Introduction to Riparian Areas

Riparian Areas:


What is a Riparian Area?

The term “riparian” is defined as "vegetation, habitats, or ecosystems that are associated with bodies of water (for example streams, springs or ponds) or depend on perennial or intermittent surface or subsurface water." Put more simply, riparian areas are the green ribbons of trees, shrubs, and herbs growing along watercourses. Some riparian features we enjoy include the cottonwood groves where we like to picnic along sandy riverbeds, the green, shady areas next to the stream where we like to fish, and wetlands with ducks, tadpoles and dragonflies.

Riparian areas occur in a wide range of climatic, hydrologic, and ecological environments. Different latitudes and altitudes can support very different riparian communities. This is caused primarily by differences in soil, water and temperature. In the western United States, riparian areas occur from high elevation montane meadows or forests through intermediate elevation woodlands to low elevation shrublands and desert grasslands.

Riparian Areas are Ecosystems. An ecosystem is a functional system that includes both a biotic part in the organisms, such as the plants and animals, and an abiotic part, which factors in their immediate environment such as soil and topography. These organisms interact both with each other and with their environment. Each ecosystem is unique because the organisms and the environment differ from other ecosystems.

The three main characteristics that define riparian area ecosystems are hydrology, soils and vegetation. These reflect the influence of additional moisture compared to the adjacent, drier uplands. Riparian areas are the transition zones between aquatic (water-based) systems and terrestrial (land-based) systems, and usually have characteristics of both. These characteristics make it habitat for a larger number of species of plants and animals.

Because riparian areas are at the margin between water and land, their soil was most likely deposited by water and could be washed away by water. Protecting soil, streambanks, or water edges from excess erosion is an important function of riparian plants. Thus, properly functioning riparian areas absorb the water, nutrients, and energy from big events and use them to recover from disturbances while improving water quality. The toughness of riparian plants with dense, strong root systems, stems that slow floodwaters, and maybe woody debris that forms pools, adds to riparian stability and habitat diversity.

Some riparian areas, especially those not functioning properly or in high energy - high sediment locations are very dynamic and disturbance-driven. Plant communities may be susceptible to rapid change, if soil and water conditions change dramatically. These changes might include:

Flooding or lack of flooding either temporary or more long term, as caused by beavers, or man-made structures;

  • Deposition of sediment on streambanks and across floodplains;
  • Dewatering of a site by a variety of means; and
  • Changes in channel location or elevation.

Where are Riparian Areas Found? Riparian areas are found at every elevation and in all landforms, and differ depending on local physical conditions (water, soil, temperature, etc.) and their location (elevation, valleys, canyons, etc.). High mountain riparian areas may be narrow and in deep ravines or canyons, while lowland floodplains in wide valleys may have large meanders. Desert washes may be sandy and only have water for a short time each year. These differences in vegetation, landform, and geology have led to a wide variety of terms used to denote riparian areas. These include riparian buffer zones, cottonwood floodplains, alluvial floodplains, floodplain forests, bosque woodlands, cienegas, and meadows.

Significant differences in water availability due to precipitation between the eastern and western United States has led to major differences in these regions’ riparian areas (See Figure 1). In the eastern United States, precipitation is much greater and riparian areas can maintain more lush vegetation than the arid regions of the western United States. Because of the higher precipitation received in the eastern United States, even the terrestrial upland ecosystems can maintain lush vegetation. As a result, it is difficult to define the boundaries between riparian areas and terrestrial uplands in the eastern United States. In contrast, in most of the western United States and particularly in the southwest, the transition between riparian and upland terrestrial systems is easily identifiable. This distinction is abrupt because the surrounding terrestrial habitat is much drier than the riparian area (Figure 1). Riparian areas in the arid western United States have different plant composition but are also more lush than their adjacent uplands. Another important difference between the eastern and western United States that influences riparian areas are the pathways that water follows to reach streams. In the eastern United States, more water infiltrates the soil resulting in more subsurface flow reaching the stream and thus, more soil moisture (Figure 1). In the western United States, there is more overland flow reaching the stream (Figure 1).

Riparian Areas: Different but the Same: Although riparian areas can differ greatly, they all have several things in commons. They are shadier, cooler, and moister than the adjacent upland environments. A wide variety of animals are attracted to these areas including insects, amphibians, reptiles, fish, birds, and mammals. Suitable habitat (food, water, and shelter) is often provided in riparian areas to support these animals which may not occur in surrounding drier areas.

In the western United States, riparian areas compromise less than 1 percent of the land area, but they are among the most productive and valuable natural resources, rivaling our best agricultural lands. They are particularly efficient at storing water, dissipating flow energies, improving water quality, trapping sediment, building and maintaining banks, and converting of solar energy. Such an important resource requires awareness on our part, and a need to learn and understand the landscapes around us.

References

  • Arizona Riparian Council. 1994. Riparian. Arizona Riparian Council Fact Sheet No. 1.
  • Chaney, E., W. Elmore, W.S. Platts. July 1993. Managing Change. U.S. Environmental Protection Agency.
  • Marti, E., S.G. Fisher, J.D. Schade and N.B. Grimm. 2000. Flood frequency and stream-riparian linkages in arid lands. In: Jones, J.B. and P.J. Mulholland (eds.), Streams and Ground Water. Academic Press. New York, NY. pp. 111-136.
  • Surber, G., B. Ehrhart. 1998. Stream and Riparian Areas Management: A Home Study Course for Managers. Montana State Extension Service. Information also available athttp://www.animalrangeextension.montana.edu/riparianmgt/index.htm
  • USDA-NRCS. August 1996. Riparian Areas Environmental Uniqueness, Functions, and Values. RCA Issue Brief #11.
  • Zaimes G. 2007. Defining Arizona's Riparian Areas and their Importance to the Landscape. In: Zaimes G. (editor), Understanding Arizona's Riparian Areas. Univeristy of Arizona Cooperative Extension, Publication # AZ1432. pp.1-13. Available at: cals.arizona.edu/pubs/natresources/az1432.pdf.

Types of Riparian Areas

Written by Mindy Pratt, Utah State University

Lentic or Lotic? The water of riparian areas makes them different from the adjacent terrestrial uplands. Water bodies can be natural such as streams, rivers, or lakes, or they can be man-made such as ditches, canals, ponds, or reservoirs. When riparian areas are part of a system with flowing water, such as streams or rivers, they are called lotic systems. In contrast, if the water in the system is stationary or moves only slowly without wind or at a spillway, such as lakes, ponds or seeps, the riparian area is referred to as a lentic system.

Lotic Systems. Lotic systems have two main divisions – natural and man-made systems. Natural systems include rivers and streams, while man-made systems include ditches and canals. Because man-made systems are quite variable and are managed solely to transport water to other areas, they do not share many characteristics with natural systems, and are not looked at as “healthy” or “unhealthy”. On the other hand, streams and rivers that occur naturally require certain characteristics in order to function, and can therefore be managed for those characteristics. In referring to lotic systems from this point on, the term will be referring to those natural systems that occur throughout the landscape. One way to classify these lotic systems is by the length of time water flows in the channel throughout the year. These can be divided into perennial, intermittent, and ephemeral systems.

Perennial streams/rivers have flow in the stream channel throughout the year. The sources of these systems include springs as well as substantial flow inputs from ground water. Stream flows can vary widely from year to year and may even dry up during severe droughts, but the ground water level is always near the surface. Perennial streams are found in both mesic (humid) and arid (dry) regions.

Intermittent streams/rivers are also connected to ground water, but flow in the stream channel typically occurs for a period of longer than a month, but shorter than a year. The majority of the water in these sytems comes from some surface source such as melting snow or springs. The ground water is immediately below the streambed even when there is no flow in the channel. In many cases the flowing or drying of these streams can be predicted by seasonal precipitation or snowmelt patterns. Typically, these streams are associated with arid and semiarid climates, but are also common in mesic regions. There are two types of intermittent streams, spatially and temporarily intermittent, and these often occur along the same watercourse.

  • Spatially Intermittent or Interrupted– water appears above the streambed in some places, while it remains below the streambed in other places.
  • Temporally Intermittent – water appears above the streambed only after a rainfall or snowmelt event. These rainfall and snowmelt events recharge the stream and water typically rises above the streambed in part because the ground water is close to the streambed surface.

Ephemeral streams/rivers only flow for a few hours or days, and normally do not flow for 30 consecutive days. Flow is most commonly in response to rainfall or snowmelt events that are of sufficient magnitude to produce overland flow. The streambed of ephemeral streams is generally well above the water table, and these systems are often known as washes or arroyos. It is easy to confuse intermittent and ephemeral streams in the arid and semiarid western United States. The primary distinguishing factor between the two is the presence or proximity to ground water. In ephemeral streams it is minimal to nonexistent.

Are Ephemeral Streams really Riparian Areas? Whether or not to include ephemeral streams as riparian areas is a main point of disagreement among scientists. The main argument against including them as riparian areas is that ephemeral streams/rivers do not have the potential to perform the entire spectrum of riparian ecological functions. The main argument for including ephemeral streams/rivers is that these areas have “many” of the characteristic ecological functions that define riparian areas. For example, these areas are frequently disturbed and unstable, they are areas of soil transport and deposition, and there is usually a higher density of vegetation along ephemeral streams/rivers. They also serve as corridors that disperse plants and serve as animal transportation routes similar to other riparian areas.

Lentic Systems A lentic ecosystem is one such as a lake or pond that contains standing water. These can also be natural or man-made, but unlike lotic systems, the two types of systems are very similar in their characteristics. In lentic systems, water generally flows into and out of the lake or pond on a regular basis. The rates at which inflow and outflow occur vary greatly and can range from days, in the case of small pools, to centuries, in the case of the largest lakes.

References

  • Surber, Gene and Bob Ehrhart. 1998. Stream and Riparian Area Management. Montana State University Cooperative Extension Service.
  • 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 1737-15. National Applied Resources Sciences Center, Denver, CO. 127 pp.
  • Zaimes G.N. (ed). 2006. Understanding Arizona’s Riparian Areas. University of Arizona Cooperative Extension, Publication #az1432. Available online at: http://ag.arizona.edu/extension/riparian/

Stream and River Classification

Classifying stream and rivers helps managers to understand to expected in specific stretches of stream. The two main methods used are:

The Strahler Classification Method or stream ordering assigns numbers to streams, with streams having no tributaries being 1st order and the numbers rising as tributaries join the stream/river flows farther from the source.

The Rosgen Classification Method takes into account a stream or river's slope, sinuosity, width/depth ratio, the degree of entrenchment, and the particle size of the streambanks and channel bottom to determine the stream type. It is more detailed than the Strahler method, and it is independent of size.


Riparian Vegetation

Riparian Vegetation is Specific Plants with a Specific Purpose. The vegetation that occurs in a healthy riparian area is both unique and important to the functionality of the riparian areas. Stabilizing types of riparian vegetation have root masses capable of withstanding most high flow events that occur in our streams and rivers. These root systems are important for the bank stability they provide. These root systems are mainly found in members of the sedge family (Cyperaceae), rush family (Juncaceae) and willows (Salicaceae). Few grasses have these capabilities. Abundance of species other than stabilizers may indicate a riparian area that is not working effectively. Some of the species that indicate this are: noxious weeds, tap-rooted herbs, annuals, Kentucky bluegrass, small clovers and plantain. Too many of these species would be a red flag that something within the riparian system is out of balance.

Other Functions of Riparian Vegetation. Riparian vegetation also influences other functions of a riparian system. Vegetation interacts directly with flowing water by providing resistance as water flows past stems and among leaves and branches. This slows the flows and affects the shape and pattern of the channel by reducing erosion and allowing deposition along the channel. The relatively stiff stems of woody vegetation may create high turbulence as flow travels around the stem and produces local pockets of erosion. Sedges, rushes and grasses, as well as other fine-stemmed vegetation, may simply bend as flow passes over them, contributing to channel roughness and capturing sediment. Riparian vegetation also traps nutrients in addition to the sediments, and reduces water and soil temperature and evaporation.

How to determine if a Riparian Area's Vegetation is Correct and Healthy. Because vegetation plays a vital role in a riparian system, not only does the correct type of vegetation need to be present and healthy, but it also needs to show evidence that vegetation is being replaced or is increasing in extent. In order to determine if this is occurring, the following items need to be evaluated:

  • Is there a diverse age-class distribution of riparian species?
  • Is there a diverse composition of riparian species?
  • Do the species present indicate that riparian-wetland soil characteristics are being maintained?
  • Is the vegetation present comprised of plants or plant communities that have root masses capable of withstanding high streamflow events?
  • Does the riparian vegetation present exhibit high vigor?
  • Is there enough riparian vegetation cover present to protect banks and dissipate energy?
  • In systems where it is needed, is there an adequate source of coarse and/or large woody material?

Understanding the riparian vegetation that should be present within a riparian area as well as the functions it should provide are important to any management plan or decision that will be made.

References

  • Dickard, M., M. Gonzales, W. Elmore, S. Leonard, D. Smith, S. Smith, J. Staats, P. Summers, D. Weixelman, and S. Wyman.. 2015. Riparian Area Management: Proper Functioning Condition Assessment for Lotic Areas. Riparian area management-proper functioning condition assessment for lotic areas (Technical Report No. 1737‐15 v. 2). Denver, CO: USDI, Bureau of Land Management.
  • Zaimes, G.N. (editor). Understanding Arizona’s Riparian Areas. University of Arizona Cooperative Extension, Publication #az1432.

Water Quality Regulations

  • Arid West Water Quality Research Project: Created to address concerns that the water quality criteria developed under the Clean Water Act - on which state water quality standards are based - may not be appropriate for arid and semi-arid ecosystems.

Watershed and Riparian Basics Resources

  • ARS Watershed Research USDA Agriculture Research Service (ARS) scientists maintain a national network of 14 research watersheds across the United States to address critical issues relating to water quantity and quality on our nations agricultural and rangelands.
     
  • California Watershed Information Technical System The goal of the Watershed Information Technical System (WITS) is to provide the information and tools to support local watershed planning, restoration, monitoring, and education via the CERES Web. CERES and its project WITS are programs of the California Resources Agency.
     
  • Managing Arid and Semi-arid Watersheds A cooperative project between the USFS Rocky Mountain Research Station and the University of Arizona: the basics of watershed management, information about riparian ecosystems of the Southwest, a searchable bibliography of resources.
  • Southwest Watershed Research Center Basic and applied research in global change, hydrology and water resources, erosion and sedimentation, water quality, and development of improved decision support systems.
     
  • Surf your watershed This EPA site allows the user to locate local watersheds and drinking water sources and provides access to watershed information of all kinds from per capita use to real-time stream flow data, indicators of watershed health, toxic releases, hazardous wastes and local citizen-based work on behalf of the watershed.
  • Watersheds Defines a watershed as "the area of land that catches rain and snow and drains or seeps into a marsh, stream, river, lake or groundwater." This site provides information and services for protecting and restoring water resources.
  • Irrigation and Water Use: Economic Research Service Briefing Room publication which investigates water allocation, water conservation, and water management issues facing irrigated agriculture.