Surface-Water Basics

The U.S. Geological Survey (USGS) has been measuring the amount of water flowing in rivers since the 19th century. Having reliable past and present streamflow information is vital for many reasons, both at the personal and national level.

The following topics provide background on some of the scientific issues regarding glaciers.

If a low-lying area near a river near you usually gets about 50 inches of rain a year, you might think "Well, that is about 1 inch per week, so that won't cause any flooding". But, nature doesn't think the same way, and often a large percentage of a year's precipitation can fall in a major storm, in a single day. Your river might not react much to a 1 inch rain, but things might be much different...

Naturally, the water running in rivers comes from precipitation that runs off the landscape into the river. But since precipitation also seeps into (and moves) into the ground, you don't often consider that a significant amount of the water flowing in rivers comes from water in the ground seeping back "up" into the river from below.

When rain falls onto the landscape, it doesn't just sit there and wait to be evaporated by the sun or lapped up by the local wildlife—it begins to move (due to gravity). Some of it seeps into the ground to refresh groundwater, but most of it flows down gradient as surface runoff. Runoff is an intricate part of the natural water cycle.

A lake really is just another component of Earth's surface water. A lake is where surface-water runoff and groundwater seepage have accumulated in a low spot, relative to the surrounding countryside.

Creeks and streams begin their lives as smaller water bodies that run downhill until they merge to form bigger rivers. Rivers are a mighty factor when it comes to shaping the physical landscape — just ask the Grand Canyon. Find out more here.

Rivers? Streams? Creeks? These are all names for water flowing on the Earth's surface. Whatever you call them and no matter how large they are, they are invaluable for all life on Earth and are important components of the Earth's water cycle.

Glaciers are a big item when we talk about the world's water supply. Almost 10 percent of the world's land mass is currently covered with glaciers, mostly in places like Greenland and Antarctica. You can think of a glacier as a frozen river, and like rivers, they "flow" downhill, erode the landscape, and move water along in the Earth's water cycle.

An aqueduct has been and continues to be an imporant way to get water from one place to another. Be it 2,000 years ago in ancient Rome, Italy or today in California, aqueducts were and are essential to get water from a place where it exists in ample supply to where it is scarce. Find out how these "ancient marvels" work.