The Water Cycle

Water never leaves the Earth! It is constantly being cycled through the atmosphere, ocean, and land. This process, known as the water cycle, is driven by energy from the sun. The water cycle is crucial to the existence of life on our planet.

The Water Cycle

During part of the water cycle, the sun heats up liquid water and changes it to a gas by the process of evaporation. Water that evaporates from Earth’s oceans, lakes, rivers, and moist soil rises up into the atmosphere.

The process of evaporation from plants is called transpiration The process of evaporation from plants is called transpiration. (In other words, it’s like plants sweating.) Evapotranspiration???

As water (in the form of gas) rises higher in the atmosphere, it starts to cool and become a liquid again. This process is called condensation. When a large amount of water vapor condenses, it results in the formation of clouds.

When the clouds become saturated with water to the point that gravity causes the water to fall back to the earth it’s called precipitation.

When rain falls on the land, some of the water is absorbed into the ground forming pockets of water called groundwater. Most groundwater eventually returns to the ocean. Other precipitation runs directly into streams or rivers. Water that collects in rivers, streams, and oceans is called runoff.

Water Budget The continuous cycle of the water cycle establishes Earth’s water budget. As a whole, the cycle, and therefore the water budget, stay balanced, but can be off balance locally. Factors like temperature, vegetation, wind, and amount of rainfall can affect local water budget.

Water Budget The local water budget can change with seasons. The desert in Australia receives a lot less rainfall per year than the tropical forests of New Zealand. Negative Budget Positive Budget

Our Water Usage On average, each person in the U.S. uses about 95,000 L of water/year. 90% of water used is returned to rivers or oceans as wastewater. Much of that water contains toxic materials and metals. So what can we do?

Who uses the most??

Water Conservation: What can we do? Government helps by enforcing conservation laws and antipollution laws, prohibiting dumping waste into bodies of water. Desalination: the process of removing salt from ocean water. It is a very expensive method.

River Systems

Oconee and Ocmulgee meeting to form the Altamaha River and ending in the ocean near Brunswick, Ga.

Eastern Continental Divide

River Systems A river system consists of a main (trunk) stream and its tributaries The land drained by these streams is called the watershed Ridges or areas of high ground that separate watersheds are called divides.

Wordle

How do we know if our local water is clean? Visual Score: Evaluates the appearance of the stream including bank erosion, riparian zone (vegetation), flow, clarity, and aquatic organisms. Out of 56. Biological Score: The amount of life in the stream, including plants and aquatic organisms. Nitrate (NO3-): High nitrate levels indicate the presence of fertilizers and/or animal waste (including sewage). >10 mg/L unsafe for drinking. pH: Measures acidity. Aquatic organisms can survive in a narrow range: 6.0-8.5 E. Coli: Indicates the presence of animal feces in water. High levels may contain harmful pathogens. 200 CFU/100ml is normal. Specific Conductivity: Measures the dissolved ions or salts and can be used as an indicator of pollution in the form of nutrients or chemicals.

Channel Erosion River Systems change continuously. Headward erosion: The channels lengthen and branch out at their upper ends, where runoff enters the streams. Slopes of erosion can affect what streams go into a watershed. Stream Piracy can occur when one stream changes to another watershed because of a high rate of erosion.

The soil, loose rock fragments, and dissolved minerals in the stream as it flows downhill is called the stream load.

Stream Discharge The volume of water moved by a stream in a given time period Speed of the river affects channel erosion, faster streams erode in a shorter amount of time.

Stream Gradient is the change in elevation or steepness of a stream

Evolution of River Channels Young streams start with steep sides and large discharge. As it ages, it becomes wider and slower and will eventually be called a river. When rivers have turns or bends, the velocity of the water is faster on the outside of the turn, causing more erosion on the outside. Deposition of soil occurs on the inside on bends.

Stages of a River System

Meanders develop in low gradient rivers.

When meanders grow so big that the river erodes and creates an abandoned meander. San Juan River, Utah abandoned meander

Stream Deposition When the stream load becomes too much for the velocity of the stream, deposition occurs. This may occur on land or in water. This is very common when a stream meets a lake or ocean because of a sharp decrease in velocity.

Deltas When sediment is deposited to a large body of water in a triangular shape it is called a delta.

Death Valley, California Alluvial Fans Occur when a stream descends a steep slope and reaches a flat plain. Form on land. Death Valley, California Lowest elevation point in North Am. Border of Cali and Nevada.

Let’s compare! Deltas: Alluvial Fans: Deposited in water Deposited on land Made up mostly of mud Made up mostly of sand and gravel Surface is relatively flat Surface is sloping

Floodplains The volume of water in nearly all streams varies depending on amount of rainfall and snowmelt in the watershed. A dramatic increase in volume can cause a stream to overflow. The area that may be covered with water during this overflow is called a floodplain.

Floodplains Natural Levees: when a stream overflows, large sediment is deposited, eventually creating ridges protecting the floodplain from floods in the future.

Do we cause floods? When construction removes vegetation, such as trees and shrubs, soil erosion will occur, allowing water to move across the ground more freely. This increases the likelihood of floods. Logging or clearing of land for development can also cause increase in flooding.

Flood Control We can help with forest and soil conservation. In developed areas, we can build structures, such as levees, to redirect water flow. Mississippi

Flood Control Most common method is building of dams. Water stored behind dams can be used for hydroelectric energy, as a freshwater supply, and irrigate farmland. California