The Flow of Water

Watersheds

The Continental Divide in Colorado

River systems are divided into regions called watersheds, which is the area of land that is drained by a water system. The largest watershed in the US is the Mississippi River watershed, which has hundreds of tributaries (a stream that flows into a lake/larger stream) that extend from the Rocky Mountains, in the West, to the Appalachian Mountains, and in the East.

There are several watersheds in the US, major and minor. Watersheds are separated from each other by an area of higher ground, known as the divide. In the US, the divide [in the US] is known as the Continental Divide.

Stream Erosion

As a stream forms, it erodes soil/rock to make a channel, which is the path that a stream follows. When a stream forms, its channel is usually thin and steep. But over time, the stream carries rock and soil downstream, and makes the channel a lot wider and deeper. When streams become longer and wider, this is what we call a river. A stream's ability to erode is influenced by three factors: gradient, discharge, and load.

Gradient

Gradient is the measure of the changes in elevation over a specific distance. A high gradient allows a stream to have more erosive energy to erode rock and soil, while the opposite has less erosive energy.

Discharge

The amount of water that a stream/river contain in a given amount of time is called discharge. The discharge of a stream increases when a major storm occurs, or when hot weather quickly melts snow. As the stream's discharge increases, its erosive energy, speed, and the amount of materials that the stream can [be able to hold] increases as well.

Load

Materials carried by a stream are called the stream's load. The size of load = [affected] = stream's speed. Fast moving streams can carry a bed load (large materials, such as pebbles and boulders), while slow-moving stream can carry a suspended load (small rocks and soil in suspension). The dissolved load is material carried in solution (material is dissolved in the water). Some of the materials in the dissolved load are sodium and calcium.

Stages of a River

Youthful River

• Erodes its channel deeper than wider
• Flows quickly due to the steep gradient
• Channel is narrow and straight
• Tumbles over rocks in rapids and waterfalls

Mature River

• Erodes its channel wider than deeper
• Not a steep gradient
• Fewer falls and rapids
• Fed by many tributaries
• Has more discharge (amount of water that a stream/river carries in a specific amount of time)

Old River

• Low gradient
• Little erosive energy
• Deposits rock and soil in/along its channel than widen and deepen its banks
• Characterized by wide, flat "flood plains" (valleys), and many bends.
• Fewer tributaries than a mature river.

Rejuvenated Rivers

• These rivers are found where the land is raised by tectonic activity.
• Land rises: Gradient becomes steeper
• Land rises: River flows more quickly
• Land rises: Due to the gradient, river cuts more deeply into the valley floor
• Terraces form, which are step-like formations that often form on both sides of a stream valley as a result of rejuvenation.