Water resource situation of the Republic of Djibouti

Transcription

1 Water resource situation of the Republic of Djibouti Omar ASSOWE DABAR Integrating Groundwater Management within River Basins January 2019 Nairobi, Kenya Regional Training Workshop on

2 Introduction The Republic of Djibouti ( 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

3 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

4 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 ( ) 350 HOLL HOLL DIKHIL Decrease in rainfall can be observed in different location. This could strongly impact groundwater recharge conditions and deteriorate the quantity and quality. 4

5 Volume annuel. Million m Groundwater situation Water resources demands Annual pumping rate millions m3/an à à 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!(

6 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 Mouloud Djibouti

7 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

8 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 ( Ma) and to thewest by the Stratoid basalts (3 1 Ma). Twenty two borehole waters were collected in this area and analysed. 8

9 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 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 PK PK PK Didjander Omar Jakka Naheel Kourtimaley 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 Na-Cl-Mg-Ca-SO 4 Iskoutir Na-Cl-Ca-SO 4 Gabla-galan Na-Cl-HCO 3 -SO 4 Hambocto F Na-Cl-Mg-Ca-HCO 3 Hambocto F Na-Cl-Mg-Ca-HCO 3 Doudoub Bololé F Na-Cl-Mg-SO 4 Doudoub Bololé F Na-Cl-Mg-SO 4 Dagandalol Na-Cl-SO 4 Dagaah-damere Na-Cl-Mg-Ca-SO 4 Mouloud-Dadin Zone Mindil Mouloud C Mouloud Dadin Na-Cl-Mg-SO 4 Na-Cl-Mg-SO 4 Na-Cl-Mg-SO 4 Na-Cl-HCO 3 9

10 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 PK PK DL DL PK DL Didjander Omar Jakka DL Naheel Kourtimaley DL DL 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 DL DL Iskoutir DL Gabla-galan DL Hambocto F DL DL Hambocto F DL DL Doudoub Bololeh F DL DL Doudoub Bololeh F DL DL Dagandalol DL DL Daagah-damere DL Mouloud Zone Mindil DL DL Mouloud C DL DL Mouloud DL DL Dadin DL 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

11 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

12 Thank you