Sources of salinity and urban pollution in the Quaternary sand aquifers of Dar es Salaam, Tanzania

The Republic of Djibouti has an area of 23,000 km2, a coastline 370 km long and a population of 820,000 inhabitants. It experiences an arid climate characterized by high daytime temperatures and low and irregular rainfall (average of 140 mm/year), resulting in continuous periods of drought. These difficult climatic conditions and the absence of perennial surface water have progressively led to an intensive exploitation of groundwater to meet increasing water demands in all sectors (drinking water, agriculture and industries). In coastal areas, seawater intrusion constitutes a significant additional risk of groundwater degradation. This study is focused on the coastal aquifer of Tadjourah which supplies water to the city of Tadjourah, currently comprising 21,000 inhabitants. The main objective of this work is to assess the current resources of this aquifer; its capacity to satisfy, or not, the projected water demands during coming years; and to analyze its vulnerability to seawater intrusion within the frame of climate change. Three RCPs (Representative Concentration Pathway) were used to simulate different climate scenarios up to 2100. The simulated rainfall series allowed to deduce the aquifer recharge up to 2100. The code Seawat was used to model seawater intrusion into the aquifer, using the recharge data deduced from the climate scenarios. The results indicate that the risk of contamination of the Tadjourah coastal aquifer by seawater intrusion is high. The long-term and sustainable exploitation of this aquifer must take into consideration the impact of climate change.

Section: Introductionmentioning

confidence: 99%

Simulation of Climate Change Impact on A Coastal Aquifer under Arid Climate. The Tadjourah Aquifer (Republic of Djibouti, Horn of Africa)

Razack

Jalludin²,

Houmed-Gaba³

2019

“…Seawater intrusion induced by groundwater development is also known in South America [21] and Australia [22]. In Africa, several cases of seawater intrusion into coastal aquifers have been reported [23] with case studies in Morocco [24][25][26], Tunisia [27], Algeria [28] and Dar es Salaam [29,30]. In Europe, seawater intrusion has been documented within many of the coastal aquifers, particularly along the North Sea [31,32] and the Mediterranean Sea and its eastern part in the archipelagos in the Aegean Sea [33][34][35].…”

Section: Overview Saltwater Intrusion Into Coastal Aquifersmentioning

confidence: 99%

Groundwater Overexploitation and Seawater Intrusion in Coastal Areas of Arid and Semi-Arid Regions

Alfarrah

Walraevens

2018

Self Cite

225

Abstract:The exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na + , K + , Mg 2+ , Cl − and SO 4 2− , which can be attributed to seawater intrusion, where Cl − is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 25 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high NO 3 − concentration in the region.

“…That is another reason why delineation of the freshwater aquifer boundary in coastal areas is of particular importance is to establish a baseline. Extreme climatic events, sea-level fluctuations, and increased groundwater abstraction from coastal aquifers disrupt the natural groundwater equilibrium condition, resulting in shifting of the freshwater/saltwater interface inland, toward the abstraction well, and seawater upconing and/or moving locally upward [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Geophysical Delineation of Freshwater–Saline Water Interfaces in Coastal Area of Southwest Bangladesh

Sarker¹,

Camp²,

Hermans³

et al. 2021

Self Cite

Insufficiency of potable water is acute in southwest (SW) coastal areas of Bangladesh. The local population ignores the depth to saltwater/freshwater interface causing many unsuccessful waters wells drilling. In this context, a combined use of borehole logs, geophysical well logs, vertical electrical soundings (VES), electrical resistivity tomography (ERT) and electrical conductivity (EC) of sampled waters was performed to identify saltwater/freshwater interface depths in this coastal part. The study shows that the depth to freshwater/saltwater interface varies from place to place occurring commonly between 190 to 285 m, and locally as shallow as 146 m. The shallow freshwater/saltwater interface depth is greatly influenced by the upconing of fresh water from the deep aquifer (DA) near the major rivers and coast compared to the landward part and is mixed with more saline waters above. Vertically infiltrated saltwater is the main cause of brackish water in the upper shallow aquifer (USA), which is hydraulically connected with the lower shallow aquifer (LSA), and not directly recharged from the Bay of Bengal in the south. The study will contribute to find out the depth of the potential freshwater aquifer and assess the aquifer vulnerability in the coastal area of SW Bangladesh.