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The use of the multi-criteria analysis for the exploration of surface irrigation potential zones : A case of the Didesa sub-basin, Abay basin, Ethiopia

Tamiru Habtamu, Dinka Megersa O.

Journal of Water and Land Development

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2023

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no. 58

198--211

EN

This paper presents a study conducted using the Multi-Criteria Analysis (MCA) to explore surface irrigation potential zones in the Didesa sub-basin of the Abay basin in Ethiopia. Physical land features, such as land use / land cover (LULC), slope, soil depth, drainage, and road proximity, along with climate factors like rainfall and evapotranspiration, and population density, were identified as criteria for the exploration. The analytic hierarchy process (AHP) is a powerful structured decision-making technique commonly used for complex multi-criteria analysis problems where multiple criteria need to be considered. The importance of the criteria was prioritised and ranked in the analytic hierarchy process (AHP). Five qualitative-quantitative based surface irrigation potential zones were identified, namely highly suitable (48.40%), moderately suitable (27.26%), marginally suitable (13.27%), not suitable (4.91%), and irrigation constraints (6.16%). The consistency of the AHP technique in the exploration of surface irrigation potential zones is evaluated by the consistency index at CI = 0.011 and confirmed the correctness of weights assigned for the individual key factor in the AHP. The accuracy of the potential zones generated in the AHP was evaluated with ground-truth points and a supervised LULC classification map. Moreover, a good agreement was made among the classes with the kappa index (KI = 0.93). Therefore, the application of the MCA for the exploration of surface irrigation potential zones was successful, and the results of the study will be useful to strengthen the irrigation in the explored potential zones.

2

Evaluation of shallow groundwater suitability for irrigation purposes : A case study from Doornfontein area, South Africa

Moges Simeneh S., Dinka Megersa O.

Journal of Water and Land Development

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2023

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no. 58

189--197

EN

The present study aims at evaluating the quality of shallow groundwater (SGW) and its suitability for irrigation purpose in the most urbanised part of Johannesburg city, South Africa. The SGW samples were collected in three consecutive years and analysed for 20 selected physicochemical parameters, and heavy metals. The results were compared with the South African water quality, and Food and Agricultural Organization irrigation water quality guidelines, and standard indices derived from laboratory outputs. The results of the study show that all physiochemical parameters and heavy metals were within the limits set by both guidelines for irrigation purposes, except for potassium (3.58 mg∙dm-3) and manganese levels (3.152 mg∙dm-3). The calculated irrigation parameter values of sodium adsorption ratio (SAR), sodium percentage (Na%), residual sodium carbonate (RSC), magnesium hazard (MH), Kelly’s ratio (KR) and permeability index (PI) were within the permissible range of irrigation water quality standards. The findings of this study provide helpful information for decision-makers such as utilisation of the studied groundwater for irrigation uses.

3

Assessment of groundwater vulnerability using the DRASTIC model: A case study of Quaternary catchment A21C, Limpopo River Basin, South Africa

Moges Simeneh S., Dinka Megersa O.

Journal of Water and Land Development

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2021

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no. 49

35--46

EN

Groundwater is a vital resource for domestic, agricultural, industrial activities and ecosystem services. Despite its multiple purposes, the resource is under significant threat owing to increasing contamination from anthropogenic activities and climate change. Hence, in order to ensure the reliability and sustainable use of groundwater for the present and future generations, effective management of groundwater (quality and quantity) is highly important. This can be achieved by identifying areas more vulnerable to contamination and implementing protective measures. The present study aims at assessing the vulnerability of groundwater using GIS-based DRASTIC index in the Quaternary catchment (A21C) within Limpopo River Basin. The vulnerability index varied from 87 to 207. About 53.6% (408 km2) of the catchment area also exhibited high risk of groundwater contamination mostly in central, north-eastern and western part of the sub-catchment. The medium and low vulnerability classes cover only 18.1% (137.5 km2) and 21.7% (165.1 km2) of the study area, respectively. The shallow groundwater at the Doornfontein Campus belongs to very high vulnerability area. The sensitivity analysis indicates that depth to water level, recharge, aquifer media, soil and topography are the important contributors to vulnerability assessment. The correlation analysis performed to validate the final vulnerability map shows a moderate positive correlation, indicating the model’s applicability to the urbanised environment. The study indicates an area that is highly vulnerable to pollution, and hence protective measures are necessary for sustainable management of the groundwater resource in the study area. The result of this study can also be further improved and verified by using other vulnerability assessment models.

4

Water productivity under deficit irrigation using onion as indicator crop

Tadesse Kassahun B., Hagos Eyasu Y., Tafesse Nata T., Dinka Megersa O.

Journal of Water and Land Development

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2020

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no. 45

171--178

EN

Improving water productivity (WP) through deficit irrigation is crucial in water-scarce areas. To practice deficit irrigation, the optimum level of water deficit that maximizes WP must be investigated. In this study, a field experiment was conducted to examine WP of the three treatments at available soil water depletion percentage (Pi) of 25% (reference), 45% and 65% using a drip irrigation system. Treatments were arranged in a randomized complete block design. The water deficit was allowed throughout the growth stages after transplanting except for the first 15 days of equal amounts of irrigations during the initial growth stage and 20 days enough spring season rainfall during bulb enlargement periods. Physical WP in terms of water use efficiency (WUEf) for treatments T1, T2, and T3 was 9.44 kg∙m–3, 11 kg∙m–3 and 10.6 kg∙m–3 for marketable yields. The WUEf and economic water productivity were significantly improved by T2 and T3. The WUEf difference between T2 and T3 was insignificant. However, T2 can be selected as an optimal irrigation level. Hence, deficit irrigation scheduling is an important approach for maximizing WP in areas where water is the main constraint for crop production. The planting dates should be scheduled such that the peak water requirement periods coincide with the rainy system.

5

Groundwater quality composition and its suitability for drinking in long-term irrigated area

Dinka Megersa O.

Journal of Water and Land Development

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2020

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no. 44

43--54

EN

This study presents the hydrochemical composition of groundwater under long-term irrigation of Wonji plain (Ethiopia) and its quality status for drinking purpose. Groundwater samples were collected from 30 groundwater monitoring tube wells installed at different parts of the sugarcane plantation and then analysed for the major physico-chemical quality parameters (pH, EC, major cations and anions) following standard test procedures. The status of groundwater for drinking was compared with WHO and other quality standards. Analytical analysis results indicated that majority of the considered quality parameters are rated above the prescribed tolerable limits for drinking set by WHO. About 97% of the water samples has water quality index in the range of very poor to unfit for drinking. The contamination index is in the ranges of low (–1.0) to high (3.6). In general, the groundwater of the area is unsuitable for human consumption without proper treatment such as boiling, chlorination, filtering, distillation, desalinaization, defluoridation, deionization, demineralization (ionexchange) and membrane processes. Since the TDS concentration is relatively small (<2000 ppm), demineralization process alone can be sufficient to bring the water to an acceptable level.

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Drought prediction in the Lepelle River basin, South Africa under general circulation model simulations

Ikegwuoha Darlington C., Dinka Megersa O.

Journal of Water and Land Development

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2020

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no. 45

42--53

EN

This study aims to evaluate changes in the frequency and severity of historical droughts (1980–2018) and then model future droughts occurrences (2019–2099) in the Lepelle River Basin (LRB), using Intergovernmental Panel on Climate Change (IPPC) General Circulation Model (GCM) simulations for two representative concentration pathways (RCP8.5 and RCP4.5). Firstly, the present-day and future hydrology of the LRB are modelled using the weather evaluation and planning (WEAP) model. Mann–Kendall tests are conducted to identify climate trends in the LRB. The reconnaissance drought index (RDI) and the streamflow drought index (SDI) are employed to explore hydro-meteorological droughts in the Lepelle River Basin, South Africa. The RDI and SDI are plotted over time to assess drought magnitude and duration. The simulated temporal evolution of RDI and SDI show a significant decrease in wetting periods and a concomitant increasing trend in the dry periods for both the lower and middle sections of the LRB under RCP4.5 as the 22nd century is approached. Lastly, the Spearman and Pearson correlation matrix is used to determine the degrees of association between the RDI and SDI drought indices. A strong positive correlation of 0.836 is computed for the middle and lower sections of the LRB under the RCP8.5 forcing. Further findings indicate that severe to extreme drought above –2.0 magnitude are expected to hit the all three sections of the LRB between 2080 and 2090 under RCP8.5. In the short term, it is suggested that policy actions for drought be implemented to mitigate possible impacts on human and hydro-ecological systems in the LRB.