River Structure

Rivers & Stream Ecology Overview

Introduction

Rivers & Stream EcologyRiver Structure with ModificationsE. Ruzycki, R. Axler

Learning Objectives

  • Understand the importance of rivers and what influences river formation.

  • Comprehend river morphology and spatial scales.

  • Comprehend the dynamics in a river/stream segment.

Importance of Rivers

  • Provide water and nutrients for agriculture.

  • Critical component of the hydrologic cycle.

  • Habitat for diverse flora and fauna.

  • Routes for exploration, commerce, and recreation.

  • Provide electricity.

  • Central to various ecological issues.

Natural Watercourses

Existence depends on:

  • Availability of surface water.

  • Presence of a channel in the ground.

  • An inclined surface.

Lotic vs. Lentic Systems

  • Lotic System: Flowing water.

  • Lentic System: Standing water.

  • Four dimensions of a lotic system:

    • Longitudinal

    • Lateral

    • Vertical

    • Time

Variation in Time and Space

The shape, size, and content of rivers are constantly changing.Formation of a close, mutual interdependence between the river and the land it traverses.

Effect of Climate on Rivers

Characteristics of rivers are related to precipitation and evaporation in their drainage areas.

Types of Rivers:

  • Perennial Rivers: Constant flow where precipitation exceeds evaporation.

  • Periodic Rivers: May run dry occasionally, with periodic precipitation.

  • Episodic Rivers: Rarely have water, found in arid climates.

Stream Corridor and Channel Morphology

Transitional upland fringe and floodplain stream channels.

Cross Section of a Channel

Components: stream channel, scarp, thalweg.

Floodplain Features

Elements include oxbow lakes, clay plugs, chutes, oxbow backswamps, splay, meander scrolls, and natural levees.

Meandering Rivers

Meander formation occurs as the streamline shifts between river banks, potentially forming an oxbow lake.

Gradient and Substrate

  • High Gradient/Slope:

    • Small meanders and coarse substrates.

  • Low Gradient/Slope:

    • Larger meanders and fine substrates.

Spatial Scale

  • Stream Segment: Defined by its beginning and a confluence or between two confluences.

  • Segment Unit: Portion of the river with uniform gradient and width.

  • Reach: Area with similar hydrologic conditions such as discharge, depth, area, and slope.

  • Pools: Areas of deep depths with slow current.

  • Riffles: Shallow, faster-moving sections of a stream.

  • Microhabitat: Small areas differing from the surrounding habitat.

Riffles, Pools, and Cascades

Riffles and pools alternate in predictable patterns.Distance between riffles: Approximately 5 - 7 channel widths.

Questions

Open floor for any questions regarding the content.