- Components and definition of the hydrologic cycle
- Water users and volume of water used
- How water is shared among people
- Distribution of water on the planet
- Define aquifer and confining layer
- Properties required for a good aquifer
All life requires water. The hydrosphere (Earth’s water) is an important agent of geologic change. It shapes our planet through weathering and erosion, deposits minerals that aid in lithification, and alters rocks after they are lithified. Water carried by subducted oceanic plates causes melting in the upper mantle material. Communities rely on suitable water sources for consumption, power generation, crop production, and many other things.
- 9.1: Prelude to Water
- n pre-industrial civilizations, control of water resources was a symbol of power. Two thousand-year-old Roman aqueducts still grace European, Middle Eastern, and North African skylines. Ancient Mayan kings used water imagery such as frogs, water-lilies, waterfowl to show their divine power over their societies' water resources. Control over water continues to be an integral part of the governmental duties of most modern societies.
- 9.2: Properties of Water
- The physical and chemical properties of water are what make it essential to life and useful to civilization. Water is a molecule made of one negatively charged (-2) oxygen ion and two positively-charged (+1) hydrogen ions, giving it the chemical formula H2O, with strong covalent bonds between the oxygen and two hydrogen ions. The shape of the water molecule allows for an uneven distribution of charge, where one side is slightly positive and one side is slightly negative.
- 9.3: Water Cycle
- The water cycle describes how water changes between solid, liquid, and gas (water vapor) phases and changes location. Water can be evaporated, which is the process where a liquid is converted to a gas. Solar energy warms the water sufficiently to excite the water molecules to the point of vaporization. Evaporation occurs from surface water bodies such as oceans, lakes, and streams and the land surface.
- 9.4: Water Basin and Budgets
- The basic unit of division of the landscape is the drainage basin. A drainage basin, also known as a catchment or watershed, is the area of land that captures precipitation and contributes runoff to a stream or stream segment. Drainage divides are local topographic high points that separate one drainage basin from another. If water falls on one side of the divide, that water goes to one stream, and if it falls on the other side of the divide, then the water goes to a different stream.
- 9.5: Water Use and Distribution
- In the United States, 355 billion gallons of ground and surface water are withdrawn for use each day, of which 76 billion gallons are fresh groundwater. The state of California accounts for 16% of national groundwater withdrawals. Utah is the second driest state in the United States behind its neighbor Nevada, having a mean statewide precipitation of 12.2 inches per year. Utah also has the second-highest per capita rate of total domestic water use of 167 gallons per day per person.
- 9.6: Water Law
- Federal and state governments have put laws in place to ensure the fair and equitable use of water. Based on the distribution of precipitation in the United States, the states are in a position that requires them to create a fair and legal system for sharing water. Because of the limited supply of water, especially in the western United States, some states have adopted a system of legally dispersing ownership of natural waters. A claim to a portion of a water source is known as a water right.
- 9.7: Surface Water
- A stream or river is a body of flowing surface water confined to a channel. Terms such as creeks and brooks are social terms not used in geology. Streams are the most important agents of erosion and transportation of sediments on the earth’s surface. They create much of the surface topography and are an important water resource. Most of this section will focus on stream location, processes, landforms, and hazards. Water resources and groundwater processes will be discussed in later sections.
- 9.8: Groundwater
- Most rocks are not entirely solid and contain a certain amount of open space between grains or crystals, known as pores. Porosity is a measure of the open space in rocks –expressed as the percentage of open space that makes up the total volume of the rock or sediment material. Porosity can occur as primary porosity, which represents the original pore spaces in the rock (e.g. space between sand grains), or secondary porosity which occurs after the rock forms (e.g. dissolved portions of rock).
- 9.9: Water Contamination
- Water can be contaminated by various human activities or by existing natural features, like mineral-rich geologic formations. Agricultural activities, industrial operations, landfills, animal operations, and small and large scale sewage treatment processes, among many other things, all can potentially contribute to contamination. As water runs over the land or infiltrates into the ground, it dissolves material left behind by these potential contaminant sources.
- 9.10: Karst
- Karst refers to landscapes and hydrologic features created by the dissolution of limestone. Karst can be found anywhere where there are limestone and other soluble subterranean substances like salt deposits. The dissolution of limestone creates features like sinkholes, caverns, disappearing streams, and towers. Karst forms when natural water, in combination with carbon dioxide, creates carbonic acid and dissolves calcite (calcium carbonate) in limestone.
Thumbnail: Violent water below Niagara Falls. Image used with permission (CC-BY; The Rafti Institute).