weighted average velocity of the fluids traveling through the swept area of the spinner blades; however, the spinner tends to respond preferentially to the most dense phase flowing through it and so can be considered as a momentum-averaging sensor. This means that when fluids of markedly different density and velocity are averaged using the current best practice we may not be calculating the most accurate spinner velocity to be used in the production log interpretation. This paper examines alternative spinner averaging approaches and then evaluates the difference on synthetic, laboratory, and real downhole data sets. We conclude from this short study that there is potential to improve the current practice of spinner interpretation, especially in gas/liquid flows, and thus provide better data for gas production allocation and gas reservoir management. Further work is needed to develop this approach.

Gas holdup probes run in a producing horizontal well on the Norwegian continental shelf are used to identify downhole flow regimes and compute the velocity of gas in intermittent flow. The observed flow regimes are compared with the predictions of a number of gas-liquid flow correlations. The theory and quality of velocity correlations are discussed.

The Siri Field on the Danish Continental Shelf is characterized by low-resistivity pay and porosities exceeding 30 PU. The reservoir sands are fine to very fine grained, well sorted with abundant iron-rich glauconite and chlorite. The microporous glauconite reduces the effective porosity and permeability and causes high initial bound water saturations. Reservoir drainage is based on water and gas flooding (SWAG injection). Producing field water-cut increases rapidly in the horizontal producers due to severe bottom aquifer coning and later injection water breakthrough. The oil production rate is constrained due to limited liquid handling capacity. Water management is hence, a primary focus area. Prior to initiating remedial workover operations, wireline tractor conveyed production inflow profiles and pulsed neutron capture gamma ray surveys were acquired. In sigma saturation monitoring a pulsed neutron source allows the decay rate of capture gamma rays to be measured. The decay rate is inversely proportional to the formation sigma, which is a linear combination of the sigma values of the rock matrix and fluid filled porosity. Knowing the matrix sigma, oil sigma, water sigma, and total porosity, the log sigma can be converted to formation saturation. The complex mineralogy of the reservoir sand with abundant and variable amounts of iron-rich glauconite significantly impacts the matrix sigma. Before sigma saturation interpretation can be made, the lithology needs to be determined more accurately than possible from standard open hole logs. A novel through casing pulsed neutron logging technique permitted well lithology determination. Using the spectral signal of the pulsed neutron capture gamma rays, a number of key matrix elements were quantified, converted to a matrix lithology, and then finally combined into a synthetic matrix sigma. This paper describes, how a single pulsed neutron tool operated in two modes (spectroscopy and sigma) permitted quantitative lithology interpretation and saturation monitoring in a complex formation environment.