STORM WATER MANAGEMENT
HYDROLOGIC CYCLE
What Is The Hydrologic Cycle?
The Hydrologic Cycle shows the path water takes from one state to another. From water storage and condensation in the atmosphere to precipitation, surface runoff and freshwater storage, infiltration and groundwater storage, marine storage to evapotranspiration and evaporation.
The water of the earth is in a constant state of flux from one state to the next. It is a true cycle, and therefore there is no true beginning or end. The USGS developed this interactive poster for the Hydrologic Cycle.
Heat from the sun causes evaporation as surface water changes from freshwater and marine storage into vapor in the atmosphere. Evapotranspiration is the transfer of water from the soil and from plants as vapor into the atmosphere. Another mode of state change for water is directly from the ice state to the vapor state, a process known as sublimation.
The solid states of water consist of ice and snow. Water can typically be found at higher elevations in solid states, as well as at the polar caps. The solid state of water represents the greatest proportion of freshwater storage in the planet, nearly 70% of global freshwater.
In the liquid form, water can be found in freshwater surface and groundwater storage, surface runoff, and groundwater discharges. This represents the amount of water readily available for human consumption.
Hydrologic Cycle and Water Pollution
The types of pollution differ from one state to the next. In the vapor state, water often combines with Sulfur and Nitrogen oxides in the atmosphere to create acidic compounds. As these new molecules condense, the acid concentrations become stronger, and the rain that falls is what is known as "Acid Rain." This is a sensitive state for water pollution, because there is no way to remove the pollutants while the water is in the atmosphere.
In the liquid state, water can contain a host of pollutants. In the liquid state water also has the ability to move pollutants from one location to another. While some pollutants can be partially removed from water in the liquid state, it is typically an energy intensive and expensive process.
As ice forms, pollutants are generally deposited in the surrounding environment. This means the ice itself is relatively pollutant free, but once the ice begins to melt the pollutants are absorbed in the water once again and begin to move where the water flows.
Removing pollutants from water in any state is always more difficult and more costly than preventing the pollution from entering the environment.
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