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Hydrologic Modification

Agricultural Practice

Some of the biggest threats to water’s quality are the modifications or changes we’ve made to the landscapes that water moves through. Explore More about the ways we’ve interfered with the natural hydrologic cycle and the effects of those changes.

The Cycle of Life
Whether you notice it or not, water is constantly on the move all around us. It’s falling to the land in the form of precipitation. It’s moving across landscapes making its way to streams. Streams are running to rivers and rivers are running to oceans. Water is evaporating and transpirating and absorbing. Water is the ultimate recycled element thanks to the hydrologic cycle, which constantly moves water from the atmosphere–down to the planet’s surface and then back into the atmosphere.

The Natural Water Cycle
In a natural system, with no human modifications, water "percolates" through many different elements (sand and dirt, rocky and grassy areas) before reaching waterways like streams and rivers. Those elements help filter out pollutants. Sometimes they act as holding areas, creating standing water waiting to go through the system. Humans have made hydrologic modifications short—working around this natural flow, forcing water more directly into waterways, and making the water more vulnerable to pollutants.

Human Modification
Modifications to the natural landscapes, like tiling and uprooting prairies, were made for many different reasons. Some were made to support agriculture; forests were cleared and lands were drained. Other modifications supported development of cities and towns, resulting in more impervious surfaces and less pervious ones. Major changes, like shifting a river’s course or straightening its flow, were made to support navigation. Whatever the reasons for the modifications, they had the same outcome—changing the way water moves through landscapes, affecting what water comes into contact with and ultimately, water’s quality.


Explore More: Water Quality
Copyright 2004, Iowa Public Television
The Explore More project is supported by funds from the
Roy J. Carver Charitable Trust
and the USDE Star Schools Program.



Hydrologic Modification to Urban Settings
What changes could be made by city planners to protect water quality?

Urban Development

The very act of development has a huge impact on water quality. More

Nonpoint Source Pollution

What are the sources of pollution and their and effects? More


Hydrologic Modifications to Agricultural Settings
North America looks very different now than it did when the European settlers first arrived. More

Government Programs
Federal programs have been developed to encourage farmers to restore environmentally sensitive acres. More

Fast Facts: An Overview of Wetlands
"The preservation of existing wetlands and the restoration of wetlands, which are both needed, is going to require a partnership between farmers and environmentalists. And it will need to be done on private land if it is to be effective." More

IPTV Market to Market Online Links

"Western Interest Still Divided Over Water Use." This Market to Market feature looks at the controversy of water rights taking place in the the western part of the country.

"Water Issues Trouble Rural America." This Market to Market feature looks at water interests of farming and rural areas. Read about flooding, drought, hydrologic modification, and more.