Overview
This lecture covers river profiles in geomorphology, focusing on definitions, characteristics, and the differences between longitudinal and cross profiles across the upper, middle, and lower courses of a river.
River Profile Definitions
- A river profile shows the shape and changes of a river from its source to its mouth.
- The longitudinal (or longitudinal) profile is a side view, showing the river's path from source to mouth.
- The cross (or transverse) profile is a view from bank to bank, showing height, width, and water depth.
Longitudinal Profile
- The longitudinal profile is concave: steep near the source and gentle near the mouth.
- It is divided into three parts: upper, middle, and lower courses.
Cross (Transverse) Profile
- The cross profile shows the width and depth of a river at any point, from one bank to the other.
- Cross profiles change shape along different courses of the river.
Graded vs. Ungraded Profiles
- A graded profile is smooth and concave, with no obstructions or irregularities.
- An ungraded profile has irregularities like waterfalls, lakes, and temporary base levels, making it uneven.
River Courses and Profile Changes
- Upper course: river channel is narrow and deep; dominated by vertical erosion.
- Middle course: channel becomes wider and deeper; lateral erosion is more prominent.
- Lower course: channel is very wide, sometimes deep; dominated by deposition of material.
River Features by Course
- Upper course: features like rapids and waterfalls form.
- Middle course: river begins to meander.
- Lower course: large meanders, oxbow lakes, deposited materials, braided streams, and floodplains are common.
Relationship Between Profiles
- Longitudinal and cross profiles are related and both change shape along the river’s course.
- Vertical erosion dominates in the upper course, lateral erosion in the middle, and deposition in the lower course.
Key Terms & Definitions
- Longitudinal Profile — side view of a river's path from source to mouth.
- Cross (Transverse) Profile — cross-sectional view from bank to bank, showing width and depth.
- Graded Profile — smooth, concave profile without obstructions.
- Ungraded Profile — uneven profile with obstacles and irregularities.
- Vertical Erosion — downward cutting erosion that deepens the river channel.
- Lateral Erosion — sideways erosion that widens the river channel.
- Deposition — accumulation of materials in the river channel.
Action Items / Next Steps
- Review course materials on river features in upper, middle, and lower courses.
- Study diagrams of longitudinal and cross profiles for better visualization.