1. Landforms of the Fluvial System

2. Objectives Describe formation and characteristics of alluvial fans
Examine landforms formed by fluvial erosion and deposition in river valleys
Investigate the evolution of river deltas

3. Introduction
Fluvial landforms built by:
Deposition
Erosion

4. Alluvial Fans
Ephemeral streams emptying from mountain valleys construct alluvial fans
Alluvial fans are fan-shaped
Formed of alluvial material
Debris flows in upper alluvial fans
More common in deserts
But can form in humid areas

5. Flow and Deposits on Alluvial Fans
Flow emptying from valley spread
Velocity decreases, sedimentation occurs
Unconfined water spreads across fan in shallow channel
Deposits are poorly stratified
Thick near mountain
Thin outward from mountains
Alluvial fans coalesce to form bajadas
Older parts of fan may develop desert varnish/pavement

6. Landforms of River Valleys-Meandering Rivers
Bends in sinuous channel termed meanders
Erosion on outside of bend
Deposition on inside of bend—Pt bar
Grow and migrate
Cut-off meanders form oxbow lakes

7. Landforms of River Valleys-Meandering Rivers
Formation of oxbow lakes

8. Landforms of River Valleys - Braided Rivers
River with multiple channels separated by sand or gravel bars
Braiding forms by deposition of bar in mid-channel
Water flows around bar forming two channels
High sediment load, steep slopes, variable discharge, loose bank materials may cause braiding

9. Landforms of River Valleys - Floodplain
Flat, low-lying ground bordering channel
Frequently flooded and sediment deposited
Levees form on channel margin
Eroded by migrating meandering
Growing pt. bar rebuilds floodplain

10. Landforms of River Valleys - Floodplain
Widening of floodplain and devleopment of large meanders in meander belts

11. Landforms of River Valleys - Floodplain
Flooding and levee development

12. Human Use of Floodplains
Farming
Development
People do not adjust well as risk grows
Flood control measures
Artificial levees, dams
Provide mostly artificial security
Must assume floods will recur

13. Terraces Benches above modern floodplain
Are older floodplains
Develop through stream incision of floodplain
Lower floodplain develops
May have paired or mostly unpaired terraces
May have aggradation before terrace formation
Increased sediment supply causes
Reduced sediment supply then results in incision
Fill terraces produced

14. Terraces
Aggradation and terrace development

15. Deltas
Triangular shaped deposits where streams empty into oceans or lakes
Coarse sediments deposited at river mouth
Fine sediments carried farther
Distributary channels form transporting water and sediments
Delta form depends on:
Discharge and sediment transported
Configuration of seafloor
Strength of currents, waves, tides

16. Delta Types

17. The Delta Profile Consists of bottomset, foreset, and topset beds
Compaction may occur causing subsidence