Stream Erosion and Landscape Development

Almost all the landscape of Earth is the result of erosion. Only small areas are constructional, including volcanoes, river plains and deltas, coral reefs, and the surfaces of glaciers and ice sheets.

Stream Health, Assessing

A stream is the central component of a landscape where water drains downslope to the lowest point via a network of drainage channels. The dynamic and complex drainage system may have taken centuries to become naturally established, and its ongoing processes can be interrupted or modified by human intervention.

Stream Hydrology

Streams are created when excess water from rain, snowmelt, or near-surface groundwater accumulates on the ground surface and begins to run downhill. This excess water from rain or snowmelt generally occurs when the water accumulates at a faster rate than the soil and organic matter (e.g., dead and decaying vegetation) can absorb the water, plants can use it, or the water can be evaporated into the air.

Stream, Hyporheic Zone of a

The hyporheic zone is defined as a subsurface volume of sediment and porous space adjacent to a stream through which stream water readily exchanges. Although the hyporheic zone physically is defined by the hydrology of a stream and its surrounding environment, it has a strong influence on stream ecology, stream biogeochemical cycling, and stream-water temperatures.

Streamflow Variability

Streams and rivers play a critical role in the hydrologic cycle that is essential for all life on Earth. A diversity of biological species, from unicellular organisms to vertebrates, depend on flowing-water systems for their habitat and food resources.

Stumm, Werner

Werner Stumm contributed distinctively to the field of water chemistry, including equilibrium studies, iron oxidation kinetics, corrosion chemistry, eutrophication, coagulation–flocculation, and, perhaps most importantly, the evolution of fresh waters and marine waters. His work resulted from careful theory, experimentation, and quantitative analysis of particle–water and air–water interfaces at the molecular and atomic scales.

Submarines and Submersibles

Underwater vehicles are called submersibles, or airtight, rigid diving machines designed for exploration while completely submerged. Submersibles are either manned or remotely operated.

Supplies, Protecting Public Drinking-Water

Drinking water comes from two major sources: groundwater and surface water. Groundwater is pumped from wells drilled into aquifers.

Supplies, Public and Domestic Water

Water supplies are needed for public, domestic (private), commercial, agricultural, and industrial uses. Public water supplies are those supplied by a public agency in populated areas for all these purposes.

Supply Development

Water resources development is the process by which the world's water sources are engineered to deliver adequate quantities of high-quality water to serve the forecasted needs of society. In the United States, the public attitude toward the development and use of the nation's waters has changed over time, as have trends in development policy and practice.

Survival Needs

Water is fundamental to all life on Earth. While it may be easy for many of us to take the availability of water for granted, growing demands on the world's water resources highlight the importance of water to everyday life.

Sustainable Development

The concept of sustainable development was popularized by the World Commission on Environment and Development in its report "Our Common Future" that was published in 1987. The Commission defined sustainable development as development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

Sverdrup, Harald

Sverdrup is a unit of measure, the system of education in Norway, and a set of equations describing the movement of ocean currents. All are named for Harald Ulrik Sverdrup.

Tennessee Valley Authority

The Tennessee Valley Authority (TVA) was created as a federal corporation in May 1933 in order to develop the Tennessee River and its tributaries for the purpose of navigation, flood control, and the production and distribution of electricity. It also provided reforestation, erosion control, industrial and community development, improved farming techniques, fertilizer development, and establishment of recreational facilities.

Theis, Charles Vernon

Charles Vernon Theis was the first to develop mathematical expressions that allow hydrogeologists to determine the characteristics of an aquifer and predict how water levels in the aquifer change during pumping.


Ocean tides are periodic rises and falls in the level of the sea, and are formed by the gravitational attraction of the Moon and Sun on the water in the ocean. Although the Moon is much smaller than the Sun, it has a greater gravitational attraction for the Earth because the Moon is much closer to Earth.


Clean water contributes to the recreation and tourism industry worldwide by accentuating beautiful beaches, white-water rivers, mountain lakes, and aquatic ecosystems such as coral reefs. Water has a powerful attraction for people.

Tracers in Fresh Water

A tracer as used in hydrology is a substance in water that can be used for tracking water movement. Tracers primarily are used to determine the direction and rate of water movement.

Tracers of Ocean-Water Masses

The oceans, atmosphere, continents and cryosphere are part of Earth's tightly connected climate system. The ocean's role in the climate system involves the transport, sequestration, and exchange of heat, fresh water, and carbon dioxide (CO2) between the other components of the system.

Transboundary Water Treaties

A transboundary waterway is defined as all territory which contributes to a stream, at least one of the tributaries of which crosses a boundary. Almost half the Earth's land surface, excluding Antarctica, and 60 percent of the world's fresh water, falls within these basins.* What this means in human terms is that most of the world's water is shared water; consequently, because all waters in these basins are connected, political arrangements are necessary for the nations which share them (i.e., coriparian nations) in order to manage them efficiently.


Historically, societies have always located near water, due partly to the fact that water enables more efficient travel compared to going over land. Waterways are critically important to the transportation of people and goods throughout the world.


A tsunami is a powerful wave, usually created by a large-scale motion of the ocean floor. Although they are almost imperceptible at sea, tsunami waves increase in height as they reach a coastline and are capable of causing great destruction.