The annual amount of rain falls runoff is estimated around 122 billion m³ of water.
Groundwater resources are estimated around 36 billion m³.
In Ethiopia, some 80% to 90% of water resources are found in the basins of large rivers such as the Abay (Blue Nile), the Tekeze, the Baro Akobo and the Omo Gibe.
1. TYPES OF SPRINGS
• Springs are named for how they flow, and there are five main
types.
Gravity spring:
• This is just what it sounds like - this form from the pull of
gravity.
• The water gets pulled down through the ground until it
reaches a layer it can't penetrate.
• Because it has nowhere else to go, it starts flowing
horizontally until it reaches an opening and water comes out
as a spring.
• These are usually found along hillsides and cliffs.
CHAPTER SEVEN: SPRINGS
2. • Artesian springs: which come from pressure in confined
aquifers forcing the water to the surface?
• The pressure inside the confined aquifer (from being
smooched between those impermeable layers) is less than
the pressure outside the aquifer, so the water moves in that
direction.
• Any cracks or holes in the land will easily let the water escape.
3. • Seepage spring: it is groundwater seeping out at the
surface?
• Seepage springs slowly let water out through loose soil or rock
and are often found in land depressions or low in valleys.
4. • Tubular spring: These springs occur in underground cave
systems, which resemble underground highways.
• These tubes, or channels, are made of limestone, and as
water moves through this type of rock, it dissolves some of it
away.
• Tubular springs are some of the largest springs on Earth, and
the tubes themselves can be so small that you can't see them
or large enough to walk through!
5. • Fissure springs: Fissures are just large cracks, so you can
probably figure out that fissure springs occur along large
cracks in the ground, like fault lines.
• Fissure springs are often used as a source of drinking water,
and sometimes scientists go looking for fissure springs when
they want to find a fault on Earth!
6. Ground water Exploration
A programme of groundwater investigations is to obtain
information on the resource through systematic collection,
synthesis, interpretation and compilation of data.
It seeks information on its occurrence, movement, storage,
recharge, discharge, quality & quantity.
It includes the study of its geological, environmental, as
well as the hydrologic and hydraulic aspects of its flow
system.
7. Cont…
A comprehensive programme for hydrological investigations
may comprise the following activities
1. Surface Investigations
i. Geological field reconnaissance, including observations
and collection of data from excavations, bore holes and
wells. The appraisal includes information on geological
factors, particularly tectonics, lithology, permeability,
fissuring and outcrop area.
ii. Geophysical surveys
a) Electrical resistivity method
b) Seismic refraction method
8. 2. Subsurface Investigation of Groundwater
i) Test drilling and preparation of lithological logs
ii) Sub-surface/bore hole geophysical logging
a) Electric logging
b) Radial logging
iii) Collection of lithological & other logs of existing bore hole &
correlation of lithological logs.
3. Hydrological Investigations
i) Preparing inventory of existing wells, giving their location,
depth, depth of water, construction features, type of pumping
equipment used, pumping records and water analysis.
ii) Study of groundwater levels - preparation of water table
contour maps, water level profiles, hydrographs and setting up of
observation grids.
9. Cont’d
iii) Collection and analysis of water samples
iV) Aquifer tests - to appraise transmissibility and storage
property of aquifers.
v) Hydrologic appraisal of the geological framework:
Geometry of aquifers & boundaries affecting recharge &
discharge of groundwater.
vi) Correlation of stream flow factors with groundwater
recharge and discharge.
vii) Estimation of seepage & recharge contribution from canals,
lakes and ponds.
viii) Study and analysis of meteorological factors; precipitation
and evapotranspiration
ix) Rainfall and infiltration studies to estimate contribution of
rainfall to groundwater recharged.
x) Hydrologic analysis of groundwater systems through
analytical & other techniques.
10. Surface investigations of Ground water
less costly than subsurface investigations.
1. Geologic Methods
• A geologic investigation begins with the collection, analysis, and
hydrogeologic interpretation of existing topographic map, aerial
photographs, geologic maps and logs, and other pertinent
records.
• This should be supplemented, when possible, by geologic field
reconnaissance and by evaluation of available hydrologic data on:
stream flow and springs; well yields; groundwater recharge &
levels; and water quality
11. 2 Geophysical Exploration
• Geophysical exploration is the scientific measurement of
physical properties of the earth’s crust for investigation of
mineral deposits or geologic structure.
• Geophysical methods are used to obtain more accurate
information about subsurface conditions, such as
type and depth of materials(consolidated or
unconsolidated),
depth of weathered or fractured zone,
depth to groundwater,
depth to bed rock, and
salt content of groundwater.
• These methods detect differences (or anomalies), of physical
properties within the earth’s crust. Density, magnetism,
elasticity, and electrical resistivity are properties most
12. The Potential
–The annual amount of rain falls runoff is
estimated around 122 billion m³ of water.
–Groundwater resources are estimated
around 36 billion m³.
–In Ethiopia, some 80% to 90% of water
resources are found in the basins of large
rivers such as the Abay (Blue Nile), the
Tekeze, the Baro Akobo and the Omo
Gibe.
12
13. • The favorable geological and hydrogeological
setting favors Central and western Ethiopis in
providing high amount of recharge from Abay
plateau
• Due to this favorable setting areas beyond Becho and
Ade’a plains such as Welmera-Ambo-Guder areas,
North Shewa, Horo and East Wellegga are also
expected to have large GW potentials for irrigation.
13
The potential…cont
14. Recent studies by MoWR indicate that the estimated
rechargeable ground water resource to be much
higher than this estimate.
This fact is supported by the presence of the 1.2 BMC
or 3,287,671 m3/day annually rechargeable
groundwater in only two plains, Becho and Ada’a
that account for only <1% of the total area of the
country.
14
The potential…cont
23. 4/22/2024 Hydrogeology of Ethiopia 23
Legedadi well pumping test Q=15 l/s
Weberi well (Fiche Area) Q ≈40 l/s
24. Borana test well results
Forolle, <10km from Ethio-Kenya Border
Pumping test, Q ≈ 10 l/s
25. GROUND WATER MANAGEMENT
• Any substances introduced into groundwater by human
activities are considered contamination.
26. • Nitrate Nitrate can enter the groundwater via excessive use of
fertilizers, including manure.
• High application rates of nitrogen-containing fertilizers
combined with the high water-solubility of nitrate leads to
increased runoff into surface water as well as leaching into
groundwater causing groundwater pollution.
27. • Pathogens
• Waterborne diseases can be spread via a groundwater well
which is contaminated with fecal pathogens from pit latrines.
• Pathogens contained in feces can lead to pollution when they
are given the opportunity to reach the groundwater, making it
unsafe for drinking. Groundwater that is contaminated with
pathogens can lead to fatal fecal-oral transmission of diseases
(e.g. cholera, diarrhea).
• Pit latrines can cause significant public health risks via
contaminated groundwater impounds.
28. • Arsenic contamination of groundwater this
pollution occurs because aquifer sediments
contain organic matter that generates
anaerobic conditions in the aquifer.
• These conditions result in the microbial
dissolution of iron oxides in the sediment and,
thus, the release of the arsenic, normally
strongly bound to iron oxides, into the water.
29. • Fluoride:
• In areas that have naturally occurring high levels of fluoride in
groundwater which is used for drinking water, both dental and
skeletal fluorosis can be prevalent and severe
30. • GROUNDWATER POLLUTION
• May be defined as the artificially induced degradation of natural
groundwater quality.
• Most pollution stems from disposal of wastes on or into the ground
and the pollutants may be of organic (e.g. chlorinated phenoxy acid
herbicides), inorganic (e.g. nitrate), biological (e.g. coliform
bacteria), physical (colour) and radiological (e.g. barium) types.]
• Methods of disposal of wastes include discharge in to the sea and
streams, placement in percolation ponds, on the ground surface,
(spreading or irrigation), in landfills, into disposal wells and into
injection wells.
31. The principal sources of pollution include
• Municipal – sewer leakages, liquid and solid wastes
• Industrial – Mining activities, tank and pipeline leakage, oil
field brines, liquid wastes
• Agriculture – Irrigation return flows, fertilizers, pesticides,
animal wastes
• Miscellaneous – saline water intrusion, septic tank and
cesspools, roadway deicing, interchange through wells.
• The sources can be point (singular location), line (with a liner
alignment) or diffuse (occupying extensive areas) sources.
32. • The aims of groundwater pollution investigation are varied,
but may include
• determination of the extent of pollution by quantifying the
amount of pollutants determination of the sources of
possible pollutants to the groundwater regime
•
33. • quantification of the contribution from different sources
• the study of the migration rate of the pollutants through
the aquifers
• model the local and regional movement of pollutants
through the aquifer and predict future water qualities
• suggestion of management strategies whereby the influence
of disposal can be minimized.
34. • Groundwater pollution is much more difficult than surface
pollution because groundwater can move great distances
through unseen aquifers.
• The method of remediation depends on the chemical nature
of the contaminant:
• pure-compound recovery is possible when groundwater is
contaminated with a compound that is not water soluble.
REMEDIATION OF CONTAMINATED GROUNDWATER
38. • Pump and treat methods typically involve pumping
contaminated groundwater out and treating it through air
striping and chemical oxidation (using ozone, chlorine, etc.).
• In-situ remediation does not involve removal of the soil and
groundwater. Organic contaminants like oil and gasoline are
less soluble in water and can often be pumped off the surface
of aquifers.
