Seasonal and tidal variations in the hydrology of Wellington harbour

Observations were made on several hydrological features of Wellington Harbour, New Zealand (41° 16’ S, 174° 51’ E) during 1970 to 1972. These suggest that the harbour is topographically partially isolated from oceanic influences, and that waters within the harbour undergo efficient mixing.

Monthly mean sea‐surface temperatures ranged seasonally between 10.5°c and 18.5°c, and some stratification was observed during summer and winter. Salinities usually ranged from 33.5‰ to 34.5‰, and water transparency by Secchi disc from 3 m to 6 m. Dissolved oxygen content ranged from 96% to 127% saturation, usually exceeding 100% saturation in surface waters.

Under normal discharge conditions during winter, the Hutt River was observed to markedly affect surface temperatures and salinities as far south as Somes Island to a depth of about 5 m.     

Early oligocene squalodont cetacean from Oamaru,New Zealand

Records of Tertiary fossil cetacea from New Zealand are revised. Probable proto‐squalodontid teeth from the McDonald Limestone Formation (Whaingaroan Stage, Lower Oligocene), Oamaru, are described, and represent the oldest cetacean remains found in New Zealand. This record demonstrates the probable extension of the Squalodontidae into the Lower Oligocene.     

Coastal Placer Deposits of Central Tamil Nadu,India

ABSTRACT

Placer mineral exploration has been undertaken along the beach of Central Tamil Nadu coast from Pondicherry to Vedaranyam. On the basis of the drainage network, geomorphology, and the coastal environment, the study area has been grouped into three sectors, North, Central, and South. Heavy mineral by Wt% shows a slightly higher abundance in the Northern sector, an enrichment of opaques in the Central sector from stations between Poompuhar and Karaikal, and a total depletion in the Southern sector. An abundance of heavies in the Northern sector is considered to be the result of a higher wave energy, and the cymatogenic downwarping of the basin during the present transgression. An enrichment of heavies in the Central sector from Poompuhar to Karaikal is attributable to the reworking of the beach ridges, which were submerged during the present transgression, and to the role of density sorting. A depletion of heavies in the Southern sector is accounted for by the absence of a terrigenous supply and the prevalence of wave shadow conditions throughout the year. The nature of the heavy mineral assemblage reflects the derivation of sediments principally from khondalites, granites, metamorphic rocks and paleo-sediments. Factor analysis also supplements the predominant role of a density factor in the segregation of heavy minerals in the study area. A five-stage model is proposed for the formation of placer deposits in the study region. The present study has disclosed rich concentrations of ilmenites in the central sector between Poompuhar and Karaikal that can be commercially exploited.     

The large penumbra: Long-distance effects of artificial beach nourishment on Posidonia oceanica meadows

We used modelling and field approaches to assess the influence of beach nourishment on a relatively distant Posidonia oceanica seagrass meadow in the NW Mediterranean. Both sediment transport models and in situ observations showed that, two years after the nourishment and under wave climates prevalent during the study period, sediment movement was restricted to shallow waters (<7 m), above meadow shallow limit. The only significant impact on seagrass meadows during this period was an increase in fine sediments, associated with vertical rhizome growth rates 1.5–1.7 times higher than normal. However, running the model with data of wave climate over several decades indicates that strong storms able to transfer these sediments much deeper, potentially burying meadows, occur with a return period of about 25 years. Taken together, our results suggest that beach nourishment could result in significant sub-lethal and lethal consequences for seagrasses that may go unnoticed with short-term evaluations.     

Application Progress and Prospect of Argus System in Beach Research in China

Reliable, continuous and long-term data is needed in order to understand precisely the evolution of a beach system. Because of the advantages of real-time, low cost, simple operation, strong adaptability, high resolution and continuous data, Argus video monitoring system has developed rapidly in recent years, and its research and application fields have gradually expanded. Composition of the Argus system was briefly introduced, and the application of this system in beach research in China was described, and the accuracy of the extracted data was analysed. It was shown that the average vertical and plane distance error is 0.145 m and 11.73 m respectively, which depends on the distance from Argus observatory. Argus system has been widely used in beach research abroad, but it is still in the early stage in China. In the future, it is expected to provide more powerful and perfect technical support in coastal engineering construction evaluation, coastal hydrodynamic monitoring and bathymetry inversion, beach tourism management and research on morphodynamic evolution of estuary sand spits.     

New insights into mineralogy and geochemistry of allanite-bearing Mediterranean coastal sands from Northern Greece

Allanite-bearing black coastal sands of Kavala (N. Greece) were studied using a combination of single-crystal XRD, EMPA, μ-XRF, bulk ICP-MS, LA-ICP-MS, μ-XANES and γ-ray spectrometry. The sands are rich in REE (ΣREE + Y: 4010 to 10,810 mg/kg), Th (236–1205 mg/kg) and other critical metals such as Nb, Ta and Co. The main REE- and Th-hosts are allanite and titanite. The allanite unit cell parameters were calculated whereas its formula was found to be (REE_0.470Ca_1.499Th_0.031) (Ti_0.031Fe⁺³_1.089Al_1.880) (Si_2.906Al_0.094O₁₂) (OH). The μ-XANES spectra showed that LREE are present in trivalent oxidation state. Analyses of the non-magnetic sand fractions showed higher LREE (12,470 mg/kg) due to accumulation of allanite. The materials showed elevated radioactivity ranging from 885 ± 13 to 3467 ± 20 Bq/kg. The obtained results provide new insights on the provenance of the sands, the abundance of REE, Th, and other immobile elements, and offer new clues for potential exploration and exploitation.     

Contingent valuation analysis of willingness to pay for beach erosion control through the stabiplage technique: A study in Djerba (Tunisia)

Beach erosion can have major economic implications because of the potential impact on coastal recreation demand – particularly for countries where coastal tourism is one of the main sources of external revenue. Djerba Island (Tunisia) falls in that category. With about 125 km of coastline, Djerba Island is one of the most important Tunisian destinations. However, the island is experiencing coastal erosion problems. The Tunisia government launched a project to fight costal erosion through the Stabiplage technique. This study provides the first economic valuation of beach erosion control in Tunisia and is the first one that focuses on the Stabiplage technique. Specifically, a contingent valuation survey is carried out to elicit the public willingness to pay (WTP) for the project. An interval payment card question format is used to obtain information about WTP from representative samples of residents and tourists in Djerba. The results reveal a positive WTP for the project. Aggregate WTP estimates range from €133,459 (median value) to €5,180,269 (mean value). These values can help inform decisions about whether to undertake the project based on either the benefit-cost ratio rule or majority voting rule.     

Sequential monitoring of beach litter using webcams

This study attempts to establish a system for the sequential monitoring of beach litter using webcams placed at the Ookushi beach, Goto Islands, Japan, to establish the temporal variability in the quantities of beach litter every 90 min over a one and a half year period. The time series of the quantities of beach litter, computed by counting pixels with a greater lightness than a threshold value in photographs, shows that litter does not increase monotonically on the beach, but fluctuates mainly on a monthly time scale or less. To investigate what factors influence this variability, the time derivative of the quantity of beach litter is compared with satellite-derived wind speeds. It is found that the beach litter quantities vary largely with winds, but there may be other influencing factors.     

Two- and three-dimensional double-sandbar system behaviour under intense wave forcing and a meso–macro tidal range

Five weeks of hourly, 10-min time-exposure video images were used to analyze the meso–macro-tidal double-barred Truc Vert Beach, SW France, under intense wave forcing. The four storms experienced, one of which with an offshore significant wave height over 8 m, induced dramatic changes in the double sandbar system. The subtidal outer bar migrated offshore rapidly (up to 30–50 m/day) and its pre-existing crescentic pattern was wiped out. The seaward-protruding parts of the outer bar barely migrated offshore during the most intense storm, whereas a landward-protruding part was shed off. Over the entire study period, the outer-bar dynamics was dominated by alongshore-averaged changes rather than alongshore non-uniform changes, while the opposite was observed for the inner bar. In addition, the outer-bar dynamics was predominantly controlled by the time-varying offshore wave conditions, whereas the inner-bar dynamics was influenced largely by the tide-range variations. Our observations put forward the key role of morphological settings (the presence of a subtidal bar and its shape) and tidal range in governing inner-bar behaviour within a double sandbar dynamics, and provide strong support for previous suggestions that sandbars cannot be studied in isolation.     

Geochemical,mineralogical and textural nature of beach placers,north-east Sri Lanka: Implications for provenance and potential resource

The Pulmoddai placer sands in Sri Lanka(9°3’23.65’’-8°51’38.83’’N and 80°55’22.91’’-81°3’32.65’’E) is considered to be one of the major rare earth element(REE) prospects world-wide. This deposit has a global significance in terms of strategic economic resources and can provide valuable insight for resource estimation and for its economic use. A detailed study of the geochemical, mineralogical, and textural properties of the heavy minerals of this region is undertaken applying the scanning electr...