Lecture 6 - Boulder and Off-Channel Habitat

Question 1

What is the minimum size of boulders that can be placed in a stream?

Answer 1

They must be greater than 0.3 m in diameter

Question 2

What are some benefits of adding boulders in streams? (6)

Answer 2

Instream cover for fish from predators

Fish holding and feeding areas in fast water

Substrate for benthic invertebrates

Increase habitat diversity by disrupting the current and forming eddies

Facilitate deposition and scouring of around them

Increases surface water turbulence which helps protect them from predators

Question 3

At what stage is suitable habitat generally limiting for salmonid species with an extended freshwater phase? (2)

Answer 3

At the parr stage rather than the fry stage because fish size increases the amount of habitat needed and thus determines the density of fish that can be sustained in an area

This is when a population bottleneck occurs (in relation to density and habitat availability)

Question 4

When is it not appropriate to use the boulder technique in restoration? (3)

Answer 4

In areas of heavy icing

In areas of instability (eg. Extremely high velocities, aggrading channels)

Be careful placing boulders at the crest if riffles as it can cause aggravation and diversion

Question 5

When is adding boulders appropriate? (3)

Answer 5

In streams lacking suitable cover

In previously channelized areas

In streams reaches deficient in large wood

Question 6

What percent of boulders in riffle-pool streams signifies poor habitat conditions for salmonids?

Answer 6

Less than 10%

Question 7

What do you need to do before implementing a boulder project? (2)

Answer 7

Conduct a stream survey to determine the need for boulder placement and the suitability of stream sections

Contact DFO and FLNRORD to consult with them, but also obtain permissions from the regular agencies (federal, provincial, municipal etc.)

Question 8

What type of boulders should you use? (2)

Answer 8

Size of boulders depends on size of the stream (eg. Velocity considerations)

Use angular, hard rock boulders placed 1-2 m apart depending on the size of the boulder

Question 9

How/where should the boulders be placed? (7)

Answer 9

In clusters of 3 or more if the stream is large enough - more effective than single boulders since the clusters are less likely to be displaced by ice or current and provide better cover for fish

Boulders should be placed in the deepest 1/3 of the stream (ie. in or near the main channel)

So not obstruct more than 20% of the stream’s cross-sectional area

If boulders are placed along the stream edge to create cover for juveniles, proceed with caution to avoid erosion

Can place boulders in the middle or tail end of riffles but not the crest (can cause aggradation and diversion)

They can be installed at the upper, middle, or lower sections of runs

Best to install at the head or tail of pools, not in the middle as the velocity is too low

Question 10

When should boulders be installed?

Answer 10

During summer low flow periods as per fish window regulations

Question 11

How far apart should boulders within clusters be spaced? (2)

Answer 11

0.5 to 1 m between boulders within a cluster, increasing with stream size

Boulders clusters can be staggered with ~2-3 m separation between them

Question 12

What else can boulder placement be used for? (4)

Answer 12

It can be used to create pool-riffle sequences

But this requires extensive knowledge of stream hydraulics

This is the only time that boulders should be placed on the crest of a riffle

Boulders are placed in a cluster on the riffle crest spaced 6X bankfull width apart

Question 13

What is the average length of a wave and a riffle pool sequence? (2)

Answer 13

A complete river wave length is 12X the bankfull width

One riffle pool sequence is 6X the bankfull width

Question 14

What way does water flow into a bend?

Answer 14

In a helical flow pattern

River flows into a bend but also vertically which creates erosion and depositional areas in a meander

Question 15

Why might off-channel habitat be the best option in some cases in coastal and interior B.C.? (2)

Answer 15

In coastal B.C., some streams have too high velocity to attempt in-stream restoration

In interior B.C., winter conditions may be too severe in the main channel but off-channels may have groundwater sources that keep the off-channel ice free

Question 16

Why is constructing off-channel habitat only necessary in some cases?

Answer 16

Only certain species and life stages of salmonids utilize off-channel areas so benefits will depend on the presence of certain species as well as the appropriate physical habitat

Question 17

What are the main types of off-channel habitat? (3)

Answer 17

Surface overflow channels
Groundwater channels
Wall-base channels

Question 18

How are natural off-channel habitats created? (3)

Answer 18

By long-term processes of

Alluvial deposition
Channel migration
Changes in stream bed elevation

Question 19

What are the differences in flow of the 3 types of off-channels? (4)

Answer 19

Surface overflow channels only carry flow during flood events

Groundwater and wall-based channels usually have relative stable flows, a moderated temperature regime, and sometimes a complex of channel and pond habitats

Question 20

Which species of salmonids are most commonly associated with off-channel habitat? (3)

Answer 20

Chum because they are noted for spawning in groundwater fed channels

Coho because they have long freshwater stages and move into off-channels as fry during spring or summer, and in the fall to overwinter (protection from high flows)

Coastal cutthroat trout

Question 21

What should you do before starting an off-channel habitat project? (7)

Answer 21

Identify target species - it is critical to confirm the fish species and life stages involved

Identify type of water source - eg. ground water or surface runoff)

Identify prospective sites - the nature of the primary water supply will guide site identification (eg. Abandoned river channels can minimize the need for excavation, must be in area with reliable, year round flow, avoid outside of steam bend where sediment can build up)

Analyze the exposure to flooding - it is important to design projects with natural floods in mind (best to design for 1 in 30 year flood so overtopping can occur and major (1 in 100 year floods) will only require some repairs

Determine access points for heavy equipment to minimize impacts to floodplain

Determine who owns the land (usually will need to call FLNRORD as it’s likely crown land)

Determine what equipment and materials are needed (eg. Suitable gravels for access road and large wood for in-channel cover)

Question 22

What should be done after choosing an area for an off-channel project? (5)

Answer 22

Once site is chosen,

Off-channel projects (especially those with surface water intakes) will require regular inspection and maintenance to ensure reliability of the water supply

A detailed site investigation must be conducted

For groundwater channels, the water table depth and characteristics (eg. Temperature, chemistry, DO) must be determined

Monitoring of the groundwater regime must be done monthly for at least a year to determine suitability

Obtain necessary regulatory agency approvals - this requires a conceptual plan, purpose etc. Submission occurs as soon as you have sufficient information and have decided that the project is technically and economically feasible

Question 23

What do detailed site investigations determine? (10)

Answer 23

Nature and suitability of alluvial materials

Quantity and quality of surface or groundwater sources

Excavation quantities

Amount and type of material, if any, that must be hauled away

Establish the stream channel alignment or pond shape

Flood protection requirements

Site topography survey

Establish benchmarks

Bore test holes to assess depth of overburden and nature and layering of substrate

Call before you dig to determine underground infrastructure

Question 24

What are the 4 basic designs for off-channel habitat? (5)

Answer 24

Groundwater fed channel for spawning and rearing/overwintering

Surface fed channel for spawning and rearing/overwintering

Wall-based channel for rearing/overwintering

Rearing and overwintering ponds

A single project may incorporate one or all of these concepts depending on water supply, terrain, target species etc.

Question 25

Some characteristics of groundwater-fed channels (6)

Answer 25

For rearing/over-wintering and spawning

Should have gravel substrate free of silt/fine sand

Water table near surface

Potential sites generally occur on floodplain benches parallel to the channel

Groundwater DO levels should be at least 5 mg/L

Excavated below lowest water table to ensure year round flow

Question 26

Some characteristics of surface-fed channels (6)

Answer 26

For rearing/over-wintering and spawning

Side channels fed by surface water are often used because ground water is not available/suitable and certain salmonids are adapted to surface water temperature regimes (all but chum)

Should have pools between run and riffle sections but no need for 6X bankfull width because it is a flow controlled setting

Sediment is a major concern so these channels should not be on high sediment-load systems (suitable intake is outside of bend)

Run and riffle sections should be similar to groundwater channel with low slope and banks lined with boulders (protect against spawning)

Need floodplain benches for flood protection

Question 27

Advantages and disadvantages of surface water channels (5)

Answer 27

Advantages: high volumes and velocities and more flexibility in project site

Disadvantages: higher possibility of significant sediment introduction, requiring more planning and effort maintaining substrate quality in addition to surface water intake

Question 28

Wall-based channel (2)

Answer 28

For rearing/over-wintering

Only found in limited areas (eg. Squamish)

Question 29

Off-channel ponds (7)

Answer 29

Off-channel ponds play a significant role in juvenile salmonid rearing and overwintering, especially coho salmon

Can be created by either: flooding and existing site through construction of a dam or dyke or
Excavating to achieve adequate water depths within or adjacent to existing watercourse

Larger ponds generally don’t support as many fish per unit area as smaller ponds (limit area to 0.1 to 0.3 ha)
For rearing/over-wintering

Pond depth should be less than a m to benefit coho and benthic insect food production but also have some deeper areas to provide security for overwintering

Aim to create a pond environment with sufficient water input to maintain dissolved oxygen

can incorporate spawning habitat into the project for recruitment

Add LWD for cover

Question 30

Operation and maintenance of off-channel habitat (3)

Answer 30

Varies considerably depending on the type and complexity of the project

Groundwater channels - require little operational effort and maintenance (just need to ensure fish access periodically and other basic features)

Surface channels and ponds - require active operation and maintenance (intake blockage is the main concern and it is also important to routinely inspect the control gate structures and substrate to determine accumulation of fine silts)