Research Institute for Groundwater

Egypt is considered an arid country. The main and almost exclusive source of water is the River Nile. The second source of water is groundwater whereas a variety of aquifer systems exist. Nile Delta aquifer is a large freshwater reservoir which is mainly replenished from irrigation activities. A proper management and development of such aquifers should be directed to satisfy water requirements. Groundwater development in the northern region is restricted due to the risks of inland movement of saline water/ fresh water interface to properly manage groundwater in this region. To achieve the proper management of groundwater resource in this region, it is important to understand the patterns of seawater movement and mixing between fresh and saline groundwater. In order to understand the salinity distribution and seawater movement, the actual heterogeneity and stratigraphy of the Nile Delta aquifer should be determined. The conventional modeling concept of the Nile Delta aquifer had assumed the aquifer as a homogenous media of graded sand and gravel with a clay cap at the top. In this study, assessment of recent stratigraphy of the Nile Delta aquifer is carried out using litho-logical data from the new drilled groups of multi depths wells. These wells has been designed and implemented especially to investigate the actual litho-stratigraphy and heterogeneity of the aquifer in the northern and middle region of the Nile Delta as a part of National Groundwater Quality Monitoring program, by Research Institute for Groundwater (RIGW). In this study, new configuration of the Nile Delta aquifer system has been obtained by assessing the Hydro-geological stratification of Nile Delta aquifer using RockWorks software. The study concluded that the northern part the aquifer is devolved into multi-layered aquifer system while in the southern part; the aquifer constitutes sand and gravel facies. Furthermore, this study assessed the Hydrochemistry status of the groundwater in the Nile Delta aquifer by using the results of chemical analysis of multi depths points (25-650 m) of the National Groundwater Quality Monitoring network. This assessment confirmed that there is a multi wedge system for the sea water intrusion in the Nile Delta aquifer. The shape and direction of the wedges differs between the different layers of the aquifer according to the salinity and density of the groundwater present in each layer. This new multi system wedge can be used to model and simulate the new conceptual and configuration of the Nile Delta aquifer to fulfill proper groundwater development and management. [Nofal E. R. , Amer M. A., El-Didy S. M. and Akram M. Fekry. Sea Water Intrusion in Nile Delta in Perspective of New Configuration of the Aquifer Heterogeneity Using the Recent Stratigraphy Data. J Am Sci 2015;11(6):281-292]. (ISSN: 1545-1003). http://www.jofamericanscience.org. 33

Holocene marine transgressions are often put forward to explain observed groundwater salinities that extend far inland in deltas. This hypothesis was also proposed in the literature to explain the large land-inward extent of saline groundwater in the Nile Delta. The groundwater models previously built for the area used very large dispersivities to reconstruct this saline and brackish groundwater zone. However , this approach cannot explain the observed freshening of this zone. Here, we investigated the physical plausibility of the Holocene-transgression hypothesis to explain observed salinities by conducting a palaeohydrogeological reconstruction of groundwater salinity for the last 32 ka with a complex 3-D variable-density groundwater flow model, using a state-of-the-art version of the SEAWAT computer code that allows for parallel computation. Several scenarios with different lithologies and hypersaline groundwater provenances were simulated, of which five were selected that showed the best match with the observations. Amongst these selections, total freshwater volumes varied strongly, ranging from 1526 to 2659 km 3 , mainly due to uncertainties in the lithology offshore and at larger depths. This range is smaller (1511-1989 km 3) when we only consider the volumes of onshore fresh groundwater within 300 m depth. In all five selected scenarios the total volume of hypersaline groundwater exceeded that of seawater. We also show that during the last 32 ka, total freshwater volumes significantly declined, with a factor ranging from 2 to 5, due to the rising sea level. Furthermore , the time period required to reach a steady state under current boundary conditions exceeded 5.5 ka for all scenarios. Finally, under highly permeable conditions the marine transgression simulated with the palaeohydrogeological reconstruction led to a steeper fresh-salt interface compared to its steady-state equivalent, while low-permeable clay layers allowed for the preservation of fresh groundwater volumes. This shows that long-term transient simulations are needed when estimating present-day fresh-salt groundwater distributions in large deltas. The insights of this study are also applicable to other major deltaic areas, since many also experienced a Holocene marine transgression.

The rising demands of groundwater for agricultural, due to the non-reliability of surface water sources have placed groundwater resource under serious pressure subjecting it to depletion and quality deterioration risks. Since, The Nile Delta aquifer is one of the most important renewable groundwater reservoirs in Egypt; it stands as the second source of water after the Nile, especially in the Nile Delta region. The Nile Delta aquifer is continuously recharged by irrigation water and through seepage from surface water. Moreover the Nile Delta aquifer is vulnerable to saltwater intrusion resulting from increasing groundwater abstraction. A 3D regional model for the Nile Delta aquifer system has been constructed to be used as a water management tool for different water management scenarios. The model was used to test the sensitivity of the aquifer to different extraction and recharge rates and investigate the system response on heads and salinity of the aquifer. The results confirmed that sensitivity of the aquifer to the tested parameters differs from one place to another.