Figure 3: The impact of sedimentation on stream flow through streambed materials.

What does “riparian” mean?

Riparian = streamside

Figure 5: Changes in stream conditions can result in barriers to fish passage.

Potential Impacts of Instream Works

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Background

Do you know what effects your proposed works may have on a watercourse? This section addresses the range of potential impacts your proposed works may have to riparian and aquatic ecosystems. It will provide additional context for the reasons why standards and best practices apply to your works and why they must be considered before you undertake works in or around water.

An ecosystem is the dynamic and interrelated complex of plant and animal communities and their non-living environment. All parts of an ecosystem, including physical, chemical, and biological components, are interconnected; that is, they affect and are affected by all other parts. The term habitat refers to the natural home of a plant or animal within an ecosystem. Aquatic habitats are those areas associated with water that provide food and shelter and other elements critical to an organism’s health and survival.

Potential Impacts of Instream Works

Healthy aquatic ecosystems are dynamic – they are always changing. Instream work carries a high risk of potential impact to water quality and quantity, fish and wildlife species, and riparian and aquatic habitats through the changes made to streams and streamside (i.e., riparian) areas. All instream works are potentially very intrusive to aquatic and riparian ecosystems (Figure 1). Instream works can break the continuity of riparian corridors, increase flows and stream power, cause temporary or permanent loss or alteration of aquatic habitats, and result in temporary or permanent loss of riparian vegetation.

Figure 1. Works near water can have significant impacts to aquatic and riparian species and habitats.

Physical Impacts: Impacts to Stream Processes

Streams are balanced dynamic systems where the extent and frequency of change can be easily affected by human activities. Streams need space to move (Figure 2) and good supporting structures (i.e., stable banks) to maintain their balance.

Figure 2: Natural channel migration within the active and historic floodplain of a stream

Works encroaching into the floodplain of a stream reduce the stream capacity and affect the dynamics of natural floodplain processes. Alterations made to a site's natural drainage patterns can have severe impacts to nearby wetlands. Human development and other activities within the upper watershed can increase the flow and energy of surface runoff, impacting in-channel habitat and increasing the need for erosion and flood protection works.

Physical and Chemical Impacts: Impacts to Water Quality

Stream water quality can be impacted by changes made to the streambed. The porous streambed, the streambed’s hyporheic zone, plays a critical role in:

• the exchange and cycling of stream waters;
• the maintenance of stream temperature regimes;
• the moderation of flow or temperature changes; and
• the provision of important habitat for stream invertebrates, juvenile fish and other aquatic life, especially during incubation, and periods of low summer or high flood flows.

Works within a stream often result in the release of fine sediments and other deleterious substances. Fish and other aquatic organisms are very sensitive to habitat quality and environmental cues such as high turbidity (i.e., cloudiness in the water). They can be killed or seriously injured or impacted by changes to water chemistry and high suspended sediment levels and they, like most other animals, prefer the most hospitable habitat that is available to them.

The introduction of fine sediments directly from digging in the stream and indirectly from run-off from the exposed soils has been documented to have severe negative impacts on all life stages of fish and other aquatic life and their habitats, including, but not limited to:

• Reduction of the availability and quality of aquatic habitats through the in-filling of critical types of habitats (e.g., pools and riffles, spawning habitats);
• Loss of the spaces between spawning gravels used to shelter eggs, alevin, juvenile fish and other aquatic organisms (Figure 3);
• Impairment of the health of fish and other aquatic organisms through the clogging and abrasion of gills and smothering of eggs and juveniles;
• Reduction of water clarity and visibility which impairs the ability of aquatic life to find food, mate, and escape predators;
• Elimination of critical food items such as insects and aquatic invertebrates through smothering and loss of habitat;
• Death of fish, amphibian, insect and other aquatic organisms.

Deleterious substances like concrete or cement products, equipment oils and fuels, and wood waste can also alter a stream’s water chemistry so severely that fish, amphibians, and other aquatic organisms may die.

Biological Impacts: Impacts to Riparian Vegetation and Fish & Wildlife Populations

Riparian Vegetation

Riparian vegetation is fundamental to the maintenance of healthy aquatic ecosystems. Vegetated riparian areas play critical roles in:

• providing woody debris that contributes to channel complexity and maintains microclimate conditions;
• buffering the effects on water quality of flow changes, such as increases in stream power and erosion, and changes in water temperature;
• buffering streams from sedimentation and pollution in surface runoff;
• contributing food and nutrients in the form of insects and organic litter fall;
• stabilizing soils through root matrices; and
• providing shade and cover to control temperature and manage predation.

Riparian areas also maintain critical aquatic and terrestrial wildlife habitats adjacent to the stream. Many of BC’s animal species use riparian zones. These habitats provide higher complexity and structural diversity of vegetation and wildlife than any found in upland areas (Figure 4).

Figure 4: Riparian Habitat - This figure demonstrates the primary riparian zone functions of a typical coastal stream in Southwest British Columbia.

Fish and Wildlife Migration

An additional impact of instream works on aquatic habitat is the potential to form a total or partial barrier to fish or wildlife migration or movement. Instream structures or changes to the stream channel may alter flow velocities or depths. Fish migration occurs in response to a variety of needs including, but not limited to spawning, rearing, feeding, escaping too high or too low stream flow conditions, escaping poor quality or polluted waters, or escaping predators. The maintenance of fish passage is typically required pursuant to Section 20(1) of the federal Fisheries Act. Figure 5 illustrates one type of barrier to fish passage.

As well as providing valuable fish habitat, non-fragmented riparian areas provide critical migratory habitats for terrestrial wildlife, amphibians and birds. Migratory bird abundance and diversity is generally greater in riparian areas, and small mammal communities tend to be more diverse along streams than other habitat types. Large mammals, such as deer and bears, use riparian areas as migratory corridors to search for food and mates, and for traveling to breeding areas or between summer and winter ranges. Interruption of these migration corridors (Figure 6) reduces habitat function and value and may cause greater human-wildlife conflict and reduced wildlife survival.

Most amphibians and some reptiles migrate to specialized aquatic areas to reproduce and many spend much of their lives in riparian areas. Shoreline works in particular can have significant impacts to the habitats and migration routes used by these species. Lakeshore stabilization works can create vertical barriers to amphibian and reptile movement, and may disturb the foreshore habitats required for breeding.

Figure 6: When Patch A has been fragmented, Patch B becomes more isolated from the Patch A remnants. This will limit movement between A and B for some species of wildlife.

Species at Risk

Many of BC's species at risk are supported by riparian and aquatic habitats. These include but are not limited to:

• Painted Turtle (lakeshore habitat);
• Pacific Water Shrew (riparian forest habitat);
• Nooksack Dace (small streams with fast flowing water and gravels),
• Pacific Giant Salamander (streams and riparian habitat),
• Oregon Spotted Frog (shallow wetlands and marsh habitat),
• White Sturgeon (large river systems), and
• Great Basin Spadefoot Toad (ponds within dry grassland habitat).

Impacts to the habitat of threatened or endangered species can have catastrophic effects on species survival and should be avoided at all times. Some species at risk have no “window” of least risk during which instream works may be permitted because of the risk of harm to the animal.

Before planning any works, review the following websites for further information on the species at risk in your area: http://www.env.gov.bc.ca/atrisk/ and http://www.env.gov.bc.ca/cdc/. The “Species Explorer” at http://www.env.gov.bc.ca/atrisk/ can also help you to find out what species at risk may be in your area. The legislation guiding the protection of species at risk, the federal Species at Risk Act, is detailed in the following section.

WITH SUCH HIGH POTENTIAL IMPACTS TO FISH AND WILDLIFE POPULATIONS AND HABITATS, INSTREAM WORKS SHOULD BE AVOIDED WHEREVER POSSIBLE.

Introduction | Legislative Requirements

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