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Über dieses Buch

This book provides a comprehensive description of groundwater resources in Ethiopia and its various dimensions (groundwater as resource, environmental functions, and socioeconomics). The prevailing knowledge of groundwater resources in Ethiopia (or elsewhere in Sub Saharan Africa) was based on geological and stratigraphic framework known nearly four decades ago (mainly 1960's and 70's). Thanks to the substantial geoscientific research since the 70's a new set of relevant geological/stratigrahpic data has been created that helps to re-define our understanding of groundwater resources in Africa as a whole and in Ethiopia in particular:

a) For the first time the basement aquifer of Ethiopia has been described hydrogeologically based on genesis of regoliths (deep weathering and striping history); clear regional difference in groundwater potential is shown for the first time; comparative accounty has been given regarding groundwater occurrence in the generally low grade basement rocks of Ethiopia (Arabian Nubian shield) and high grade basement rocks of the rest of Africa.

b) For the first time groundwater occurrence in multilayred sedimentary rocks account for spatial variation in degree of karstification; deformation history, and stratigraphy.

c) The vast volcanic aquifers of Ethiopia which have previously classified based on their ages are now reclassified based on age, morphology (eg. groundwater in plateau volcanics, groundwater in shield volcanics) and aquifer structure.

d) The loose alluvio lacustrine sediments which were known as least extensive in previous works based on areal cover are in fact shown to host the most voluminous groundwater resources in Ethiopia. These aquifers have now been described based on their geomorphology, extent, and genesis.

The aim of this book is to use these newly created knowledge to redefine the understanding of groundwater resources in Ethiopia.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
There is variable definition for groundwater. Agronomists define groundwater as any water below the ground. For engineers groundwater is often termed as subsurface water and occurs below the ground. For hydrogeologists groundwater is water in the saturated zone. A number of other names are attributed to groundwater. This include: sub surface water, under groundwater and groundwater. Rocks in which groundwater occur are also named differently. Aquifer is a rock that holds and transmits water at an economical rate. Aquiclude is a rock that doesn’t hold or transmit water at economical rate. Aquitard is a rock that holds water but doesn’t transmit the water to wells at economical rates. Groundwater exists inside fractures of rocks or inside open spaces called porosities of rocks. Open spaces are formed either after or during the formation of the rocks themselves.
Seifu Kebede

Chapter 2. Groundwater Occurrence in Regions and Basins

Abstract
The broad volcanic plateau (Fig. 1.2) accounts for about 25 % of Ethiopian landmass. The Ethiopian volcanic plateau is a thick monotonous, rapidly erupted pile of locally deformed, flat lying basalts consisting of a number of volcanic centers with different magmatic character and with a large range of ages.
Seifu Kebede

Chapter 3. Very Shallow and Shallow Groundwaters

Abstract
Alluvial terrain covers less than 25 % of the land surface of the country (Fig. 3.1) however, major prolific aquifers and larger groundwater storage lay in this zone (Fig. 1.1). Investment on groundwater schemes is, could therefore, much more feasible in the regions underlain by alluvial aquifers.
Seifu Kebede

Chapter 4. Geochemistry and Water Quality

Abstract
Water quality is the measure of physical, chemical, radiological and biological property of water. Water quality poses limits on the suitability of water use for a particular development purpose.
Seifu Kebede

Chapter 5. Isotope Hydrology in Water Cycle Studies in Ethiopia

Abstract
Isotope hydrology is a proven tool in understanding hydrological processes such are recharge rate and recharge mechanism, surface water groundwater interaction, time scale of processes, origin of pollution etc. The tool is even more powerful when used in understanding of hydrology of arid and semi arid regions. Given that half of Ethiopia is an arid or semi arid region, isotope hydrology could provide the much needed knowledge for groundwater resources management. The purpose of this chapter is therefore to first briefly describe the tool itself and then to show some cases studies where isotopes have been used to retrieve hydrological information in Ethiopia.
Seifu Kebede

Chapter 6. Functions of Groundwater

Abstract
Groundwater has storing, filtering and transforming capacities, and regulates atmospheric, hydrological and nutrient cycles. Groundwater stores and partly transforms CO2, energy, plant nutrients and other chemical substances. Groundwater can act as sink in the carbon cycle. Groundwater can immobilize or break down a multitude of pollutants, for example from waste disposal. Contaminants may build up and subsequently be released in different ways, in some cases exceeding regulatory thresholds. Sustaining biodiversity is an essential ecological function of the land. In turn, the biological activity on the land and in the soil contributes to its properties and characteristics, which are essential for its productive functions. Groundwater maintains wetlands and their ecosystems. Groundwater makes part of base flows of rivers and support river in ecosystem. Groundwater is principal pathway though which solute (such as silica, nitrate, and cations) enters into lake and ultimately supports the phytoplankton and zooplanktons. Groundwater sustains aquatic ecological functions in rivers, lakes, riparian zones and estuaries require huge volumes of water. Fresh water sustains biomass growth in terrestrial ecosystems, and provides key ecological services—maintaining biodiversity, sequestering carbon and combating desertification. Groundwaters are principal pathways of essential and non essential exotic trace elements in nature to get to the human metabolism.
Seifu Kebede

Chapter 7. Groundwater Potential, Recharge, Water Balance: Vital Numbers

Abstract
Groundwater potential is measured by (a) recharge rate and mechanism, (b) aquifer storage and transmission properties, and (c) suitability of the water from water quality point of view and (d) the response of the aquifer to changes such as climate, seasonality, artificial withdrawal and pollution.
Seifu Kebede

Chapter 8. Groundwater Human Health and Sanitation

Abstract
Chemical and biological materials circulating or stored in the environment get to human body via different pathways including the food we eat, the water we drink and the air we breathe, the materials we touch. Groundwaters play a unique role in acting as pathway via which certain exotic chemical and biological materials are introduced into human physiology.
Seifu Kebede

Chapter 9. Groundwater as Strategic Resource

Abstract
Groundwater resource is the pillar of socio-economic activity and environment functions. Unlike in most part of Africa where groundwater is stored in extensive continental scale groundwater reservoirs, the groundwater resources of Eastern Africa are known for their low storage and shallow circulation.
Seifu Kebede

Chapter 10. Groundwater Management

Abstract
Groundwater management or managed groundwater development deals with legal, institutional, financial and technical aspects. Here more technical aspect of groundwater management with a brief touch to legal aspect is addressed. Groundwater management deals with managing uncertainty. Better groundwater management practice is that which factors uncertainty. Better management increases success of water schemes and increase efficiently. Management of groundwater operates within the national and international laws. Having appropriate institutional framework (e.g. linkage across institution in dealing with data, information and knowledge) is key to water resources management.
Seifu Kebede

Backmatter

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