EARTHS WATER By: Kamiya J. Avery W. LaMarcus J. and JaMarcus W.

SURFACE WATER

Surface Water Basics

Lakes and reservoirs

Rivers

Rivers and the landscape

Sediment in rivers

Rivers of the world

Use of streamflow information

Seasonal streamflow patterns

Sea level and climate

Glaciers and icecaps

Watersheds

RIVERS AND STREAMS

The Chattahoochee River, Atlanta, Georgia, USA. The river serves many purposes, from drinking water to wildlife habitat to a recreation spot for the whole city. Credit: National Park Service.

Most of the water you see flowing in rivers comes from precipitation runoff from the land surface alongside the river. Of course, not all runoff ends up in rivers. Some of it evaporates on the journey downslope, can be diverted and used by people for their uses, and can even be lapped up by thirsty animals. Rivers flow through valleys in the landscape with ridges of higher land separating the valleys. The area of land between ridges that collects precipitation is a watershed or drainage basin. Most, but not all, precipitation that falls in a watershed runs off directly into rivers - part of it soaks into the ground to recharge groundwater aquifers, some of which can then seep back into riverbeds.

LAKES AND RESERVOIRS

Hidden Lake, Glacier National Park, Montana, is nestled in the high mountains, and runoff from the steep slopes of surrounding landscape helps to keep the lake full.Credit: Lisa McKeon, USGS

A lake really is just another component of Earth's surface water. A lake is where surface-water runoff (and maybe some groundwater seepage) have accumulated in a low spot, relative to the surrounding countryside. It's not that the water that forms lakes get trapped, but that the water entering a lake comes in faster than it can escape, either via outflow in a river, seepage into the ground, or by evaporation. And if humans live nearby, then water levels can be affected by water withdrawals for human needs.

GROUNDWATER Some water underlies the Earth's surface almost everywhere, beneath hills, mountains, plains, and deserts. It is not always accessible, or fresh enough for use without treatment, and it's sometimes difficult to locate or to measure and describe. This water may occur close to the land surface, as in a marsh, or it may lie many hundreds of feet below the surface, as in some arid areas of the West. Water at very shallow depths might be just a few hours old; at moderate depth, it may be 100 years old; and at great depth or after having flowed long distances from places of entry, water may be several thousands of years old.

Groundwater occurs only close to the Earth's surface. There must be space between the rock particles for groundwater to occur, and the Earth's material becomes denser with more depth. Essentially, the weight of the rocks above condense the rocks below and squeeze out the open pore spaces deeper in the Earth. That is why groundwater can only be found within a few miles of the Earth's surface.

Groundwater is an important part of the water cycle. Groundwater is the part of precipitation that seeps down through the soil until it reaches rock material that is saturated with water. Water in the ground is stored in the spaces between rock particles (no, there are no underground rivers or lakes). Groundwater slowly moves underground, generally at a downward angle (because of gravity), and may eventually seep into streams, lakes, and oceans.

AQUIFERS

WELLS

Dug wells

Hacking at the ground with a pick and shovel is one way to dig a well. If the ground is soft and the water table is shallow,then dug wells can work. Historically, dug wells were excavated by hand shovel to below the water table until incoming water exceeded the digger's bailing rate . The well was lined with stones, brick, tile, or other material to prevent collapse, and was covered with a cap of wood, stone, or concrete. They cannot be dug much deeper than the water table -- just as you cannot dig a hole very deep when you are at the beach... it keeps filling up with water!

Driven wells

Driven wells are still common today. They are built by driving a small-diameter pipe into soft earth, such as sand or gravel. A screen is usually attached to the bottom of the pipe to filter out sand and other particles. Problems? They can only tap shallow water, and because the source of the water is so close to the surface, contamination from surface pollutants can occur.

Drilled wells

Most modern wells are drilled, which requires a fairly complicated and expensive drill rig. Drill rigs are often mounted on big trucks. They use rotary drill bits that chew away at the rock, percussion bits that smash the rock, or, if the ground is soft,large auger bits. Drilled wells can be drilled more than 1,000 feet deep. Often a pump is placed at the bottom to push water up to the surface.

THE END KAMRYN AVERY JAMARCUS LAMARCUS