These resources are brought to you by the Cooperative Extension System and your Local Institution

Welcome

eXtension is an interactive learning environment delivering the best, most researched knowledge from the smartest land-grant university minds across America.

Find a U.S. Institution

eXtension: more mind reach

Have a question? Try asking one of our Experts

Print

Riparian Health - Understanding if the Channel is in Balance with the Soil and Water Being Supplied

Last Updated: January 25, 2012

View as web page

The Balance Between the Channel and the Water and Sediment

An example of a channel which is in balance with the sediment being supplied.

Viewed over very long periods of time and under relatively stable climate regimes, undisturbed channels and their floodplains exist in a state of relative equilibrium. Streams transport water and sediment out of a watershed, and channels are constantly adjusting to account for changes in the water and sediment. These erosion and deposition processes generally offset each other. Excessive erosion or deposition indicates that this process is out of balance. In order to determine if the stream is in balance, the following questions must be answered

Are sinuosity, width/depth ratio, and gradient in balance with the channel? Could the uplands be contributing to riparian degradation? Are floodplains and channel characteristics able to dissipate energy? Is the channel vertically stable?

Warning Signs

Mid-channel bars are an indicator that there is excess sediment being supplied to the channel.

Some warning signs that might indicate that a stream is out of balance with the water and sediment load, that may indicate declining health or “unraveling” of riparian areas include:

Braided Channels - Natural channels can be classified as either single thread or braided channels. While some braided channels are natural, most braided channels reflect unnaturally high sediment loads, and indicate the process is out of balance. (For more information on naturally braided channels, refer to the Rosgen Classification Method).

Mid-Channel Bars – Excessive sediments being transported through the system can form mid-channel bars that indicate excessive erosion upstream. Examples of what might cause this include runoff after a wildfire, excess road density or poor road design, or stream incision farther up the watershed.

Unstable Streambanks – An increase in the amount of water flowing through the system will require the channel to adjust to the higher flow and the energy that is associated with it. The increase in flow requires the channel to widen to enable room for the increased discharge and energy. Sheared banks are the most common evidence of widening of the channel. One example of a channel needing this type of adjustment would be a transmountain diversion that takes water from one watershed and puts it in the stream of another. This generally requires a change in both channels. The dewatered channel may eventually lack channel capacity for undiverted bigger flows.

Fine materials on the channel bottom - The presence of fine sediments (silts, clays and decomposing organic material) on the channel bottom may indicate that not enough water is running through the system or that there is too much sediment entering the stream. This is especially the case when sediments remain in place through one or more high flow events. Fine sediments cover fish spawning areas as well as change the composition of macro-invertebrates (bugs) in the stream, which also affects fish populations.

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/

Browse related Articles by tag: rangelands, rangeland water

Have a specific question? Try asking one of our Experts

Unlike most other resources on the web, we have experts from Universities around the country ready to answer your questions.