Phreatic Level Research Articles

Tectonic uplift, sea level changes and Plio‐Pleistocene evolution of a coastal karst system: the Mount Saint Paul (Palawan, Philippines)

AbstractThe St. Paul karst (Palawan, Philippines) is a tropical coastal karst, consisting of towers, cones, huge depressions and large caves. This area hosts the Puerto Princesa Subterranean River (PPSR, 24 km long), whose main entrance is a large spring along the coast and which is one of the largest cave complexes in eastern Asia.A geomorphological study performed by several field surveys and a morphometric analysis of the digital terrain model (DTM) and 3D cave models, allowed formulation of a first evolutionary framework of the karst system. The DTM was extracted from maps and aerial photographs in order to find different generations of ‘relict’ landforms, through the morphometric analysis of topographic surface and karst landforms.Several features suggest a long and multi‐stage evolution of the karst, whose age ranges from Pliocene to present. The southern and northern sectors of the area differ in their altimetric distribution of caves. In the southern sector, some large caves lie between 300 and 400 m asl and were part of an ancient system that developed at the base level of a past river network. In the northern sector, some mainly vadose caves occur, with a phreatic level at 120–130 m asl. An important phase of base‐level cave development is well documented in the inactive passages of PPSR at 50–80 m asl. Morphological features, such as horizontal solution passages and terraced deposits, suggest a phase of stillstand of the base level, which is recorded in the topography as low‐relief surfaces at 40–50 m asl. The age of this phase is probably Early Pleistocene, on the basis of assumed uplift rates. The more recent caves are still active, being located at the current sea level, but they show more than one cycle of flooding and dewatering (with calcite deposition). In the PPSR, several morphologic features, such as two main water level notches at +12·4 and +7·7 m asl and terraced alluvial deposits, suggest that the lower and active level passed through more than two high‐stands of sea level and so it could have formed throughout most of the Middle‐Late Pleistocene. Copyright © 2010 John Wiley & Sons, Ltd.

Application of ground penetrating radar (GPR) to delineate clay layers in wetlands. A case study in the Soto Grande and Soto Chico watercourses, Doñana (SW Spain)

The potential utility of ground penetrating radar (GPR) in delineating the geometry of clay layers under two watercourses of the Doñana National Park (SW Spain) has been checked. The interpretation of the GPR profiles, calibrated with piezometers, shows the presence of two clay layer roughly continuous along some 2 km. The work allowed to gain insight about the watercourses relationship with groundwater. Up to now, watercourses in the area have been associated as a matter of fact to the intersection of the water table with the topography. But this work shows the existence of shallow, roughly continuous clay layers under the watercourses that may generate perched phreatic levels even if the regional water table is too deep to crop out. Thus, the GPR proved to be very helpful and suitable in supporting hydrogeological studies in wetlands.

Nonlinear aspects of phreatic water filtration

Horizontal gravity filtration of groundwater in soil is considered. Under Boussinesq approximation, the problem is reduced to a one-dimensional nonlinear parabolic equation in phreatic water level. The problem of linearizing the original equation is discussed. The comparison of gravity-filtration problem solutions in the nonlinear and linearized formulations shows considerable discrepancies to exist between the solutions, especially, for boundary problems with mixed boundary conditions, when the value of the function is not fixed on the right boundary. An analytical solution is obtained for steady-state flow from a water body into the soil with subsequent leakage into underlying beds. Two regimes are shown to exist: one with an infinite exponential tail, and another in the form of a finite groundwater mound. A new approach is proposed to the linearization problem—quasilinearization with the use of the Burgers equation.

Remarks upon numerical solutions of infiltration into a soil profile

A methodology of time-step estimation for numerically solving the Richards equation is discussed. Its importance in simulating water movement in unsaturated—saturated soils is shown for infiltration into a soil profile by applying various time-step estimations and boundary conditions for different soils. In order to test the results of the computations, infiltration theory was applied. According to infiltration theory, the pressure head in the initially unsaturated part will not take positive values as long as the moisture front has not reached the phreatic level, or, in the case of a profile with a free-draining lower boundary, it is not saturated at the base. In other cases, the appearance of positive values of the pressure head produces incorrect values for the inflow rate q.

The role of capillary water in the stability of tailing dams

Tailings storage facilities are complex geotechnical structures. The present paper focuses on the study of a case-history, a tailing dam from the nickel industry located in Cuba, with the objective of gaining knowledge about the geotechnical behaviour of such structures. The dam behaviour was modelled by means of a coupled hydro-mechanical finite element formulation. Due to the low permeability of tailings, the phreatic surface in the deposit remains high during and after its construction. Steady-state flow regime would be reached only several decades after closure. Moreover, capillary rise causes the saturation degree to stay high in the whole storage. Under the action of rain storms, phreatic levels rise quickly due to the presence of capillary water. Following the end of the storm, phreatic levels fall slowly because of the low hydraulic conductivity. The results of the analysis show that the stability of the dam strongly depends on capillary phenomena. In the light of this conclusion it seems reasonable to propose including the measurement of capillary water in the standard monitoring schedule of tailing dams.

Contaminación por nitrógeno en el sistema “río-acuífero aluvial” de la cuenca del Jarama (Comunidad de Madrid, España) ¿Origen agrícola o urbano?

Nitrogen pollution in the “river-alluvial aquifer” system of the Jarama catchment (Comunidad de Madrid, Spain): Agricultural or urban origin? A hydrochemical characterization of the “river-alluvial aquifer” system in the Quaternary deposits of the Jarama catchment has been performed, including the rivers Jarama, Henares, Manzanares, Taju˜ na and a part of Tajo, as well as the alluvial aquifer associated to the said fluvial net. The roles of agriculture and urban uses have been explored as possible sources of nitrogen pollution in surface and underground water resources. Two sampling campaigns were performed, in March (at the end of the winter) and in August of 2005 (when irrigation water demand was at its highest), with water samples collected at 35 sampling stations (16 wells on the alluvial aquifer and 19 fluvial stations). The medium and low areas of the Manzanares, Jarama, Taju˜ na, and Tajo rivers did not meet the standards of quality established by the Tajo Catchment Hydrologic, due to high levels of ammonia, QOD and. electric conductivity, attributable to the incorporation of water treatment effluents originating from urban areas, (in some areas, conductivity levels could be explained by the geological context). The medium and low areas of the alluvial aquifer (in each subcatchment) showed very high values of nitrate concentration and conductivity, making its use unsuitable for drinking and restricting it for agricultural irrigation. A clear concordance was found between the spatial distribution of nitrate pollution in the alluvial aquifer and the agricultural irrigated areas. Using the N/P ratio as an indicator of the agricultural or urban origin it is interpreted that nitrogen pollution is mainly of urban origin in the rivers and of agricultural precedence in the alluvial aquifer (attributable to the bad management of fertilization and irrigation). The problem is compounded when water from nitrogen polluted rivers is used for irrigation, transferring nitrogen of fluvial origin into the alluvial aquifer with the irrigation return flows (urban nitrogen + fertilizers nitrogen). On the other hand, it has been observed that the excess of irrigation reverts the natural dynamic of the aquifer, producing rises of the phreatic level in extensive areas during the summer. These results provide a scientific basis to consider the declaration of the Quaternary alluvial deposits of the Jarama catchment as a Vulnerable Zone to nitrate contamination of agricultural origin, as established in the Directive 91/676/EEC.

Stabilisation of a progressive railway embankment slip

A walkover survey of a side embankment on the West Coast Mainline railway (UK) revealed significant movement of the twin track, a waterlogged trackbed and general deterioration of the slope. Ground investigations and monitoring indicated that in addition to shallow washout failures and formation pumping problems at trackbed level, the embankment was at limiting equilibrium with progressive downslope movement occurring along a deep-seated shear zone within underlying strata of glacial till and laminated clay (weathered mudstone/siltstone). Phreatic level increases during rainstorm events, in combination with winter groundwater maxima, induced artesian pressures on the underside of the steeply sloping shear zone which triggered step increases in the shear displacements. Other factors included the gradual post-peak decline in shear strength due to creep; internal weathering; cyclic, transitory stress increases caused by passing trains and densification of the overlying embankment fill. The upgrade works reduced the hazard of further embankment movement affecting the track and comprised the installation of stabilising piles along the mid-embankment slope in order to arrest the deep-seated slide (factor of safety, FOS = 1.2), the construction of an earth buttress and regrading works in order to reduce the upper slope gradient (preventing shallower slips and wash-out failures, FOS ≥ 1.3) and improved site drainage.

Modelling the effect of canal bed elevation on seepage and water table rise in a sand box filled with loamy soil

The HYDRUS 2D finite difference two-dimensional water balance model was experimentally tested for transient and steady state seepage flux, mound height, and piezometric water level from soil surface as a function of time and horizontal distance from the centre of the canal (half width = 45 cm) under different canal bed elevations (20, 0, −40, −80 and −120 cm denoted as experiments D1, D2, D3, D4 and D5, respectively) and constant water head of 5 cm in a sand box (200 cm × 170 cm × 150 cm) filled with Hisar loam soil. Differences of means between measured and predicted values of infiltration flux, seepage flux and mound height as tested by paired t test were not found significant (P = 0.05). Seepage flux and mound height increased with increasing canal bed elevation. Phreatic level depths were everywhere much shallower than the piezometric water level depths in experiments D1, D2 and D3. However, in experiments D4 and D5 both phreatic and piezometric levels were at similar depths. The seepage parameters and mound height increased, and water table depth decreased, linearly with increasing canal bed elevation. Lowering the canal bed to 120 cm below the soil surface reduced the seepage rate to that of lined canals. The projections in a large flow domain also revealed that lowering the canal to −2 and −4 m below soil surface stabilized the water table at 2.5 and 4.5 m below soil surface, respectively. The practical implications are that open drains should be used for irrigation in areas underlain with a brackish groundwater aquifer and gravity canals may be allowed only where groundwater aquifer is of good quality and sub-surface water withdrawal is practiced for irrigation.

WATER CONTROL AND CEREAL MANAGEMENT ON THE BRONZE AGE IBERIAN PENINSULA: LA MOTILLA DEL AZUER

Summary. Archaeological research conducted in the La Mancha region (central area of the Iberian Peninsula) has made it possible to identify motillas. This specific type of archaeological site consists of a central fortification surrounded by an inhabited area. They appear in high densities throughout the plains of this area, distributed at regular intervals and located in places where the phreatic level is closest to the surface and the water has low salinity. The strong relationship between sites and water has subsequently been supported by fieldwork, especially in the Motilla del Azuer settlement, where a complex well that was cut into the natural terrace to reach the phreatic level has been documented. Research has also demonstrated that the large‐scale storage of cereals was another significant function. The quantity and capacity of the different storage systems documented in two large enclosures suggest that these sites were engaged in the control and management of cereals.

Irrigation agriculture and groundwater. The case of Miralbueno aquifer (Spain)

A great number of flood irrigation districts which have low irrigation efficiency due to the high permeability of their soils cannot undertake a generalised changeover to pressurized irrigation systems in the short term. This work seeks to study the effects which the changeover of the irrigation system in the Irrigation District Nº V of Bardenas (Spain) would have on the hydric regime of the Miralbueno aquifer; also to evaluate different alternatives to improve water management based on the use of groundwater. For this, a model of the aquifer was made with the help of the Modflow 2000 software and different scenarios were simulated. The results indicate that generalised conversion to pressurized irrigation systems will cause a decrease in the average phreatic level (1.20 m) and in the volume of water drained by the ditches (49% less). Until this measure is taken, the irrigation efficiency of the agrarian system could be increased notably by intensifying the reuse of groundwater by means of: a) the construction of intercepting drainages to reuse groundwater in flood irrigation again, and b) the construction of appropriately distributed wells for drip irrigation of the current area of vegetables.

Environmental impact assessment using FORM and groundwater system reliability concept: case study Jining, China

In this paper, fist-order reliability method (FORM) is used to evaluate the impacts of uncertainties posed by traditional deterministic models on the environment in Jining, China. Because of groundwater contamination in shallow aquifer, and an increase in water demand, the new wells target the confined aquifer with constant pumping rate of 5,000 m3/d. Using Theis equation, the groundwater drawdown is analyzed to determine whether the confined aquifer will be contaminated. Although the piezometric level is higher than the phreatic level by 11.0 m, the risk of drawdown is still 19.49% when the pumping rate of 5,000 m3/d is maintained for 2 years. The deterministic model indicates a drawdown of 8.94 m which is lower than the maximum tolerance drawdown of 11.0 m. The sensitivity and uncertainty analysis reveal that the model result is more sensitive to transmissivity than specific yield, while the reliability analysis offers significant information for the decision makers. This approach exposes and minimizes the risk of undesirable consequences such as groundwater contamination.

Numerical modelling of surfacewater/groundwater flows for freshwater/saltwater hydrology: the case of the alluvial coastal aquifer of the Low Guadalhorce River, Malaga, Spain

This applied research deals with the numerical modelling and transient simulation of the joint surfacewater/groundwater flows that characterize the freshwater/saltwater hydrology of the coastal alluvial valley of the Low Guadalhorce River, Malaga, Spain. The MELEF model used was mainly adapted and calibrated for a simulation period of two hydrological years 1989/1990–1990/1991, before the current channelling of the river, where floods and low precipitations have been recorded. The model calibration process was performed with the aid of phreatic levels measured in numerous wells and piezometers, as well as recharges from precipitation and irrigation on the alluvial surface, which was also assessed by the hydrologic model SSMA-2. The present numerical approach can predict the forthcoming hydrology of the coastal alluvial of the Guadalhorce River after its final channelling.

Modelagem de incertezas na análise espaço-temporal dos níveis freáticos em uma bacia hidrográfica

O objetivo deste trabalho foi avaliar a oscilação dos níveis freáticos em uma bacia hidrográfica, no período seco, e modelar a variabilidade espaço-temporal desses níveis por meio de técnicas geoestatísticas multivariadas. A área de estudo foi o alto da Bacia do Rio Jardim, Distrito Federal. O regime hídrico dessa região é marcado pela sazonalidade, com períodos chuvosos (outubro a abril) e secos (maio a setembro) distintos, que determinam o comportamento dos níveis freáticos. Quanto aos fenômenos com indexação espaço-temporal, a geoestatística propõe soluções pelo modelo linear de co-regionalização, permitindo a quantificação e mapeamento das reservas hídricas subterrâneas. Quantificaram-se o volume perdido de água e o risco associado às estimativas pelas medidas de incerteza, criando-se cenários críticos do volume do aqüífero explorado na seca. Na seca, observou-se decréscimo de água nesse aqüífero. O mapa do quantil 10% indicou áreas favoráveis ao uso da água, em que os níveis freáticos oscilaram menos. O mapa do quantil 90% indicou áreas com grandes oscilações dos níveis freáticos que contribuem mais para drenagem e recarga do aqüífero.

Liquefaction phenomena associated with historical earthquakes in San Juan and Mendoza Provinces, Argentina

Mendoza and San Juan provinces which represent the most seismically active regions of Argentina have been affected by at least nine destructive earthquakes with magnitudes ⩾6.3 in the period 1861–1997. During these events, earthquake-induced liquefaction processes have caused the most severe damages in properties and fields impacting adversely on regional development and economy. Analysing historical liquefaction data we corroborated the relation between liquefaction phenomenon with sediment grain size and depth of phreatic level. We also noted that even the distance from liquefaction features to epicentres increases with earthquake magnitude, previous empirical relations for distance/magnitude are not enough accurate to predict liquefaction feature distance. Moreover, we suggest that when physical conditions of terrain are suitable, liquefaction phenomenon can occur even at greater distances than those established by empirical manner. In addition, regarding potential risk for this seismically region, the most liquefaction vulnerability areas were established taken into account the historical data and the presence of Holocene–Pleistocene deposits with present higher phreatic level. Our findings are essential for future proper territorial planning and they should be useful for minimize economical losses caused by secondary effects in these seismic regions of Argentina.

Real-time forecasting of water table depth and soil moisture profiles

We present a method for real-time forecasting of water table depth and soil moisture profiles. The method combines a simple form of data-assimilation with a moving window calibration of a deterministic model describing flow in the unsaturated zone and local as well as regional drainage. The local drainage level is calibrated on-line using a moving window calibration. Assigning more weight to the last available measurements then yields a form of model adaptation that is in between on-line calibration and data-assimilation (i.e. a simplified form of Newtonian nudging). Five-day hydrological forecasts are performed based on 5-day weather forecasts, while on-line observations of phreatic level and soil moisture content are assimilated on a daily basis. Advantages of the proposed method are that it improves the real-time forecasts compared to off-line calibration and ordinary moving window calibration and that it yields physically consistent soil moisture profiles.

Effect of climatic fluctuations on body mass of a Mediterranean vole, Microtus cabrerae

The Cabrera vole ( Microtus cabrerae) is a microtine rodent endemic to the Mediterranean bioclimatic region of the Iberian peninsula. We investigated body mass variation in a population monitored during monthly trapping sessions from April 1997 to April 1999. No significant differences in body mass were found between adult males and females; also no seasonal pattern of body mass variation was detected. Likewise, no correlation was found between the monthly body mass average and rainfall, probably due to the peculiar characteristics of the habitats used by M. cabrerae. These consist of areas with high soil moisture and high phreatic level; thus, these features act as a buffer and maintain fresh vegetation when rainfall is scarce. Consequently, body mass of the population does not depend directly on rainfall. Body mass and body condition scarcely fluctuated before summer 1998, but decreased significantly from that season to winter 1998, in coincidence with the severe drought recorded in summer–autumn 1998, which affected the quality of food available to the Cabrera vole, and resulted also in a suppression of reproduction up to 3 months. Given the predicted climate change trend in the Iberian peninsula, the particular reproduction characteristics of the Cabrera vole, and the destruction of their habitats by human activities, we strongly recommend the protection of the habitats occupied by this rodent species.

Infiltration process and groundwater table raising in a paddy field area

The water coming from the soil surface after the saturation of the soil stratum over the groundwater table at field saturation raises the groundwater level. The soil structure and the soil texture characterize the infiltration process. The resultant of the gravitational force and the capillary forces gives the energy to the water molecules to push the entrapped air out of the pores, reaching a full saturation of the soil thereby raising the phreatic level. There is a complex interaction between the agent forces on the water and the air resistant forces in the soil micro-pores. In the irrigation of paddy fields a groundwater level stable condition is reached when there is equilibrium between the capillary forces. A stable soil stratum with pressured air is always present in the soil over the phreatic level. From the collected data it seems that the soil stratum thickness from the soil surface to the groundwater table is proportional to the modulus of the capillary force. In a stable surface ponding depth, as the groundwater table rises, the level growing velocity may be assumed to be proportional to a medium hydraulic conductibility of the soil stratum. As the phreatic level approaches the saturated soil surface, the rising rate gradually changes until it gets to a point of equilibrium where the groundwater table is stationary at stable surface conditions. Under these conditions, as the surface water depth changes the phreatic level also changes.

Paleoalterações e Carbonatos em Depósitos Aluviais na Região de Santa Maria, Triássico Médio a Superior do Sul do Brasil

Five types of paleo-weathering and carbonate precipitation were recognized in fine-grained deposits of the Alemoa Member, Santa Maria Formation, Middle to Upper Triassic of southern Brazil. The fauna and flora found in these lithologies are important dating tools, but only in a generic way, misleading the time involved in periods of deposition and non deposition. The identified types of deposits are (i) reddish mudstones, with none or little paleo-weathering, (ii) mottled mudstones, with incipient pedogenesis, mainly mottling, destratification, animal and vegetal colonization, (iii) carbonate veins, with more evidences of exposure and root action, (iv) carbonate siltstones/sandstones, where restricted fluvial deposits are cemented by phreatic carbonate, and (v) carbonate nodules and lenses, in which small lenses of a very compact calcrete are at the top and in the center of carbonated siltstone/sandstone beds, distinguished by its crystalinity, hardness and brighter color. The recorded microfacies point to a cyclic variation of the mainly high phreatic level, forming cracks and pedotubules (pedogenesis) filled with carbonate and Fe and Mn oxides (phreatic). The identification of five distinct pedofacies and the stratigraphic correlation in the sedimentary package of the Alemoa Member (base, middle or topmost position) suggest a probable association of paleo-weathering processes and vertebrate preservation. Near channel facies, mainly at the base and top, present smaller exposure periods and higher variations on the phreatic level, and consequently, the best preserved vertebrate fossils. On the other hand, facies which are far from the channel, record more subaerial exposure and more significant phreatic variation, leading to more advanced (although still incipient) paleo-weathering and carbonate precipitation, and to a worst fossil preservation.

The dynamic form of rainwater lenses in drained fens

Inflow of nutrient poor alkaline groundwater is generally seen as a prerequisite for the development of species rich fen vegetation. Drainage and groundwater abstraction may lead to the development of so-called rainwater lenses in the upper groundwater of fens, which prevent upward seeping alkaline groundwater from reaching the fen root zone. This threatens the conservation of the species rich vegetation. To provide insight in rainwater lens dynamics as a basis for conservation and restoration of fen biodiversity, numerical groundwater flow model simulations were performed for a hypothetical case area in the Netherlands. The simulations indicate that drainage canal surface water levels mainly affect the phreatic level in the fens, while groundwater inflow fluxes mainly affect the thickness of the rainwater lens. Increasing thickness of a semi-confining surface layer results in a rise in phreatic level. As the phreatic level reaches the soil surface, the rainwater lens may split in two as a result of groundwater discharge windows, which come into existence in the centre of the parcel. The effect of seasonal recharge fluctuations on the rainwater lens appears small. Spells of dry and wet years have a considerably larger effect especially on the lower boundary of the rainwater lens, resulting in thinner lenses during spells of dry years. Most simulations show rainwater lens thicknesses well exceeding rooting depths of fen plants. This is inconsistent with the fact that fen vegetation is found in nature reserves for which the simulations are considered representative. Chemical buffer processes in the soil may explain this inconsistency, masking an acidification process under way. As buffer capacities become exhausted over time, acidification and fen deterioration will occur at a certain future moment. To arrive at more definite conclusions about this hypothesis, our simulations of convective groundwater flow need to be supplemented by modelling of hydrochemical processes in rainwater lenses, followed by verification at actual field locations.

The dynamic form of rainwater lenses in drained fens

Inflow of nutrient poor alkaline groundwater is generally seen as a prerequisite for the development of species rich fen vegetation. Drainage and groundwater abstraction may lead to the development of so-called rainwater lenses in the upper groundwater of fens, which prevent upward seeping alkaline groundwater from reaching the fen root zone. This threatens the conservation of the species rich vegetation. To provide insight in rainwater lens dynamics as a basis for conservation and restoration of fen biodiversity, numerical groundwater flow model simulations were performed for a hypothetical case area in the Netherlands. The simulations indicate that drainage canal surface water levels mainly affect the phreatic level in the fens, while groundwater inflow fluxes mainly affect the thickness of the rainwater lens. Increasing thickness of a semi-confining surface layer results in a rise in phreatic level. As the phreatic level reaches the soil surface, the rainwater lens may split in two as a result of groundwater discharge windows, which come into existence in the centre of the parcel. The effect of seasonal recharge fluctuations on the rainwater lens appears small. Spells of dry and wet years have a considerably larger effect especially on the lower boundary of the rainwater lens, resulting in thinner lenses during spells of dry years. Most simulations show rainwater lens thicknesses well exceeding rooting depths of fen plants. This is inconsistent with the fact that fen vegetation is found in nature reserves for which the simulations are considered representative. Chemical buffer processes in the soil may explain this inconsistency, masking an acidification process under way. As buffer capacities become exhausted over time, acidification and fen deterioration will occur at a certain future moment. To arrive at more definite conclusions about this hypothesis, our simulations of convective groundwater flow need to be supplemented by modelling of hydrochemical processes in rainwater lenses, followed by verification at actual field locations.