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Spatial and temporal variability of rainfall: case of Bizerte-Ichkeul Basin (Northern Tunisia) 总被引：1，自引：0，他引：1
This study examines spatial and temporal variability of rainfall in Bizerte-Ichkeul Watershed. The basin, located in the extreme north of Tunisia, covers an area of 3084 km2. Thirteen rainfall stations, with continuous monthly precipitation records over the period (1970–2011), were considered in the analysis. Two methods were used. In the first, the dimensionless standardized precipitation ratio is applied to examine precipitation temporal variation. The second method is represented by continuous wavelet analysis for the precipitation spatial analysis and the identification of the origin of its variability. The study of temporal variability of annual rainfall showed severe persistent and recurrent drought episodes over the period (1977–2001). Wavelet analysis resulted in detecting the modes and origins of precipitation variability. Three energy bands were clearly identified: (1, 2–4, and 4–8 years) for the entire watershed. The visualization of the power distribution showed that the observed modes of variability are different in their power distributions from one station to another. The approach adopted allowed the identification of two groups with the same precipitation frequency and temporal variation. These groups were defined according to the difference in occurrence of the frequency band for each station. 相似文献
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Josep Mas‐Pla Agustí Rodríguez‐Florit Manel Zamorano Carles Roqué Anna Menció David Brusi 《水文研究》2013,27(16):2352-2366
Intensive pumping in urban coastal areas is a common threat to water resource quality due to seawater intrusion. In those areas where subsurface water resources are not usually used for human consumption or irrigation, intensive pumping is associated with other activities like the lowering of the water table necessary to support underground structures and building foundations. This activity also increases the likelihood of soil settlement that affects building stability and the corrosion of concrete structures due to groundwater salinity. Under these circumstances, the awareness of a certain municipality (Calonge, NE Spain) of the potential effects of groundwater withdrawal upon foundations has led to an integrated approach to anticipate seawater intrusion related to urban development. Geological mapping and correlation of borehole logs, electrical resistivity tomography, and hydrochemical data provide comprehensive knowledge of the geology and hydrogeology of the area and act as screening tools necessary to discern the influence of hydrological processes in coastal areas. Developing Strack's analytical solution, new comprehensive, dimensionless expressions are herein derived to determine the critical pumping rate necessary to prevent seawater intrusion, as well as to reproduce the evolution of the wedge toe and the water table stagnation point under different withdrawal rates. Furthermore, the Dupuit–Forchheimer well discharge formula allows the estimation of the effects of the water table lowering due to such critical pumping in the surrounding building foundations. Field data from the Calonge coastal plain illustrate this approach and provide assessment criteria for future urban development and planning. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Maria F. Loreto Nevio Zitellini Csar R. Ranero Camilla Palmiotto Manel Prada 《Basin Research》2021,33(1):138-158
We present a new tectonic map focused upon the extensional style accompanying the formation of the Tyrrhenian back‐arc basin. Our basin‐wide analysis synthetizes the interpretation of vintage multichannel and single‐channel seismic profiles, integrated with modern seismic images, P‐wave velocity models, and high‐resolution morpho‐bathymetric data. Four distinct evolutionary phases of the Tyrrhenian back‐arc basin opening are further constrained, redefining the initial opening to Langhian/Serravallian time. Listric and planar normal faults and their conjugates bound a series of horst and graben, half‐graben and triangular basins. Distribution of extensional faults, active throughout the basin since Middle Miocene, allows us to define an arrangement of faults in the northern/central Tyrrhenian mainly related to a pure shear which evolved to a simple shear opening. At depth, faults accommodate over a Ductile‐Brittle Transitional zone cut by a low‐angle detachment fault. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variation throughout the back‐arc basin combined with wide‐angle seismic velocity models allows to explore the relationships between shallow deformation, faults distribution throughout the basin, and crustal‐scale processes as thinning and exhumation. 相似文献
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Lourdes L��pez-Merino Ana Moreno Manel Leira Javier Sigr�� Pen��lope Gonz��lez-Samp��riz Blas L. Valero-Garc��s Jos�� Antonio L��pez-S��ez Manola Brunet Enric Aguilar 《Journal of Paleolimnology》2011,46(3):453-467
We present a study of two short sediment cores recovered from Lago Enol, in the Picos de Europa National Park, Cantabrian Mountains, northern Iberia. We inferred past climate conditions and anthropogenic impacts using geochemical and biological (pollen and diatoms) variables in the dated sequences, in conjunction with temperature and precipitation data collected since 1871 at meteorological stations in the region. The record provides evidence of environmental changes during the last 200 years. At the end of the Little Ice Age (~1800?C1875 AD) the region was characterized by an open landscape. Long-term use of the area for mixed livestock grazing in the mountains, and cultivation of rye during the nineteenth century, contributed to the expansion of grassland at the expense of forest. Warmer temperatures since the end of the nineteenth century are inferred from a change in diatom assemblages and development of the local forest. Socioeconomic transformation during the twentieth century, such as livestock changes related to dairy specialization, planting of non-native trees, mining activities, and management of the national park since its creation in 1918, caused profound changes in the catchment and in the lake ecology. The last several decades (~1970?C2007 AD) of the Lago Enol sediment record are strikingly different from previous periods, indicating lower runoff and increasing lake productivity, particularly since AD 2000. Today, the large number of tourists who visit the area cause substantial impacts on this ecosystem. 相似文献
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Assessment of soil erosion risk using SWAT model 总被引：3，自引：2，他引：1
Manel Mosbahi Sihem Benabdallah Mohamed Rached Boussema 《Arabian Journal of Geosciences》2013,6(10):4011-4019
Soil erosion is one of the most serious land degradation problems and the primary environmental issue in Mediterranean regions. Estimation of soil erosion loss in these regions is often difficult due to the complex interplay of many factors such as climate, land uses, topography, and human activities. The purpose of this study is to apply the Soil and Water Assessment Tool (SWAT) model to predict surface runoff generation patterns and soil erosion hazard and to prioritize most degraded sub-catchment in order to adopt the appropriate management intervention. The study area is the Sarrath river catchment (1,491 km2), north of Tunisia. Based on the estimated soil loss rates, the catchment was divided into four priority categories for conservation intervention. Results showed that a larger part of the watershed (90 %) fell under low and moderate soil erosion risk and only 10 % of the watershed was vulnerable to soil erosion with an estimated sediment loss exceeding 10 t?ha?1?year?1. Results indicated that spatial differences in erosion rates within the Sarrath catchment are mainly caused by differences in land cover type and gradient slope. Application of the SWAT model demonstrated that the model provides a useful tool to predict surface runoff and soil erosion hazard and can successfully be used for prioritization of vulnerable areas over semi-arid catchments. 相似文献
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Water Flow, Trophic Depletion, and Benthic Macrofauna Impoverishment in a Submarine Cave from the Western Mediterranean 总被引：1，自引：0，他引：1
Mikel Zabala Tecla Riera Josep Maria Gili Manel Barange Agustin Lobo Josep Peñuelas 《Marine Ecology》1989,10(3):271-287
Abstract. Biotic zonation and severe impoverishment of benthic macrofauna are two of the most conspicuous features of submarine caves. The prevailing explanation assumes trophic depletion caused by reduction of water flow. However, no isolation of water was found in the studied Catalan submarine cave, even in the wall microlayer. Fluorescein diffusion was so fast that it was detectable everywhere in the cave already only a few minutes after the injection. The rate of dissolution of plaster spheres was even greater in the cave than in a nearby tunnel – without benthic macrofauna impoverishment – showing a considerable water flow. The oxygen concentration of water in dialysis bags placed at varying distances from the cave walls showed that no wall microlayer gradients were present.
Biochemical gradients did not indicate any decrease in food supply. Although photosynthetic pigment concentration generally decreased inside the cave, and although the gradients were not linear but formed different patterns throughout the cave, the BOD5 , the POM, the C:N ratio, the [3 H]-thymidine incorporation rate, and the ETS activity were higher in the inner part of the cave. There was an accumulation of detritic material and bacteria in the inner parts that constitute a plausible food supply for benthic macrofauna.
If neither water motion nor food supply can be invoked, research into the causes of zonation and disappearence of benthic macrofauna is proposed to be carried out on biotic interactions and behavioural processes. 相似文献
Biochemical gradients did not indicate any decrease in food supply. Although photosynthetic pigment concentration generally decreased inside the cave, and although the gradients were not linear but formed different patterns throughout the cave, the BOD
If neither water motion nor food supply can be invoked, research into the causes of zonation and disappearence of benthic macrofauna is proposed to be carried out on biotic interactions and behavioural processes. 相似文献
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Manel Prada Franois Lavou Muhammad Mudasar Saqab Brian M. O'Reilly Sergei Lebedev John J. Walsh Conrad Childs 《Basin Research》2019,31(1):59-76
The Porcupine Basin is a Mesozoic failed rift located in the North Atlantic margin, SW of Ireland, in which a postrift phase of extensional faulting and reactivation of synrift faults occurred during the Mid–Late Eocene. Fault zones are known to act as either conduits or barriers for fluid flow and to contribute to overpressure. Yet, little is known about the distribution of fluids and their relation to the tectono‐stratigraphic architecture of the Porcupine Basin. One way to tackle this aspect is by assessing seismic (Vp) and petrophysical (e.g., porosity) properties of the basin stratigraphy. Here, we use for the first time in the Porcupine Basin 10‐km‐long‐streamer data to perform traveltime tomography of first arrivals and retrieve the 2D Vp structure of the postrift sequence along a ~130‐km‐long EW profile across the northern Porcupine Basin. A new Vp–density relationship is derived from the exploration wells tied to the seismic line to estimate density and bulk porosity of the Cenozoic postrift sequence from the tomographic result. The Vp model covers the shallowest 4 km of the basin and reveals a steeper vertical velocity gradient in the centre of the basin than in the flanks. This variation together with a relatively thick Neogene and Quaternary sediment accumulation in the centre of the basin suggests higher overburden pressure and compaction compared to the margins, implying fluid flow towards the edges of the basin driven by differential compaction. The Vp model also reveals two prominent subvertical low‐velocity bodies on the western margin of the basin. The tomographic model in combination with the time‐migrated seismic section shows that whereas the first anomaly spatially coincides with the western basin‐bounding fault, the second body occurs within the hangingwall of the fault, where no major faulting is observed. Porosity estimates suggest that this latter anomaly indicates pore overpressure of sandier Early–Mid Eocene units. Lithological well control together with fault displacement analysis suggests that the western basin‐bounding fault can act as a hydraulic barrier for fluids migrating from the centre of the basin towards its flanks, favouring fluid compartmentalization and overpressure of sandier units of its hangingwall. 相似文献