Development of a modelling methodology for the investigation of riparian hydrological processes

The riparian zone is in intimate contact with the river and, as such, is a critical zone for understanding hydrological problems. This paper presents a general modelling methodology for the assessment of riparian hydrological processes. It is applicable to a wide range of riparian spaces and incorporates current expertise in numerical methods. A core part of the modelling methodology is the random walk particle method (RWPM). We develop an RWPM as part of the ESTEL2D subsurface flow model, test it against analytical solutions and apply it to the simulation of parcels of water as they move through the riparian zone. The modelling methodology provides a new opportunity to assess fundamental hydrological process issues such as the proportioning of pre‐event and event water storm runoff, and reversals of flow in floodplains. Copyright © 2005 John Wiley & Sons, Ltd.     

A long-term series of zooplankton monitoring of a shallow coastal water of the southern Baltic

Data on the seasonal variability of the quality and quantity of zooplankton are presented for the shallow eutrophic Darss-Zingst estuary. These data are the result of a monitoring programm from 1969–1995. Copepods and rotifers were the main components of the biomass. They showed a pattern of seasonal fluctuation which remained unchanged during the whole period of investigation. Copeods were dominant in spring and autumn and had their maximum in summer. Considerable biomass peaks of cladocerans were observed only in some years in connection with low salinities and high temperatures. A peak of meroplanktic larvae of polychates was observed in late autumn since 1989. Copepods were inversily correlated with the pH-value. An inverse correlation was also found between rotifers and water temperature.     

The shoreface-connected ridges along the central Dutch coast — part 2: morphological modelling

The hydrodynamic and sediment transport processes on the Dutch inner-shelf were studied on the basis of short- and medium-term (days, month) field experiments during fair-weather and storm conditions. The primary goal of this study was to identify the mechanisms that may be responsible for the formation and maintenance of the shoreface-connected ridges in the study area. The hydrodynamic field observations do not consistently support existing theoretical models explaining the formation of such ridges. Instead, the water motion appears to be dominated by wind- and density-driven effects. A review of literature indicates that other field studies also fail to observe the flow response expected from theory. Sediment transport during fair-weather is very episodic, with bed load transport slightly dominant over suspended load transport. The sediment transport processes during storms are dominated by the mean fluxes, with waves acting as a stirring mechanism. The contribution of wave-oscillatory fluxes cannot be neglected and may be directed with and against the waves. Long-wave fluxes are present, but very small.     

Shoreline evolution of the Holland coast on a decadal scale

The decadal evolution of the dunefoot position along 120 km of the Holland coast is analysed. Firstly, a new definition of dunefoot is introduced based on hydrodynamic and morphologic considerations, which is not affected by local and instantaneous processes occurring immediately before the bathymetric survey. The dunefoot evolution over decadal scales indicates the existence of spatial and temporal oscillations in the shoreline position with magnitudes of 2–3 km length and a periodicity of 4–15 years. Two main controlling factors of this behaviour are identified: (1) influence of sub-aqueous bar systems, and (2) changes in the storm-wave conditions reaching the coast. Although the precise controlling processes of the relation between the dunefoot and the subaqueous profile still remain unclarified, we introduce the concept that the development of a morphological bar cycle requires a fixed amount of time-integrated forcing that is proportional to the cumulative effect of storm waves. Beach mobility along the Holland coast on decadal scales (10–20 m) is similar or lower than mobility introduced by storms or by seasonal cycles. However, it is important to consider these changes for the possible implications on the local vulnerability of the coast to extreme events. Copyright © 1999 John Wiley & Sons, Ltd.     

Luminescence dating of Weichselian interstadial sediments from the German Baltic Sea coast

A cliff outcrop called Kluckow, in the Baltic Sea area, with a (glacio-) fluvial to (glacio-) lacustrine succession, provides a unique opportunity to resolve uncertainties in the timing and extent of several poorly constrained Weichselian ice advances. Based on a detailed lithofacies analysis, we selected four sampling horizons for luminescence dating to determine a depositional chronology. We measured both coarse-grain quartz and potassium-rich feldspar for age determination using optically stimulated luminescence (OSL) and post-IR infrared stimulated luminescence (pIRIR). Furthermore we addressed potential problems such as incomplete bleaching and quartz saturation effects. The resulting luminescence-chronology, supported by one radiocarbon age, illustrates a depositional time interval of the investigated sequence between ∼62 and ∼22 ka. Within this sequence a mussel-bearing fluvial sand indicate interstadial climate conditions at approximately 46 ka. The upper part of the section is composed of a 4 m thick glaciolacustrine silty clay and an overlying glaciofluvial sand; the latter yielded an OSL age of ∼22 ka. Shortly after these sequences formed, the subsequent ice advance (indicated by the overlying till sheet) reached the study area. Based on our new chronology and lithofacies analysis, we conclude that the Scandinavian Ice Sheet did not reach the study area between ∼62 and ∼22 ka.     

Adriatic coast as a microcosm for global genotoxic marine contamination--a long-term field study

Global changes in the marine environment and the continuing disposal of genotoxic xenobiotics are increasing the importance of environmental pollution monitoring and of biomonitoring programs. Current approaches focus on investigations at regional and local levels in an attempt to precisely define the nature and extent of any potential environmental crisis. We have initiated, for the first time, a long-term biomonitoring program focusing on the Croatian coast of the Adriatic Sea to contribute to a more detailed understanding of marine genotoxic effects using the mussels Mytilus galloprovincialis Lam., collected along the eastern Adriatic coast over a period of five years (1998-2002), as a key test organism. The integrity of DNA in its gill homogenate was examined by the Fast Micromethod. The strand scission factor (SSF) values, as a measure of DNA integrity, DNA damage or incomplete repair have been used for the ranking of sampling sites with respect to significant genotoxic stress due to the influence or effects of genotoxic xenobiotics. The region of Split (Kastela Bay) proved to be the area with the heaviest load of genotoxic agents. The investigation of harmful effects in the ecosystem based on biomonitoring of genetic and other agents, not only on local levels but also on a wider scale, is considered as an important step in marine environmental management.     

Factors influencing variability of mercury input to the southern Baltic Sea

The southern Baltic countries have been identified as significant sources of Hg into the sea. Are anthropogenic activities the sole source? How do meteorological parameters influence the deposition? Studies on input of Hg to the Baltic were conducted in 2008–2012 in the Polish coastal stations. The riverine load was found to depend directly or indirectly on the amount of precipitation and catchment type. Input of atmospheric Hg increased along with the number of precipitation episodes from remote maritime air masses, as well as with the number of days when continental air masses from regional (when domestic heating prevailed) and remote sources moved over the Baltic, during the heating season. During the non-heating season metal input was found to be proportional to episodes of rain from continental regional air masses and to the number of days under influence of continental and maritime air masses from regional sources.     

OSL chronology for a sediment core from the southern Baltic Sea: A continuous sedimentation record since deglaciation

A chronology based on optically stimulated luminescence (OSL) dating is presented for the late- and post-glacial evolution of the southern Baltic Sea (15 ka to present). During this period, large water level and salinity changes occurred in the Baltic Basin due to opening and closing of connections to the North Atlantic. Previous attempts to establish a chronology for these palaeoenvironmental changes have mainly been conducted in coastal settings where organic material for ¹⁴C dating is abundant. Many of these records are, however, discontinuous due to the large water level fluctuations. In contrast, in the relatively deep water of the Arkona Basin, the sediment record is expected to be more or less continuous. The single aliquot regenerative dose (SAR) procedure was used to date 32 samples of fine quartz sand from a 10.86 m long sediment core from the centre of this basin (45 m water depth). Tests of luminescence characteristics confirmed the suitability of the material for OSL dating and the ages agree well with the available AMS ¹⁴C ages on shells. The Baltic Ice Lake drainage to the North Atlantic appears to occur 11.6 ka, agreeing with other published evidence. However, we suggest that the main marine Littorina transgression appears in the Arkona Basin at about 6.5 ka, rather than at 8.5 ka, as previously thought.     

Differences in the abiotic parameters of water in coastal lakes in the light of the EU water framework directive: An example of the Polish southern Baltic coast

Coastal lakes have a specific hydrological regime determined by the influence of sea and inland water and the local hydrographic conditions. There are several problems concerning the protection and assessment of water quality of these bodies. The most important features differentiating coastal lakes from other lakes are: high salinity, a wide range of seasonal and short-term water quality changes, and specific aquatic ecosystems adapted to these conditions. These matters have not been sufficiently taken into account in the existing classifications and typologies of lakes in Poland. The problem has not been solved by the establishment of the adequate reference conditions and new guidelines for the classification of water status (which are being prepared according to the Common Strategy for the Implementation of the Water Framework Directive) regarding inland surface waters (rivers and lakes) and marine waters (coastal and transitional). An important issue is to define criteria which would help to distinguish all those hydrographic objects and to establish water quality standards for them.     

Quartz OSL sensitivity as a proxy for storm activity on the southern Brazilian coast during the Late Holocene

Natural cycles of irradiation during burial and bleaching due to solar exposure during transport increase the Optically Stimulated Luminescence (OSL) sensitivity of quartz sand grains. The relationship between the OSL sensitivity and sediment transport allows to discriminate quartz sand grains with different depositional histories. In this paper, we evaluate the variation of OSL sensitivity in quartz grains deposited during the progradation of the Ilha Comprida barrier on the southern Brazilian, coast. Changes in sand sensitivity recorded by barrier growth since 6 ka ago are controlled by the variation in the proportion of low versus high sensitivity quartz grains. Low sensitivity grains with short sedimentary history are supplied by the Ribeira de Iguape River and reach the barrier through southward alongshore currents during fair weather conditions. Storm conditions shift the alongshore currents to northeast and permit the transport of high sensitivity grains with long sedimentary history from distal southern coastal sectors to the barrier. Therefore, the input of distal sediments for the Ilha Comprida barrier depends on the frequency and intensity of storms. Thus, the OSL sensitivity can be used as proxy for storm activity. The variation of OSL sensitivity through time indicates that the Ilha Comprida barrier changed from a relatively stable to an unstable storm pattern around 2 ka ago. Periods with increased storm activity peaked around AD 500, AD 1500 and AD 1850, approximately on the boundaries of the Medieval Climate Anomaly and the Little Ice Age.     

Development of the SAR TT-OSL procedure for dating Middle Pleistocene dune and shallow marine deposits along the southern Cape coast of South Africa

Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions.     

Observations and conceptual modelling of morphological coupling in a double sandbar system

Nearshore sandbars, located in <10 m water depth, can contain remarkably periodic alongshore undulations in both cross‐shore position and depth. In a double sandbar system, the alongshore spacing of these morphological patterns in the inner sandbar may be identical to those in the outer sandbar. Although this morphological coupling has been observed previously, its frequency and predominance remain unclear. In this paper, we use a 9.3‐year dataset of daily low‐tide time exposure images from the double‐barred beach at Surfers Paradise (Gold Coast, Australia) to analyse the temporal and spatial characteristics of morphological coupling within a double sandbar system. We distinguish five types of morphological coupling between the inner and outer sandbars, of which four coincide with a downstate progression of the outer bar. Coupling is either in‐phase (with a landward perturbation of the inner bar facing an outer‐bar horn) or out‐of‐phase (with a seaward perturbation of the inner bar facing an outer‐bar horn), where the coupled inner‐bar features either consist of rip channels or, predominantly, perturbations of the low‐tide terrace. Cross‐correlation of the image‐derived inner‐ and outer‐bar patterns shows coupling to be a common phenomenon in the double sandbar system studied here, with coupling in 40% of the observations. In contrast to previous observations of sandbar–shoreline coupling at single‐barred beaches, in‐phase coupling (85% of all coupled bar patterns) predominates over out‐of‐phase coupling (15%). Based on our observations and bathymetries assimilated from the images for a restricted set of coupling events, we hypothesize that the angle of offshore wave incidence, wave height and depth variations along the outer sandbar determine the type of flow pattern (cell circulations versus meandering currents) above the inner bar and hence steer the type of coupling. Copyright © 2012 John Wiley & Sons, Ltd.     

Seasonal variation of polychlorinated biphenyl concentrations in the southern part of the Baltic Sea

The impact of seasonal fluctuations in forcing factors such as atmospheric concentration, temperature, and biological productivity on the concentration of polychlorinated biphenyls (PCBs) in the surface water of the southern part of the Baltic Sea was investigated. Water samples were collected on eight cruises over 2 years. A clear seasonal variability in dissolved PCB concentrations was observed with higher levels in summer than in winter and spring. This was attributed to changes in atmospheric concentrations and water temperature, based on measurements showing the PCB levels in the atmosphere and surface water to be close to a partitioning equilibrium. Concentrations in the suspended particulate material (SPM) fraction were also variable, and when the quotient of the organic carbon normalised concentration in SPM and the dissolved concentration was calculated (i.e., the bioaccumulation factor (BAF)), a seasonal pattern was observed which was consistent with kinetic limitations on partitioning into particles caused by plankton growth. However, seasonal variability in the partitioning properties of the SPM may also contribute to this variability.     

Contemporary hydrodynamics and morphological change of a microtidal estuary: a numerical modelling study

Contemporary hydrodynamics and morphological change are examined in a shallow microtidal estuary, located on a wave-dominated coast (Port Stephens, NSW, Australia). Process-based numerical modelling is undertaken by combining modules for hydrodynamics, waves, sediment transport and bathymetry updates. Model results suggest that the complex estuarine bathymetry and geometry give rise to spatial variations in the tidal currents and a marked asymmetry between ebb and flood flows. Sediment transport paths correspond with tidal asymmetry patterns. The SE storms significantly enhance the quantities of sediment transport, while locally generated waves by the westerly strong winds also are capable of causing sediment entrainment and contribute to the delta morphological change. The wave/wind-induced currents are not uniform with flow over shoals driven in the same direction as waves/winds while a reverse flow occurring in the adjacent channel. The conceptual sediment transport model developed in this study shows flood-directed transport occurs on the flood ramp while ebb-directed net transport occurs in the tidal channels and at the estuary entrance. Accretion of the intertidal sand shoals and deepening of tidal channels, as revealed by the model, suggest that sediment-infilling becomes advanced, which may lead to an ebb-dominated estuary. It is likely that a switch from flood- to ebb-dominance occurs during the estuary evolution, and the present-day estuary acts as a sediment source rather than sediment sink to the coastal system. This is conflictive to the expectation drawn from the estuarine morphology; however, it is consistent with previous research suggesting that, in an infilling estuary, an increase in build-up of intertidal flats/shoals can eventually shift an estuary towards ebb dominance. Thus, field data are needed to validate the result presented here, and further study is required to investigate a variety of estuaries in the Australian area.     

Wave climate simulation for southern region of the South China Sea

This study investigates long-term variability and wave characteristic trends in the southern region of the South China Sea (SCS). We implemented the state-of-the art WAVEWATCH III spectral wave model to simulate a 31-year wave hindcast. The simulation results were used to assess the inter-annual variability and long-term changes in the SCS wave climate for the period 1979 to 2009. The model was forced with Climate Forecast System Reanalysis winds and validated against altimeter data and limited available measurements from an Acoustic Wave and Current recorder located offshore of Terengganu, Malaysia. The mean annual significant wave height and peak wave period indicate the occurrence of higher wave heights and wave periods in the central SCS and lower in the Sunda shelf region. Consistent with wind patterns, the wave direction also shows southeasterly (northwesterly) waves during the summer (winter) monsoon. This detailed hindcast demonstrates strong inter-annual variability of wave heights, especially during the winter months in the SCS. Significant wave height correlated negatively with Niño3.4 index during winter, spring and autumn seasons but became positive in the summer monsoon. Such correlations correspond well with surface wind anomalies over the SCS during El Nino events. During El Niño Modoki, the summer time positive correlation extends northeastwards to cover the entire domain. Although significant positive trends were found at 95 % confidence levels during May, July and September, there is significant negative trend in December covering the Sunda shelf region. However, the trend appears to be largely influenced by large El Niño signals.     

Aeolian dynamics of transgressive dunefields on the southern Mozambique coast,Africa

A relatively unknown coastal zone of southern Mozambique in Africa is covered by vast mobile and stabilized dunefields. The aeolian dynamics of these transgressive dunefields are studied based on mobility and stability models, statistical analysis of climate data and topographic profiles. Detailed analyses of regional winds, rainfall records, atmospheric temperature records and annual monitoring of dune migration rates helped to find reliable data about instantaneous aeolian sand transport rates, wind drift potential, dune mobility and dune migration rates. The data obtained suggest that the coastal transgressive dunefields are controlled by the southeast winds, availability of loose sediments on the beach, the presence of headland boundary between Maputo and Gaza provinces and the appropriate deposition spaces between the coastline and lacustrine‐lagoon systems. Two distinctive segments of transgressive dunefields were identified in the region studied, including the northern segment of Maputo province with active (mobile) and semi‐vegetated dunes that migrate 23 m/yr landward, and Gaza province dunefields with stabilized (vegetated) and semi‐vegetated dunes. The data obtained in this research have considerable potential to make a valuable contribution to the study of coastal dunefields. Copyright © 2018 John Wiley & Sons, Ltd.     

Development and validation of a morphological model for multiple sediment classes

The complexity of sediment dynamics in aquatic systems can be better understood by applying numerical models. The development of a comprehensive morphological model is presented in this paper.The model aims to predict the sediment transport and bed evolution in natural systems composed of different sediment types. The morphological model was implemented in MOHID, a modelling system that solves the three-dimensional hydrodynamics and advection-diffusion transport of suspended sediments. Multiple sediment classes were taken into account(non-cohesive and cohesive) considering the effects of sediment mixtures and bed consolidation on resistance to erosion. To represent bottom stratigraphy, the bottom column can be divided into several layers. The key points of the simulated processes are discussed in this paper. Model results are assessed in six test cases through comparison with analytic solutions or experimental data. The outcomes demonstrate the model's capacity to simulate the transport dynamics of non-cohesive and cohesive sediments. The speed up of morphological changes by an acceleration factor permitted modelling bed evolution for long time periods.Moreover, a test case for the Tagus Estuary demonstrated the model's capacity for generating realistic sediment distribution based on the local hydrodynamic conditions. Limitations in the availability of bed composition data can be overcome by considering a warm-up run to provide realistic initial conditions for further predictions of morphological developments.     

Two-dimensional equilibrium morphological modelling of a tidal inlet: an entropy based approach

The management of tidal inlets requires the accurate prediction of equilibrium morphologies. In areas where the flow from rivers is highly regulated, it is important to give decision makers the ability to determine optimal flow management schemes, in order to allow tidal inlets to function as naturally as possible, and minimise the risk of inlet closure. The River Murray Mouth in South Australia is one such problem area. Drought and the retention of water for irrigation and urban water consumption have limited the amount of water entering the estuary. As a result, sediment from the coastal environment is being deposited in the mouth of the estuary, reducing the effect of further coastal interactions. Currently, situations such as this are modelled using traditional process-based methods, where wave, current, sediment transport and sediment balance modules are linked together in a time-stepping process. The modules are reapplied and assessed until a stable morphology is formed. In this paper, new options for modelling equilibrium morphologies of tidal inlets are detailed, which alleviate some of the shortfalls of traditional process-based models, such as the amplification of small errors and reliance on initial conditions. The modelling problem is approached in this paper from a different angle and involves the use of entropy based objective functions, which are optimised in order to find equilibrium morphologies. In this way, characteristics of a system at equilibrium can be recognised and a stable system predicted without having to step through time. This paper also details the use of self-organisation based modelling methods, another non-traditional model application, where local laws and feedback result in the formation of a global stable equilibrium morphology. These methods represent a different approach to traditional models, without some of the characteristics that may add to their limitations. Responsible Editor: Alejandro Souza     

N-view reconstruction: a new method for morphological modelling and deformation measurement in volcanology

We present a method of reconstructing volcanic morphology using multiple digital views (N-view), captured at different angles around an object. This approach uses recent advances in the field of Computer Vision to provide accurate 3-D measurements of volcanic surfaces. Videogrammetry (digital image reconstruction) is used, as it is best adapted to numerical processing. The method is tested and now used in the laboratory on analogue volcanic cones. The method begins with calibrating the camera and finding image positions, using an accurate N-view calibration method. This is done by estimating internal and external parameters of the camera using several views of a specially constructed calibration target. The N-view reconstruction of the real object is then done by iteratively deforming an initial theoretical model of the surface. Laboratory tests show that reconstruction accuracy is about 10⁻⁴ m for a distance between the object and the camera of 0.5 m, and is potentially several orders of magnitude higher for surfaces of finer texture and using higher precision sensors. This is easily high enough to be useful for the accuracy required for morphological studies. It is also sufficient for monitoring most types of volcano deformation. The technique has the potential to detect morphology changes of the order of mm. Use of the method in the field requires a slightly different approach from that in the laboratory: textures and lighting are more variable, and the sensor and ground control point location and model calibration must be done differently. We provide case studies from laboratory tests and qualitative image analysis for two field cases: Piton de la Fournaise (Indian Ocean) and Santaguito (Guatemala). These illustrate the technique’s potential and explore problems of field application. Using current sensors, the method has the potential to provide sufficient precision for fine (mm–cm) scale reconstruction, and will represent a valuable, simple and flexible tool when compared with classical stereophotogrammetry techniques.