Hydrogeochemical evolution of groundwater in a Mediterranean coastal aquifer, Mersin-Erdemli basin (Turkey)

In this study, hydrogeologic and hydrochemical information from the Mersin-Erdemli groundwater system were integrated and used to determine the main factors and mechanisms controlling the chemistry of groundwaters in the area and anthropogenic factors presently affecting them. The PHREEQC geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into four categories: (1) silicate weathering reactions; (2) dissolution of salts; (3) precipitation of calcite, amorphous silica and kaolinite; (4) ion exchange. As determined by multivariate statistical analysis, anthropogenic factors show seasonality in the area where most contaminated waters related to fertilizer and fungicide applications that occur during early summer season.     

冬季浙闽沿岸水分布的短期变动与风的关系初探

利用1999年7月至2003年5月期间的遥感数据,包括AVHRR海表层温度、QuikSCAT风场和风应力数据,在分析4年内月平均遥感温度场和风场特征与历年现场观测所获得的认识一致的基础上,选取2002年002-008天这一连续晴空的时段,尝试建立简单的沿岸冷水影响面积表征方法,初步探讨了冬季台湾海峡浙闽沿岸水分布的短期变动与风应力之间的关系。结果表明,风是决定冬季台湾海峡海表层温度逐日变动的关键因素,日平均SST与风应力的相关系数R2达到0·90。采用温度法(SST≤17℃)和温度空间距平法(≤-1℃)表征的浙闽沿岸水影响面积的变化趋势基本一致,而且影响面积的逐日变动与风应力显著相关,二者的相关系数R2分别达到0·90和0·91。     

On Extending The Flux-Profile Similarity Theory To Include Quasi-Homogeneous Conditions In The Marine Atmospheric Surface Layer

In order to apply Monin–Obukhov similarity theory to estimatethe profiles of mean quantities and surface fluxes from bulk meteorological parameters, the assumptions of homogeneityand stationarity must be valid. Unfortunately, in coastal zones as well as many other regions of interest, theseassumptions are often violated. In this paper, an extension to the theory is presented that considers systematically varyingstate variables. Along-wind variations of windspeed, atmospheric stratification, and roughness are examined with respectto their relative importance to momentum flux divergence, and the drag coefficient is shown to be systematicallylower in coastal zones. For profiles of scalars, an analysis of the set of quasi-homogeneous terms is only speculated,and the relative importance for the terms will strongly depend on which scalar is of interest.     

Formation of a shelfbreak front by freshwater discharge

The circulation and transport of freshwater generated by an idealized buoyant source is studied using a three-dimensional primitive equation model. Freshwater enters the continental shelf, turns anticyclonically and moves downstream in the direction of Kelvin wave propagation. In the region close to the source, the flow reaches an equilibrium in the bottom boundary layer so that freshwater does not spread offshore any further. This offshore equilibrium distance increases as we move downstream until the freshwater is able to feel the presence of the shelfbreak. A shelfbreak front forms and the shelfbreak prevents any further offshore spreading of freshwater in the bottom boundary layer.Two complimentary mechanisms are responsible for the slow cross-shelf migration of freshwater and subsequent trapping of shelfbreak fronts: bottom stress and topographic changes. The shelfbreak creates an active, dynamic process preventing leakage from the continental shelf region to the slope region. However, the dynamical process that traps the front to the shelfbreak is still unclear.The location of the shelfbreak front depends on four dimensionless parameters: scaled inlet volume transport, scaled breadth, scaled “diffusivity” and scaled shelf width. We develop empirical relations for predicting the location of the frontal bottom intersection, given these parameters.     

Managed relocation: an assessment of its feasibility as a coastal management option

Managed relocation is explained and examined as an option to add to the usual categories considered in relation to managing coastal erosion. The paper considers the relocation of buildings in one unit, as opposed to demolition and re-construction. The standard coastal erosion management options are briefly noted and how managed relocation can fit into these options is explained. This paper focuses on four case studies. Two examples are from the USA and two from the UK; of these, two (one in each of the UK and USA) took place during the nineteenth century. Managed relocation is proposed as being feasible in particular cases, particularly where there are isolated historic or high value buildings.     

A model for grain-size sorting over tidal sand ridges

A model was developed and analyzed to quantify the effect of graded sediment on the formation of tidal sand ridges. Field data reveal coarse (fine) sediment at the crests (in the troughs), but often phase shifts between the mean grain-size distribution and the bottom topography occur. Following earlier work, this study is based on a linear stability analysis of a basic state with respect to small bottom perturbations. The basic state describes an alongshore tidal current on a coastal shelf. Sediment is transported as bed load and dynamic hiding effects are accounted for. A one-layer model for the bed evolution is used and two grain size classes (fine and coarse sand) are considered. Results indicate an increase in growth and migration rates of tidal sand ridges for a bimodal mixture, whilst the wavelength of the ridges remains unchanged. A symmetrical externally forced tidal current results in a grain-size distribution which is in phase with the ridges. Incorporation of an additional external M₄ tidal constituent or a steady current results in a phase shift between the grain-size distribution and ridge topography. These results show a general agreement with observations. The physical mechanism responsible for the observed grain-size distribution over the ridges is also discussed.Responsible Editor: Jens Kappenberg     

A Numerical Study on Coastal Defence at Chennai and Related Management Strategies

Chennai coast, right from the inception of Madras harbourin the year 1876, has been experiencinghostile conditions such as (i) coastal erosion, (ii) sandbar formation at the entrance to inlets, (iii) sea water ingression and (iv) change insea bed elevation, etc. In addition, construction of a new satellite harbour, about18 km north of Madras harbour has produced a negative impact on the delicatecoastal features such as (i) Pulicat lake, (ii) Ennore shoals, etc. Construction ofthis satellite harbour has led to the accumulation of sand south of the southbreakwater of the harbour and its accelerated growth is of concern to an inletlocated 2.6~km south of the harbour. `Coastal erosion', a perennial problemassociated with north Chennai sea front for the past 100 years has been addressedin this paper. The paper discusses on a long term solution and details of themethodologies to be adopted for effective management of the coast. Thesolution presented in this paper is based on numerical model study consideringthe nearshore currents and wave induced sediment transports.     

Environmental impact of an urban landfill on a coastal aquifer (El Jadida, Morocco)

The El Jadida landfill is one among many uncontrolled dumping sites in Morocco with no bottom liner. About 150 tons/day of solid wastes from mixed urban and industrial origins are placed directly on the ground. At the site of this landfill, the groundwaters circulate deeply (10–15 m) in the Cenomanian rock (calcareous–marl), which is characterised by an important permeability from cracks. The soil is sand–clay characterized by a weak coefficient of retention.The phreatic water ascends to the bottom of three quarries, which are located within the landfill. These circumstances, along with the lack of a leachate collection system, worsen the risks for a potential deterioration of the aquifer.To evaluate groundwater pollution due to this urban landfill, piezometric level and geochemical analyses have been monitored since 1999 on 60 wells. The landfill leachate has been collected from the three quarries that are located within the landfill. The average results of geochemical analyses show an important polluant charge vehiculed by landfill leachate (chloride = 5680 mg l⁻¹, chemical oxygen demand = 1000 mg l⁻¹, iron = 23 000 μg l⁻¹). They show also an important qualitative degradation of the groundwater, especially in the parts situated in the down gradient area and in direct proximity to the landfill. In these polluted zones, we have observed the following values: higher than 4.5 mS cm⁻¹ in electric conductivity, 1620 and 1000 mg l⁻¹ respectively in chlorides and sulfate (), 15–25 μg l⁻¹ in cadmium, and 60–100 μg l⁻¹ in chromium. These concentrations widely exceed the standard values for potable water.Several determining factors in the evolution of groundwater contamination have been highlighted, such as (1) depth of the water table, (2) permeability of soil and unsaturated zone, (3) effective infiltration, (4) humidity and (5) absence of a system for leachate drainage. So, to reduce the pollution risks of the groundwater, it is necessary to set a system of collection, drainage and treatment of landfill leachates and to emplace an impermeable surface at the site of landfill, in order to limit the infiltration of leachate.     

Holocene-emerged notches and tectonic uplift along the Jalisco coast, Southwest Mexico

This paper presents the preliminary results from a study of Holocene-emerged shorelines, marine notches, and their tectonic implications along the Jalisco coast. The Pacific coast of Jalisco, SW Mexico, is an active tectonic margin. This coast has been the site of two of the largest earthquakes to occur in Mexico this century: the 1932 (Mw 8.2) Jalisco earthquake and the 1995 (Mw 8.0) Colima earthquake. Measurement and preliminary radiocarbon dating of emergent paleoshorelines along the Jalisco coast provide the first constraints upon the timing for tectonic uplift. Along this coastline, uplifted Holocene marine notches and wave-cut platforms occur at elevations ranging from ca. 1 to 4.5 m amsl. In situ intertidal organisms dated with radiocarbon, the first ever reported for the Jalisco area, provide preliminary results that record tectonic uplift during at least the past 1300 years BP at an average rate of about 3 mm/year. We propose a model in which coseismic subsidence produced by offshore earthquakes is rapidly recovered during the postseismic and interseismic periods. The long-term period is characterized by slow tectonic uplift of the Jalisco coast. We found no evidence of coastal interseismic and long-term subsidence along the Jalisco coast.     

Suspended sediment transport along an idealised tidal embayment: settling lag, residual transport and the interpretation of tidal signals

We present semi-analytical solutions for suspended sediment concentration (SSC) and residual sediment transport in a simple mathematical model of a short tidal embayment. These solutions allow us to investigate in some detail the characteristic tidal and semi-tidal variation of SSC and the processes leading to residual sediment transport, including settling and scour lags, the roles of ‘local’ and ‘advective’ contributions, and the presence of internally or externally generated overtides. By interpreting the transport mechanisms in terms of the classic conceptual models of settling lag we clarify how these models may be expressed in mathematical terms. Our results suggest that settling lag is usually a more important process than scour lag, and that a local model which neglects advection may predict the direction of net sediment transport incorrectly. Finally, we discuss our results in the context of other transport processes and morphodynamic feedback.