by Mansour GUEYE, Abdoul Aziz GNING, Fatou NGOM DIOP and Raymond MALOU
Original Research
The drought that began in the Sahel in the late 70s has led to a drying up of most surface water bodies and a decrease of ground water level. In the north coast of Cap-Verde, the Retba lake is one of the few depressions that have preserved its water and experienced all the same, a very important salinization. This saline ecosystem plays an important role in the economy of the area due to the exploitation of salt deposits. However, it is now threatened by a significant reduction of the water surface. Its backup requires a good knowledge of the environment and the interactions between the different reservoirs, namely the lake, groundwater and ponds. To study the relationship between different parts of the hydro system, a network, monitoring the groundwater table including 41 village wells across the watershed, has been established. All observation points and the level of the lake were leveled with the reference 0 IGN. Water samples were taken at the wells, lake and ponds and source for chemical analysis. The results of the altimetric study indicated that the lake is below sea level, at odds of -5.26 m and a good part of the watershed is under the level of the sea. Hence its vulnerability of being invaded by the ocean water due to the difference in altitude. Water table monitoring shows different movements from one point to another due to the interference of several factors in the process of charging and discharging of the water table. Thus, some wells are only under the influence of climate parameters (rain and evaporation), while others are fed or drained by lateral flow. Water chemistry is dominated by two chemical facies: calcic and chloride facies (Ca-cl) and sodium chloride-facies (Na-Cl). Na and Cl ions control mainly the mineralization water and cationic exchange is the main factor controlling water chemistry even if other processes such as anthropic pollution could occur. These cationic exchanges reflect the intrusion of seawater into the sand aquifers. These results also show that in the late dry season, water ponds have a chemical signature very close to seawater. This shows that the ponds that are in the north of the lake is an outcrop of the Sea that feeds the lake permanently. The lake water is a mixture of seawater and groundwater whose evaporation causes sedimentation of salt exploited by local people. Monitoring of the groundwater level, the lake level and the chemical analysis shows a connection between the lake, the groundwater, the ocean and ponds.
American Journal of Water Resources. 2016, 4(4), 91-101. DOI: 10.12691/ajwr-4-4-3
Pub. Date: October 31, 2016
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by V. U. Nkemdirim, G. C. Alozie and Ike Felix
Original Research
The importance of potable water has been documented by many researchers. However, one major challenge in Nigeria is the ability for both rural and urban areas to access a clean water supply. This study examined the spatial analysis of the quality of groundwater supply in selected urban centres of Abia State. To achieve this, 13 borehole water samples were collected using purposive sampling technique. The parameters tested include; Temperature (°C), pH value, Electrical conductivity (µs), Total suspended solids (mg/l), Biological Oxygen demand (BOD),Turbidity (NTU), Sulphate (So4), Chloride (Cl), Nitrate (No3), Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Zinc (Zn), Iron (Fe) Copper (Cu) and Lead (Pb). The results of the water samples were compared with the WHO quality standards. The analyses revealed that the quality of water supply is inadequate. For instance, temperature in all the sampled sites ranged from 27.1°C - 29.7°C which is above the WHO value of 26.6°C, while the pH values (5.79 - 6.81) were lower than the WHO value of 7 – 8.5, indicating mildly acidic. Similarly, electrical conductivity, total suspended solids, biological oxygen demand, sulphate, nitrate, and chloride values were all below the WHO values. All the hypotheses were tested using analysis of variance. It was observed that significant variations exist between Ohafia and Umuahia, Ohafia and Aba, but no significant difference exists between Umuahia and Aba. Thus, the null hypothesis (H0) was accepted in all, that “there are no significant variations in the physicochemical content as regards the sampling points in the zones. The study recommends amongst others that water should be boiled before use, or through the use of alum, water guard, or through disinfection with the use of chlorine.
American Journal of Water Resources. 2016, 4(4), 83-90. DOI: 10.12691/ajwr-4-4-2
Pub. Date: October 09, 2016
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by Stanley K. Maloi, Joseph K. Sang, James M. Raude, Urbanus N. Mutwiwa, Bancy M. Mati and Caroline W. Maina
Original Research
Reservoir sedimentation can adversely affect the storage capacity of water bodies; reduce flood attenuation, change water quality, damage valves and conduits amongst others. This study investigated sedimentation rate in Ruiru reservoir as a measure for monitoring water resource management using capacity survey method. Water depth was measured using a transducer fitted on the side of the boat which also recorded corresponding geographic positions with an inbuilt GPS receiver. About 5000 points covering approximately 36 hectare of the water surface were surveyed. A total of eleven sediment sampling points were identified in the reservoir in which five were strategically selected at location near entry from respective streams. The depth of sediments, which relate to the quantity of sediment deposition from the streams ranged between 600 mm and 2100 mm. Ruiru stream demonstrated the highest level of sediment influx into the dam while Ngeteti stream had the least. The reservoir volume was calculated to be 2,632,347m3 and estimate volume of the sediments 389,245 m3, which is a 13.1% storage capacity loss. A related recent study noted storage capacity loss of 11%, which shows that the reservoir has lost about 11-14% of its storage capacity in 65 years. Results further showed that the Area Specific Sediment Yield (ASY) was 38.84 Mg ha-1 y-1, which is higher than the tolerable soil loss of 2 to 18 Mg ha-1 y-1 for the tropics, but is within the range of 10 - 200 Mg ha-1 y-1 typical of savanna ecosystems. These findings are useful to water resource managers because they can help in computing the useful life of a reservoir.
American Journal of Water Resources. 2016, 4(4), 77-82. DOI: 10.12691/ajwr-4-4-1
Pub. Date: September 29, 2016
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