Freshman_Geography_Lecture_4

Course Overview

• Course Title: Geography of Ethiopia and the Horn

• Instructor: Belete Ejigu (PhD), Assistant Professor of Urban Planning and Development

• Institution: Addis Ababa University College of Natural and Computational Science

• Course Level: Freshman Course

• Date: January 2021

Chapter Four: Drainage Systems and Water Resource of Ethiopia and the Horn

Objectives

• Learners will be able to:

  • Describe major drainage systems in Ethiopia and the Horn.

  • Examine surface and ground water resource potentials.

  • Recognize economic potentials of the water sector in Ethiopia.

Introduction to Water Distribution

• Earth's Surface: 71% covered by water, mostly seas and oceans.

  • Water Composition:

    • 97.5% saline (oceans and seas)

    • 2.5% fresh water

      • 68.7% in glaciers

      • 30.1% in ground water

      • 0.8% in permafrost

      • 0.4% in surface water

Surface Water Resources

• Types: Lakes, rivers, atmosphere, soils, wetlands are surface waters.

• Distribution Issues:

  • Unevenly distributed due to:

    • Latitudinal variations

    • Climatic conditions

    • Topographic setups

• Ethiopia's Water Resources: Large volume of ground and surface water due to diverse topography and higher rainfall; recognized as the "water tower of Eastern Africa."

Major Drainage System of Ethiopia

• Concept of Drainage: Water flows through well-defined channels.

  • Components: Principal river and tributaries.

  • Regions: Separated by water divides, resulting from geological processes and topography.

Types of Drainage Systems in Ethiopia

1. Western Drainage System

2. Southeastern Drainage System

3. Rift Valley Drainage System

1. The Western Drainage Systems

• Significance: Largest drainage system, drains 40% of Ethiopia, carrying 60% of annual water flow.

• Major River Basins:

  • Tekeze River

  • Abay River

  • Baro-Akobo River

  • Ghibe (Omo) River

Abay River

• Characteristics:

  • Largest river by discharge and area (199,812 km²).

  • Flows approximately 1,450 km from Lake Tana to join White Nile.

• Streams: More than 60 streams drain Abay, including Ghilgel Abay (Little Abay).

Tekeze River

• Details:

  • Drains 82,350 km².

  • Significant erosion resulting in varied topography.

  • Flows into Sudan as Atbara River.

Baro-Akobo and Ghibe/Omo Rivers

• Baro-Akobo: Drains wettest highlands, covers 75,912 km².

• Ghibe/Omo: Drains 79,000 km²; both contribute to Sobat River in South Sudan.

2. The Southeastern Drainage Systems

• Major Rivers: Wabishebelle and Ghenale, originating from Arsi, Bale, Sidama, and Harerghe plateaus.

  • Ghenale River Basin: 171,042 km², named Juba in Somalia.

  • Wabishebelle River Basin: 202,697 km², does not reach Indian Ocean.

3. The Rift Valley Drainage System

• Characteristics: Low rainfall, high evaporation.

• Major River: Awash River with 114,123 km² basin area.

• Flow Direction: Streams flow in multiple directions, ending in interconnected lakes/marshes.

Additional Sub-basins

• Afar Drainage: Very low stream flow, characterized by high evaporation.

• Southern Rift Valley: Features lakes with streams supplying water.

Water Resources of Ethiopia

Rivers

• Ethiopia has many rivers originating in highlands, forming major watersheds.

General Characteristics of Ethiopian Rivers

• Typically originate above 1500 meters a.s.l.

• Transboundary nature.

• Seasonal fluctuations due to rainfall patterns.

Lakes

• Types: Highland lakes, rift valley lakes, and man-made lakes.

• Significant Lakes: Lake Tana, crater lakes, and dams.

Ground Water Resources

• Lower groundwater potential, estimated between 12-30 BMC.

Water Resource Potential and Development

Hydroelectric Power Potential

• High potential for hydroelectric generation, estimated at 45,000 MW.

• Significant Projects:

  • GERD: Aims for 6,400 MW.

  • Gilgel Gibe III: Operational with 1,870 MW.

Limitations on Irrigation and Transportation

• Rugged terrain limits river use for irrigation and transport; Baro is only navigable river.

Fishing and Recreation

• Rich fisheries, main production from Lake Tana & Lake Chamo.

• Lakes provide recreational opportunities and necessary resources.

Discussion Questions

1. Discuss the major drainage systems of Ethiopia.

2. Explain the hydroelectric and fishing potential of Ethiopian water resources.

3. State the major characteristics of Ethiopian rivers.