Stream erosion has shaped the landscape of the planet. Constructional areas are limited, and include volcanoes, river plains and deltas, coral reefs, and the surfaces of glaciers and ice sheets. Mountain ranges are built by forces within the Earth, but individual mountains are only the remnants left behind by the erosion of the valleys that separate them. The continually eroding valleys are the active, evolving part of the landscape.

Rivers have been credited with up to 90 percent of the total sediment transported to the sea, although this journey can take many human lifetimes. All of the sediments that eventually end up in the sea were at some time, a part of the continental landscape.

Rivers and Landscape Shaping

Stream erosion occurs when water flowing through a channel is able to transport sediment downstream. The amount of sediment transported depends mainly on the volume of flow, which is related to the size of the drainage basin and can fluctuate immensely. Volume of streamflow, or discharge, is measured in cubic meters per second. Most riverbed erosion occurs during times of high discharge.

New landscapes can be created by constructional forces, such as a volcanic eruption, the melting of a glacier, or the uplift of the ocean floor. On a new landscape, river runoff follows an irregular path downhill towards sea level, forming lakes in closed basins and then overflowing to continue downhill. This pre-mature drainage is called a consequent system because it is a direct consequence of the preexisting landscape.  As time goes on, the drainage network becomes more streamlined. Water cuts new paths and consolidates others as it follows the path of least resistance to sea level. Drainage networks become sophisticated but simplified, as they shape the landscape and adjust to their climate region.

As rocks erode, rivers gradually change their courses to keep their path of least resistance. Where a river crosses rocks resistant to erosion, it generally cuts a steep, narrow canyon. This occurs because the river is unable to erode the underlying rock at the rate that the river erodes the rock downstream, creating a steep gradient. An example of this process is a wide, open valley in the mountains with a flat running stream, while upstream you find a steep, narrow gorge cut through rocks that were unable to be eroded at the rate the valley was.

Sediment Transportation

There are three ways sediment is transported in a river: in a solution, suspended, or as bed load.

Solution load - These are sediments that are dissolved in the water. Solution load is generally higher where water flow is derived from mainly groundwater and where local bedrock, such as limestone, is prone to chemical weathering.

Suspended load - These are sediments that are not dissolved in the water, but are present in them. They are suspended in the water. These usually include fine sediments such as clay and silt. They are suspended mainly by turbulence, and will settle out when they have been dormant for awhile.

Bed load - These are sediments that roll, skip, or slide across the stream bed. There will be periods of time that these sediments are settled at the bottom of the bed, and times when they are being transported, depending on turbulence.

This photo taken by me from a plane flying near Las Vegas, Nevada clearly shows the effect of stream erosion on this landscape. Over time, the stream has eroded the surrounding bedrock and was able to maintain its flow, making it a subsequent stream. 

For more information, visit
The Water Encyclopedia

The American Geosciences Institute

Wetlands are Essential - Ramsar Convention

Wetlands are an essential part of our planet's hydrologic system. They are vital to the health of waterways and surrounding communities. They provide essential services, both environmentally and economically. Wetlands include swamps, marshes, and bogs, and can vary greatly in soil composition, climate, topography, vegetation, water chemistry, etc. Wetlands found in flood plains or near waterways are connected to surface water, while there are other wetlands that have a stronger connection to ground water.

Wetlands provide habitat to one of the most biologically rich ecosystems on the planet. According to the Environmental Protection Agency, numerous species rely on wetlands for reproduction, food, and shelter. For some forms of life, including wood ducks, muskrat, and cattails, wetlands are their sole habitat. Many bird species food, nest, and raise their young in wetlands. Some species of migratory birds, in fact, are so dependent on certain wetlands that they would become extinct of those wetlands were destroyed. Wetlands provide habitat for water lilies, turtles, fish, frogs, snakes, alligators, waterfowl, and mammals.

Wetlands help trap flood waters, recharge groundwater supplies, filter pollution, provide habitat, and provide recreation. Because they are able to provide habitat and recreation, that makes them vital to economic health as well. Most commercial and game fish breed and raise their young in coastal marshes and estuaries, including enhaden, flounder, sea trout, spot, croaker, and striped bass. Shrimp, oysters, clams, and blue and Dungeness crabs need these wetlands for food, shelter, and breeding grounds. Recreation can offer an important economic influx as well.

      The Ramsar convention was a convention held in Iran in 1971 with representatives from 18 industrial countries to prepare the first comprehensive treaty regarding wetlands. The treaty addresses the conservation and sustainability of wetlands. It is the only global convention that has focused on an ecosystem. The Convention defines wetlands broadly, including lakes and rivers, underground aquifers, swamps and marshes, wet grasslands, peatlands, estuaries, tidal flats, mangroves, coral reefs, and all human-made sites such as reservoirs, fish ponds, and rice paddies. Ramsar does not cover deep oceans. Its mission statement reads, "The conservation and wise use of wetlands through local, regional and national actions and international cooperation as a contribution towards achieving sustainable development throughout the world.” They define the wise use of wetlands as, "their sustainable utilization for the benefit of humankind in a way compatible with the maintenance of the natural properties of the ecosystem” Today, there are 2040 Wetlands of International Importance, or "Ramsar sites," totaling at 193 million hectares. Some criteria for classifying these areas can include the support of important biodiversity or an important life-cycle site for species, such as turtles, waterbirds, and fish.

The idea to form the Convention occurred in 1962, but it took eight years to actually realize it. Managing wetlands is a global challenge, and the member countries of the Convention recognize the value of having one international treaty dedicated to a single ecosystem. The Ramsar Convention recognizes the importance of wetlands for human well-being, including the importance in goods and services as well as food and water security. The model supports practical and "wise" use, hopefully lending to sustainable practices.

Strouds Run is a man-made reservoir, which would be classified as a wetland under Ramsar

For more information:
The Nature Conservancy
EPA Wetland Fact Sheet 
PowerPoint about Ramsar
The World Wildlife Foundation