What Is A River & How Are Rivers Formed
What Is A River & How Are Rivers Formed
By Marisa Repasch
Defining the natural resources provided by rivers and how we can maintain them for future generations and how river restoration projects are vital to clean water and wildlife animals.
Rivers are arguably the most important natural resources for life on our planet. They deliver fresh water, nutrients, and food from humid mountains to dry lowlands. They provide a network for transportation across continents, and habitats for fish, birds, and mammals. Rivers can only offer these functions in their natural conditions. Engineering has changed the natural dynamics of rivers, such that rivers no longer provide these functions. Today, many people may not even know what a natural river looks like.
Government agencies have started to push efforts for river restoration, to regain the functions our rivers once performed. But how do we know what a river’s natural conditions should be?
Defining A Natural Baseline For River Restoration Techniques
River restoration projects aim to rejuvenate native fish populations, to restore water quality, or to rebuild natural floodplains. For every restoration project, a natural baseline needs to be established to define an end goal and a management plan. This baseline is essentially what a river looked like before human alteration. Defining a baseline for river restoration is challenging, but scientists and engineers are working to understand the characteristics and functions of natural rivers.
Characteristics of a Natural River
Natural rivers do not have straight channels. Their channels are often sinuous, winding across the floodplain. A river’s shape is ultimately a function of the local climate, geology, and hydrology.
Natural rivers are free to move. Natural river banks are composed of sediment and soil that can be easily eroded in floods or high flow conditions. Lateral mobility drives the exchange of sediment and nutrients between the channel and the floodplain, helping floodplain vegetation growth. Lateral erosion also enables nutrient and sediment delivery to the coast.
Natural rivers have great variability in water flow. During rain storms, river levels rise. Water and sediment can spill out onto the floodplain, rejuvenating wetlands. Trees and other plants on the floodplain need variability in the water table to maintain intermittent access to water.
Natural rivers carry sediment. Rivers carry soil and rock naturally eroded from mountains and deliver that material to the coasts. This delivery helps to maintain sand on beaches and deltas, which are economic hotspots.
Natural rivers have high biodiversity. Riparian forests provide habitats for many animals. Plants also uptake metals and contaminants from runoff and groundwater. Soils within river corridors also filter runoff, enhancing river water quality.
The Impacts Of River Engineering
Civilization was built along the banks of rivers. Evolving from the earliest civilizations in Mesopotamia, the largest cities in the world now sit on the banks of major rivers. To protect civilizations from the unpredictable nature of rivers, we built structures to stabilize their channels and control their water levels.
Deforestation is one of the most common forms of human intervention on river ecosystems. Vegetation is often clear cut to make way for riverfront development. This leads to immediate habitat loss, bank destabilization, and increased runoff.
Dams diminish the upstream to downstream connectivity of rivers. These structures reduce water flow and prevent flooding, leading to dry wetlands and less floodplain productivity. Dams also prevent sediment from moving downstream, leading to coastal land loss and lower nutrient supplies.
Levees or artificial embankments eliminate lateral mobility of the channel. These structures eliminate the exchange of sediment and nutrients between the channel and floodplain, leading to long-term degradation of the ecosystem.
Canals divert water for transportation or for irrigation. These structures can create barriers to wildlife trying to access a river. Canals can also result in wetland drainage and drying, driving habitat loss and ecosystem degradation.
While these engineering practices help to develop economic activity around rivers, we are now aware of their negative impacts on river health. River restoration requires finding the right balance between economic development and a river’s natural characteristics.
What Does Your Local River Look Like?
Do you live near a river, stream, or creek? If so, what does it look like? Is it a straight channel, or is it sinuous? What material makes up the river banks? Is there vegetation along the river banks? Is there a dam or levees? If you live in a city, it’s likely that you will identify more man-made features than natural features. If you live closer to the wilderness, you may be lucky enough to find a natural river.
Protecting Our Remaining Natural Rivers
Natural rivers keep our river water clean, provide habitats for wildlife, and serve as places of recreation. Upon realization that many rivers in the United States had become heavily altered from their natural conditions, President Lyndon Johnson signed the National Wild and Scenic Rivers Act in 1968. This act provided funding and legislative means to protect and enhance rivers. This includes their free-flowing conditions, water quality, habitats, ecosystem services, historical values, and recreational opportunities. Rivers designated as “Wild and Scenic” may be managed by the Forest Service, Bureau of Land Management, National Park Service, U.S. Fish and Wildlife Service, state agencies, or Native American Indian reservations. As of April 2019, the National Wild and Scenic Rivers System included 226 rivers, totaling 13,412 river miles.
Several individual states have also created programs to preserve the natural resources provided by their rivers. By changing the zoning rules and regulating the use of rivers and their corridors, these programs prevent further engineering of rivers with high value. Learn more about you can help protect your local rivers near you.
How To Preserve More Natural Rivers
You can help federal agencies decide what rivers are chosen as wild and scenic! Federal and state agencies assess the value of rivers and can accept public input to help them determine a river’s value. If you know of a natural river that should be preserved, check to see whether it has been designated as wild and scenic.
If you find that the river is not yet protected, write a report detailing the ecological, cultural, and recreational services you believe it provides. Take photos of the river’s natural features, demonstrating how both people and wildlife benefit from the river and its surrounding landscape. Identify potential threats to the river’s health. This may motivate agencies to take more immediate action. Send that information to the agency responsible for that river, and ask them to consider it to be a wild and scenic river. Be specific about the location that should be protected, as entire rivers often cannot be protected. Another option is to contact your local press office to submit an opinion piece, or to suggest an article be written about the river. A news article may grab the attention of local governments and convince them to take legislative action to preserve natural river resources.
You can find more ideas for taking action with Ocean Blue Project to help cleanup rivers, planting trees, or a beach cleanup near you.
M. Repasch is a research scientist who studies the geomorphology and biogeochemistry of rivers. She travels the world to find natural rivers and study the sediment and nutrient fluxes carried by those rivers.