Understanding the dynamics of sediment transport and erosion-deposition patterns in the locality of a coastal structure is vital to evaluating the performance of coastal structures and predicting the changes in coastal dynamics caused by a specific structure. The nearshore hydro-morphodynamic responses to coastal structures vary widely, as these responses are complex functions with numerous parameters, including structural design, sediment and wave dynamics, angle of approach, slope of the coast and the materials making up the beach and structures. This study investigated the sediment transport and erosion-deposition patterns in the locality of a detached low-crested breakwater protecting the cohesive shore of Carey Island, Malaysia. The data used for this study were collected from field measurements and secondary sources from 2014 to 2015. Sea-bed elevations were monitored every two months starting from December 2014 to October 2015, in order to quantify the sea-bed changes and investigate the erosion-deposition patterns of the cohesive sediment due to the existence of the breakwater. In addition, numerical modelling was also performed to understand the impacts of the breakwater on the nearshore hydrodynamics and investigate the dynamics of fine sediment transport around the breakwater structure. A coupled two-dimensional hydrodynamics-sediment transport model based on Reynolds averaged Navier-Stokes (RANS) equations and cell-centered finite volume method with flexible meshing approach was adopted for this study. Analysis of the results showed that the detached breakwater reduced both current speed and wave height behind the structure by an average of 0.12 m/s and 0.1 m, respectively. Also, the breakwater made it possible for trapped suspended sediment to settle in a sheltered area by approximately 8 cm in height near to the first main segment of the breakwater, from 1 year after its construction. The numerical results were in line with the field measurements, where sediment accumulations were concentrated in the landward area behind the breakwater. In particular, sediment accumulations were concentrated along the main segments of the breakwater structure during the Northeast (NE) season, while concentration near the first main segment of the breakwater were recorded during the Southwest (SW) season. The assessment illustrated that the depositional patterns were influenced strongly by the variations in seasonal hydrodynamic conditions, sediment type, sediment supply and the structural design. Detached breakwaters are rarely considered for cohesive shores; hence, this study provides new, significant benefits for engineers, scientists and coastal management authorities with regard to seasonal dynamic changes affected by a detached breakwater and its performance on a cohesive coast.

A project for mangrove rehabilitation purpose has been carried out at intertidal area of Carey Island, Peninsular Malaysia in early 2009. As part of the project, a detached low-crested breakwater has been constructed near the bare degraded mangrove area to reduce wave energy and storm surges forcing the site. The breakwater is also expected to trap the sediment behind its structure as well as soil nutrients needed for mangrove seedling. This study attempts to evaluate the changes of seabed elevation and geochemical in soil around the degraded mangrove area after 6 years implementation of the breakwater's structure. Seabed elevations at degraded mangrove area (rehabilitated area) and concentration of soil nutrients at three locations (rehabilitated area, non-rehabilitated area and natural forest area) were monitored on October 2015. The seabed elevations on October 2015 are compared to the seabed elevation in January 2009 to determine the seabed level changes. In addition, the values of soil nutrients at rehabilitated area were compared to soil nutrients at non-rehabilitated area and natural mangrove forest to evaluate the geochemical condition of soil at mangrove degradation area for preparation of mangrove seedling planting. The results present that there is an increment of seabed elevations at the degraded mangrove area after 6 years construction of the breakwater (approximately 32 cm in average). The results also show a significant increase in the amount of soil nutrients on the top soil (approximately 0 to 20 cm depth) especially carbon, nitrogen and potassium at degraded mangrove area with almost similar to soil nutrients in natural mangrove forest. It demonstrate that the condition of degraded mangrove area after 6 year implementation of the breakwater is conducive for replanting the mangrove seedlings to restore the endangered mangroves at intertidal area of Carey Island, Peninsular Malaysia.

A pipe with sudden expansions are used in a wide variety of engineering applications such as hydraulic, civil, and nuclear industries. Flow through a pipe with sudden expansion about its head loss becomes local head loss as the boundary changes. The dynamic water pressure for the rapidly varied flow corresponding to the local head loss has remained inconclusive and inaccurate. It is partly due to the complexity of the vortex involved and partly because of limitations of the traditional experiments. Therefore, in this study, the methods based on theoretical analysis and numerical simulation were employed for the prediction of the influence scope of a plane pipe with sudden expansions. A parametric study is performed for the expansion ratios are 1.5, 2, 3, 4, 5 and in a Reynolds number range of 10 - 100000. On the basis of numerical results, an existing correlation of the influence scope is also extended to take into account the effect of the scale effect additionally. The simulation results show that the influence scope of local head loss is affected greatly by expansion ratio and Reynolds number of the plane pipe, and expansion ratios occurring from the sudden expansions are less sensitive to the Reynolds number. The obtained research results have shown that for the cases when Reynolds number is relatively small (Re < 2000), the recirculation degree (L/D, where L is the length of recirculation zone, D is the diameter of the latter pipe) increases significantly with the increase of the Reynolds number; and for the cases when the Reynolds number is larger (Re > 10000), the recirculation degree changes slowly with the Reynolds number. In general, the length of the influence scope is logarithmically related to the Reynolds number.

Coastal defence structures such as detached breakwaters have been used alternatively to reduce the coastal erosion problems in the world. Behind their efficiency, detached breakwater causes complex changes to the coastal hydro-morphologies because of variation in the sediment type, climate condition and design of the structures. This study aims to evaluate the impact of parameter changes of a detached breakwater on coastal morphologic changes. Three model cases of detached breakwater with different lengths and positions have been set up. MIKE 21 Mud Transport model interrelated with MIKE 21 Hydrodynamic model was performed to simulate the deposition-erosion patterns in the locality of detached breakwater for different lengths and positions of the breakwater. The results show that the detached breakwater with available empty gap gives lowest negative impact to the cohesive coastal areas with considerable reduction of the erosion problems.

A 3D hydraulic-thermodynamic mathematical model is established to predict the temporal and spatial distribution of temperature in a large reservoir in different time scale inflow temperature condition, and a further research on the influence mechanism of inflow temperature on the water temperature structure is made. it is found that the convection current between the upper and the lower of the reservoir always appear when the storage heat in a reservoir decreases; the stratification phenomenon appears in most time of a year in a large reservoir which is controlled by the climate, and there is a close relationship between the water temperature distribution and the inflow temperature. Different inflow temperature has different affected area where the density current propagates, in the affected area, the difference of water temperature distribution occurs by the cumulative effect of the previous months, for the other area, the more detailed the inflow temperature is, the more accurate the simulation results are.