The Hydrologic System


What is the Hydrologic System?

The Hydrologic System is the entire cycle of water movement. It is also known as the water cycle. Rainwater infiltrates the soil and then the water is absorbed by plants, evaporates, or runs off into other surface waters. The energy from the sun is what drives the system.

The majority of water is located in oceans (97.6%).The remaining water is located in glaciers (1.9%), ground water (0.5%), and lakes and rivers (0.02%). It may seem like there is plenty of water, yet very little of the water that exists is appropriate and accessible for human use.

The amount of time that water replenishes differs depending on the water source. The water in rivers on average is renewed every sixteen days. The water in the atmosphere is replaced every eight days. The water in lakes, glaciers, oceans, and ground water can take hundreds to thousands of years to be completely renewed. The actions of humans are making it harder for the hydrologic system to process efficiently.

Human Impact:


The Earth's water supply is constant. However, humans have the ability to alter the water supply by daily activities. In every generation, the ideal living standard has increased. Higher populations result in an increase of economic and industrial growth. The human population has increased significantly as well. This strains the Earth's natural resources, including water. Higher population results in withdrawing more water from rivers, lakes, and aquifers. This damages local resources, habitats, and threatens the future water supply. Higher population also leads to larger amounts of waste water being discharged. This pollutes water resources, and the hydrologic system can not replenish the water fast enough. If the human population continues to grow as predicted, the earth is going to be under tremendous stress from trying to support all forms of life. Our activities can alter the hydrologic system by changing the quantity and quality of water that is produced by the system.

Actions that Harm the Hydrologic System:

  • Withdrawing large amounts of water
  • Constructing roads, homes, and industrial buildings
  • Removal of trees and vegetation
  • Filling in ponds
  • Using water resources as a garbage disposal

All of these actions harm the hydrologic system because runoff can not be filtered or slowed down before being distributed into other bodies of water. As a result, the amount of water that infiltrates is decreased and  the amount of storm water runoff increases. This then creates more problems such as erosion, flooding, and destruction of habitat.


Water Resource:

As human population increases water is becoming more limited. Yet, people expect clean and affordable water at easy access. Michigan and the surrounding states of the Great Lakes are fortunate to have a huge water supply so close to home. The Great Lakes are a very valuable and vulnerable resource. They hold 90% of the fresh surface water in North America. The Great Lakes are going to play a large role in environmental policies as water becomes more scarce. There has already been discussion of transporting water from the Great Lakes to western states.