Translated Into English by Mr.TEMZI Mehdi
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Translated into english by Mr.TEMZI Mehdi STUDY OF WATER QUALITY IN NORTH-WEST ALGERIA (CASE OF UPPER CHELIFF BASIN) TOUHARI FADHILA ** Higher National School for Hydraulics Blida-ALGERIA Abstract Surface water and groundwater are important and essential resources in many countries and often play a key role in water supply both for drinking and irrigation. During the last decades, water demand has significantly increased, especially in developing countries, because of population growth, improvements in standard of living, development of industry, agriculture and because of urbanization. This has led to increasing pressures on groundwater resources. Excessive abstractions of groundwater over the past decades to meet these demands have resulted in serious troubles: decrease in the level of water-table, groundwater quality degradation and ecosystems deterioration. It is, therefore, essential to quantify and analyze the quantity and quality of water reserves and to find ways to manage this resource in order to ensure sustainability thereof. The main aim searched for in this context is to get to study the quality of groundwater and surface water in the Upper Cheliff region. The aims of our study are as follows: Give an overview into quality parameters and into methodology of the study for underground and surface water. Location and presentation of the study area and its characteristics as well as analysis of the key climate and hydrologic conditions. Stress the natural geologic and hydrologic setting and the piezometry with regard to the chemical quality. Assess then the quality of surface water through quality charts achieved and their interpretations for each dam. The study of chemical parameters evolution in the time and space, by addressing mechanisms of the acquisition of the groundwater mineralization. Our efforts will also concern the dependencies and relationships between the various physical and chemical parameters of the water and origins thereof. Identify the pollution sources and their impacts on the Upper Cheliff underground water * D o c t o r a l thesis of Sciences. ** Thesis advisor: Mr.MEDDI Mohamed, Professor – E.N.S.H BLIDA. Introduction Water can be scarce in some places, such as arid and semi-arid, or may be quite simply of poor quality in other places. It is certain that the increase in water demand for human activities will 1 Translated into english by Mr.TEMZI Mehdi accentuate the constraint on this resource. In addition, natural factors such as drought or geological constraints affect the drinking water supply and distribution. In this context, this study adds to earlier researches, and this to provide a scientific overview, qualitatively and quantitatively, of the current state of the upper Cheliff area. The quality of waters of this region has undergone, in recent years some, deterioration because of uncontrolled urban waste, intensive use of artificial manures and fertilizers in agriculture and its disorderly utilisation. These elements alter the chemistry of the water and make it unsuitable for desired uses. It is in this context that this study was conducted in order to analyze the quality of water at the aforesaid region. I. Presentation of the study area The study area corresponds to the Upper Cheliff basin, and is located 110 km South-West of Algiers, and is part of the Cheliff drainage basin (Figure 01). The upper Cheliff area is an agricultural vocation requiring sprinkler irrigation due to a semi-arid continental climate with very dry summers (interannual temperature fluctuates from 13 to 19°C, with a monthly maximum of more than 30 °C recorded in July) and rainfall winter episodes sometimes causing spectacular flooding of Cheliff wadi. The building of dams (Ghrib, Deurdeur, Harreza and Sidi Mhamed Ben Taiba and Ouled Mellouk) enabled the control of the wadis’s flows and the provision of irrigation water from April to September. Interannual average pluviometry varies between 300 and 500 mm. It is more concentrated in altitudes on the south slopes of Zaccar and on the north slopes of the Ouarsenis. Across the Upper Cheliff basin, annual potential evapotranspiration ranges from 1,200 to 1,500 mm according to the map of potential evapotranspiration in northern Algeria Figure 1: Location map of the Upper Cheliff catchment basin. II. Geology and Hydrogeology of the Upper Cheliff area 2 Translated into english by Mr.TEMZI Mehdi The Upper Cheliff plain is located between 36° 12' and 36° 30' North latitude and 02° 02' and 2° 44' East longitude. It is bordered to the North by the dolomitic limestone of Jebel Zaccar (1,578 m altitude) and the sandstones of Jebel Gantas, to the South by the first foothills of the clayey-marly and sandstone Ouarsenis massif (figure 02). One enters the plain at the East by the Djendel sill at 308 m and comes out at the West by the Doui sill at 248 m a.s.l. (Mania, 1990). The plain of Upper Cheliff corresponds to a vast depressed and subsiding area with East-West orientation where Miocene, Pliocene and Quaternary sediments have accumulated. The cross lithological sections done in the plain of Upper Cheliff, show the synclinal attitude of different formations constituting the sub-soil. M e d i t e r r e a n S e a . T u n i s i a i T u n i s M o r o c c o A l g e r i a Figure 02: Simplified geological map according to the 1/50.000 of Miliana. Further to the piezometric campaigns conducted in high and low water in 2002 and 2008, we found that piezometric maps show the same morphology and the same attitude of piezometric curves. The groundwater flows are from the borders towards central axis of the valley before taking a East-West direction in a parallel to the main river of Cheliff wadi, but with a certain increase in piezometric level due to ground water recharge following a high annual pluviometry during 2008. However, we notice that there is a certain local disturbance at the central and southern area of the plain in 2008, due to the ground-water overdraft to ensure irrigation. 3 Translated into english by Mr.TEMZI Mehdi Figure 03: Figure 03: Water-level map in period of High water and low water, 2002. III. Quality of surface water This work will be the subject of a quality assessment study of dams’ waters on the basis of the monitoring of physical-chemical parameters, which is provided by the National Agency for Water Resources (ANRH) for a-10 year period (1999-2008). We give, first, the state of the dam’s water quality when the latter is equipped with a monitoring network, then, the origin and the amount of pollution received by each catchment area of the dam. Monitoring and evaluation of the qualitative status of water require a measurement network of water quality, regular analyzes, interpretation of those analyzes and a comparison of results with accepted quality standards. The study for the water quality of Upper Cheliff dam will deal with the five (05) operating dams Ghrib, Deurdeur, Harreza and Ouled Mellouk. These dams are monitored for water quality through the existence of ANRH monitoring stations. Figure 04: Index of annual average quality of Ghrib Dam water (1999-2008) 4 Translated into english by Mr.TEMZI Mehdi The importance and severity of pollution are confirmed by the results observed in the study of the surface water quality in the region of Upper Cheliff, namely: • Water quality records show a degradation of the aforementioned quality for all dams (an organic pollution expressed in COD) over time. In actual fact, the recorded quantity of COD often exceeds 50 mg / l, and that of the OM also exceeds 15 mg / l. This pollution is due to wastewater disposal and eutrophication process. • Water dams show a very high salinity (dry residue = 2,574 mg / l in 2008 for Ghrib dam waters, + - standard = 1,500 mg / l). The content of nitrogen substances in waters (NH4 , NO2 ) in 2008 is high in O. Mellouk dam. This pollution is due to oxidation of the nitrogenous organic material. • The polluting load reaching catchment areas of the dams is characterized by the polluting load of breeding establishments firstly and by its high value in almost all catchment areas secondly. IV. Hydrogeochemical groundwater characterization This chapter deals with groundwater chemistry and will enable us trying to explain the behavior, the origin and the evolution of chemical elements described for the explanation of hydraulic functioning of geohydrologic unit. The study is mainly based on information from four (04) sampling campaigns, achieved from 47 watering places in 2002, and 50 watering places in 2008, all the places are spread over the territory. As the plain of Upper Cheliff is agricultural, a particular interest will be given to the plain. Figure 05: Ground-water inventory of the Upper Cheliff plain. Pearson correlation matrix (Swan and Sandilands 1995) was used to find relationships between two or many elements. The analysis of the correlation matrix (Table 01) can retain the correlated elements in pairs with a significant correlation coefficient (r). It is noted that in 2002, the R.sec is perfectly correlated with calcium (R = 0.78), magnesium (R = 0.75), sodium (R = 0.85), chlorides (R = 0.94) and sulphate (R = 0.69). On the other hand, there was a slight increase in correlation coefficients in 2008 for calcium and magnesium ions. Table 01: Correlation matrix between variables. 5 Translated into english by Mr.TEMZI Mehdi 2+ 2+ + + - -2 - - Variables Ca Mg Na +K Cl SO4 HCO3 NO3 R.Sec Ca2+ 1 Mg2+ 0.79 1 Na++K+ 0.33 0.43 1 Cl- 0.77 0.76 0.80 1 -2 SO4 0.38 0.57 0.61 0.46 1 - HCO3 0.17 0.10 0.24 0.13 0.14 1 - NO3 0.04 -0.06 -0.32 -0.16 -0.40 -0.09 1 R.Sec 0.75 0.78 0.85 0.94 0.69 0.26 -0.20 1 The highest concentrations of these elements are found south of the plain, on the left bank of Cheliff wadi, and near the towns of Djendel, Bir Ouled Khelifa and Djelida.In fact, the discharging of domestic waste water from agglomerations which are situated in the plain (17 discharges points) and estimated at 15,000 m3 /d, without this water being treated beforehand, affects adversely the quality of groundwater.