Recharge-discharge relations of groundwater in volcanic terrain of semi-humid tropical highlands of Ethiopia : the case of Infranz Springs, in the Upper Blue Nile

The major springs in the Infranz catchment are a significant source of water for Bahir Dar City and nearby villages, while sustaining the Infranz River and the downstream wetlands. The aim of the research was to understand the hydrogeological conditions of these high-discharge springs and the recharge-discharge relations in the Infranz catchment. The Infranz catchment is covered by highly pervious and young quaternary volcanic rocks, consisting of blocky, fractured, and strongly vesicular scoriaceous basalt. At the surface, these rocks crop out as lineaments forming ridges, delimiting closed depressions in which water accumulates during the rainy season without causing surface runoff. Geology and geomorphology thus combine to produce very favorable conditions for groundwater recharge. Three groundwater recharge methods were applied to estimate groundwater recharge and the results were compared. Groundwater recharge was calculated to be 30% to 51% of rainfall. Rapid replenishment raises the groundwater level during the rainfall period, followed by a rapid decline during the dry season. Shallow local flow paths discharge at seasonal springs and streams, while more regional and deeper flow systems downstream sustain the high-discharge springs and perennial Infranz River. The uptake of 75% of spring water for the water supply of Bahir Dar City, local extraction for domestic and small-scale irrigation use from springs, rivers and hand-dug wells, encroaching farming, and overgrazing are exacerbating wetland degradation

Evaluation and application of multi-source satellite rainfall product CHIRPS to assess spatio-temporal rainfall variability on data-sparse Western margins of Ethiopian Highlands

The spatio-temporal characteristic of rainfall in the Beles Basin of Ethiopia is poorly understood, mainly due to lack of data. With recent advances in remote sensing, satellite derived rainfall products have become alternative sources of rainfall data for such poorly gauged areas. The objectives of this study were: (i) to evaluate a multi-source rainfall product (Climate Hazards Group Infrared Precipitation with Stations: CHIRPS) for the Beles Basin using gauge measurements and (ii) to assess the spatial and temporal variability of rainfall across the basin using validated CHIRPS data for the period 1981-2017. Categorical and continuous validation statistics were used to evaluate the performance, and time-space variability of rainfall was analyzed using GIS operations and statistical methods. Results showed a slight overestimation of rainfall occurrence by CHIRPS for the lowland region and underestimation for the highland region. CHIRPS underestimated the proportion of light daily rainfall events and overestimated the proportion of high intensity daily rainfall events. CHIRPS rainfall amount estimates were better in highland regions than in lowland regions, and became more accurate as the duration of the integration time increases from days to months. The annual spatio-temporal analysis result using CHIRPS revealed: a mean annual rainfall of the basin is 1490 mm (1050-2090 mm), a 50 mm increase of mean annual rainfall per 100 m elevation rise, periodical and persistent drought occurrence every 8 to 10 years, a significant increasing trend of rainfall (similar to 5 mm year(-1)), high rainfall variability observed at the lowland and drier parts of the basin and high coefficient of variation of monthly rainfall in March and April (revealing occurrence of bimodal rainfall characteristics). This study shows that the performance of CHIRPS product can vary spatially within a small basin level, and CHIRPS can help for better decision making in poorly gauged areas by giving an option to understand the space-time variability of rainfall characteristics

Hydrogeochemical and trace element contamination investigation, Northern Ethiopia, Asgeda Tsimbla Sub catchment area, And its implications to recent chronic liver disease

Chronic liver disease is recently becomes the most sever disease to residents of northern Ethiopia (Shire area) which was started 1980. Pervious health study reviles that this liver disease is not caused by virus and there is a fear that it can be caused by toxic chemical pollutants from the water they used to drink. Therefor the main objective of this study is to identify which geochemical elements cause this disease and its associations, to map their spatial distribution and lithological associations, to see how using compositional data analysis improves analyzing association within geochemical elements as compared to normal (classical) statistical method and to simulate how nitrate and carbon from the recent fertilizer practice can change the dissolution rate of trace elements by changing redox system of aquifers. During filed work 16 water 16 soil and 14 rock samples were collected. Chemical analysis of trace elements was done by Inductively Couple Plasma Mass Spectrometer (ICP-MS) for water and Optical Emission Spectrometry (ICP/OES) for soil and rock samples. Statistical analysis was done by different software s like excel, past, R, CoDaPack and PHREEQC for redox reaction simulation. The analysis reveals that the potable quality of water is poor and the possible cause of this disease could be Pb and Zn at the eastern and As at the western part of the study area and also it could be caused by the interaction of elements of additive or synergetic effects. The high value of; TDS, pH, sulfate, association of Cu, Fe, Mo and Mn with Pb and Zn in water samples and high sulfur and Polar organic compounds in the rock samples indicates that the incidence of liver disease at eastern part of the study area is related to graphite schist type of rock which could be related to the organic sulfide minerals. There is lack of pattern in association of trace elements within water, soil and rock samples which could be because of the dispersion process and the high transmissivty of highly fractured aquifers found in the study area. Compositional data analysis does not improve the relationship analysis between geochemical pollutants. This could be because of in compositional data analysis data are transformed in logratio which is a logarithmic function. This logarithmic and ratio function removes the influence of anomalous values which are the crucial values that cause different biotoxic effect to human health. The reason for the recent occurrence of this liver disease could be related to the recent fertilizer practice. The simulation indicates that nitrate and carbon could change the dissolution of trace elements from sulfide minerals in the anoxic zone of aquifer system by change the redox system of a given aquifer. Trace element pollution study is a complex science it needs a lot of investigation

The dynamics of urban expansion and land use/land cover changes using remote sensing and spatial metrics: the case of Mekelle City of northern Ethiopia

Information on the rate and pattern of urban expansion is required by urban planners to devise proper urban planning and management policy directions. This study evaluated the dynamics and spatial pattern of Mekelle City’s expansion in the past three decades (1984–2014). Multi-temporal Landsat images and Maximum Likelihood Classifier were used to produce decadal land use/land cover (LULC) maps. Changes in LULC and spatial pattern of urban expansion were analysed by post-classification change detection and spatial metrics, respectively. The results showed that in the periods 1984–1994, 1994–2004, and 2004–2014, the built-up area increased annually by 10%, 9%, and 8%, respectively; with an average annual increment of 19% (100 ha year−1), from 531 ha in 1984 to 3524 ha in 2014. Between 1984 and 2014, about 88% of the gain in built-up area was from conversion of agricultural lands, which decreased by 39%. Extension of existing urban areas was the dominant growth type, which accounted for 54%, 75%, and 81% of the total new development during 1984–1994, 1994–2004, and 2004–2014, respectively. The spatial metrics analyses revealed urban sprawl, with increased heterogeneity and gradual dispersion in the outskirts of the city. The per capita land consumption rate (ha per person) increased from 0.009 in 1984 to 0.014 in 2014, indicating low density urban growth. Based on the prediction result, the current (2014) built-up area will double by 2035, and this is likely to have multiple socioeconomic and environmental consequences unless sustainable urban planning and development policies are devised

Groundwater Vulnerability mapping of Mekelle city and surroundings, Tigray region, Ethiopia

Mekelle, the regional capital of Tigray, faces difficulties managing and monitoring the quality of its water resources. The identified geological formations in the area are fractured limestone, fractured limestone shale-marl intercalation, and fractured dolerites. The hydrogeological setting of the Mekelle area is strongly controlled by geology and associated tectonic and non-tectonic geological structures. In comparison to other locations of Tigray, Mekelle and its environs have a higher concentration of various governmental and nongovernmental industries. Agricultural and mining activities, landfill sites, fuel and gas stations, health centers, car wash stations, garment and textile factories, and mega industries, are among the identified possible sources of water resource contamination in the area. Most of the water wells are found either within or around the agricultural lands and industrial zones. Chemicals and wastewater discharged from those industries, as affluent, are the sources of anthropogenic water resources pollution. The impacts and extent of pollution sources are not thoroughly investigated in the area. In this context, water resource vulnerability mapping was performed using the DRASTIC method and hydrogeological settings evaluation to identify the most vulnerable areas to anthropogenic pollution. The potential sources of groundwater pollution in the area were inventoried and mapped. The final DRASTIC vulnerability map with indexes ranging from 54 to 140 is classified into four classes: low (54 –75.5), moderate (75.5 – 97), high (97 – 118.5), and very high (118.5 – 140) vulnerability indexes. A modified DRASTIC vulnerability method was developed, that includes lineament density and land use thematic layers. The modified DRASTIC vulnerability map with indexes ranging from 91 to 192 is also similarly classified into four classes: low (91 – 116), moderate (116 -141), high (141 – 166), and very high (166 – 192). Single parameter sensitivity analysis and map removal sensitivity analysis were performed. The results from single parameter analysis show the impact of the vadose zone, depth to the water table and aquifer media have higher effective weightings (mean effective weightings = 23.7%, 22.9%, and 16.9%, respectively). In addition, the map removal sensitivity analysis confirms high variation of the vulnerability index is expected from the removal of impact of the vadose zone (1.5 %) and depth to the water table (1.4 %), respectively. Nitrate, used to validate both models, indicates a positive, moderate correlation (with Pearson’s correlation coefficient, r, of 0.681 and 0.702) for the DRASTIC and modified DRASTIC indexes, respectively. A comparison of both maps shows that the significant pollution sites are located in areas with high to very high vulnerability. The results of this research will directly aid water resources protection, pollution studies, and monitoring tasks of the Mekelle area

Vulnerability Mapping of Groundwater Resources of Mekelle City and Surroundings, Tigray Region, Ethiopia

Abstract: The management and monitoring of the quality of water resources in the Mekelle area are challenging, due to both geogenic and anthropogenic impacts. The extent of these impacts and the sources of pollution in this area has not been thoroughly investigated. In this article, a mapping of water resources vulnerability was carried out using the DRASTIC method and a modified DRASTIC vulnerability map was produced. Single-parameter and map-removal sensitivity analyses were performed on the relevant rates and weights. A final DRASTIC vulnerability index, varying from 54 to 140, was divided into four vulnerability classes: low (225.7 km2), medium (302.8 km2), high (307.2 km2), and very high (187.6 km2); the values in the parentheses indicate the corresponding areal coverage of each class. Similarly, a modified DRASTIC vulnerability index, ranging from 91 to 192, was divided into four vulnerability classes: low (166.4 km2), medium (266.8 km2), high (338.0 km2), and very high (252.2 km2) Nitrates were used to validate both models. in which moderate positive correlations (with Pearson’s correlation coefficient, r) of 0.681 and 0.702 were calculated for the DRASTIC and modified DRASTIC indices, respectively. A comparison of the two maps showed that significant sources of pollution are located in areas with high to very high vulnerability. The results of this research work can be used for the protection and monitoring of groundwater resources in the Mekelle area

Water resources studies in headwaters of the Blue Nile Basin : a review with emphasis on lake water balance and hydrogeological characterization

The Lake Tana Basin, comprising the largest natural lake in Ethiopia, is the source and the uppermost part of the Upper Blue Nile Basin. In this review paper, research papers, mainly on the rainfall-runoff modeling and lake water balance, and on the hydrogeology, have been reviewed. The earlier water balance estimation attempts used simple conceptual and statistical approaches and calculate on a monthly timescale. More recent research has been using advanced semi-physically or physically based distributed hydrological models. Accordingly, mean annual precipitation over the lake was estimated in the range 36.1-53.1%; lake evaporation at 45.3-57.5%; river inflow (all gauged and estimated ungauged) at 43.6-63.9%; and river (lake) water outflow at 0-9.2%. With the few isotope studies, groundwater inflow and outflow are found insignificant. Different studies had estimated groundwater recharge, ranging from 57 mm to 850 mm. The basin has a heterogenous aquifer system consisting of different volcanic rocks and alluvio-lacustrine sediments. Generally, groundwater with low TDS, Ca-Mg-HCO3 type, isotopically relatively enriched, and high TDS, Na-HCO3 type, isotopically relatively depleted, water types have been identified. In this paper, major research gaps such as aquifer hydraulic characterization, surface-groundwater interaction, groundwater flow and groundwater balance have been identified. Hence, future research shall focus on the groundwater resources, so that existing surface water studies are updated and future water usage options are explored