Flowing Water and Riparian Habitats

The Necanicum River in Oregon's Coast Range.
The Necanicum River in Oregon's Coast Range. Photo Credit: Herman Biederbeck, ODFW

Flowing Water and Riparian Habitats include all naturally occurring flowing freshwater streams and rivers throughout Oregon as well as the adjacent riparian habitat.

Ecoregions

All ecoregions.

Characteristics

Flowing streams and rivers are a key feature of the Oregon landscape and natural resources heritage. Flowing water habitat also includes springs, seeps, and intermittent streams. Flowing water is of significant conservation concern under climate change, with changes in precipitation patterns, snowmelt cycles, and fire frequency. The headwaters of many streams are fed by snowmelt, and the flowing freshwater systems are crucial to iconic Northwest salmon and steelhead as well as amphibians, dragonflies, and other Strategy Species.

Riparian habitat zones are adjacent to flowing water in rivers and streams as well as springs, seeps, terraces, and many low-elevation alluvial floodplains. They occur at all elevations, from valley bottom floodplains to alpine torrents, and are shaped through seasonal flooding, scour, and soil deposition.

Riparian zones are the dynamic interface between land and flowing water. The plant assemblages and communities in riparian zones help buffer inputs and the cycling of nutrients. The vegetative composition and structure of riparian zones is a function of elevation, stream gradient, floodplain width, and disturbance events such as flooding.

Throughout most of the state, riparian vegetation is comprised mostly of deciduous trees and shrubs, such as big-leaf maple, alders, aspen, cottonwood, dogwood, willows, and Oregon white ash. Conifers, such as pines, firs, and spruce, dominate some riparian zones at higher elevations. The vegetative composition of riparian zones is also influenced by elevation and precipitation patterns. Riparian shrublands may include willows, red osier dogwood, western birch, hawthorn, alder, and chokecherry. Riparian meadows are dominated by grasses, sedges, and rushes. Riparian habitats provide food, cover, and breeding sites for many fish and wildlife species throughout the year.

The Flowing Water and Riparian Strategy Habitat does not include irrigation structures or other man-made waterbodies. Natural lakes are covered separately, and the riparian zones around the edges of those lakes are included within the Wetlands Strategy Habitat.

Conservation Overview

Flowing water and the riparian habitat found along its banks are defined together as a Strategy Habitat because their distribution and conservation roles are interconnected.

Water is crucial for all fish and wildlife, and high quality freshwater aquatic systems provide essential habitat to many at-risk species, including important spawning and rearing habitat for salmonids, breeding habitat for amphibians, and habitat for freshwater mussels and other invertebrates. Flowing water is important to connect ecosystem services from higher elevations throughout the year. In many locations throughout Oregon, water flow and hydrology have been impacted by barriers (e.g., roads, dams, and culverts) and irrigation diversions that can reduce water flow and interfere with fish and wildlife migration. Channelization and development can restrict the natural ability of streams to meander over time, limiting the quality and availability of these habitats, as well as affecting floodplain function.

Riparian habitats often have high species diversity and are critical for wildlife. These habitats are important to species that prefer moist shrubby or forested habitats. Riparian areas provide essential wintering habitat and travel corridors for birds, amphibians, reptiles, mammals, and other wildlife. In arid areas, such as the Blue Mountains and Columbia Plateau ecoregions, riparian habitats can provide abundant insects, plants, and moisture throughout the year. Riparian meadows include natural spring-seep habitats that are extremely important for a wide variety of species, including Greater Sage-Grouse chicks and butterflies.

In addition to providing habitat for birds and other wildlife, riparian habitats have important ecological functions. Healthy riparian vegetation protects banks from erosion, influences in-channel aquatic habitats, maintains favorable water temperature for fish through shading, filters runoff, and provides nutrients to support terrestrial and aquatic life. Riparian vegetation creates meanders in streams and rivers and increases habitat complexity in valley bottoms. In the Northern Basin and Range ecoregion, riparian vegetation can protect against scour from summer storms. Riparian habitats link upland and aquatic habitats. Upland habitats have a critical role in watershed function and affect riparian and aquatic habitats, particularly in drier, low-elevation sites.

Riparian habitats have declined from historical levels and are now greatly reduced in area and connectivity, especially those in low-elevation areas and valley bottoms. Development, logging, roads, agricultural practices, and grazing can degrade riparian habitat. Removal or reduction of riparian habitat allows runoff containing fertilizers and other contaminants to more easily reach flowing water and further impact aquatic habitat.

Oregon’s Planning and Regulatory Background for Riparian Habitats

Steps have been taken through Oregon’s planning and regulatory framework to address riparian habitat conservation issues. Cooperative restoration projects have benefited riparian-dependent species on forest and agricultural lands. In many cases, these efforts have focused on improving habitat quality in smaller, fish-bearing streams. Streamside buffers implemented through the Northwest Forest Plan (NWFP) on public land and the Oregon Forest Practices Act on private land are designed to protect riparian health in forested landscapes. On agricultural lands, Agricultural Water Quality Management Area Plans and Rules have been adopted across the state to address riparian conditions and other water quality issues. While each riparian rule is slightly different depending on the local area, the riparian rules generally require agricultural activities to allow establishment, development, and maintenance of riparian vegetation consistent with site capability to provide moderation of solar heating, filtration of overland flow, and streambank stability.

Oregon has initiated a riparian assessment framework to track changes in riparian condition on agricultural lands over time. Riparian areas across the state will likely be conserved by a variety of measures, including a combination of existing regulatory and non-regulatory state and federal programs. These are designed to control degradation of riparian habitats and improve water quality. The DEQ’s completion of Total Maximum Daily Loads will also bring more specificity to the recovery process. For urban and rural residential development, some guidelines are provided through local land use ordinances adopted to address Statewide Planning Goal 5 requirements for riparian vegetation. Given the background addressing conservation in riparian habitats, some limiting factors to conservation remain.

Limiting Factors and Recommended Approaches

Limiting Factor: Water Quantity

Water availability is limited in some parts of the state, and concern increases under a changing climate. Low flows are associated with higher water temperature and higher nutrient and contaminant concentrations. Riparian bottomland habitats compete for water with other uses, particularly in the Blue Mountains, Columbia Plateau, East Cascades, and Northern Basin and Range ecoregions. In eastern Oregon, agriculture consumes much of the available water. Diversions occur at all major streams, and most valley bottoms have multiple canals that divert water. As a result, riparian habitats no longer support the many channels and sinuosity that are characteristic of healthy stream systems.

Recommended Approach

Where possible, maintain flow following the natural hydrological cycle. Improve irrigation efficiency. Lease water for instream use. In cooperative voluntary approaches that allow for purchase of instream water rights, prioritize use for agricultural purposes providing the greatest economic benefit. Maintaining streamflow and water storage is especially important to riparian conservation in eastern Oregon ecoregions. Provide incentives and information about water usage and sharing at key times of low flow conditions (e.g., late summer).

Limiting Factor: Invasive Aquatic Species

Invasive fish species (e.g., bass, crappie, bluegill, yellow perch, bullhead, carp) can compete with, prey on, or hybridize with native fish (e.g., steelhead, rainbow trout) and amphibians. For example, in the Columbia Basin, non-native carp can overgraze aquatic vegetation and stir up sediment, depriving native fish and amphibians of egg-laying sites or preventing eggs from absorbing enough oxygen to develop. Alterations in hydrology can make the habitat more susceptible to invasive plants, invertebrates, and fish.

Recommended Approach

Restoration of aquatic habitats to conditions that support native fish and wildlife is the best strategy to prevent invasive species. Maintaining historical hydrological regimes ensures that habitat conditions best support native fish and wildlife. Work with community partners to restore flow and water input levels. Where necessary, work to minimize predation on sensitive native species. Where non-native aquatic species threaten Strategy Species, consider site-appropriate tools (e.g., mechanical or chemical treatment) in locations and during seasons where they will not harm native amphibians, fish, or invertebrates. Educate and inform people about the problems that can be caused by invasive species.

Limiting Factor: Passage Barriers and Channel Complexity

Fish and wildlife depend on natural flow regimes and substrates for breeding, foraging, cover, and migration. Dams, road culverts, or log puncheons can alter or affect in-stream flow. The large dams on almost all of the Cascade rivers disrupt natural hydrologic regimes, which decreases the amount of bottomland habitat, and impacts anadromous fish passage upstream and downstream. Misaligned culverts with the downstream end above the water level disconnect stream passage corridors and may force wildlife to cross roads where they are vulnerable to vehicles and predators. Undersized or improperly sized culverts can alter the transport of sediment and wood, creating an uneven distribution of habitat. These effects can degrade riparian habitat and impact riparian-associated fish and wildlife. Additionally, altered flow regimes can contribute to higher temperatures in some streams. Channel complexity is also important for fish and wildlife. Woody debris and other structures provide nutrient cycling and refugia from predators and high temperatures.

Recommended Approach

Where possible, work with landowners and regulatory agencies to restore natural flow conditions on streams impacted by barriers. Eliminate passage barriers or improve passage at existing barriers to provide travel corridors for fish and wildlife. Remove or replace culverts or other passage barriers with structures that mimic natural conditions as closely as possible (e.g., bridges or open-bottom arch culverts). Determine potential effectiveness of providing passage around dams for fish and wildlife (e.g., amphibians, reptiles, mammals). Develop new habitat sites where possible. Provide sufficient channel complexity to maintain ecological benefits for fish and wildlife. Support and encourage beaver dam-building activity.

Limiting Factor: Pollution

Non-point source pollution sometimes contains fertilizers, pesticides, or oil-based pollutants at levels high enough to cause significant lethal or sub-lethal effects in native fish and wildlife. Point source pollution from industrial practices can contain high levels of contaminants. Point and non-point source pollution are both of particular concern in more highly populated regions. In some areas, particularly the Rogue River and its tributaries, increasing use of recreational motor vehicles (e.g., jet boats) has the potential to degrade water quality with runoff, or to harass aquatic or riparian-associated wildlife.

Recommended Approach

Increase awareness of the impacts of urban runoff and pesticide applications. Increase awareness and manage timing of applications of potential aquatic contaminants. Improve compliance with water quality standards and pesticide use labels administered by the DEQ and U.S. Environmental Protection Agency (EPA). Work on implementing Senate Bill 1010 (ODA) and DEQ Total Maximum Daily Load water quality plans. Carefully consider recreational vehicle use and timing on sensitive or “wild and scenic” water bodies. Increase interaction of rivers and floodplains. Encourage opportunities for restoration of “fringe” wetlands and channel meander to increase water storage. Reduce stormwater runoff and increase permeability in urban areas, allowing more water to seep into the ground. Use stormwater catchment basins designed for larger volume, longer residence, and a high degree of shading to mimic the delay, treatment, infiltration, and cooling functions of natural wetlands. During restoration, remove pipes and provide stream channels to promote flow, nutrient, and oxygen exchange. Where possible, provide sufficient room to restore meanders and other functions.

Limiting Factor: Water Temperature

Aquatic animals have specific requirements for a tolerable temperature range. Moreover, warmer water holds less dissolved oxygen. Water temperature often is too warm for native aquatic life because of alterations in stream flow, thermal pollution, or reduced riparian shading. Recommending optimal water temperatures is difficult because of a lack of understanding about historical temperature regimes.

Recommended Approach

Maintain or increase riparian habitat cover to provide shading and other benefits. Where appropriate, revegetate degraded riparian areas. Minimize release of unnaturally warm water in the fall and summer by altering intake/release structures. Maintain and restore in-stream flow to help preserve favorable water temperatures. (KCI: Water Quality and Quantity)

Limiting Factor: Sedimentation

Sediment flows into streams from various human activities, as well as natural processes, covering eggs of native fish and amphibians, making them more susceptible to infection, and potentially burying aquatic mollusks and freshwater mussels.

Recommended Approach

Reduce run-off of sediment from logging, agriculture, grazing, roads, and other activities that could disturb soil or destabilize streambanks. For example, work with the ODA to promote implementation of area-wide water quality management plans under Senate Bill 1010 so that farmers and ranchers know which actions they can implement to address water quality problems in their watershed. Strategies include terracing fields, filtering run-off before it enters aquatic systems, installing sediment control basins to reduce erosion, and practicing conservation tillage. Water quality credit trading programs to control sediment loads (and other pollutants) can help to ensure good water quality levels. When constructing new roads, consider sediment removal capabilities in road design. Maintain and restore riparian and wetland vegetation to filter sediments.

Limiting Factor: Loss of Riparian Habitat, Floodplain Function, and Habitat Complexity

A high percentage of low-elevation and valley bottom riparian habitats have been altered or lost. Riparian vegetation often is lost as habitat is converted to other uses. In several areas around the state, large cottonwood trees and gallery forest have been cleared and diked, leading to altered hydrological regimes and other impacts. Development within historical floodplains can restrict the natural ability of streams and riparian habitats to meander, limiting the creation and maintenance of new aquatic and riparian habitats. In some cases, floodplains have been converted to other uses, and riparian habitats no longer exist. Non-adherence to best management practices, such as removal of riparian vegetation, can cause sedimentation that damages aquatic areas, loss of habitat complexity, and increased water temperatures that adversely affect aquatic habitat. Loss of streamside vegetation leads to bank erosion. Grazing and dam construction can degrade riparian habitats. Urban development has led to stream channelization and vegetation loss in some areas. Losses of riparian complexity and connectivity limit the value of these important places for wildlife to meet crucial life history needs.

Recommended Approach

Restore riparian zones that will provide the full array of associated ecological functions. Enhance or re-establish the extent and connectivity of existing riparian habitats. Use voluntary cooperative efforts (i.e., Conservation Reserve Enhancement Program) and incentive programs to conserve, maintain, and restore riparian habitats on private lands. Identify and apply lessons learned from successful riparian restoration efforts on private lands to future projects. Develop tools and financial incentives to assist with streambank stabilization and decrease downstream soil movement. Improvements in riparian habitats and hydrology can also improve the quality of remaining wetland habitats. Maintain and restore riparian buffers, and minimize impacts from road-building on public lands. Where appropriate, allow beavers to continue maintaining habitat complexity, particularly in the Coast Range and parts of eastern Oregon. Maintain channel integrity and natural hydrology. Where feasible, work to restore historical hydrological conditions. Ensure that adequate riparian vegetation remains following management activities, so riparian vegetation can continue to prevent erosion, preserve water quality, and promote water temperatures favorable for fish. Restore lost vegetation through planting of native trees, shrubs, and ground cover. Manage for future sources of large woody debris. Maintain and/or expand existing tracts of large trees. For example, cottonwood trees greater than 20 inches in diameter offer benefits to riparian habitat function.

Limiting Factor: Riparian Habitat Degradation

In the Blue Mountains, Northern Basin and Range, East Cascades, and Columbia Plateau ecoregions, historical overgrazing has led to soil erosion, poor regeneration of hardwood trees and shrubs, changes in plant species composition and structure, and degradation by invasive plants. Although some areas are slowly recovering, many miles of stream are still lacking adequate riparian vegetation. Ongoing grazing impacts remain in some areas, especially at low and mid elevations. Western juniper is encroaching in some riparian areas of eastern Oregon.

Recommended Approach

In cooperation with landowners, land managers, and grazing lessees, encourage approaches such as off-site watering that keep livestock out of riparian areas. Develop and implement grazing regimes that are compatible with riparian conservation objectives. Selectively fence restoration sites or other high priority areas to exclude ungulates, at least until riparian vegetation recovers. Evaluate impacts by encroaching western juniper, and remove juniper from upper reaches of higher elevation watersheds, if appropriate. Plant riparian vegetation using native species at priority sites. Continue to work with landowners and grazing permittees to support riparian conservation and land management objectives.

Limiting Factor: Invasive Plants in Riparian Habitat

Invasive plants, such as knapweeds, knotweeds, reed canary grass, and thistles, degrade riparian habitats by competing with native plants. In the Columbia Plateau and Northern Basin and Range ecoregions, pasture grasses and cheatgrass commonly dominate the understory. In some riparian areas in the Northern Basin and Range, Columbia Plateau, and East Cascades ecoregions, overgrazing has resulted in poor regeneration of hardwood trees and shrubs.

Recommended Approach

Control key invasive plants using site-appropriate tools, including mechanical, biological, and chemical treatments. Use chemical treatments carefully and where compatible with water quality concerns, focusing on spot treatment during the dry season. In the Columbia Plateau and Northern Basin and Range ecoregions, focus control at low-elevation sites, unless near streams where seeds could flow downstream. Provide information to local governments and landowners about potential invasive plants. Where necessary (e.g., some areas in the Northern Basin and Range, East Cascades, and Columbia Plateau ecoregions), develop and implement grazing management regimes that are compatible with riparian conservation objectives.

Resources for more information