Physical geographyLesson 2 of 2 in the course Rivers and fluvial processes

Floodplain Formation, Ecology, and Flood-Risk Management

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

A floodplain is more than the flat land beside a river: it is a landscape shaped by repeated flooding, erosion, and sediment deposition. This lesson introduces floodplain features and explains how rivers build them over time.

A floodplain is land adjacent to a river that extends from the riverbanks toward the base of the surrounding valley and is inundated when river discharge is high. Its soils commonly contain clay, silt, sand, and gravel deposited by floodwaters.

All flashcards

What is a floodplain?
Land beside a river, extending from its banks toward the valley base, that may be inundated when discharge is high. It commonly contains river-deposited sediment.
What is lateral accretion?
Sideways growth of sediment deposits as a river channel migrates. In a meander, erosion occurs on the outer bank while a point bar builds on the inner bank.
How does vertical accretion occur?
During overbank flow, floodwater spreads across the floodplain and deposits sediment in layers, gradually building the surface upward.
What distinguishes a natural levee from a crevasse splay?
A natural levee is a raised ridge beside a river channel, formed by rapid deposition during overbank flow. A crevasse splay is a fan- or delta-shaped deposit spread beyond a break in the riverbank.
What is avulsion?
Avulsion is the abandonment of a channel belt and establishment of a river course in a different position on the floodplain. It can redirect floodwaters and produce catastrophic flooding.

Quiz questions

  1. Which description best defines a floodplain?Answer: Land beside a river that may flood when discharge is high.
  2. Why are floodplain deposits generally coarser near the river channel than farther away?Answer: Coarser sediment settles as floodwater slows near the channel; finer particles travel farther.
  3. What forms when floodwater passes through a break in a riverbank and deposits sediment beyond it?Answer: A crevasse splay.
  4. In flood-risk planning, what does a flood’s return period estimate?Answer: How often a flood of a specified size is expected over the long term.
  5. In United States flood-risk mapping, what is the floodway?Answer: The channel and adjacent land that must remain free of flow-obstructing encroachments.

Based on the Wikipedia article Floodplain, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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