Water resource situation of the Republic of Djibouti Omar ASSOWE DABAR Integrating Groundwater Management within River Basins 15-17 January 2019 Nairobi, Kenya Regional Training Workshop on
Introduction The Republic of Djibouti (23 000 km 2 ) is localized in the Horn Africa. 70% of the population live in urban areas, 58% live in the capital (Djibouti city). Djibouti is an arid country which receives, on average, 150 mm of rain annually and has no permanent source of surface water. Access to water in Djibouti is a major challenge for the development of socioeconomic activities. Harnessing surface and groundwater to improve access to drinking water for vulnerable populations is a Government priority 2
Geological situations Geological Setting The republic of Djibouti is one of several African countries located on the East African Rift System (EARS). About 90% of the geological formations are volcanic rocks and 10% are sedimentary formations. The groundwater in Djibouti is controlled by volcanic and sedimentary aquifers. Volcanic aquifers systems are mainly represented by the Dalha basalts, the stratoid basalts and the Mabla rhyolites. Dalha basalts sequence Coastal plain sediments 3
Climatological conditions Précipitation (mm) The Republic of Djibouti is characterized by arid to semiarid climate. Two seasons predominate : - Cool season (winter) from October to April (20 C and 30 C ) - Hot season (summer) from May to September (30 C and 45 C) with high rate of Evapotranspiration amounting to 2000 mm per year Précipitation trends (1960 1990) 350 HOLL HOLL 300 250 200 1960 1965 1970 1975 1980 1985 1990 180 170 DIKHIL 160 150 140 130 1960 1965 1970 1975 1980 1985 1990 Decrease in rainfall can be observed in different location. This could strongly impact groundwater recharge conditions and deteriorate the quantity and quality. 4
1.7 2.6 3.2 Volume annuel. Million m3 12.5 15.2 15.2 19.3 22.9 29.4 28.5 40.8 51.0 Groundwater situation Water resources demands Annual pumping rate millions m3/an 0 0.01 à 0.1 0.1 à 0.5 0.5 à 1 1 à 2 plus de 10 TADJOURAH!( OBOCK!( The extreme climate condition explains the lack of permanent rivers, and has led the country to exploit the only available water resources, which are represented by groundwater in the basaltic aquifer. The population of Djibouti relies heavily on groundwater resources for drinking water and irrigation purposes. 60 ARTA!( DJIBOUTI!( Rural (population+bétail) Urbain Agriculture 40 Total DIKHIL!( ALI SABIEH!( 20 0 2005 2010 2015 5
Water level m Cl- (mmol/l) Groundwater situation Groundwater degradations The continuous and severe increase of water demands, due to the rapid population growth, have led to overexploitation of groundwater, and have severely depleted its quantity and quality. 1984 1986 1988 1990 1992 1994 70 80 Mouloud 90 100 40 30 20 10 Djibouti 0 1960 1970 1980 1990 2000 6
Groundwater monitoring Surface water mobilisation : Surface water hydrology monitoring-early warning system-ambouli With the arid climatic regime, most watercourses in the Republic of Djibouti are temporary and run for only a few days after any rain event (wadis). Limnigraph 7
Geochemical characterization of the Bara volcano-sedimentary aquifer (Republic of Djibouti) : Case study The UNDP is financial supported a program for developing agro-pastoral as a climate change adaptation strategy for poor rural communities in the south-eastern part of the republic of Djibouti (Bara area). The context of this project is based on the settlement of a hundred families in this area. All boreholes are used for drinking purpose. The study area is located in the south-eastern part of the country. The Petit Bara and Grand Bara zones correspond to sedimentary basins limited to the East by the Dalha basalts (8.3 4.3Ma) and to thewest by the Stratoid basalts (3 1 Ma). Twenty two borehole waters were collected in this area and analysed. 8
Geochemical characterization of the Bara volcano-sedimentary aquifer (Republic of Djibouti) : Case study Groundwater Classification The groundwater have moderate to high EC values (from 957 to 4846 S/cm), temperature values between 27 and 43 C, and moderately alkaline ph ranging from 7.31 to 8.38. The Depth of the boreholes in this area ranges between 80 and 200 m Most of sampled groundwaters are brackish (10 g/l TDS 1 g/l) with the exception of several fresh waters (TDS 1 g/l) from North of Petit Bara (#1 #4), Grand Bara (Hambocto F1) and Dadin3. Samples Petit Bara Zone T ( C) Depth (m) ph EC (µs/cm) TDS PK48 36 133 7.75 956.9 666 PK50 38 90 7.97 1127 795 PK51 39 135 7.75 1204 811 Didjander 28 170 7.96 2876 1617 Omar Jakka 38 161 7.79 2958 2015 Naheel 39 155 6564 3668 Kourtimaley 37 165 7.8 7731 3254 Hydrochemical types Na-HCO 3 -Cl Na-HCO 3 -Cl Na-HCO 3 -Cl Na-Cl Na-Cl Na-Cl-Ca Na-Cl-Ca Grand Bara Zone Awraoussa 1 36 195 7.81 2692 1842 Na-Cl-Mg-Ca-SO 4 Iskoutir 32 181 7.81 3258 2363 Na-Cl-Ca-SO 4 Gabla-galan 27 156 8.38 2200 1519 Na-Cl-HCO 3 -SO 4 Hambocto F2 35 190 7.26 1896 1329 Na-Cl-Mg-Ca-HCO 3 Hambocto F1 38 150 7.31 1464 988 Na-Cl-Mg-Ca-HCO 3 Doudoub Bololé F2 36 103 7.62 2337 1576 Na-Cl-Mg-SO 4 Doudoub Bololé F1 41 93 7.48 4143 3173 Na-Cl-Mg-SO 4 Dagandalol 43 113 7.8 2871 1879 Na-Cl-SO 4 Dagaah-damere 39 170 7.71 4846 3484 Na-Cl-Mg-Ca-SO 4 Mouloud-Dadin Zone Mindil 36 80 7.46 2630 1824 Mouloud C 39 115 7.49 3035 2075 Mouloud 4 39 140 7.33 2880 1965 Dadin 3 34 139 7.43 1388 980 Na-Cl-Mg-SO 4 Na-Cl-Mg-SO 4 Na-Cl-Mg-SO 4 Na-Cl-HCO 3 9
Geochemical characterization of the Bara volcano-sedimentary aquifer (Republic of Djibouti) : Case study Groundwater Classification Using statistical method (PCA and HCA) The geochemical data were classified into distinct groups according to the common variables they share using 13 variables (ph, EC, TDS, Ca 2 +, Mg 2 +, Na +, K +, HCO 3-, Cl -, SO 4-, F -, NO 3-, Br - ). Ca Mg Na K Li NH 4 HCO 3 Cl SO 4 NO 3 F Br NO 2 Site Petit Bara Zone PK48 26.75 22.74 151.6 4.1 0.017 0.01 347.84 100.09 65.65 12.43 0.825 0.41 0.006 PK50 24.9 22.19 187.66 4.36 0.04 DL 352.87 146.99 77.92 17.73 0.705 0.715 DL PK51 23.1 21.07 222.9 4.34 0.01 DL 307.88 189.05 88.86 14.81 0.78 0.85 0.003 Didjander 88 63.18 383.99 18.45 0.9 0.13 237.09 609.5 197.62 32.49 0.01 2.88 0.033 Omar Jakka 89.95 68.86 435.67 8.45 0.022 DL 218.97 697.75 234 54.31 0.425 2.69 0.002 Naheel 215 231 852 11 0.2 0.43 95 1987 608 119 0.9 1.74 0.08 Kourtimaley 368 165 1080 32 DL DL 61 2410 572 122 0.245 1.78 0.008 Cluster 1 Cluster 1 contains six samples that characterize waters with low mineralization (805 EC (μs / cm) 1464). This group corresponds to Na- Cl-HCO 3 water type. (South petit Bara and Dadin) Grand Bara Zone Awraoussa 1 116.96 65.9 321.24 11.65 0.041 DL 140.76 519 295 71 0.64 2.59 DL Iskoutir 145.73 65.19 440.13 8.165 0.015 DL 100.94 818.47 319.19 50.76 0.28 3.5 0.009 Gabla-galan 36.17 50.32 382.5 7.94 0.037 0.13 235.06 356 192.93 247.48 0.385 2.26 DL Hambocto F2 115 66.78 169.53 4.98 0.0103 DL 209.68 269.19 131.17 255.67 0.595 2.35 DL Hambocto F1 58.37 38.69 185.97 4.08 0.01 DL 239.72 249.78 112.53 49.83 1.01 1.27 DL Doudoub Bololeh F2 70.97 61.92 327.53 7.65 0.0175 DL 166.09 517.22 240.18 55.075 0.675 2.085 DL Doudoub Bololeh F1 165 134.78 507.45 13.13 0.03 DL 107.71 1120.4 418.7 59.11 0.61 4.125 DL Dagandalol 88.54 57.43 453 8.26 0.037 DL 213.31 572.09 334 142.02 0.885 2.5 DL Daagah-damere 199.28 123.44 653 15.30 DL 0.8 95 1271.5 486.5 62 0.09 5.29 0.21 Mouloud Zone Mindil 55.11 92.56 361.21 9.75 0.015 DL 283.67 481.35 301.09 47.3 0.52 2.51 DL Mouloud C 82.15 79.79 442.92 10.94 0.015 DL 188.86 686.89 336.51 79.6 0.425 2.73 DL Mouloud 4 96.52 92.21 377.29 8.31 0.028 DL 177.47 625.53 329.03 75.78 0.615 2.56 DL Dadin 3 46.96 26.37 217.5 5.07 0.03 DL 443.57 157.32 102.89 33.82 1.51 0.4 0.07 Cluster 2 Cluster 2 contains twelve different water samples characterized by moderate mineralization. (Grand Bara-Mouloud) Cluster 3 Cluster 3 contains four different water samples characterized by very high mineralization (4143 EC (μs / cm) 7731). This group correspond to Na-Mg- Cl-SO 4 water type (between GB and PB). 10
Geochemical characterization of the Bara volcano-sedimentary aquifer (Republic of Djibouti) : Case study Groundwater Contaminations Some of the groundwater analyzed present high nitrate concentration (up to 50 ppm ; WHO). The lowest values are found in Petit Bara and Dadin, while the highest values are found in Grand Bara (up to 250mg/L in alluvium groundwaters from boreholes #13 and #18; up to 150 mg/l in basalt groundwaters from #11 and #12) and in the central area (up to 120 ppm in #7 and #8). It should be noted that people living in the Republic of Djibouti are mostly nomad, and hence have no agricultural tradition. The local nomads, who raise goats and cheeps, do not have a fixed settlement, hence not septic tanks. Therefore, in many cases, natural soil might contribute mainly for nitrate concentrations in the study area as observed in some semi-arid or arid regions over the world. 11
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