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Problem of Salinity in Coastal Aquifers of Tunisia University of Hawaii, Manoa Honolulu, April 2, 2015 DR. MOHAMED FETHI BEN HAMOUDA Fulbright Visiting Scholar Division of Earth and Ocean Sciences Duke University, NC, USA CNSTN, Isotope Hydrology and Geochemistry Unit, Tunisia 1 Kelibia Beach, Tunisia Coastal Zones WR Strategic variable Population availability growth Agriculture WR Industry And Tourism Population Severe and irregular increasingly urban and Climate concentrated along the coast Increasing water demand OVEREXPOITATION PIEZOMETRIC DROP INCREASE OF WATER SALINITY 2 Causes of salinisation of aquifers? Natural and anthropogenic Water Air Pollution Vapeur Waste water Mines Drainage Acid Industrial dump rain Evaporation Continental Evaporites Surface Water Infiltration, Evaporation Pumping Water irrigation return Irrigation Seawater Groundwater Salinisation Geothermal Water Dilution /mixing Magmatic Rocks Sedimentary brines Primary Secondary Dissolution of mines wastes Marin Evaporites 3 What are the Consequences? Economic and social Loss of fresh water: water-quality degradation Environment: Loss of biodiversity: replacement by halotolerant species Human health: inorganic pollutants: Nitrates, Arsenic, Selenium, Boron and radioactivity Loss of fertile soils Collapse of agricultural Immigration, exodus to the cities 4 Geochimical and et Isotopic tools Tracers of salinity Cations (Ca, Mg, Na, K) Anions (Cl, SO4, Br, NO3) stable and radioactive 18O, 2H, 13C, 3H, 14C Isotopes 5 Problem of salinity in four coastal aquifers Sampling and Djeffara: 29 measurement Sousse: 30 Côte orientale: 47 El Haouaria :35 6 Climate and Hydrology Sub humid to Semi arid and arid climate Mediterranean Mild winter )16°C ( Hot summer ) 30°C( P= 570, 440, 320, 180 mm/a ETP = 1100, 1750, 1300 mm/a • No perennials rivers • Small rivers carry water • Intense storm cause surface runoff • O. Laya and wadi akarit major wadis reaching the coast • The wadis discharge into Hydrographic network and salty lakes Isohyetes Map of Tunisia 7 Evolution Evolution of exploitation Débit (l/s) 2500 3000 3500 4000 4500 2000 1950 1952 Exploitation 1954 1956 1958 1960 ( 1962 1950 1964 of 1966 - Djeffara 2003 1968 1970 ) 1972 1974 aquifer 1976 1978 1980 La Nappe profonde de la Côte Orientale 1982 Djeffara-Gabès Expl-Djeffara 1950-2003 (l/s) 1984 6 1986 120 1988 Nb de forages 5 1990100 Exploitation 4 199280 1994 3 60 (Mm3) 1996 (Nbdeforage) 2 199840 2000 1 20 2002 0 0 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 La Nappe profonde d'El Haouaria Djeffara plain Djeffara El Haouaria plain HaouariaEl Eastern Eastern Coastal 6 60 5 50 4 40 3 30 (Mm3) (Nb de forage) 2 20 Nb de forages 1 10 Exploitation 0 0 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 8 Evolution of piezometry in El Haouaria plain 18 16 P41 Average: 3.38 m 14 P42 12 10 8 N.P (m) N.P 6 4 2 0 juin-72 juin-77 juin-82 juin-87 juin-92 juin-97 juin-02 juin-07 11 % Années This decrease ranges from 1 to more than 14 m according to the location of the well 4 average: 2.83 m 8862 2 8894 0 -2 N.P (m) N.P -4 -6 5 % -8 juin-72 juin-77 juin-82 juin-87 juin-92 juin-97 juin-02 juin-07 Années Continued decline of piezometry 1 to over 11m Métouia 6 (N°IRH ) 26 Reducing artesian 25 pressure 24 Depletion wells 23 22 Springs dry NP (m) 21 20 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1960 9 Consequences 6 8684 P19 9 892 8315 5 4 3 RS (mg/l) RS 2 1 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Années Temporal evolution of the salinity (g / l) at the Eastern coastal aquifer 10 Geological and Hydrogeological setting Geological block diagram at the Cap Bon (Ben Hamouda et al, 2011) Miocene and Oligocene outcrop in Jebel Sidi Abderrahmane Pliocene and Quaternary outcrop near the coast at the Eastern shallow aquifer Quaternary covers the plain of El Haouaria 11 Shallow unconfined Deep confined Hydrogeologic cross section SW-NE (Ben Hamouda et al, 2013) 12 Djeffara Four aquifers levels Shallow: Quaternary (Pontien) Miocene sands Senonian limestone Continental Intercalaire Hydrogeologic cross section in Djeffara aquifer (Ben Hamouda et al, 2013) 13 North-western Sahara Aquifer System NWSAS Great Oriental Erg 2.5 billion 3m in 2000 to 7,8 billion 3m in 2050 14 15 The « Continental Intercalaire » (C.I.) aquifer 1200 km 0 m -1 km -2 km 16 17 Piezometric Maps Kelibia El Haouaria Mer Méditerranée Sidi Daoud Dar Allouch Korba Km Azmour Mer 0 2 4 Méditerranée Quaternary aquifer Nabeu l Characterized by a grounwater divide Plio-quaternary aquifer Flow south and north Main flow: O-E toward the center of the plain and Alongside wadis moves towards the east and west and towards the sea 18 Oued Laya Aquifer Djeffara aquifer Groundwater flow Groundwater flow towards the sea towards the sea Groundwater is recharged by rain and runoff and from a vertical leakage (up flow) from Djeffara 19 Continental intercalaire Main flowpaths under the Great Oriental Erg 20 Salinity map : Eastern Coast El Haouaria plain Kelibia Kelibia Mer Méditerranée El Haouaria Menzel Temime Sidi Menzel Horr Daoud 10 Dar Allouch Tafelloune 8 Korba Mer Méditerranée Mer Méditerranée Azmour Korba Quaternary aquifer Béni Khiar Nabeul High salinity level at Haouaria (depression area) 5-6 g/l Nabeul Plio-quaternary aquifer Near the coast, Salinity 2 to 3 g/l, littoral High salinity in Korba Tafelloune barrier 6-8 g/l, 20 to 30 g/l 21 Salinity map O. Laya Salinity map nothern Djeffara Salinity varies from 2 to 10 g/l Salinity varies from 3 to 8 g/l 22 Estimation of the mixing with seawater using chloride as a conservative tracer (Barbecot, 1999) Cl Cl F sample fresh Clsea Cl fresh F sea is fraction of Seawater (0<F<1) 23 Kelibia the % SW 1 à 30 % Max of SW is 70 % (13143/2) 66 % in the 11186/2 3 % in the 11829/2 Heterogeneity of Mer Méditerranée processus Of salinisation H: P 31 & P34, F< 1 % Korba Confirmation absence of Seawater intrusion Nabeul Map of Estimation of mixing with seawater (%) 24 Piper Diagram Mixted chemical profile Na-Cl and Ca-Cl water type Anions: Cl> SO4 et HCO3 Cations: Na> Mg et Ca Wells whose waters are contaminated by seawater are turning into Ca-chloride water, different from seawater (NaCl water type). 25 The [Na+]/[Cl-] relationship Indicates contribution of Halite dissolution to the mineralisation GW 140 marine ratio Halite Djeffara 120 Sousse Haouaria Côte Orientale 2 parallel trends 100 Na/Cl > 1 reflecting 80 Income of Na to GW system Na (meq/l) 60 WRI 40 Ion exchange 20 Na –Ca Clay minerals 0 0 20 40 60 80 100 + O.M Seawater intrusion: Chloride (meq/l) Na/Cl<sw Na is retained and Ca is released 26 The [Br-]/[Cl-] relationship A distinctive geochemical fingerprint 1.0E-02 Seawater Br/Cl=sw 8.0E-03 Haouaria Seawater intrusion Côte Orientale 6.0E-03 Sousse Relationship not distinctive 4.0E-03 Br/Cl (molar) 2.0E-03 Sea spray Influence on the infiltrated 0.0E+00 0 10 20 30 40 50 60 70 80 90 100 rain water Chloride (meq/l) Brine contamination 27 The SI gypsum / SO4 relationship Precipitation, 1 disolution and 0.8 Ion exchange 0.6 0.4 0.2 0 0 10 20 30 40 50 60 70 80 90 100 Water is -0.2 unsaturated -0.4 Gypsum Djeffara -0.6 Vs. gypsum SI -0.8 Sousse and anydrite -1 Haouaria -1.2 Côte Orientale Progressive -1.4 Saturation Vs -1.6 increase in -1.8 -2 SO4 SO4 (meq/l) 28 High salinity linked to the geology : presence of gypsum XRD Spectrum of gypsum found in the geologic formations 29 2 18 Isotopes Stables ( H, O) 1st group: -1 ‰ < 18O < -4 ‰ -8 -7 -6 -5 -4 -3 -2 -1 0 0 Probable seawater Mixing line with sea water intrusion -10 nd -20 2 group: Recent Water 18 SMOW -4 ‰ < O< -5 ‰ - Old water Recharge from -30 H (‰)V 2 rainwater d Shallow Eastern Coast Global meteoric water line GMWL -40 rd Local meteoric line of Tunis Carthage 3 group Deep Eastern Coast : -4.9 < 18O< -6 Djeffara Shallow Haouaria -50 Fingerprint of old Deep Haouaria water. Sousse Paleowater -60 th d18O (‰) V-SMOW 4 group: Paleowater from CI and Djeffara 2 18 Plot of d H ‰ Vs. d O ‰ (V-SMOW) 30 Relation 18O/[Cl-] 100000 Marine pole Seawater (SMOW, 19500) 10000 Paleowater Recent water Sal: SWI + Evap. 1000 Rain water (mg/l) (-4.4 ‰,10) Shallow Eastern Coast Recent water (300, Chlorides 100 Old water Deep Eastern Cost 2000 mg/l) Sea water Tunis-Carthage rain 10 Shallow Haouaria Sal: WRI + C. Exch Deep Haouaria Tunis-Carthage Sousse rain pole Djeffara Old water 1 -8 -7 -6 -5 -4 -3 -2 -1 0 (100, 400 mg/l) d18O (V-SMOW) Paleowater (1000, 3000 mg/l) Relation entre Cl- et d18O ‰ (V-SMOW) Diss. Halite 31 12,0 Plio quaternaire Miocène 10,0 Plot of Tritium Vs Chlorides Oligocène Eau post-nucléaire 8,0 3 6,0 Le H identify differents water types : Eau récente 4,0 Tritium (U.T) 2,0 Group post-nuclear Eau ancienne 0,0 Low content in Cl 0 500 1000 1500 2000 2500 3000 3500 4000 Fast infiltration in the rivers Chlorures (mg/l) 12.0 Group recent water Recharge durind last 10.0 Quaternaire decade Eau post-nucléaire Pliocène 8.0 High salinity 6.0 Group Old water Tritium (UT) Tritium Eau récente 4.0 3H (<1 UT) 2.0 Eau ancienne 0.0 0 500 1000 1500 2000 2500 3000 Chlorures (mg/l) 32 (3H et 14C) 6.0 1000 GAB 4 GAB 10a 5.0 100 GAB 14 GAB 15 MRT (years) MRT 4.0 10 GAB 21 0.1 1 10 all others Tritium (TU) 3.0 H (TU) 3 2.0 1.0 0.0 -8.00 -7.00 -6.00 -5.00 -4.00 -3.00 -2.00 Oxygen-18 )‰( Correlation between tritium and δ18O in Djeffara aquifer Map of distribution corrected ages in Oued Laya aquifer indicator of recent recharge The coastal zone is an area of recent and renewable water.