Flash floods are among the most severe hazards which have disastrous environmental, human, and economic impacts. This study is interested in the characterization of flood hazard in Gabes Catchment (southeastern Tunisia), considered as an important step for flood management in the region. Analytical hierarchy process (AHP) and geographic information system are applied to delineate and characterize flood areas. A spatial database was developed based on geological map, digital elevation model, land use, and rainfall data in order to evaluate the different factors susceptible to affect flood analysis. However, the uncertainties that are associated with AHP techniques may significantly impact the results. Flood susceptibility is analyzed as a function of weights using Monte Carlo (MC) simulation and Global sensitivity analysis. AHP and MC–AHP models gave similar results. However, compared to AHP approach, MC–AHP confidence intervals (95%) of the overall scores had small overlaps. Results obtained were validated by remote sensing data for the zones that showed very high flood hazard during the extreme rainfall event of June 2014 that hit the study basin. 相似文献
Paléocène-Early Eocene phosphate outcrop in the Ras-Draâ deposit (Tunisia) comprises alternances of P-rich strata (P2O5 ≥ 18%) and P-poor ones (P2O5 ≤ 2%). In phosphate rich strata, P is concentrated in rounded grains—so-called pellets—(28% ≤ P2O5 ≤ 38%) embedded in a matrix—so-called exogangue—much poorer in P (P2O5 # 7%) than pellets. The study of pellets (whose size lies mainly between 100 and 500 μm), of their surrounding matrix and of poorly phosphatic sediments, interlayered between the phosphatic strata, has been performed by optical microscopy and various chemical analyses, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) and punctual chemical analyses by EDS (Energy Dispersive Spectroscopy). Mineralogical and chemical studies of the Tunisian phosphatic pellets show that the basic mineralogical component of these grains is carbonate-fluor-apatite, or francolite. The structural formula of a representative specimen of francolite in the basin is as follows: (Ca4.63Mg0.13Na0.22)(PO4)2.51(CO3)0.48(OH0.77F0.23). The mineralogy of the constituents of the sediment surrounding pellets comprises carbonates, clays, silica (opal, quartz). Microscopic observations of Ras-Draâ phosphorites, added to geochemical results, establish that pellets are small bodies, allochtonous to their matrix and whose composition is independent of that of this matrix. Fecal cylindrical bodies and subspherical pellets, the latest being supposed to proceed from the fecal bodies by fragmentation, are considered to have been formed by fishes, as P-rich and organic matter-rich faeces. These faeces turn out to be resistant to mechanical dispersion and to chemical diffusion of soluble elements from and in direction of sea water. This closeness is responsible for the strong reducing conditions having prevailed inside and during the pellets diagenesis. 相似文献
This study examines spatial and time evolutions of the principal constituents of the
Tunisian background aerosols under Sirocco wind circulations. Aerosols coming from the Sahara
Desert were found to be loaded with particulate matter, especially silicon. The aerosols were
shown to have varying geochemical behaviour along the ``South-North" displacement of the Saharan
plumes, depending on the wind flow characteristics, geomorphologic features and the nature of
soils swept by the wind. In the south and the center part of the country, the transfer of aerosol
constituents to the soil (by gravity and/or impaction) was probably predominated by localized
enrichment phenomena. The latter are reinforced by the effect of turbulent winds over bare soils,
wind wakes and probably selective disintegration, especially in the vicinity of the geomorphologic
features of central Tunisia. These relatively high features, extending over important distances,
appear to be of paramount importance for the phenomena of redistribution of aerosol constituents
even during periods without Sirocco wind circulations. In the northern section of the country,
aerosol constituent concentrations dropped to almost 50%, in spite of the abundance of localized
turbulent winds. This may be explained by the effect of forests and the relatively dense vegetation
cover, which clearly reinforces the transfer phenomena to the soil and the attenuate of dust
entrainment. 相似文献
Many photogrammetric and GIS applications, such as city modelling, change detection and object recognition, deal with surfaces. Change detection involves looking for differences between two surface models that are obtained from different sensors, for example an optical sensor and a laser scanner, or by the same sensor at different epochs. Surfaces obtained through a sampling process may also have to be compared for future processing (for example transformation parameter estimation and change detection). Surface matching is therefore an essential task in these applications. The matching of surfaces involves two steps. The first step deals with finding the correspondences between two surface points and/or patches. The second step requires the determination of transformation parameters between the two surfaces. However, since most surfaces consist of randomly distributed discrete points and may have different reference systems, finding the correspondences cannot be achieved without knowing the transformation parameters between the two surfaces. Conversely, deriving the transformation parameters requires the knowledge of the correspondence between the two point sets. The suggested approach for surface matching deals with randomly distributed data sets without the need for error prone interpolation and requires no point-to-point correspondence between the two surfaces under consideration. This research simultaneously solves for the correspondence and the transformation parameters using a Modified Iterated Hough Transform for robust parameter estimation. Several experiments are conducted to prove the feasibility and the robustness of the suggested approach, even when a high percentage of change exists. 相似文献
Impacts of irrigation with treated wastewater effluents on soils and groundwater aquifer in the vicinity of Sidi Abid Region
(Tunisia) are evaluated. The groundwater aquifer was monitored by several piezometers, where monthly water levels were registered
and groundwater salinity was evaluated. This resulted in characterizing the spatial and temporal evolution of the hydrochemical
and hydrodynamic properties of the aquifer, showing thereby the impact of artificial recharge. Piezometric maps for pre-recharge
and post-recharge situations were developed and a comparison study of both piezometric situations was considered. The piezometric
evolution map showed a generalized rise of the piezometric level in the vicinity of the irrigation zone. The extent of recharge
was shown to increase with time as the groundwater level increase, which was localized in the vicinity of the irrigation area,
reached more extended zones. Several groundwater samples were withdrawn from wells and piezometers and analyzed. Examining
the corresponding physical and chemical parameters showed an increase in the concentrations of nutrients (28 mg/l for NO3 and 3.97 mg/l for NH4) in the groundwater aquifer below the irrigation zone, which confirms again the infiltration of treated wastewater effluents.
The evolution of soil salinity was examined through chemical analysis of soil samples. Electric conductivities of soils were
generally shown to be less than 4 mS/cm while the irrigation water has an electric conductivity that may reach 6.63 mS/cm.
This might be explained by the phenomenon of dilution and the capacity of soils to evacuate salts downward. 相似文献
The Dena rainstorm in Iran in March and April 2019 caused about US$ 8.3?×?109 damage in the country; however, it resulted in the replenishment of half of the dam reservoirs and 35% of ponds and lakes. Also, it increased the volume of groundwater stored in aquifers by 3.6?×?109 m3. In arid and semiarid regions such as most parts of Iran, which usually face water scarcity, getting water from rainstorms is essential for replenishing water resources. This research aims to quantify the direct and indirect effects of the Dena rainstorm on the replenishment of Iran’s groundwater storage using the groundwater balance method and water-table fluctuation method. Studies showed that the main mechanisms for replenishment of groundwater storage due to the rainstorm included increases in precipitation recharge, surface runoff recharge, and artificial recharge, and reductions in irrigation withdrawal and evapotranspiration, while the contribution of each factor is estimated to be about 23, 28, 2, 15, and 32%, respectively.