Stream gradient

Stream gradient (or stream slope) is the grade (or slope) of a stream. It is measured by the ratio of drop in elevation and horizontal distance.^[1] It is a dimensionless quantity, usually expressed in units of meters per kilometer (m/km) or feet per mile (ft/mi); it may also be expressed in percent (%). The world average river reach slope is 2.6 m/km or 0.26%;^[2] a slope smaller than 1% and greater than 4% is considered gentle and steep, respectively.^[3]

Stream gradient may change along the stream course. An average gradient can be defined, known as the relief ratio, which gives the average drop in elevation per unit length of river.^[4] The calculation is the difference in elevation between the river's source and the river terminus (confluence or mouth) divided by the total length of the river or stream.

^ Zimmer, David William; Bachmann, Roger W. (1976). A Study of the Effects of Stream Channelization and Bank Stabilization on Warm Water Sport Fish in Iowa: the effects of long-reach channelization on habitat and invertebrate drift in some Iowa streams. Iowa Cooperative Fishery Research Unit, Iowa State University.
^ Cohen, Sagy; Wan, Tong; Islam, Md Tazmul; Syvitski, J.P.M. (2018). "Global river slope: A new geospatial dataset and global-scale analysis". Journal of Hydrology. 563. Elsevier BV: 1057–1067. doi:10.1016/j.jhydrol.2018.06.066. ISSN 0022-1694.
^ "Classifying Your Stream Slope". streamhandbook.org. 2019-01-20. Retrieved 2023-10-23.
^ Shaw, Lewis C. Pennsylvania Gazetteer of Streams Part II (Water Resources Bulletin No. 16). Prepared in Cooperation with the United States Department of the Interior Geological Survey (1st ed.). Harrisburg, PA: Commonwealth of Pennsylvania, Department of Environmental Resources (no ISBN).

[1] Zimmer, David William; Bachmann, Roger W. (1976). A Study of the Effects of Stream Channelization and Bank Stabilization on Warm Water Sport Fish in Iowa: the effects of long-reach channelization on habitat and invertebrate drift in some Iowa streams. Iowa Cooperative Fishery Research Unit, Iowa State University.

[Cohen2018-2] Cohen, Sagy; Wan, Tong; Islam, Md Tazmul; Syvitski, J.P.M. (2018). "Global river slope: A new geospatial dataset and global-scale analysis". Journal of Hydrology. 563. Elsevier BV: 1057–1067. doi:10.1016/j.jhydrol.2018.06.066. ISSN 0022-1694.

[SH2019-3] "Classifying Your Stream Slope". streamhandbook.org. 2019-01-20. Retrieved 2023-10-23.

[Streams_II-4] Shaw, Lewis C. Pennsylvania Gazetteer of Streams Part II (Water Resources Bulletin No. 16). Prepared in Cooperation with the United States Department of the Interior Geological Survey (1st ed.). Harrisburg, PA: Commonwealth of Pennsylvania, Department of Environmental Resources (no ISBN).

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