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UNESCO-IHE Institute for Water Education, Delft (2011)

Mapping the total water cycle for communities making use of rainwater harvesting systems in rural Ethiopia

Desta, T.W.

Titre : Mapping the total water cycle for communities making use of rainwater harvesting systems in rural Ethiopia

Auteur : Desta, T.W.

Etablissement de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2011

Résumé
In many of the developing countries water scarcity is a significant problem due to the population growth and climate change. In the future the scarcity is expected to only grow : the expected population growth will put extra pressure on the resources in the form of increased supply of water for domestic use, agriculture, and industrial uses. Rainwater harvesting (RWH) is often mentioned as a method to collect clean fresh water at minimal costs. Rural Ethiopia also suffers from a lack of sufficient good quality freshwater. Since 2009, Water Board Velt & Vecht and RAIN Foundation have been combining efforts, in order to work together on improving and strengthening rainwater harvesting (RWH) programmes in Ethiopia using sand dams as an underground storage tank. Yet, the systems were designed for domestic use only, whereas now the water is also used for irrigation and feedstock drinking. This leads to issues of multiple water use, quantity and quality. The study area for this research is rural Ethiopia, Dire Dawa region. This study assesses three of the existing sand dams namely Halibusa sand dam, Hawale sand dam and Haseliso sand dam and additionally Halibusa spring water source, Halibusa borehole water source and Dire Dawa tap water source. Results are based on the data collected from the above sources ; five samples were collected from each source, filtered and measured according to the standard methods for the examination of the water quality. Analysis of Chemical parameters, pH, Dissolved Oxygen (DO), Sulphate (SO4), Phosphate (Po4), Nitrite (NO2) , Nitrate (NO3), Free Chlorine, Total Chlorine, Electric Conductivity(EC) and Total Dissolved Solids (TDS) were done. Physical parameters, Turbidity, Temperatures, Colour, Odour and Taste were measured. And microbial parameter Escherichia Coli (E- Coli) Bacterial enumeration (E-Coli) were conducted by the membrane filtration technique and measured by plate count method. According to the analysis Halibusa sand dam, Haseliso sand dam and Haseliso borehole water sources, the results complied with the guidelines with the exception of E-Coli are too much to count and the max value for E-Coli should be 0 according to WHO, This shows that the rainwater harvested in Halibusa sand dam, Haseliso sand dam and haseliso bore hole are not E-Coli free. The rainwater samples contained E-Coli which are common in the areas where there is open defecation of humans and livestock. The exceedance of the guidelines for E-Coli may be caused by the open defecation and the sand dams are not well protected so the livestock also use the same water source and defecates there and the water is polluted. The physical parameter also it has a bad odor due to the Algae formation on the surface of the sand dam of Halibusa sand dam. The rainwater quality of Hawale sand dam is in the acceptable limit in all parameters measured. All the parameters are complied with the WHO guidelines. The absence of bacterial contamination in the Hawale sand dam could be from the protected upstream areas that minimize the contamination of the water source from faecal matters and solid wastes. In order to characterize the existing water sources Halibusa spring water source, and Dire Dawa tap water were also analyzed. Halibusa spring water is the source which is piped from long distance and which is owned by the Government and it has some contribution for the community. According to the result the spring water is complied with the WHO guidelines except for some chemical parameters like Electric Conductivity (EC) which is 1641 æS/cm, and according to WHO it is 1000 æS/cm for drinking water, and Total Dissolved Solids (TDS) 794 mg/l, and according to WHO it is 500 mg/l for drinking water, and also for microbial parameter the E-coli is uncountable and according to the guidelines it should be 0. The spring water quality is poor for drinking but still the community uses as one source, specially the students from the village use this water source. The cause for this quality maybe the water is collected in the above ground tank and it is not cleaned and Algae formation is in the tank. The source also is not protected from the start ; just the water is piped from the spring source. The spring is near the open defecation area. Just for comparison purpose five samples also collected and filtered and measured from Dire Dawa tap water using standard methods. Dire Dawa Tap water complied with the WHO guidelines in all parameters. In order to give solutions for multiple water use options and to map the total water cycle by using rainwater harvesting, 57 years (1951-2007) rain fall data collected and analyzed to design additional storage tanks at house hold level and school level. To investigate the multiple water use before intervention and which impacts RWH structures might have and to get more insights and understanding, into the needs of beneficiaries questionnaires were prepared and interview conducted for the data collection. In order to map the total water cycle for communities making use of rainwater harvesting systems this thesis brings on the one hand source protection by providing better sanitation or by education to end open defecation, on the other hand by extending the operation of the dam to a treatment system. From the different solutions given like extension of hydraulic retention time by extending the extraction well by 30m, building two compartments, improving the water quality by adding horizontal roughing filter , pond sand filter utilization and using a sand dam as slow sand filter, it is found that adding horizontal roughing filter gives a better solution for E-coli removal. With the infiltration rate 1.8m/h it has removal efficiency of 94%. According to literatures it is found that if we reduce the infiltration rate to 1m/h horizontal roughing filter can remove E-coli totally and the best results will be expected

Sujets  : rainwater harvesting ; water cycle ; Water quality ; water scarcity ; rural areas ; Ethiopia

Présentation

Page publiée le 3 janvier 2017, mise à jour le 13 octobre 2018