Geography chapter 4

water covers approximately ___% of the Earth's total surface

71

The earth water divided in to

• Alkaline(salt) water = 97.5%

• Fresh water = 2.5%

the earth fresh water devided into

1. Glaciers (68.7%)

Large masses of ice that remain frozen for long periods. Most of Earth's fresh water is stored here.

2. Groundwater (30.1%)

Water stored beneath the Earth's surface, inside soil and rocks. Wells and springs can provide access to it.

3. Permafrost (0.8%)

Ground that remains frozen for at least two consecutive years.

4. Surface water (0.4%)

Water found on the Earth's surface, including rivers, lakes, wetlands and water in the atmosphere and soil (as described in your textbook)

Why is freshwater distributed unevenly?

Three major factors influence its distribution:

Latitude: Different locations receive different amounts of solar energy, influencing their climate and rainfall.

Climate: Some regions receive heavy rainfall, while others experience drought and desert conditions.

Topography: Mountains, valleys and plains influence rainfall, river flow and water storage.

For example, tropical regions may receive considerable rainfall, while desert regions receive very little.

three geographical characteristics that contribute to Ethiopia's water resources

1. Complex topography

Ethiopia has:

Massive highlands.

Rugged terrain (uneven and mountainous land).

Low plains.

These different landforms influence rainfall, river formation and water movement.

2. Relatively higher rainfall

Many parts of Ethiopia receive considerable rainfall, which contributes to rivers, lakes and groundwater.

3. Nearness to the equator

Ethiopia is located relatively close to the equator. Its geographical location influences its climate and rainfall patterns.

Together, these factors contribute to Ethiopia's considerable water resources

Why is Ethiopia called the Water Tower of Eastern Africa?

Because Ethiopia's highlands are the source of several major rivers that flow into neighbouring countries.

For example:

• Blue Nile (Abay).

• Tekeze.

• Baro-Akobo.

• Omo.

The highlands receive rainfall, and water flows from higher elevations towards lower elevations, forming rivers.

That's why Ethiopia is commonly called the Water Tower of Eastern Africa

___% of Ethiopia's total land area is covered by water bodies

0.7

___BCM Estimated surface water potential of Ethiopia

124.4

Drainage means

The flow of water through well-defined channel

Drainage system means

is branched network of stream channels together with the adjacent land slopes they drain

Source (headwater)

The place where a river system begins.

Mouth

The place where a river system ends

A drainage basin

is the entire geographical area from which a river and its tributaries collect water

water divide(topographic divide)

is a high area of land, such as a mountain ridge, that separates two drainage basins

What determines drainage patterns?

1. Geological processes: Processes that shape the Earth's surface over time.

2. Nature and structure of rocks: Different rocks have different levels of resistance to erosion and permeability.

3. Topography: The physical features of the land, such as mountains, plateaus and valleys.

4. Slope: The steepness and direction of the land.

5. Amount and periodicity of flow: How much water flows and how regularly it flows.

For example, a region with heavy rainfall may have more streams and rivers than a dry desert region

The general patterns of major river basins in Ethiopia are determined by topographical structures which can be clarified as:

A. Outward-sloping Western and Southeastern plateaus

B. Inward-sloping escarpments of the Rift Valley

C. Faults and joints

Factor Meaning

A. Outward slopes-Rivers flow away from the plateaus.

B. Inward slopes-Rivers flow towards the Rift Valley, creating inland drainage.

C. Faults and joints-Cracks and fractures influence river courses

The three broadly classified drainage system

1,Western

2,Southeastern

3,Rift Valley

What is The largest Drainage System

The Western Drainage Systems

___% of Ethiopia's total land area is covered by western drainage system

40

___% of the ethiopia's annual water flow is get from western drainage system

60

The four major river basins In western drainage system

1. Abay

2. Tekeze

3. Baro-Akobo

4. Ghibe (Omo)

True/false

Abay flows westward.

Tekeze flows westward.

Baro-Akobo flows westward.

Ghibe (Omo) flows southward

True

True/false for Abay river basin

Drainage basin area: 199,812 km².

Length: Approximately 1,450 km.

Carries approximately 65% of the annual water flow of the Western Drainage System

Elevation 500-4261 m above sea level

True

Which river basin of western drainage system go east and bend 180 to go west

Abay river basin

Regions covered by abay river basin

Amhara, Oromia and Benishangul-Gumuz

Abay rises from

Lake Tana. Some sources also identify the area around Sekela and Choke Mountain

Where does abay end?

It flows into Sudan and joins the White Nile at Khartoum. Together, the Blue Nile and White Nile form the main Nile River

How many tributaries abay has

More than 60

The largest tributary of abay

Ghilgel Abay

True/false about tekeze river basin

Basin area: 82,350 km².

Carries approximately 12% of the annual water flow of the Western Drainage System.

Mean annual flow: 8.2 BCM.

Elevation range: 536–4,517 metres above sea level

True

Major tributaries of tekeze

Angereb and goang

Where tekeze ends

The Tekeze River crosses into Sudan, where it is known as the Atbara River.

It eventually joins the Nile system

What does erosion produce in Tekeze basin?

• Tablelands: Elevated areas with relatively flat tops.

• Plateau blocks: Large elevated sections of land.

• Isolated mountain groups: Mountains separated from surrounding highlands.

True/false about Baro-akobo river basin

Basin area: 75,912 km².

Carries approximately 17% of the annual water flow of the Western Drainage System.

Mean annual flow: 23.6 BCM

True

Regions covered by Baro-akobo

parts of Benishangul-Gumuz, Gambella, Oromia and the former SNNPR

_____River flows across an extensive marshy land

Baro river

Marshy land means

is an area of low-lying land that is frequently flooded or saturated with water

Where does Baro-Akobo ends

The Baro and Akobo rivers join to form the Sobat River in South Sudan.

The Sobat then joins the White Nile.

Remember: Baro + Akobo = Sobat

True/false about ghibe(omo) river basin

Basin area: 79,000 km².

Carries approximately 6% of the annual water flow of the Western Drainage System.

Mean annual flow: 16.6 BCM

True

What makes Ghibe (Omo) different?

Unlike Abay, Tekeze and Baro, which flow generally westward, Ghibe (Omo) flows southward

Where does ghibe(onto) ends?

to the Chew-Bahir at the mouth of Lake Turkana

Which river basins Drain the wet highlands of south and southwestern Ethiopia

Baro-akobo and ghibe(omo) river basins

_____drainage system covers the entire south eastern of Ethiopia

Southeastern drainage system

The Southeastern Drainage Systems Include the highland of

Arsi, Bale, Sidama and Hararghe

The rivers of southeastern drainage system generally flow towards the____

Southeast

the Southeastern Drainage Systems carry approximately ___% of Ethiopia's annual water flow

25

Which drainage system flows to Water-deficient plains

the Southeastern Drainage Systems

The two major rivers in the Southeastern Drainage Systems

Ghenale and wabishebelle

Catchment are of ghenale

171,042 km².

Regions of ghenale

Oromia, SNNPR and Somali regions

True/false

Ghenale has fewer tributaries than Wabishebelle.

However, it carries more water than Wabishebelle

True

True/false

Ghenale reaches the Indian Ocean

True

Ghenale in somalia called

Juba river

Catchment area Wabishebelle

202,697 km²

Region of wabishebelle

Oromia, Harari and Somali regions

True/false

Wabishebelle is the longest river in Ethiopia

True

True/false

Wabishebelle is the largest river in Ethiopia by catchment area

True

True/false

Wabishebelle has mainly left-bank tributaries and

Most of its tributaries are intermittent

True

True/false

Despite its large size wabishebelle does NOT reach the Indian Ocean

True

Where does wabishebele ends

end of its journey it flows parallel to the coast before its water disappears in the sands, just near the Juba River

Where does ghenale ends

In Mediterranean Sea

the riftvalley drainage system also called

inland drainage system

why The Rift Valley drainage system is called an inland drainage system

because its rivers and streams generally do not flow into the sea or ocean.

Instead, their water ends up in lakes, marshes, or inland depressions, where it may eventually evaporate or seep into the ground

three characteristics of the Rift Valley Drainage System

Low rainfall: The area receives relatively little rain.

High evaporation: Much of the water changes into water vapor because of heat.

Small catchment area: The area from which rivers collect water is relatively limited

drainage area of riftvalley is restricted by____

the outward sloping highlands

the Rift Valley drainage system mainly collects water from

• The slopes of the escarpments.

• The floor of the Rift Valley itself

Escarpment means

A steep slope or cliff separating two relatively different elevations

True/false

the catchment area of the The rift valley DS is small

True

the only major river basin in rift valley drainage system is ___

Awash

True/false

In the Rift Valley drainage systems, there is no one general flow direction, as the streams flow in all directions. Following the Rift Valley orientation

True

True/false about awash

Characteristic Information

Catchment area 114,123 km²

Average annual discharge 4.9 billion m³

Length 1,250 km

Origin Shewan Plateau

General direction Northeast

Final destination in a maze of small lakes and marshy area; the largest of which is Lake Abe on the Ethio-Djibouti border

True

The most utilized river in Ethiopia is

Awash

Which drainage sub-basin have no stream flow

Afar drainage sub-basin

Why Afar drainage sub-basin have no streams

Little rainfall.

Very high temperatures.

Very high evaporation

The two important lakes in Afar drainage sub-basin

Lake Afrera

Lake Asale (Assale)

How was the lakes of Afar drainage sub-basin Lake Afrera Lake Asale (Assale) formed

their formation is related to tectonic activities.

Remember, tectonic activities are movements and processes involving the Earth's crust, particularly the movement of tectonic plates.

These movements helped create depressions where water accumulated.

An important distinction: These lakes did not form because of significant rivers flowing into them

Southern Rift Valley sub-basin Also called

Lakes Region

Why Southern Rift Valley sub-basin have many lakes

the lakes occupy fault depressions.

Let's understand that:

A fault is a fracture or break in the Earth's crust.

Movements along faults can create depressed areas.

Water accumulates in these depressions, forming lakes.

Small rivers flowing down from nearby mountains also supply water to these lakes

Southern Rift Valley sub-basin Rivers flow in to lakes

Meki - Lake Ziway

Katar - Lake Ziway

Bilate - Lake Abaya

Segen - Lake Chew Bahir

Lake ziway - Bulbula - Lake Abijatta

Lake langano - Horocolo - Lake Abijatta

Majority of the rivers originate from _____areas and cross the Ethiopian boundary

Highland

True/false

Altogether, Ethiopian rivers form 12 major watersheds separating the Mediterranean Sea from the Indian Ocean drainage systems

True

General Characteristics of Ethiopian Rivers

 Almost all major rivers originate from the highlands elevating more than 1500 meters

above sea level,

 Majority of Ethiopian rivers are trans-boundary,

 Due to the marked seasonality of rainfall, Ethiopian rivers are characterized by extreme

seasonal fluctuation. In the wet season, runoff is higher and rivers are full bursting their

banks, destroying small bridges, damage roads and flooding low lands; during the dry

seasons they became mere trickles of water or even dry up,

 Due to surface ruggedness they have rapids and waterfalls along their course,

 They have cuts, steep-sided river valleys and deep gorges along their courses,

 Rivers in Ethiopia flow on steep slopes having steep profiles.

 Some of the rivers serve as boundaries, both international and domestic administrative

units

Why are most Ethiopian lakes clustered in the Rift Valley?

First, remember what we learned about the formation of the Great Rift Valley.

The Rift Valley was formed through tectonic movements that stretched and fractured the Earth's crust. These movements created faults, depressions and basins.

Some of these depressions became natural containers for water.

Here's how it happened:

• Tectonic forces fractured the Earth's crust.

• Some blocks of land sank between major faults.

• These sinking areas formed depressions or basins.

• Rainwater and rivers collected in these depressions.

• Over time, lakes developed.

This is why most Ethiopian lakes are located in the Rift Valley

What does "clustered along the system forming a linear pattern" mean?

Clustered: Located close to one another.

Linear pattern: Arranged in a line.

Look at the Ethiopian Rift Valley: many lakes are arranged in a north-to-south direction, following the shape of the Rift Valley

Why do some Ethiopian lakes dry up or gradually lose water?

This is a very interesting geographical question.

A lake's water level depends on the balance between:

Water entering the lake (rainfall, rivers and underground water).

Water leaving the lake (evaporation, outflow and underground drainage).

If more water leaves than enters over a long period, the lake shrinks.

There are several reasons this can happen:

A. Climate change and drought

When rainfall decreases, less water enters the lake. At the same time, high temperatures can increase evaporation.

B. High evaporation

Some Ethiopian lakes are found in hot areas. Water evaporates from their surfaces, particularly during dry periods.

C. Human activities

Excessive withdrawal of water for irrigation.

Diversion of rivers that feed lakes.

Deforestation and land degradation in catchment areas.

D. Changes in river inflow

When rivers supplying a lake carry less water, the lake may gradually lose its volume.

types of Ethiopian lakes

A. Tectonic lakes

B. Lake Tana

C. Crater lakes

D. Man-made lakes (Artificial lakes)

Tectonic lakes mean

are lakes formed in depressions created by movements of the Earth's crust.

For example:

Many lakes in the Ethiopian Rift Valley.

Lake Ashenge in Tigray

Remember: Tectonic movements create depressions, and water collects in them to form lakes.

Largest lake in Ethiopia

Lake Tana

Where does Lake Tana locate

northwestern highlands

How was lake Tana formed

Tana depression developed through two processes:

Slow sinking: The land gradually subsided, creating a depression.

Lava flow: Lava accumulated between the Gojjam and Gondar massifs, helping to block or contain the depression.

As a result, water accumulated and formed Lake Tana.

Let's clarify two words:

Massif: A large, relatively compact group of mountains or elevated land.

Subsidence: The gradual sinking of the Earth's surface

Crater lakes are

These are lakes formed inside volcanic craters or calderas.

How do they form?

• A volcanic eruption creates a crater or depression.

• Rainwater and sometimes groundwater collect inside it.

• The depression gradually fills with water, forming a crater lake

Example of crater lake

• Bishoftu crater lakes.

• Wonchi Lake (near Ambo).

• Hayk Lake (near Dessie).

• Crater Lake on Mount Zikwala

Man-made lakes (Artificial lakes) Are

These are lakes created by human activities, particularly by constructing dams across rivers.

Why do people create them?

• Hydroelectric power generation.

• Irrigation.

• Water supply.

• Other development purposes

Example of Man-made lakes (Artificial lakes)

Lake Koka

Created by the Koka Dam on the Awash River.

Fincha Lake

An artificial reservoir associated with hydroelectric power generation.

Melka Wakena Lake

An artificial reservoir associated with the Melka Wakena hydropower project

The largest lake in the Main Ethiopian Rift lake system

Lake Abaya

Chew Bahir

Located at the southern end of the Rift Valley.

It is a marshy area (wet, waterlogged land).

It receives drainage from the Segan and Woito rivers

Chew bahr drained by

Segan and woito rivers

The deepest lake in Ethiopia

Lake shala

The shallowest lake in Ethiopia

Lake ziway

Subsurface water means

Ground water