Working with Nature in Wadden Sea Ports

Wadden Sea ports are situated at the border of the UNESCO World Heritage site Wadden Sea. Because of the protected status of this area, developing new economic activities is not straightforward. However, maintaining and developing port activities is needed to safeguard the economic viability of the Wadden Seasocio-economic region. In this paper we illustrate that sustainable port development is feasible when adopting a Working with Nature approach. This approach facilitates a design in which the proactive utilization and/or provision of ecosystem services serves as part of the engineering solution. We introduce four Working with Nature concepts that can be used in port designs, i.e. 1) optimising dredging strategies, 2) enhancing saltmarsh development, 3) creating estuarine gradients, and 4) optimising flow patterns. Based on theseconcepts, three case studies have been identified and pilot projects initiated. In the Port of Harlingen a pilot project has started in which an optimized dredging strategy is combined with saltmarsh development. Around the Port of Delfzijl an estuarine gradient is combined with the construction of a salt marsh and dredgedsediment is used for dike strengthening. For the Port of Den Helder, a new design is proposed in which the concepts of enhancing salt marsh development, creating estuarine gradients and optimizing flow patterns are combined. Our conclusion is that even in a World Heritage site such as the Wadden Sea, portdevelopment is possible when ecosystem services are used and provided for, and when a Working with Nature concept is put at the heart of the design

Morphodynamics of a cyclic prograding delta: the Red River, Vietnam

River deltas are inhabited by over 60% of the world population, and are, consequently, of paramount agricultural and economical importance. They constitute unique wetland envi ronments which gives river deltas ecological importance as well. Additionally, many deltas contain large accumulations of oil, gas, and coal, which further increase their economical value. More than 50% of the world population lives in Asia, most of which on the large deltas of the Ganges, Brahmaputra, Irrawaddy, Chao Praya, Mekong, Pearl, Yangtze, Yel low, and the Red River. The high population density that characterizes these deltas implies a large pressure on the natural resources, resulting in a decrease in sediment supply (dam construction, irrigation works), subsidence (lowering of the groundwater table), and loss of the natural sea defence (destruction of mangroves). Global climate change may provide additional threats through accelerated sea-level rise and changing weather patterns. In South-East Asia, river floods and typhoons are expected to occur more often and as a direct result, coastal erosion and flooding will become increasingly common. Like many other Asian deltas, the delta of the Red River, in the North of Vietnam, is char acterized by an alongshore alternation of irregular but rapid accretion and severe erosion. Locally, coastal erosion has been so severe (exceeding 2 km in the past decades) that entire villages have been lost to the sea; in contrast, the coastline experienced accretion up to 5 km elsewhere. The central objective of my research was to under stand the mechanisms that regulate the medium term (time scales of decades to centuries) patterns of erosion and accretion of the Red River Delta (RRD), and in particular that of the main branch of the Red River, the Ba Lat. The growth of the Ba Lat delta is cyclic, with a barrier that forms alongside the river mouth every 100 years. The present day barrier is about 30 km long. Alternating phases of seaward delta progradation and subsequent development of barrier-spit systems are commonly observed near many river mouths. However, the explanations offered in literature for this cyclic progradation vary considerably. The classical model for barrier development is that developed for the Mississippi delta. In their model, delta lobe switching results in a period of sediment starvation, during which former river mouth sediments are reworked into a barrier. This appears to be more or less the same for the Ebro and the Huanghe delta, but this type of barrier formation may not be very representative of other delta systems worldwide. For example, barriers on the Mississippi form on a retreating delta, while in many delta systems (including the Ba Lat) barriers are associated with actively growing delta systems. In the Ba Lat Delta, there are no indications that there was a change in sea level, wave activity, or sediment supply within the period of barrier formation. Additionally, the evolution of other branches of the Red River delta such as the Tra Ly and Day rivers is also cyclic: the Day River is just developing barriers while the Tra Ly is in-between the Ba Lat and the Day river. It seems that the cyclic growth pattern of the Ba Lat is regulated by internal dynamics of the system rather than to changing external forcing

The role of terrestrial sediment on turbidity near Singapore's coral reefs

10.1016/j.csr.2013.12.001Continental Shelf Research7675-88CSHR

Sediment trapping in the Zeebrugge Coastal Turbidity Maximum

The mechanisms leading to the formation and maintenance of a Coastal Turbidity Maximum (CTM) along the Belgian coastline was investigated using a complex 3D numerical model. Interpretation of model results suggests that the sediment concentration in this CTM may have strongly increased as a result of human interventions in the 1980’s. The large amount of sediment that became availablethen triggered self-organizing mechanisms that maintain or strengthen the CTM.Environmental Fluid Mechanic

Comment on "On the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi-diurnal tide" by P.L. Woodworth, D.L. Blackman, D.T. Pugh and J.M. Vassie [Estuarine, Coastal and Shelf Science 64 (2005) 235-240]

The present paper comments on a recent publication by Woodworth et al. [Woodworth, P.L., Blackman, D.L., Pugh, D.T., Vassie J.M., 2005. On the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi-diurnal tide. Estuarine, Coastal and Shelf Science 64 (2¿3), 235¿240.]. It is shown how tidal asymmetries associated with astronomical tides can be accounted for in an extreme sea level analysis, despite the difficulty of deriving probability distribution functions if a large number of tidal constituents are considered. The use of the term spring¿neap cycle in a diurnal tidal regime is discusse

Comment on "On the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi-diurnal tide" by P.L. Woodworth, D.L. Blackman, D.T. Pugh and J.M. Vassie [Estuarine, Coastal and Shelf Science 64 (2005) 235-240]

The present paper comments on a recent publication by Woodworth et al. [Woodworth, P.L., Blackman, D.L., Pugh, D.T., Vassie J.M., 2005. On the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi-diurnal tide. Estuarine, Coastal and Shelf Science 64 (2¿3), 235¿240.]. It is shown how tidal asymmetries associated with astronomical tides can be accounted for in an extreme sea level analysis, despite the difficulty of deriving probability distribution functions if a large number of tidal constituents are considered. The use of the term spring¿neap cycle in a diurnal tidal regime is discusse

Residual flow and tidal asymmetry in the Singapore Strait, with implications for resuspension and residual transport of sediment

The Singapore Strait connects the South China Sea, where tides are dominantly diurnal, to the dominantly semidiurnal Indian Ocean. At this transition, the tidal water level oscillations are observed to be semidiurnal while the tidal current oscillations are mixed, diurnal to fully diurnal. Due to the interaction of the diurnal constituents with the semidiurnal M2 tide, the tides are strongly asymmetric. Both residual flows and subtidal flows, with periodicities of 2 weeks to 1 year, are strong. In order to analyze and explain the hydrodynamics around Singapore, a well-documented and calibrated regional tidal model application was further improved and validated. Analysis of the results of this model shows that the diurnal tidal wave is primarily standing, with an amphidromic point close to Singapore, explaining the dominantly diurnal current and semidiurnal water level oscillations. Analysis of the model results further indicates that the fortnightly constituents in the subtidal flow are probably compound tides, with a combined amplitude over 10 cm/s. Pronounced yearly and half-yearly cycles in spring tidal current amplitude and asymmetry exist, resulting from interaction of the diurnal and the semidiurnal spring-neap cycles, compound tides, and the monsoon currents. A simple analytical transport formula was applied to determine the relative importance of tidal asymmetry and residual flows, verified with a full sediment transport model. With fine sediment being more sensitive for residual flow and coarser sediment for tidal flow, a pronounced divergence in sediment transport pathways may exist, depending on the grain size.Hydraulic EngineeringCivil Engineering and Geoscience

Mixing and stratification in a tropical tidal embayment subject to a distributed freshwater source

The Bay of Banten provides an example of a semicircular shallow tidal embayment in a tropical ROFI (Region Of Freshwater Influence), subject to a mixed,mainly diurnal tidal regimeand amonsoon-driven residual circulation. A partially inactivated delta shapes the east coast of the bay and constitutes a distributed source of freshwater during the wet season. Measurements of flow velocity, salinity and temperature were taken at two contrasting sites in the bay, to investigate stratification dynamics throughout a spring–neap cycle. Bulk Richardson numbers are shownto vary both at tidal and subtidal frequencies, and indicate that thewater column occasionally remains stratified all through a tidal cycle. About half of the variance of the subtidal flow can be explained from wind forcing. The wind-driven flowvaries between 1 and 5% of the wind speed,with a pronounced difference between the twolocations under study. Stratification was further analyzed by estimating the contributions of advection by the depth–mean flow, tidal straining, vertical advection and heating, to variation in potential energy anomaly (PEA). To do so, horizontal gradients in density and PEAwere estimated frommulti-linear regression analysis. The obtained results show that spatial gradients of density and PEA can reverse sign frequently in the absence of strong mixing, associated to pulses of freshwater discharge. The freshwater discharge, in turn, is distributed over small streams. The contribution of vertical mixing was found to be relatively small, and none of the remaining terms were clearly dominant. Estimates of the boundary layer thickness of clockwise and anticlockwise rotary components of the tidal flow show the impact of baroclinic processes on velocity profiles

Numerical study on mixing and stratification in the Ebb-Dominant Johor Estuary

Journal of Coastal Research291201-215JCRS