Riparian Health

Two of the three attributes used to assess rangeland health are 1) hydrologic function and 2) soil/site stability.

1. Hydrologic function refers to the site's capacity to capture, store, and safely release water from rainfall, run-on moisture, and/or snowmelt (where relevant). Two important components of hydrologic function are the site's ability to resist a reduction in it's hydrologic function following a disturbance or management action, and the site's ability to recover it's hydrologic capacity following degradation.

2. Soil/site stability refers a site's capacity to limit redistribution and loss of soil resources (including nutrients and organic matter) by wind and water.

The best way to protect hydrologic function and site stability is to maintain the proper amount and kind of vegetation on the site. This should be a primary management goal, or at least at a minimum, a major consideration for any rangeland vegetation management project. When a site lacks proper hydrologic function and soil/site stability, it can lose fertile topsoil, which ultimately reduces the areas productivity and resource value. 

Evaluating a Healthy Stream

1. A riparian area is considered healthy, or properly functioning, when it contains adequate vegetation, proper landform, or large woody debris which will:

  • Dissipate stream energy associated with high water flow thereby reducing erosion and improving water quality
  • Filter sediment, capture bedload, and aid floodplain development
  • Improve flood-water retention and ground-water recharge
  • Develop root masses that stabilize stream banks against cutting action

2. Develop diverse ponding and channel characteristics to provide the habitat and the water depth, duration, and temperature necessary for fish production, waterfowl breeding, and other uses, and

 3. Support greater biodiversity.

Not All riparian Areas Are Equal. It is important to remember that not all riparian areas are created equal. As stated above, “adequate vegetation, land form, or large woody debris” or any combination of these may be required to keep a riparian area functioning and healthy. For example, in most western Oregon riparian areas, large woody debris, or fallen trees, must be present to dissipate energy, capture bedload, and aid floodplain development. However, many areas in the Great Basin do not have the potential or require large woody debris to dissipate stream energy. Where they do, the wood is generally smaller; instead this is accomplished through the presence of vegetation such as willows, sedges, and rushes.

The Right Components Bring about the Right Characteristics. When the components necessary are present to dissipate energy associated with high flows, a number of physical characteristics or changes are evident. These include:

  • Reduced erosion
  • Sediment filtering or deposition
  • Improved floodwater retention

As these physical attributes of the system begin to function, they start the process of developing ponding and channel characteristics that provide habitat for fish, waterfowl, and other uses. It is important to note that the physical attributes have to be in working order to sustain the channel characteristics that provide the habitat for these resource values.

When these physical aspects are not present, changes have to be made that allow them to recover. A change such as acquiring vegetation leads to other physical changes, which allows the systems to begin to function. Recovery starts with acquiring the right elements to dissipate energy, which begins to put the physical processes into working order and they provide the foundation to sustain desired condition.

Water and soil conditions provide the basic structure of a riparian area, and as long as this basic structure has not been seriously altered, the maintenance and even improvement of a riparian area are often relatively easy. Without them, plants lose their resilience and systems fall apart. Then, little stresses can keep them from recovery.

Attributes That Are Warning Signs. Some specific attributes may indicate that a riparian area is “unhealthy” or “unraveling.” The primary physical features to consider in determining this are:

  • Evidence of channel downcutting
  • Evidence of channel widening
  • Amount, location, and causes of bare ground and
  • Amount of fine materials on the bottom of the channel

Vegetation Is the Easiest Attribute to See. Vegetation plays a critical part in the health of a riparian area. It is also important for management because plant communities often provide the first indicators of changes to the system. Important factors to consider when looking at riparian vegetation include:

  • The types and amounts of plants present,
  • How well they are fulfilling riparian functions,
  • The amount of foraging and browsing pressure being exerted on certain plants, and
  • The mix of age classes of woody species, if present.

If these attributes, or lack of them, are issues in a riparian area, it could indicate that the riparian area is in need of management changes to bring it back into a healthy and functioning condition.

For more information, or help in determining the health of a stream, contact:

  1. Your local Cooperative Extension agent
  2. Land management agencies that administer the land, such as the Bureau of Land Management or U.S. Forest Service
  3. Natural Resources Conservation Service personnel for riparian areas on private property.

References