Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Distinguish between stream competence and capacity. (B)

Short answer

In summary, stream competence refers to a stream's ability to transport particles of a certain size and weight, which depends on the stream's velocity. Stream capacity, on the other hand, refers to the total sediment load a stream can carry downstream and is dependent on both the competence and the amount of water in the stream.

Step-by-step solution

Define Stream Competence

Stream competence is the measure of a stream's ability to transport particles of a given size and weight. It depends on the velocity of the water flow, as faster currents can carry larger and heavier particles. As the stream's velocity increases, so does its competence.

Define Stream Capacity

Stream capacity, on the other hand, refers to the total amount of sediment a stream can transport downstream. It is dependent on both the competence and the amount of water moving through the stream. Higher stream capacities are found when the flow rates are high and the stream has a high competence.

Highlight the Differences

Now that we have defined both terms, we can outline their differences: 1. Stream competence is a measure of the size and weight of particles a stream can transport, while stream capacity refers to the total sediment load a stream can carry. 2. Stream competence is a function of the stream's velocity, while capacity is a function of both the stream's velocity and the amount of water in the stream. 3. Stream competence focuses on individual particle characteristics, while capacity considers the total sediment load. In summary, stream competence is about the ability of a stream to transport particles of a certain size and weight, whereas stream capacity is about the total sediment load a stream can transport downstream.

Key concepts

Sediment Transport

Picture a gently flowing creek, and you can almost see the dance of tiny pebbles and grains of sand swirling with the current. This is sediment transport, a fundamental process in creating the landscapes we see around us. But how does it work?

At its core, sediment transport is all about movement. Streams and rivers, like conveyor belts, pick up, carry, and eventually deposit different types of sediment. These little travelers come in all shapes and sizes, from fine silt that can float for miles to hefty boulders that only move during furious floods. The stream's muscle for this work is its velocity, fluid of sufficient speed can lift and roll even chunky bits along its bed. But velocity is just one part of the story.

The amount and type of sediment that can be carried is also influenced by other factors, such as water volume and the sediment's own characteristics - round grains roll easier than angular ones, for example. Beyond that, the riverbed's slope and roughness also have a say, by either helping to accelerate particles or trapping them momentarily.
Each stream finds its balance, achieving a dynamic equilibrium where the amount of sediment carried equals the amount available for transport. This balance is what shapes our changing landscapes slowly but persistently.

Stream Velocity

When we discuss rivers and streams, we often picture water merely flowing from one point to another. However, the speed of this flow, known as stream velocity, is a prime mover in the world of fluvial dynamics. It's not just about speed; it's a vital player in what a stream can carry and how it sculpts the environment.

Stream velocity varies greatly depending on several environmental conditions. It can be influenced by the slope or gradient of the stream bed, the channel shape, and the roughness of the bed materials. Imagine pouring water down a slide versus a staircase—the former will surely flow more smoothly and swiftly.

Factors Affecting Stream Velocity

Several factors can influence stream velocity:

• Gradient: Steeper slopes increase the water's energy, leading to faster flow.
• Channel Shape: A narrow, deep channel reduces friction and allows higher speeds compared to a wide, shallow one.
• Roughness: Smooth riverbed materials allow water to slide easier than rough, irregular ones.

These factors are not only pivotal for determining a stream's competence but also affect its erosion and deposition patterns, constantly shaping the river's course and the landscape it traverses.

Fluvial Geomorphology

Ever been mesmerized by the winding paths of rivers on a map, or the way canyons carve their stories into stone? What you're appreciating is the art and science of fluvial geomorphology, the study of how rivers interact with and shape the landscape. It stretches beyond the flow of water; it's an exploration into the tapestry of processes that etch the surface of the Earth.

Rivers are the artists of this domain, using water as their brush and sediments as their palette. They can create features such as meandering bends, oxbow lakes, alluvial fans, and deltas. Their actions are dictated by stream velocity, load, and the capacity to carry sediments — their toolkit influenced by both nature and human activity.

Key Features Shaped by Fluvial Processes

Notable landforms that result from these processes include:

• River Valleys: Carved by the prolonged erosion from a river's flow.
• Floodplains: Formed from sediment deposited during floods.
• Levees: Natural embankments built by successive floods.
• Deltas: Built from sediments deposited where a river meets a standing body of water.

These ever-changing environments are a result of interconnected geological processes and the persistent force of moving water. As such, fluvial geomorphology provides a fascinating window into the past and present shape of our natural world.