Chapter 17: Problem 10

Describe how a drainage network changes, along its length, from headwaters to mouth.

Short Answer

Expert verified

As the drainage network progresses from headwaters to mouth, the river size generally increases due to more tributaries contributing to the total volume of water. The river shape changes from straight and narrow with a steep valley to more sinuous and meandering with a gentler slope in the middle and lower reaches. The river gradient usually decreases from steep at the headwaters to less steep downstream due to natural erosion processes and sediment deposition. River flow typically increases along the length as more water from tributaries is incorporated and channel roughness decreases. Factors influencing these changes include underlying geology, climate, and human activities.

Step by step solution

Understand the Components of a Drainage Network

A drainage network is a system of rivers, streams, and tributaries that transports water from the headwaters (the source) to the mouth (where the water drains into a larger body of water, such as a sea or ocean). The main components of a drainage network include the river size, shape, gradient, and flow, as well as factors that influence these characteristics (e.g., geology, climate, and human activities).

Changes in River Size

Along the length of the drainage network, the size of a river generally increases as it moves from the headwaters to the mouth. As water moves downstream and the drainage network incorporates more and more tributaries, the total volume of water in the river increases. This causes the width, depth, and cross-sectional area of the river channel to become larger.

Changes in River Shape

The shape of a river channel can also change along its length. In the upper reaches of a drainage network, near the headwaters, the river might be relatively straight and narrow, with a steep valley. As the river moves into the middle and lower reaches, the valley slope often becomes gentler, resulting in the river taking on a more sinuous or meandering shape as it flows through its floodplain.

Changes in River Gradient

The gradient of a river, or the angle at which it descends along its course, usually decreases from the headwaters to the mouth. In the upper reaches of a drainage network, the gradient is steeper as the river flows through more rugged or mountainous terrain. As the river progresses downstream, the gradient becomes less steep due to a combination of factors such as natural erosion processes and sediment deposition.

Changes in River Flow

The flow of the river, or the amount of water passing through its channel at a given time, typically increases as it moves from the headwaters to the mouth. As previously mentioned, the river's size increases as it incorporates more water from tributaries. Additionally, the river's velocity may increase due to a combination of the greater volume of water and a decrease in channel roughness, which reduces the amount of friction acting against the flow of water.

Influencing Factors

Changes in the drainage network along its length can be influenced by various factors, such as underlying geology, climate, and human activities. For example, the bedrock and soil types can affect the shape, gradient, and resistance to erosion of a river. Climate, including precipitation and evaporation rates, can influence the volume of water transported through the drainage network. Finally, human activities such as urbanization, agriculture, and damming can have significant impacts on the characteristics and behaviors of a drainage network.

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Describe how a drainage network changes, along its length, from headwaters to mouth.

Short Answer

Step by step solution

Understand the Components of a Drainage Network

Changes in River Size

Changes in River Shape

Changes in River Gradient

Changes in River Flow

Influencing Factors

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