Simulation of groundwater level in a coastal aquifer

Abstract

The groundwater levels can have a significant impact on structures and infrastructures of coastal areas. The simulation of the hydraulic behavior of coastal aquifers is very important due to its specific boundary conditions. In this study, the groundwater level in the Bandar-e-Gaz coastal aquifer in the Gorgan Gulf region located in northern Iran is simulated using the MODFLOW mathematical model. The modeling of the coastal aquifer behavior carried out in two calibrations (steady and unsteady states). The validation periods (unsteady state), the mean absolute error (MAE) and mean bias error (MBE) were used to evaluate the results. The values of MAE and MBE criteria for the steady state were 0.31 (m) and –0.08 (m), while the average of these criteria in the unsteady state in calibration period were 0.46 and –0.39, and in the validation period were 0.42 (m) and –0.31 (m), respectively. The mentioned results confirm the precision of the model for the entire simulation period, they also indicate that the simulation has a limited underestimation behavior. Moreover, it shows that the precision of the results has a negligible variability, which means the simulation also has considerable reliability. The highest and lowest amount of error in the winter and summer seasons are in accordance with the lowest and highest seawater levels, and it shows the significant sea effect on the hydraulic behavior of the coastal aquifer.     

Real surface conductivity component as indicator for the hydraulic conductivity

Estimation of hydraulic conductivity from surface resistivity measurements is one of the most difficult and challenging hydrogeophysical targets. The promising side of this relation is the analogy between electric current flow and water flow, whereas the grand ambiguity is the non-dimensionality between both two quantities. Imaginary surface conductivity component is used recently to deduce the hydraulic conductivity via complex resistivity measurements. Since there are similar properties between imaginary (out-of-phase) and real (in-phase) surface conductivity components, the latter is used in this paper to predict the hydraulic conductivity. Two mathematical parameters were determined to express the electrical equivalent of hydraulic conductivity in sand and clay systems based on the mode of electrical double-layer formation in both systems. The reliability of the proposed method is tested through applying on two datasets representing sand and clay systems. The first dataset is a clean sand and gravel aquifer in the Keritis basin in Chania, Crete, Greece. The second is mostly clayey sand aquifer in Wadi El-Assuity, Egypt. Application of the present approach in these two cases resulted in promising nearly identical values with the measured hydraulic conductivity via pumping test or geometric hydraulic conductivity via grain size analysis.     

Leachability of radium-226 from industrial phosphogypsum waste using some simulated natural environmental solutions

This study investigated the leaching of radium-226 from phosphogypsum (PG) waste produced from the fertilizer industry by synthetic solutions that replicate water that may contact the waste in natural conditions. The results indicated that the activity concentration of Ra-226 in the PG was 461 ± 12 Bq kg^?1 and compared with other studies carried out worldwide. The leached percentage of Ra-226 represents the exchangeable fraction loosely bounded in the matrix of the PG waste. The leached fraction of Ra-226 was 6.5 ± 0.6 and 9.0 ± 0.5% when the waste was exposed to rainwater and saline solution, respectively. It is also found that the leaching fraction increased 10–12 ± 0.4% when the waste was exposed to the admixture of saline solution containing Sr²⁺ or Ba²⁺ cations, whereas it was lowered to 4–5 ± 0.5% in the presence of carbonate or sulfate anions. When the PG is used as an economic fertilizer, the irrigation water can leach 7.8 ± 0.6% of Ra-226 that could contribute to plant uptake, thereby to animal and/or human consumption. The primary tests of the drinking water (well and tap resources) consumed by the populations surround the PG facility showed that the activity concentration of Ra-226 was below the minimum detectable activity.     

A quantitative assessment of groundwater resources in the Middle East and North Africa region

The Middle East and North Africa (MENA) region is the world’s most water-stressed region, with its countries constituting 12 of the 15 most water-stressed countries globally. Because of data paucity, comprehensive regional-scale assessments of groundwater resources in the MENA region have been lacking. The presented study addresses this issue by using a distributed ArcGIS model, parametrized with gridded data sets, to estimate groundwater storage reserves in the region based on generated aquifer saturated thickness and effective porosity estimates. Furthermore, monthly gravimetric datasets (GRACE) and land surface parameters (GLDAS) were used to quantify changes in groundwater storage between 2003 and 2014. Total groundwater reserves in the region were estimated at 1.28 × 10⁶ cubic kilometers (km³) with an uncertainty range between 816,000 and 1.93 × 10⁶ km³. Most of the reserves are located within large sedimentary basins in North Africa and the Arabian Peninsula, with Algeria, Libya, Egypt, and Saudi Arabia accounting for approximately 75% of the region’s total freshwater reserves. Alternatively, small groundwater reserves were found in fractured Precambrian basement exposures. As for groundwater changes between 2003 and 2014, all MENA countries except for Morocco exhibited declines in groundwater storage. However, given the region’s large groundwater reserves, groundwater changes between 2003 and 2014 are minimal and represent no immediate short-term threat to the MENA region, with some exceptions. Notwithstanding this, the study recommends the development of sustainable and efficient groundwater management policies to optimally utilize the region’s groundwater resources, especially in the face of climate change, demographic expansion, and socio-economic development.     

An overview of the diagenesis of the Upper Jurassic carbonates of Jubaila and Hanifa formations, central Saudi Arabia

The Jubaila Formation (Upper Jurassic) in central Saudi Arabia has been divided into lower, middle, and upper parts purely on lithologic grounds. Each part consists of a major lower unit of lime mudstone and a minor upper unit of grainstone. This persistent change in the limestone facies is interpreted as a reflection of repeated shoaling up in the depositional shelf environment. It is a normal marine carbonate sequence that varies in thickness from 85 to 126 m. In the Hanifa Formation, the lowermost brown ledges in the section comprise a series of coarsening upward sequences which generally terminate in a fossiliferous/peloidal packstone and grainstone and subordinately lime mudstone facies. The middle slope member is yellow, blocky weathered shale and marl. Above this slope member are several thick beds of brown-coated fossiliferous wackestone, packstone, and grainstone with the association of lime mudstone in certain levels. These are fairly resistant ledges due to the occurrence of stromatoporoids. Dedolomitization occurs in the Jubaila Formation in various textural forms which include composite calcite rhombohedra, zonal dedolomitization, regeneration of predolomitization fabric of the limestone, and coarsely crystalline calcite mosaics with or without ferric oxide rhombic zones. Rhombohedral pores commonly occur in intimate association with dolomite, possibly resulting from the leaching of calcitized dolomite rhombohedra. The regional dedolomitization was most likely brought about by calcium sulfate solutions reacting with dolomites. The source of sulfate solutions is the dissolved anhydrite deposits of the Arab–Hith Formations, sometime before their erosion, and it takes place at or near an exposed surface. The Hanifa Formation shows various diagenetic features. These include dolomitization, dedolomitization, micritization, cementation, and recrystallization. Most of the examined samples of the Hanifa carbonates are dolomitized and subsequently dedolomitized as evidenced by the presence of iron-coated dolomite rhombs partially or completely calcitized. Dolomite also occurs in the lime mudstone, wackestone, packstone, and grainstone facies, while leaching of wackestone and packstone and dedolomitization of dolomite and dolomitic limestone followed by recrystallization are common processes.     

Pattern recognition of major asperities using local recurrence time in Alborz Mountains, Northern Iran

In this study, seismic data recorded during the period 01/01/1996 to 09/01/2009 has been used to evaluate the seismic hazard potential along the Alborz region, Northern Iran. The technique of mapping local recurrence time, T _L, is used to map major asperities, which are considered as the areas with maximum hazard. We calculated T _L from a and b values which are in turn derived from the frequency–magnitude relation constants within a radius of 30 km about every corner point of a 10-km spacing grid. Since b value is inversely related to applied stress, the areas with lowest b values and/or shortest T _L are interpreted to locate the asperities or the areas of maximum seismic hazard. To test this method, we computed T _L map using seismic catalogues before and after the 2004 Baladeh earthquake of M _w 6.2. The local recurrence time map before the earthquake shows anomalously short T _L in the epicentral region of the Baladeh earthquake a decade before its occurrence. The T _L map after the earthquake indicates that this large event has redistributed the applied stress in the Alborz region. The microseismicity of the region after the Baladeh earthquake, however, suggests that there are two anomalies in T _L map positioned in Alborz. The places where these anomalies are observed can be considered as the areas with maximum seismic hazard for future large earthquake in the Alborz region.     

The structural inventory of a small complex impact crater: Jebel Waqf as Suwwan,Jordan

The investigation of terrestrial impact structures is crucial to gain an in‐depth understanding of impact cratering processes in the solar system. Here, we use the impact structure Jebel Waqf as Suwwan, Jordan, as a representative for crater formation into a layered sedimentary target with contrasting rheology. The complex crater is moderately eroded (300–420 m) with an apparent diameter of 6.1 km and an original rim fault diameter of 7 km. Based on extensive field work, IKONOS imagery, and geophysical surveying we present a novel geological map of the entire crater structure that provides the basis for structural analysis. Parametric scaling indicates that the structural uplift (250–350 m) and the depth of the ring syncline (<200 m) are anomalously low. The very shallow relief of the crater along with a NE vergence of the asymmetric central uplift and the enhanced deformations in the up‐range and down‐range sectors of the annular moat and crater rim suggest that the impact was most likely a very oblique one (~20°). One of the major consequences of the presence of the rheologically anisotropic target was that extensive strata buckling occurred during impact cratering both on the decameter as well as on the hundred‐meter scale. The crater rim is defined by a circumferential normal fault dipping mostly toward the crater. Footwall strata beneath the rim fault are bent‐up in the down‐range sector but appear unaffected in the up‐range sector. The hanging wall displays various synthetic and antithetic rotations in the down‐range sector but always shows antithetic block rotation in the up‐range sector. At greater depth reverse faulting or folding is indicated at the rim indicating that the rim fault was already formed during the excavation stage.     

Decrease in the clear air transmission at Helwan Observatory site

Clear air atmospheric transparency of eight nights at Helwan Observatory site during autumn period of 1987 have been determined using the yellow filter GG5. The prevailing atmospheric transmission extends to 58%. A comparison with previous values obtained with the same filter and site during autumn period of 1963 shows a considerable decrease at the present years in the clear air transmission of the site of Helwan. This can be attributed to the aerosol pollution of the site caused mainly by the increase of the industrial centers at Helwan Zone. Clear air atmospheric transparency values at the beginning of winter season and at spring season are also given.     

Floods in Bangladesh: A question of disciplining the rivers

Bangladesh has been experiencing floods more frequently than ever before. Since 1947, she has been hit by extremely devastating floods in 1954, 1955, 1956, 1962, 1963, 1966, 1968, 1969, 1970, 1971, 1974, 1976, 1984, 1987, and 1988. Each year's highest flood record and damage costs have been broken by that of the subsequent year. All means of communication become paralysed. People lose food grains, domestic animals, homesteads, and lives. They remain marooned without food and drinking water until relief arrives. Despite huge spending on flood control, the intensity of the floods has been increasing. Therefore, speculation is naturally rife about the causes.The aim of this paper is to identify the factors which contribute to these devastating floods, and then to recommend an appropriate strategy for effective flood control. The geography, geology, and hydrology of Bangladesh are briefly discussed. The whole of the country is a huge river basin criss-crossed by as many as seven hundred rivers, tributaries, and distributaries, having a total length of 22 155 km.The river-beds are rendered shallow by heavy deposits of alluvial earth each year and tend easily to cause inundations. The quantum of silt carried by the river systems into Bangladesh is estimated to be 2.4 × 10⁹ tonnes/yr.Disciplining the rivers means keeping the rivers navigable all year round, removing excessive deposits of silt where they threaten to block a channel, preventing widening by erosion, contracting the width where the river is excessively wide, and last but not least, preventing construction whose eventual impact might prove harmful.Natural disasters do not respect political frontiers, nothing can stop them, but their adverse impact could be minimised. The author emphasises the need for employing the abundant cheap manpower, local materials, and indigenous technology for flood control projects.