Hydrological Survey Research Articles

Water circulation and hydrological structure in the active layer of the 50-mile near-shore zone of the Russian sector of the black sea in August 2004

The water dynamics and hydrological structure in the active (oxygen-containing) layer are considered on the basis of the hydrological survey carried out in the 50-mile near-shore zone of the Russian sector of the Black Sea in August 2004 and over the permanent section from Gelendzhik to the central part of the sea. Five mesoscale eddy structures of different signs were observed in the Main Black Sea Current between Sochi and the Kerch Strait. Such a dynamic situation contributed to the intensive horizontal water exchange between the near-shore and open sea waters as well as to the redistribution of water masses over the vertical in the active sea layer, which is indicated by the deepening of the top boundary of the hydrogen sulfide zone in the Russian sector of the sea by 15–20 m.

Modulation of homogeneous space-time rainfall cascades to account for orographic influences

Abstract. The development of efficient space-time rainfall downscaling procedures is highly important for the implementation of a meteo-hydrological forecasting chain operating over small watersheds. Multifractal models based on homogeneous cascade have been successfully applied in literature to reproduce space-time rainfall events retrieved over ocean, where the hypothesis of spatial homogeneity can be reasonably accepted. The feasibility to apply this kind of models to rainfall fields occurring over a mountainous region, where spatial homogeneity may not hold, is herein investigated. This issue is examined through the analysis of rainfall data retrieved by the high temporal resolution rain gage network of the Sardinian Hydrological Survey. The proposed procedure involves the introduction of a modulating function which is superimposed to homogeneous and isotropic synthetic fields to take into account the spatial heterogeneity detected in observed precipitation events. Specifically the modulating function, which reproduces the differences in local mean values of the precipitation intensity probability distribution, has been linearly related to the terrain elevation of the analysed spatial domain. Comparisons performed between observed and synthetic data show how the proposed procedure preserves the observed rainfall fields features and how the introduction of the modulating function improves the reproduction of spatial heterogeneity in rainfall probability distributions.

Sensitivity of goodness-of-fit statistics to rainfall data rounding off

An analysis based on the L-moments theory suggests of adopting the generalized Pareto distribution to interpret daily rainfall depths recorded by the rain-gauge network of the Hydrological Survey of the Sardinia Region. Nevertheless, a big problem, not yet completely resolved, arises in the estimation of a left-censoring threshold able to assure a good fitting of rainfall data with the generalized Pareto distribution. In order to detect an optimal threshold, keeping the largest possible number of data, we chose to apply a “failure-to-reject” method based on goodness-of-fit tests, as it was proposed by Choulakian and Stephens [Choulakian, V., Stephens, M.A., 2001. Goodness-of-fit tests for the generalized Pareto distribution. Technometrics 43, 478–484]. Unfortunately, the application of the test, using percentage points provided by Choulakian and Stephens (2001), did not succeed in detecting a useful threshold value in most analyzed time series. A deeper analysis revealed that these failures are mainly due to the presence of large quantities of rounding off values among sample data, affecting the distribution of goodness-of-fit statistics and leading to significant departures from percentage points expected for continuous random variables. A procedure based on Monte Carlo simulations is thus proposed to overcome these problems.

Basalt weathering in Central Siberia under permafrost conditions

Chemical weathering of basalts in the Putorana Plateau, Central Siberia, has been studied by combining chemical and mineralogical analysis of solids (rocks, soils, river sediments, and suspended matter) and fluid solution chemistry. Altogether, 70 large and small rivers, 30 soil pore waters and groundwaters and over 30 solids were sampled during July to August 2001. Analysis of multiannual data on discharge and chemical composition of several rivers of the region available from the Russian Hydrological Survey allowed rigorous estimation of mean annual major element concentrations, and dissolved and suspended fluxes associated with basalt weathering. For the rivers Tembenchi and Taimura that drain monolithologic basic volcanic rocks, the mean multiannual flux of total dissolved cations (TDS_c = Ca + Mg + Na + K) corrected for atmospheric input is 5.7 ± 0.5 t/km 2/yr. For the largest river Nizhniya Tunguska—draining essentially basic rocks—the TDS_c is 6.1 ± 1.5 t/km 2/yr. The overall CO 2 consumption flux associated with basalt weathering in the studied region (∼700,000 km 2) achieves 0.08 × 10 12 mol/yr, which represents only 2.6% of the total CO 2 consumption associated with basalt weathering at the Earth’s surface. The fluxes of suspended matter were estimated as 3.1 ± 0.5, 9.0 ± 0.8, and 6.5 ± 2.0 t/km 2/yr for rivers Taimura, Eratchimo, and Nizhniya Tunguska, respectively. Based on chemical analyses of river solutes and suspended matter, the relative dissolved versus particulate annual transport of major components is C inorg ≥ C org > Na + K > Ca > Mg > Si > Fe ≥ Mn ≥ Ti ≥ Al which reflects the usual order of element mobility during weathering. According to chemical and mineralogical soil and sediment analyses, alteration of basalt consists of (1) replacement of the original basaltic glass by Si-Al-Fe rich amorphous material, (2) mechanical desegregation and grinding of parent rocks, leading to accumulation of “primary” hydrothermal trioctahedral smectite, and (3) transformation of these trioctahedral (oxy)smectites and mixed-layer chlorite-smectite, into secondary dioctahedral smectite accompanied by removal of Ca, Mg, and Fe, and enrichment in Al. No vertical chemical differentiation of fluid and solid phases within the soil profile was identified. All sampled soil pore waters and groundwaters were found to be close to equilibrium with respect to chalcedony, gibbsite, halloysite, and allophanes, but strongly supersaturated with respect to goethite, nontronite, and montmorillonite. Over the annual cycle, the contribution of atmospheric precipitation, permafrost melting, underground reservoirs, litter degradation, and rock and soil mineral weathering for the overall TDS_c transport in the largest river of the region (Nizhniya Tunguska) is 9.3 ± 3, 10 ± 5, 10.5 ± 5, 25 ± 20, and 45 ± 30%, respectively. In the summertime, direct contribution of rocks and soil mineral weathering via solid/fluid interaction does not exceed 20%. The main unknown factors of element mobilization from basalt to the river is litter degradation in the upper soil horizon and parameters of element turnover in the vegetation.

Orographic influences in rainfall downscaling

Abstract. The problem of rainfall downscaling in a mountainous region is discussed, and a simple methodology aimed at introducing spatial heterogeneity induced by orography in downscaling models is proposed. This procedure was calibrated and applied to rainfall data retrieved by the high temporal resolution rain gage network of the Sardinian Hydrological Survey.

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.

Modeling of Circulation and Propagation of Contaminating Impurities in the Balaklava Bay

The Princeton Ocean Model is adapted to the water area of the Balaklava Bay for the numerical analysis of circulation. The calculations are performed with the help of the diagnostic method by using the data of the hydrological survey carried out in the bay in August 1992. We study the structure of the surface and bottom currents in the analyzed period as well as the vertical circulation of waters and the circulation averaged over the depth. The obtained three-dimensional fields of currents are used for the numerical analysis of the process of propagation of passive contaminating impurities from the sources located on the coasts of the Balaklava Bay.

Winter upper ocean circulation in the Western Iberian Basin—Fronts, Eddies and Poleward Flows: an overview

An overview of the winter circulation and upper ocean structure offshore of Western Iberia is presented. The focus is on winter slope currents, fronts and mesoscale eddies, as well as on the connection of these local features to the large-scale circulation of the region. Satellite sea surface temperature; sea surface elevation data from altimetry; cross-shore and meridional hydrological surveys and current meter observations, mainly obtained during winter periods, are used to illustrate features of the winter upper ocean structure and of the generation and evolution of the Iberia Poleward Current. A schematic/hypothetical model of winter upper ocean circulation on the scale of the Western Iberian Basin is given which attempts to systematize and resolve certain ambiguities in the existing circulation schemes and in the concepts and terminology used to describe observed features in the area.

Geophysical and stratigraphical research into deep groundwater and intruding seawater in the mediterranean area (the Salento Peninsula, Italy)

Abstract. Geological, geophysical and hydrological surveys were performed in an area between Lecce to the North and Otranto to the South on the Lower Adriatic coast of Italy in order to verify the ``state of health'' of the ground water in the deep aquifer, which is characterised by Mesozoic carbonatic formations and is permeable due to fracturing and karstic phenomena. This area was chosen because it is highly urbanised, and contains many wells, some of which were intensively studied from a geological and hydro-geological point of view in 1987. The first phase of the research consisted of a stratigraphical and geological study, based on geological surveys of the surface and the subsoil by direct observation of borehole cores and the collection and analysis of existing stratigraphical data on wells in the area. The stratigraphical and hydrogeological data are kept in the archives of local agencies. The collected data were organised in a single database managed by an appropriate software (ARCVIEW). Numerous geological cross sections of the territory were studied in order to characterise the subsoil. Subsequently, multi-parameter surveys (O2, pH, temperature, TDS, conductivity) were carried out on the water-column of certain wells selected from those studied in 1987. This was to verify possible changes in the state of the groundwater since 1987. The surveys were carried out in two different periods (May and September) in order to identify potential differences between rainy and dry periods. Moreover, electrical tomography was used to characterise the various subsurface geological formations and possible saline water intrusion where direct information collected from the wells was lacking. From the research conducted it was possible to effect a stratigraphical characterisation of the subsoil and to verify overexploitation of the water resources resulting from the increasing number of wells, and the consequent deterioration of the aquifer due to saline water intrusion. The research also confirms the validity of geophysical methods for the study of hydro-geological issues.

Chemical weathering of silicate rocks in Aldan Shield and Baikal Uplift: insights from long-term seasonal measurements of solute fluxes in rivers

A reassessment of available information from the Russian Hydrological Survey on long-term seasonal measurements of water, suspended matter and dissolved major element discharges in ∼30 small and large watersheds draining acid silicate rocks (granites, gneisses, quartzites, shales) of the Aldan Shield and Baikal Uplift was combined with new data on river water chemistry for three granitic watersheds in order to calculate the fluxes of elements due to chemical weathering. In accord with data on world rivers, a positive correlation between chemical erosion rate and runoff is observed. The majority of cations are removed during summer monsoon. The spring flood yields 10–20% of the annual flux and the winter season accounts for only 5–15%. The mean multi-annual flux of total dissolved solid which is largely dominated by Ca (60–80%) on the Siberian Craton is comparable with that of temperate zones but higher than that of the Canadian Shield for similar runoff values, rock composition and annual temperatures. Important element recycling due to litter degradation and weathering acceleration via organic ligands produced by abundant vegetation over permafrost soils is invoked to explain these results.

Evaluation and monitoring an on-going landslide in volcanic sediments – a case study for an open pit mine, Turkey: Part 1

TKI (Turkish Coal Enterprises) has been operating an open pit lignite mine since late 1970s in a town called Çan which is situated in the north-west of Turkey. There is a ceramic factory, which is one of the biggest in Europe as far as capacity is concerned, operating very close to the lignite open pit mine. In 1999, a catastrophic earthquake demolished not only the cities and towns located on the Northern Anatolian fault zone but also triggered a landslide on the ceramic factory site benches of the Çan lignite open pit. The susceptibility of artificial slopes to failure during earthquakes is a wellknown event. This paper summarises geological, geomorphological and hydrological surveys of the area and the work done to define the slip surface by means of inclinometer surveys. Geotechnical parameters collected from all local geological formations were used later in the slope stability analysis. Details of the studies undertaken since the beginning of the landslide are given in this paper.

Winter geostrophic currents and eddies in the western Iberia coastal transition zone

The results of a fine-resolution hydrological survey conducted in the western Iberia coastal transition zone in February 2000 are used to describe the vertical structure of the density field and geostrophic currents in the Central Water (CW) layer. The vertical density distribution was characterized by the presence of three pycnocline layers: (i) at the surface driven by the buoyancy input of a low-salinity plume, (ii) at about 200 m ( σ θ =27.0), below the surface mixed layer and, (iii) in the transition layer between the Central and Mediterranean Water at depths close to 600 m ( σ θ =27.3). It is shown that the density distribution at the depth of the deeper pycnocline controls much of the geopotential anomaly field when the reference level is below the lower Mediterranean Water core (≃1200 m) , leading to a high sensitivity in the geostrophic velocity profiles to the choice of the reference level. The use of a reference level above 600 m artificially reduces the flow in the lower CW layer (27.0< σ θ <27.3) where significant volume transports are found when a reference level at 1400 dbar is used. In particular, the presence of an equatorward flow at about 400 m in the near-slope region at 41°N was found to be responsible for the volume transport of 0.3 Sv in the direction opposite to the same volume transport in the upper CW layer ( σ θ <27.0), a feature not reported in previous studies based on field data. In the northernmost sections, the flow in the lower CW layer was directed in the same poleward direction as the upper layer in the near-slope region, leading to a deep signature in the poleward current with a maximum volume transport increase from 0.5 Sv in the upper CW layer to 1.1 Sv in both the layers. Schematic views of the non-divergent circulation in two isopycnal CW layers are used to present the main flow paths and volume transports associated with the mesoscale eddy field.

Water flux estimates in the central Mediterranean Sea from an inverse box model

Seasonal hydrological surveys and long‐term current measurements carried out during a wide investigation of the central Mediterranean, connecting the eastern and western parts of the basin with the Tyrrhenian Sea, are used to estimate the absolute geostrophic flow through the region applying an inverse methodology. The inverse box model prescribes conservation of water properties (mass, heat, and salt) inside closed boxes of water, as well as the imposition of mean fluxes by direct current measurements. The model result is a mean circulation of the region during four different periods, along with simultaneous evaluation of water fluxes through the three boundary sections and the associated uncertainties. The overall situation, besides confirming previous qualitative knowledge on the mean circulation at all levels, provides a novel quantitative pattern of the water mass exchange in a region that is crucial for the assessment of a more realistic budget for the whole basin. The positive results obtained indicate that the inverse method may be considered an effective powerful tool for successful applications at regional scale.

Thermochaline Convection in the Edge-Ice Zone in the Barents Sea to the East of Spitsbergen

The analysis of the thermochaline (double-diffusive) convection in the edge-ice zone of the Barents Sea to the east of Spitsbergen was performed by using the data of two hydrological surveys of the Norwegian Polar Institute in 1999 and 2000. The Turner's model, where the critical Rayleigh number is determined by using the empirical relationship between the Nusselt number and the Rayleigh number normalized to its critical value, was used for analysis. The results of calculation of thickness of the convective layer were compared with the data of supervision. The estimates of the vertical convective velocity were obtained.

The importance of hydrogeological and hydrological investigations in the residential area: a case study in Burdur, Turkey

Water resources in residential areas are negatively affected by floods. In addition, many aquifers are contaminated as a result of urbanization. Great damage caused during earthquakes are partly attributed to the residential pattern which ignores the potential effect of groundwater. Hydrogeological and hydrological surveys must be carried out in the residential areas to determine the interaction between water and residential development of all types.

Circulation in the French mediterranean coastal zone near Marseilles: the influence of wind and the Northern Current

Current meters were moored for a year both in and beyond the Cassis Bay to study the dispersion of muds discharged at a depth of ∼300 m, through a pipe, a few km from the coast and at the head of a submarine canyon. The east–west orientation of the coastline and a marked orography constrain the major winds to easterlies or westerlies. Empirical orthogonal function analysis shows that both wind regimes create a significant down-wind circulation, with the latter inducing also intense upwelling. Characteristics of the Northern Current, which flows along the slope, have been defined using a fine-grid hydrological survey. A narrow continental shelf allows the Northern Current to reach often the coastal zone in the study area; thus, the overall water circulation in the embayment is westward. In winter, this current develops steep mesoscale meanders and penetrates easily through the canyon, into the bay. Hence, although the coastal circulation near Marseilles is partly down-wind, it is dependent mainly on the Northern Current (on both general and meso-scales). The mesoscale variability cannot be predicted without monitoring the Northern Current itself.

A Model of the Sevastopol'skaya Bay. Reproduction of the Vertical Structure of Temperature and Salinity Fields in 1997–1999

We discuss the results of a numerical experiment carried out within the framework of the most complete one-dimensional (integrated over the horizontal coordinates) version of the quasiisopycnic multilayer model taking into account the processes of diapycnic mass, heat, and salt exchange and the diffusion coefficients chosen according to the theory of double diffusion. The indicated experiment reproduces the vertical thermohaline structure of waters in the Sevastopol'skaya Bay and its variability in 1997–1999. For numerical computations, we use the actual data of meteorological observations and measurements of the discharge of the river Chernaya and the sea level. The comparison of the numerical results with the data of monthly hydrological surveys reveals their good agreement (not only qualitative but also quantitative).

A geomorphological model of intertidal cove marshes with application to wetlands management

Detailed topographic and hydrologic surveys were conducted in five intertidal cove marshes in an outer coastal plain landscape to test the hypothesis that the equilibrium geologic state of intertidal habitats residing in similar landscape situations conforms to a consistent geometric form. The equation V=1571.84 A 1.70 ( R 2=96.2%) describes the relationship between hectares of marsh ( A) and cubic meter volume at mean high tide ( V). An empirical relationship between tide height and volume was found to obey the power series V p= L 2.38 ( R 2=99.6%), where V p is volume as a percent of full pool and L is water height as a percent of mean high tide. A dimensionless index describing the relationship between area and volume is consistent for each marsh and approaches 0.10. A channel form parameter describing width to channel depth ratios is of consistent value for four of the five marshes. These provide evidence of deterministic rather than stochastic geologic development. The benefits of applying natural basin shape patterns in the design and engineering of created/restored intertidal marshes are highlighted and a generic basin is modeled (based on the geometrical section of a paraboloid retained by simple integration) as an example of the potential applicability of the study.

Fronts, jets, and counter-flows in the Western Iberian upwelling system

The results of a fine resolution hydrology survey conducted off the northern Portuguese coast at the end of the upwelling season are presented. The most striking features were the upwelling front and the associated southward jet. Counter-flows were detected both over the slope and at the inner-shelf. The southward current is surface intensified with maximum values of about 40 cm s −1 and diverges to the south of the observed area recirculating both onshore and offshore. Along the slope, a warmer and saltier poleward current interacts with the jet generating an anticyclonic eddy about the Aveiro Canyon. Possible mechanisms of topographic forcing and filament development in the zone are discussed. Inshore, a coastal current advects warmer water northward creating a second front at the inner-shelf. The surface layers to the coastal side of the upwelling front are dominated by a low salinity lens, which we proposed to name the Western Iberia Buoyant Plume (WIBP). The equatorward flow, the coastal current and the stratification input of the WIBP introduce strong complexity into the dynamics of this double-frontal upwelling system. The plume is stirred being partially advected to the south and offshore while entrained in the upwelling jet. On the shore side, the plume is advected to the north by the coastal counter-flow. A conceptual model of circulation is presented.

Variability of the Azores Current during October–December 1993

The surface circulation is investigated during the autumn of 1993 in the vicinity of the Azores Current 18–28°W 31–36°N during the SEMAPHORE experiment. A total of 125 drifters were tracked by satellite, some of which were drogued, some not, some with long tethers and some were mixed layer drifters drogued at 15 m depth. The different types of drifters respond differently to the wind, the wave action and the mixed layer currents, resulting in differences in drifts sometimes exceeding 10 cm s −1. These effects can be partially taken into account statistically. After doing that, the different drift data were combined to map the near-surface quasi-geostrophic flow. The major currents in the area have a width of 100 km or larger, and changes in the shear happen over a shorter scale. The data density is sufficient to resolve scales of 50–100 km for 11 days averaged circulation and sea surface temperature (SST). The maps produced every 5 days portray the surface evolution of the Azores Current and of the eddy field for 2 months. The changes are large in the area where the Azores current interacts with a large anticylonic eddy A 1 associated with a Meddy. There are some closed eddy circulation present throughout the period, whereas other structures are relatively short-lived (a month or less). The general features of this analysis are reproduced in analyses of the circulation from altimetric data. The resolution of this analysis is much larger than what was earlier obtained from the hydrological surveys, enabling us to estimate the quasi-geostrophic mesoscale divergence field from the horizontal vorticity budget. The quasi-geostrophic horizontal vorticity advection provides the largest contribution to divergence and contributes to a series of convergence and divergence patches in the order of 1×10 −7 s −1 associated with the various ridges and troughs of the Azores Current. Although uncertainty is high in these estimates, this suggests that vertical temperature advection does not contribute much to the surface temperature evolution at the mesoscales of these surveys. Horizontal temperature advection is estimated from the current and surface temperature analysis. Away from the frontal area near 25°W, horizontal temperature advection is significantly non-zero, but does contribute only a small portion of the observed temperature change at the mesoscales. The budgets suggest that the area south of A 1 was the site of subduction in October–November.