Yi Pan

Full-Scale HPTRM-Strengthened Levee Testing under Combined Wave and Surge Overtopping Conditions: Overtopping Hydraulics, Shear Stress, and Erosion Analysis

ABSTRACT Pan, Y.; Li, L.; Amini, F., and Kuang, C., 2013. Full-scale HPTRM-strengthened levee testing under combined wave and surge overtopping conditions: overtopping hydraulics, shear stress, and erosion analysis. Post–Hurricane Katrina investigations revealed that most earthen levee damage occurred on the levee crest and landward side slope as a result of wave overtopping, storm surge overflow, or a combination of both. This study was conducted to investigate the hydraulic parameters and erosion characteristic of one levee strengthening technique, a high-performance turf reinforcement mat (HPTRM), under combined wave and surge overtopping conditions, about which little is known. Because the HPTRM system can only be tested using a full-scale model, a full-scale laboratory study on combined wave and surge overtopping of a levee crest and landside slope strengthened by the HPTRM was conducted in a two-dimensional laboratory wave/flow flume. The overtopping hydraulic features were summarized during the tests. The time series of flow thickness and velocity at five locations on the levee crest and landside slope were measured. Soil erosion and stem and blade loss were measured during the test intervals. New empirical equations were developed to estimate the average overtopping discharge. Based on the distribution of the overtopping discharge, combined wave and surge overtopping was divided into two cases: a surge-dominated case and a wave-dominated case. New equations were developed to estimate the mean flow thickness, root-mean-square wave height, mean velocity, and velocity of the wave front on the landside slope. The shear stress and average overtopping velocity on the landside slope and levee crest were calculated. The characteristics of soil loss and grass stem and blade loss on the HPTRM-strengthened levee were given. A “maximum soil loss” was found for each measuring point.

Performance Evaluation of a Beach Nourishment Project at West Beach in Beidaihe, China

Abstract This paper presents a detailed study of a beach nourishment project in Beidaihe, China. The study consists of a detailed assessment of a small-scale trial project that was carried out during May to June in 2008 to create two bathing sites on West Beach and a numerical evaluation of scheme options for the full project involving beach nourishment, groins, and submerged breakwaters. The monitoring data indicate that the nourished beach in the small-scale project was slowly eroding but in February of the following year the beach was still 20 m wider than it was before the project. The long-term shoreline evolution was then predicted using the generalized model for simulating shoreline change, which was calibrated to reproduce the posttrial project shoreline. The model indicates that without follow-up nourishment, the nourished beach created by the trial project will cease to be suitable for bathing in just 2–3 years. As to the full project the numerical evaluation of various scheme options indicates that the east groin plays a key role in protecting the beach in the long term and the removal of a rock jetty at east end of the beach in 2002 is identified as one of the major causes for the present severe erosion of West Beach. On the basis of the simulation results an optimum scheme for the project is proposed.

Comparison of wave fields caused by four proposed beach nourishment schemes in Beidaihe, China

The erosion of west beach in Beidaihe has become severe in the recent years. In order to nourish the beach, four different engineering nourishment schemes are proposed. As a near shore project, wave is the main force in the sea area of west beach. Based on the information above, wave fields in the sea area of west beach under both ordinary wave condition (S, Hs=0.7m, T=3.2s) and strong wave condition (NE, Hs=1.5m, T=4.7s) are analyzed. The result shows that beach nourishment with two jetties and three submerged breakwaters protects the west beach most effectively.

Effects of Submerged Breakwater on Hydrodynamics and Shoreline Change of the East Beach of Beidaihe, Bohai Bay, China

ABSTRACT Kuang, C.; He, L.; Gu, J.; Pan, Y.; Zhang, Y.; Yang, Y.; Qiu, R., and Zhang, J., 2014. Effects of submerged breakwater on hydrodynamics and shoreline change of the East Beach of Beidaihe, Bohai Bay, China. The beaches in Beidaihe of Bohai Bay of China have been eroded since 1950s, clearly evidenced by sand coarsening, rock outcropping, and slope steepening. Beach nourishment is a common coastal management strategy used to protect beaches from erosion along sandy coastlines, and it has already been applied to recover several beaches of Beidaihe since 2008. In this paper, the effects of a submerged breakwater used as part of a beach nourishment project on hydrodynamics and shoreline changes of the East Beach of Beidaihe are presented. First, the brief descriptions of phase I and phase II of the beach nourishment project of East Beach are given. And then numerical models, including tidal current model, wave model, and one-line model for simulating hydrodynamics (tidal currents and waves) and shoreline changes are established and verified by field measurements. These well-verified numerical models are adopted to compute the tidal current fields, wave fields, and shoreline changes of East Beach with and without the submerged breakwater. The results show that the submerged breakwater plays a very important role in protecting East Beach to a certain degree. The effects of alterations of the freeboard and the width and the length of the submerged breakwater on shoreline changes are also discussed, and the results show that increasing the above three parameters will better protect the beach. Overall, a submerged breakwater can play a certain role in protecting a beach against erosion; additional beach nourishment is needed to stabilize East Beach in long term.

Erosion Resistance of HPTRM Strengthened Levee from Combined Wave and Surge Overtopping

Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and land-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. This study addresses erosion resistance performance of a levee strengthening technique—high performance turf reinforcement mat under combined wave and surge overtopping conditions using full-scale flume tests as well as erosion function apparatus (EFA) tests. Based on the results of full-scale flume tests, an “upper limit” of soil loss is observed for certain flow conditions. Erosion rate was presented as a function of velocity and freeboard. The effect of duration of overtopping on the erosion depth is also determined. The results of EFA tests indicate that the presence of grass roots substantially improve the critical velocity and soil erodibility.

Influence of Three Levee-Strengthening Systems on Overtopping Hydraulic Parameters and Hydraulic Equivalency Analysis between Steady and Intermittent Overtopping

AbstractDifferent types of strengthening systems were introduced to protect the crest and land-side slope of the levees against surge overflow and wave overtopping after Hurricane Katrina. Three levee-strengthening systems, roller-compacted concrete, articulated concrete block, and high-performance turf reinforcement mat, were investigated through full-scale laboratory tests in this study. Hydraulic performances of these three levee-strengthening systems were compared to determine the effect of strengthening systems and to provide the equivalency analysis between surge-only overflow and combined wave and surge overtopping. The findings of this study indicate that the high-performance turf reinforcement mat system has the strongest effect in reducing and smoothing the overtopping discharge and in reducing the flow velocity and wavefront velocity on the land-side slope, whereas roller-compacted concrete has the weakest effect. Equivalency analysis between surge-only overflow and combined wave and surge over...

Assessment of a Measure for Water Exchange Strengthening of Artificial Headland Bays Based on Shoreline Change and Flushing Time

ABSTRACT Pan, Y.; Kuang, C.; Gu, J.; He, L.; Zhang, Y.; Yang, Y.; Qiu, R., and Zhang, J., 2014. Assessment of a measure for water exchange strengthening of artificial headland bays based on shoreline change and flushing time. Artificial headlands are used around the world to form headland bays to contain beach materials. However, the artificial headland would weaken the water exchange in the bay and in some cases would make the water quality deteriorate. In this paper, we propose reserving a tidal channel in the landward end of the artificial headland, thus enabling the tidal current to pass through the channel, as a solution. The effects of the tidal channel on the weakening of beach protection and the strengthening of water exchange were investigated via numerical studies based on a beach nourishment project. A shoreline change model was set up to investigate the weakening of the beach protection. Four project schemes were simulated, and the results indicated that weakening of the beach protection is acceptable and the response of the shoreline to the tidal channel is influenced by the state of the beach. A three-dimensional (3D) flow model and a 3D constituent transport model were applied to evaluate the strengthening of water exchange using flushing time as the indicator. The results indicate that the reservation of the tidal channel induces an approximate 50% reduction in flushing time. The specific reduction amount of the flushing time is influenced by the length of the tidal channel, the tidal condition, and the direction of the artificial headland. The conclusions suggest that the tidal channel is a feasible and effective measure to strengthen the water exchange in an artificial headland bay at the cost of an acceptable loss of beach protection effect.

Numerical study of shoreline changes by emergency beach nourishment project at the Middle Beach of Beidaihe, China

Beach nourishment is a common coastal management strategy used to protect beach from erosion along the sandy coastlines. This method has been successfully applied to an emergency project at the West Beach of Beidaihe in the summer of 2008 and the full West Beach nourishment project in 2009–2010, which is the direct base of this study. Some basic information about the emergency engineering area at the Middle Beach is firstly described. The shoreline change of this area, including the analysis of beach width in five monitoring profiles in the bathing places of Middle Beach, is then discussed. After that a numerical model based on one-line theory is established and the numerical results agree well with the measured shorelines, which indicates that the model is appropriate and is qualified to predict the shoreline change of the Middle Beach. With the same model and parameters, long-term performance of the project is predicted, and the result shows that without follow-up nourishment and project, the bathing places can remain suitable for bathing for about 10 a. It is suggested to nourish the beach in time and carry out the beach nourishment project for the full Middle Beach in Beidaihe.

Modelling of a non-buoyant vertical jet in waves and currents

A generic numerical model using the large eddy simulation (LES) technique is developed to simulate a non-buoyant vertical jet in wave and/or current environments. The experimental data obtained in five different cases, i.e., one case of the jet in a wave only environment, two cases of the jet in a cross-flow only environment and two cases of the jet in a wave and cross-flow coexisting environment, are used to validate the model. The grid sensitivity tests are conducted based on four different grid systems and the results illustrate that the non-uniform grid system C (205×99×126 nodes with the minimum size of 1/10 jet diameter) is sufficiently fine for the modelling. The comparative study shows that the wave-current non-linear interaction should be taken into account at the inflow boundary while modelling the jet in wave and cross-flow coexisting environments. All numerical results agree well with the experimental data, showing that: (1) the jet under the influence of the wave action has a faster centerline velocity decay and a higher turbulence level than that in the stagnant ambience, meanwhile the “twin peaks” phenomenon exists on the cross-sectional velocity profiles, (2) the jet under a cross-flow scenario is deflected along the cross-flow with the node in the downstream, (3) the jet in wave and cross-flow coexisting environments has a flow structure of “effluent clouds”, which enhances the mixing of the jet with surrounding waters.

Postnourishment Evolution of Beach Profiles in a Low-Energy Sandy Beach with a Submerged Berm

AbstractSubmerged berms are an increasingly used coastal defense structure for beach nourishment because of their eco-friendly nature. A beach-nourishment project that included sand placement on th...