Flowing Water

Rivers then and today have many functions, including the generation of electricity, the supply of water, transportation, the harvesting and cultivation of fish, recreational uses, and the transportation of sediment.^1,2

Streams and rivers are formed as rainfall travels as surface runoff into the channels of streams and rivers or through groundwater stores in which groundwater emerges from springs onto the surface. As water emerges from groundwater springs and merges into other streams, the width of the channel and the water flow generally increases, and as it increases in size, the stream may be identified as a river.³ (As noted by Hildrew and Giller, “There is really no formal definition of this change, and terminology is largely a point of view and culturally determined”).⁴

[1] Dhir, “Wetland, Watershed, and Lake Restoration.”

[2] Marsh and Fairbridge, “Lentic and Lotic Ecosystems.”

[3] Hildrew and Giller, The Biology and Ecology of Streams and Rivers.

[4] Hildrew and Giller.

The various factors affecting the natural functioning of rivers include water pollution, the extraction and increased demand of water, the manipulation of stream channels, the use of water for hydropower, expansion of agriculture, overfishing, introduction of alien species, and artificial light and noise, which disrupt the normal behaviour of aquatic species. Additionally, climate change, especially its associated increased temperatures, is threatening freshwater ecosystems through diminished areas of these waterbodies, altered precipitation patterns, and more frequent flooding and drought events.¹

Water pollution comes from various agricultural and industrial sources, and incorporates many contaminants, which range from pesticides to plastic particles and endocrine disruptors. Additionally, agriculture contributes to increased sedimentation as soil erosion washes sediments into nearby streams.²

In urban regions, the area of impervious surfaces is much greater, leading to decreased infiltration and increased amounts of runoff that makes its way into streams. Urban streams therefore have more frequent flooding events than forested streams. They also typically have higher concentrations of chemicals that are received from wastewater, storms sewers, and runoff. Additionally, since many cities have combined sewer and stormwater pipes, rainstorms will contribute to sewer overflows, resulting in effluents released into urban streams.³

[1] Hildrew and Giller.

[2] Hildrew and Giller.

[3] Meyer, “Urban Aquatic Ecosystems.”

With the factors influencing lotic ecosystems, restoration is an important consideration for streams and rivers. Streams are often impacted by the modification of its channels, and restoration therefore involves the reversal of these changes, such as the widening of the stream’s channels and the regrowth of its riparian vegetation.¹ The restoration of streams and rivers is often much more intricate though, and includes not only structural modifications, but also physical, chemical, and biological methods to alter water flow and restore plants and aquatic species. Restoration of rivers and streams aims to promote channel-floodplain connectivity and restore the natural water and sediment dynamics, which can be done in a multitude of different ways. These methods, however, involve many different stakeholders and a comprehensive understanding of the respective watershed.²

[1] Dhir, “Wetland, Watershed, and Lake Restoration.”

[2] Dhir.

Dhir, Bhupinder. “Wetland, Watershed, and Lake Restoration.” In Handbook of Ecological and Ecosystem Engineering, edited by Majeti Narasimha Vara Prasad, 1st ed., 247–59. Wiley, 2021. https://doi.org/10.1002/9781119678595.ch13.

Hildrew, Alan, and Paul Giller. The Biology and Ecology of Streams and Rivers. 2nd ed. Oxford University PressOxford, 2023. https://doi.org/10.1093/oso/9780198516101.001.0001.

Marsh, G. Alex, and Rhodes W. Fairbridge. “Lentic and Lotic Ecosystems.” In Environmental Geology, 381–88. Encyclopedia of Earth Science. Dordrecht: Kluwer Academic Publishers, 1999. https://doi.org/10.1007/1-4020-4494-1_204. Meyer, J.L. “Urban Aquatic Ecosystems.” In Encyclopedia of Inland Waters, 367–77. Elsevier, 2009. https://doi.org/10.1016/B978-012370626-3.00236-2.