Forces of Moving Water

Key Vocabulary Write these in your journal Energy: the ability to do work or cause change. Kinetic Energy: energy an object has due to its movement Abrasion: wearing away of rock by a grinding action Load: the amount of sediment that a river carries Slope: the amount the river drops toward sea level over a given distance. Volume of Flow: the volume of water that moves past a point on the river in a given time. Stream bed shape: the amount of friction between the water the and the stream bed. Friction; the force that opposes the motion of one surface as It moves across another surface. Turbulence: a type of movement of water in which rather than moving down stream the water moves every which way.

Work and Energy The waters of the Merrimack River could drive machines because a river’s water has energy. Energy is the ability to do work or cause change. There are two kinds of energy. Potential energy is energy that is stored and waiting to be used later. The Marricmack’s water begin with potential energy due to their position above sea level. Kinetic energy is the energy an object has due to its motion. As gravity pulls water down a slope, the water’s potential energy changes to kinetic energy that can do work.

Takoto Dam, is a dam in the Nagano Prefecture, Japan, completed in 1958 . It harnessThe power of flowing water

When energy does work, the energy is transferred from one object to another. At the textile mills along the Merrmack River, the kinetic energy of the moving water was trasnferred to the spinning machines. It became mechanical energy harnessed for human purpose-making cloth. But all along a river, kinetic energy does not work. A river is always moving sediment from the mountains to the sea. At the same time, a river is also eroding its banks and valley.

Merrimack River – the cotton mills in Lowell, Massachusetts, Were built in the 1820’s. the mills employed young women From the farms and small towns of New England. A that time, it was unusual for women. To work outside the home. The hours of work oat a mill were long and pay was low. But mill work helped these women to earn and save their own money. Most later returned to their home towns.

How Water Erodes and Carries Sediment Gravity causes the movement of water across Earth’s land surface. But how does water cause erosion? In the process of water erosion, water picks up and moves sediment. Sediment includes soil, rack, clay, and sand. Sediment can enter rivers and streams in a number of ways. Most sediment washes or falls into the river as a result of mas movement and runoff. Other sediment erodes from the bottom or sides of the river. Wind may also drop sediment into the water.

What evidence of sediment movement is present? How would this river carry sediment?

Abrasion is another process by which a river obtains sediment Abrasion is another process by which a river obtains sediment. Abrasion is wearing away of rock by grinding action. Abrasion occurs when particles of sediment in flowing water bump into the streambed again and again. Abrasion grinds down sediment particles. For example, boulders become smaller as they are moved down a streambed. Sediment also grind and chip away at the rock of the streambed, deepening and widening the stream’s channel.

The amount of sediment that a river carries is its load The amount of sediment that a river carries is its load. Gravity and the force of the moving water cause the sediment load to move down stream. Most large sediment falls to the bottom and moves by rolling and sliding. Fast-moving water actually lifts sand and other, smaller, sediment and carries it downstream. Water dissolves some sediment completely. The river carries these dissolved sediments in solution.

Erosion and Sediment Load The power of a river to cause erosion and carry sediment depends on several factors. A rivers slope, volume of flow and the shape of its streambed all affect how fast the river flows and how much sediment it can erode. A fast-flowing river carries more and larger particles of sediment. When a river slows down, its sediment load is deposited. The larger particles of sediment are deposited first.

Slope Generally, if a river’s slope increases, the water’s speed also increases. A river’s slope is the amount the river drops toward sea leverl over a given distance. If a river’s speed increases, its sediment load and power to erode may increase. But other factors are also important in determining how much sediment the river erodes and carries.

Volume of Flow A river’s flow is the volume of water that moves past a point on the triver in a given time. As more water flows through a river, its speed increases. During a flood, the increased volume of water helps the river to cut more deeply into its banks and bed. A flooding river may have hundres of times more eroding power than the river has at other times. A flooding river can carry huge amounts of sand, soiil, and other sediments. It may move giant boulders as if they were pebbles.

Streambed Shape A streambed’s shape affects the amount of friction between the water and the streambed. Friction is the force that opposes the motion of one surface as it moves across another surface. Friction, in turn, affects a river’s speed. Where a river is deep, less water comes in contact with the stream bed. This reduces friction and allows the river to flow faster. In a shallow river, much of the water comes in contact with the streambed. Therefore frictions increases reducing the river’s speed.

A stream bed is often full of boulders and other obstacles A stream bed is often full of boulders and other obstacles. This roughness prevents the water from flowing smoothly. Roughness thus increases friction and reduces the river’s speed. Instead of moving down stream, the water moves every which way in a type of movement called turbulence. For example, a stream on a gentle slope. Friction and turbulence slow the stream’s flow. But a turbulence stream or river may have great power to erode. The shape of a river affects the way it deposits sediment. Where a river flows in a straight line, the water flows faster near the center of the river than along its sides. Deposition occurs along the sides of the river, where the water moves more slowly. If a river curves, the water moves fastest along the outside of the curve. There the river tends to cut into its band. Sediment is deposited on the inside curve, where the water speed is slowest.

Review QUestions How can moving water on Earth’s surface do work? Ho does a river collect sediment? What are three factors that affect a river’s sediment load? Describe three ways that sediment moves in a river. What effect does increased slope have on a river’s speed and sediment load? explain

Build a Diagram Be prepared to create a diagram based on this weeks lessons. The movement of water in rivers and streams. How water erodes the land under and around it. Look at your vocabulary make sure that you know what the words are and how you can make a diagram with them.