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Riparian Health - Point Bars

Last Updated: August 16, 2011

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The Formation and Maintenance of Point Bars

Point Bars are part of the natural erosion and deposition process for some channel types.

The formation and extension of point bars into channels is a natural depositional process for some channel types. Point bars are formed when the higher velocity flows on the outside of meander bends erode the bank, and then deposit that sediment on the inside of a meander bed where velocities are lower. It is crucial that vegetation colonizes these deposits as they extend over time to maintain a balance. Point bars forming and then gaining finer sediments stabilized by vegetation is how folldplains form in these channel types. If vegetation cannot maintain a balance, energies during high flows accelerate erosion, which affects sinuosity, gradient, and access to the floodplain resulting in the degradation of the riparian-wetland area. The vegetation present needs to be riparian-wetland plants that have root masses capable of withstanding high-flow events. Point bars are most common in Rosgen's B and C channel types.

Warning Signs

Some warning signs that sediment is not being captured on point bars, which may indicate declining health or “unraveling” of riparian areas include:

Point bars without vegetation. A lack of vegetation on point bars (given that it has had sufficient time to establish), may not maintain a consistent channel pattern and this can increase stream slope or gradient, causing downcutting and increased sediment loads.

Point bars are repopulating with non-riparian vegetation. If point bars are revegetating with plants that don’t have the root masses capable of holding soils, further erosion could occur.

References

Surber, G., B. Ehrhart. 1998. Stream and Riparian Areas Management: A Home Study Course for Managers. Montana State Extension Service. Information also available at http://www.animalrangeextension.montana.edu/riparianmgt/index.htm

USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference TR 1737-15. 124 pp. More Information available at: http://www.blm.gov/or/programs/nrst/index.php

Zaimes G.N. (editor). Understanding Arizona’s Riparian Areas. University of Arizona Cooperative Extension, Publication # az1432. Available online at: http://ag.arizona.edu/extension/riparian/

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