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TERRAIN STABILITY HAZARD, SEDIMENTATION

HAZARD AND HYDROLOGIC RISK ASSESSMENT Blocks EGG2, EGG3, EGG5, and EGG6

Egmont, BC Project Number: 19-123 June 22, 2020 Client: Rurik Muenter, RPF CHARTWELL CONSULTANTS LTD. 210-275 Fell Avenue North Vancouver, BC V7P 3R5

Eryne Croquet, M. Sc., P. Ag., P. Geo.

STATLU ENVIRONMENTAL CONSULTING LTD. 1-45950 Cheam Avenue

Chilliwack, BC V2P 1N6

www.statlu.ca

BLOCKS EGG2, EGG3, EGG5, AND EGG6 TERRAIN, SEDIMENTATION, AND HYDROLOGIC ASSESSMENT CHARTWELL

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RECOMMENDATIONS SUMMARY

Statlu Environmental Consulting Ltd (Statlu) was retained by Tsain-ko Forestry Development Corporation (Tsain-ko) to assess hydrologic risk, sedimentation hazard, and terrain stability hazard assessments for four proposed cutblocks (Blocks EGG2, EGG3, EGG5, and EGG6) near Egmont, BC.

Terrain Stability Hazard

Terrain within Blocks EEG2, EGG3, EGG5, and EGG6 has low terrain stability hazard. No

block boundary adjustments are required. Existing and proposed roads in the area were not

assessed for terrain stability hazard because they cross terrain with gentle to moderately steep

slopes with gradients consistently less than 60%.

Sedimentation Hazard

Harvest of the blocks presents a low sedimentation hazard because of the lack of connectivity

to downslope sensitive receptors and the gentle to moderate slopes in the area.

Most of the road segments present low sedimentation hazard because of the lack of

connectivity to sensitive receptors.

The following road segments have moderate sedimentation hazard:

Where Quarry Rock Road (0+425) and Br. Road EGG3-07 (0+031) cross Stream

EGG3-A.

Where Br. Road EGG6-01 (0+649) crosses Stream EGG6-A and passes near a wetland

(0+448 to 0+649)

Quarry Rock Road (0+000 to 0+077), where it is close to Stream EGG3-A

Implementation of the general and specific remedial measures prescribed in Sections 5.2 and

5.3 will reduce the post-construction sedimentation hazard to low.


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Hydrologic Risk

The Face 1 unit will have a moderate likelihood of detectable changes to watershed hydrology

for at least 8 years after harvest. This likelihood can be reduced to low likelihood by reducing

the proposed harvest by 2.9 ha or deferring harvesting of at least 2.9 ha for 8 years or more. It

is likely that after harvesting, if no reduction in harvested area occurs, Stream EGG6-A would

see higher peak flows in fall and winter and also slightly higher low flows in late summer, but

that the low flow period in summer and fall would last for longer than it does at present. These

detectable effects would persist for up to eight years after harvesting before returning towards

pre-harvest levels.

There is one licensed water POD on Comeau Creek (Stream EGG6-B), and field investigation

indicated that it is presently unused. Therefore, there is currently low risk to Comeau Creek

water users from the proposed harvesting in the Face 3 catchment.


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CONTENTS

1.0 Introduction ................................................................................................................................. 1

2.0 Overview of Setting and Downslope Resources ....................................................................... 1

2.1 Bedrock and Surficial Geology ......................................................................................... 2

2.2 Weather and Climate ......................................................................................................... 2

2.3 Wind .................................................................................................................................... 3

3.0 Downslope Resources and Elements at Risk ............................................................................ 3

3.1 Water License PODs .......................................................................................................... 4

4.0 Terrain Stability Hazard .............................................................................................................. 5

4.1 Roads .................................................................................................................................... 5

5.0 Sedimentation Hazard Evaluation ............................................................................................. 6

5.1 Roads .................................................................................................................................... 7

5.1.1 Rock Quarry Road ......................................................................................................... 7

5.1.2 Br. Road EGG3-02 ......................................................................................................... 7

5.1.3 Br. Road EGG3-07 ......................................................................................................... 7

5.1.4 Br. Road EGG6-01 ......................................................................................................... 7

5.2 Specific Erosion and Sediment Control Recommendations ......................................... 8

5.3 General Erosion and Sediment Control Options ........................................................... 8

6.0 Hydrologic Risk Assessment .................................................................................................... 10

6.1 Watershed Characteristics ............................................................................................... 10

6.2 Hydrologic Risk ................................................................................................................ 13

6.3 Hydrologic Recovery ........................................................................................................ 14

6.4 Hydrologic Risk ................................................................................................................ 15

6.5 Recommendations ............................................................................................................ 15

7.0 Conclusion .................................................................................................................................. 16

7.1 Terrain Stability Hazard .................................................................................................. 16

7.2 Sedimentation Hazard ..................................................................................................... 16


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7.3 Hydrologic Risk ................................................................................................................ 17

8.0 Limitations .................................................................................................................................. 17

9.0 Closure ........................................................................................................................................ 18

References ........................................................................................................................................... 19

APPENDICES

Figures .......................................................................................................................... 20

Methodology ............................................................................................................... 23

Rationale for Assessment and Definition of Hazard and Consequence .............. 24

Definitions ................................................................................................................... 26

Sedimentation Hazard Assessment Methodology .................................................. 30

Hydrologic Risk and Risk Assessment Methodology ............................................ 32

Rationale for Hydrologic Assessment ...................................................................... 35


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1.0 INTRODUCTION

Statlu Environmental Consulting Ltd (Statlu) was retained by Tsain-ko Forestry Development Corporation (Tsain-ko) to assess hydrologic risk, sedimentation hazard, and terrain stability hazard assessments for four proposed cutblocks (Blocks EGG2, EGG3, EGG5, and EGG6) near Egmont, BC. Chartwell Consultants Ltd. (Chartwell) laid out the blocks and facilitated Statlu’s assessment. The assessment considers the potential risks posed by the proposed harvesting to terrain stability, sedimentation, watercourses, water intakes, and hydrologic resources, and presents mitigation options.

Eryne Croquet, M. Sc., P. Ag., P. Geo from Statlu assessed the blocks on April 30, 2020 with Rurik Muenter, RPF, of Chartwell. The weather was warm and dry at the time of the assessment and there were no barriers to normal visibility within the blocks. The assessment route is shown on Figure 1 (Appendix 1). We spent approximately 3 hours in the blocks. We viewed streams, locations where roads crossed streams, and we attempted to located mapped water license points of diversion (PODs).

Statlu’s assessment methods and rationale are described in Appendices 2 and 3, commonly

used terms are defined in Appendix 4, sedimentation hazard assessment methods are described

in Appendix 5, and hydrological assessment methods are in Appendices 6 and 7.

2.0 OVERVIEW OF SETTING AND DOWNSLOPE RESOURCES

Blocks EGG2, EGG3, EGG5, and EGG6 are located west of Egmont, BC, on the north side of

Egmont Road, near North Lake.


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2.1 Bedrock and Surficial Geology

The bedrock underlying the blocks is two diorite units (iMapBC, 2020). The contact between

the units trends northwest/southeast and passes through Blocks EGG3 and EGG6. An

unnamed formation of dioritic intrusive rock lies to the west of the contact. Quartz diorite,

including Cloudburst, Ashlu Creek, and Ward Point Plutons is east of the contact. The bedrock

exposed in a small quarry adjacent to Block EGG3 is competent diorite.

The surficial materials are near the blocks are a thin veneer of well-drained rubbly sandy till

and organic veneers in wetlands and areas with poor drainage. Some of the soils near the blocks

have cemented horizons that might contribute to wetland formation by preventing water

infiltration.

2.2 Weather and Climate

Climatic information is important for terrain stability studies because it describes general

weather trends, including the frequency and intensity of precipitation that in turn, gives clues

about possible antecedent moisture conditions and provides guidance for environmental

shutdown of operations. Climate is difficult to describe in mountainous terrain because long-

term weather stations are clustered in valley bottoms in populated areas of the province.

The nearest long-term climate station is at Woodfibre, 20 km south of the blocks (Environment

Canada, 2020). Data for the thirty-year period ending in 2010 show mean annual precipitation

is 2804 mm, with 75% falling between October and the end of March. Mean annual snowfall is

64 cm.

ClimateWNA is a climate model that uses data from western North America to predict climate

characteristics for locations distant from weather stations (Wang et al., 2016). The climate near

the blocks in the 1981 to 2010 interval had a mean annual temperature of 10 °C, mean annual

precipitation of 1370 mm with 78% occurring between October and April of each year. The

precipitation as snow was 57 cm. The reference evapotranspiration was 620 mm.


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The highest stream flows in the region occur as a result of precipitation events, specifically

heavy fall and winter rains. Snowmelt does not contribute significantly to peak, low or mean

annual flows due to low elevation and the blocks’ position near the ocean.

2.3 Wind

Winds in the area commonly flow up and down Jervis Inlet and across the Strait of Georgia.

The blocks are exposed to these winds.

3.0 DOWNSLOPE RESOURCES AND ELEMENTS AT RISK

The blocks are located on the low hills to the north of North Lake, and the area to be harvested

includes parts of catchments that flow to North Lake and North Creek as well as catchments

that flow directly to tidewater on the slopes to the north and west of the North Creek catchment.

The North Lake watershed is not designated as a community watershed or fisheries sensitive

watershed, but it is important habitat for several species at risk, including western painted

turtle, marbled murrelet, and northern red legged frog1. The turtle species that lives in North

Lake has been the focus of community-based habitat rehabilitation work. The blue-listed

northern red legged frog lives in wetlands, ponds and forest areas with intact ground cover in

the watershed.

North Lake is about 130 m to 250 m downslope of Blocks EGG3 and EGG2. None of the

streams that flow across the blocks drain directly into the lake, but Stream EGG3-B flows into

the lake from a wetland that is bordered by Block EGG3.

North Creek drains North Lake. The creek is 100 m to 300 m downslope of Block EGG3. Stream

EGG3-A is a tributary to North Creek, and flows under both the Egmont Road and the North

Lake FSR before it reaches North Creek.

1 https://www.scrd.ca/files/File/Community/Planning/NRAC/2019-JUN-27%20NRAC%20Agenda.pdf


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Egmont Road and forestry roads lie between the blocks and North Lake. The blocks are also

upslope of cabins on Agamemnon Bay. Identification of other downslope resources, including

timber, recreational, archaeological, etc. is beyond the scope of this report.

3.1 Water License PODs

There are six mapped water license points of diversion (PODs) near the proposed blocks

(Table 1). Five are licensed for domestic use and one is for ponds and aquaculture. In the field,

we visited the mapped intake locations for Earl Brook and Comeau Creek. The POD for

Dawson Creek is located several hundred meters away from the blocks and no streams from

within the blocks flow to Dawson Creek. The PODs on North Lake are located in the lake and

the associated infrastructure is on private property which we could not trespass on to inspect.

The Earl Brook POD was not located in the field, despite examining all stream channels near

and downstream of their mapped locations. It is possible that either the water intake or

associated infrastructure such as pipes and tanks are located at places distant from the

provincially mapped locations, or that there is no intake infrastructure associated with this

water license.

The POD for Comeau Creek is not located as shown on the provincial maps. BCTS located the

intake on Stream EGG6-B, about 400 m north of the mapped location. The intake consist of a

wood box mesh filters and a 1 inch polyurethane pipe waterline. The intake is not currently

used and the residences that relied on the water are abandoned.

Table 1: Water License PODs in the area.

Stream Name Licence Number Priority Date Status Purpose Quantity Units

Dawson Creek C052253 19780822 Current Domestic 2.273 Md

Earl Brook C028987 19631114 Current Domestic 9.092 Md

North Lake C040356 19720627 Current Domestic 2.273 Md

North Lake C124290 20080923 Current Domestic 2.273 Md

North Lake C039507 19711213 Current Pond & Aquaculture 0.113 Ms

Comeau Creek C059745 19830829 Current Domestic 2.273 Md


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4.0 TERRAIN STABILITY HAZARD

The blocks lie in an area with two terrain types, wetlands in the lowlands and till-veneered

bedrock hummocks in the uplands. The area was divided into polygons based on homogenous

terrain stability hazard, surficial materials, and slope gradients (Figure 1).

Polygon A comprises the uplands, where the proposed blocks are. The terrain has hummocky

topography with a well-drained rubbly sandy till veneer. The slopes are short, with irregular

morphology in profile and rounded to smooth topography along contour. Slope gradients

range from 10% to 50%, with most slopes around 30%.

The blocks will be harvested using ground-based methods. The terrain stability hazard in

Polygon A is low.

Polygon B comprises the wetland areas that lie outside the blocks or in reserves. These are

lowland areas, with generally flat topography and slope gradients of 10% or less, except locally

on hummocks. The surficial materials are a silty glaciomarine or till deposit overlain by a very

poorly drained organic veneer. Polygon B has very low terrain stability hazard.

Landslides in and near the blocks would be most likely to occur where roads cross streams and

would most likely occur as a result of poor road maintenance.

4.1 Roads

Proposed roads in the blocks were not assessed in detail for post-construction terrain stability

hazard because they cross terrain with gentle gradients and low to very low terrain stability

hazard and roads constructed on this terrain will also present low to very low hazard.


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5.0 SEDIMENTATION HAZARD EVALUATION

Sedimentation hazard depends on erodibility of the surficial materials and proximity of

sensitive receptors, or locations that could experience adverse effects from increased

sedimentation. The sensitive receptors near the blocks include the streams that drain the area,

North Lake, and North Creek.

I defined sedimentation hazard polygons for the block, and segments for the roads, based on

surficial materials, slope form and gradient, and proximity to downslope sensitive receptors

(Figure 2). The methodology used in assessing sedimentation hazard are described in

Appendix 5.

Polygon 1 includes Blocks EGG2, EGG3, EGG5, and EGG6. Polygon 1 receives a large amount

of precipitation. The topography has slope gradients between 20% and 50%, with short, broken

morphology. The soil is thin, with sandy loam to loam textures and about 20% coarse

fragments. These factors add up to high erosion potential.

Sediment delivery potential is determined based on proximity to watercourses and the slope

gradients. Polygon 1 has no streams within it and has moderate slope gradients, resulting in

low sediment deliver potential.

The resulting sedimentation hazard for Polygon 1 is low.

Polygon 2 is outside the blocks. It includes streams, riparian areas, and wetlands. Its

characteristics for determining erodibility include slope gradients from about 10% to 20%, with

short, broken morphology. It has thin soils with silty clay loam to clay loam textures and about

20% coarse fragments. It has moderate erosion potential. The sediment delivery potential is

low, mainly because the slope gradients are less than 20%. The resulting sedimentation hazard

is low.

Polygon 2 includes the wetland that lies between North Lake and Block EGG3. The wetland

has very flat topography and will serve as a sediment sink to capture any sediment from the

southern patch of Block EGG3 before it can reach North Lake, about 250 m from the block

boundary.


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5.1 Roads

Roads are an important factor to consider when determining sedimentation hazard. Roads

have high erosion potential because they expose soil to runoff. The sediment delivery potential

for roads depends on stream crossings and proximity to watercourses. For example, stream

crossings are a pathway for material eroded from the road to deposit in streams.

Most existing and proposed road segments have low sediment delivery potential because the

roads are far away from sensitive receptors and do not cross streams. Road segments within

20 m of identified sensitive receptors have moderate or high sediment delivery potential,

depending on the slope gradient between the road and the stream.

5.1.1 Rock Quarry Road

The existing Rock Quarry Road has moderate sedimentation hazard from Sta. 0+000 to 0+077

because it closely follows Stream EGG3-A, a tributary of North Creek. It crosses the stream at

Sta. 0+425. The topography close to the stream is gentle, which reduces the likelihood that

sediment from the road will reach the stream.

5.1.2 Br. Road EGG3-02

Br. Road EGG3-02 will be reconstructed where it follows the headwater reaches of Stream

EGG3-A. The road has moderate sedimentation hazard along the segments within 20 m of the

stream.


Br. Road EGG3-07 crosses Stream EGG3-A at Sta. 0+031. It has moderate sedimentation

hazard on the segments near the crossing.


Br. Road EGG6-01 the headwaters of Stream EGG6-A before crossing a wetland and NCD-5.

The stream crossing is at Sta. 0+649 and the wetland is between Sta. 0+448 to 0+649. The

segment of the road close to these sensitive receptors has moderate sedimentation hazard.


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5.2 Specific Erosion and Sediment Control Recommendations

In order to reduce sedimentation at these locations, prevent water flowing in roadside ditches

from reaching the streams or sensitive receptors by dewatering ditches onto the forest floor

before the crossing. Do not yard across streams except at designated crossings.

I observed a damaged culvert on the existing Rock Quarry Road (Figure 2). It should be

replaced to prevent a blockage that could force water to flow down the road. In addition, piled

fill is located between the Rock Quarry Road and Stream EGG3-A. The fill could become a

source of sediment if it is disturbed during road maintenance. Either leave these piles as they

are or remove them completely.

5.3 General Erosion and Sediment Control Options

It is important to minimize erosion potential and subsequent sedimentation in regions of the

harvest area where timber will be yarded, especially where ground-based yarding is

recommended. The following are general recommendations for reducing erosion potential and

subsequent sedimentation:

• Equipment operators should be adequately trained and experienced to mitigate ground

disturbance.

• Use slash or brush matting to prevent soil disturbance during ground based harvesting.

• Equipment should be tracked rather than rubber tired.

• Ground based harvesting should occur under dry conditions, particularly on slopes steeper

than 30%.

• After harvesting, cover any areas of exposed soil with slash and/or promote rapid

revegetation of disturbed areas through seeding and/or planting an appropriate grass and

legume seed mix.

For those road segments with moderate or high sedimentation hazard, general hazard

mitigation options include:

• Construct roads and ditches under dry conditions. “Dry conditions” in this context refers

to soil moisture and should not be confused with wet weather shutdown thresholds for


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unstable terrain. Appropriate thresholds for precipitation for dry conditions are

approximately 10 to 15 mm/24 hr for rainfall or a similar amount of snowmelt. Restarting

operations after a shutdown will depend on soil drainage class; well-drained surficial

material may take 12 hours to dry out after the rain. Operators should judge dry conditions

on the ground. Visual indicators of dry conditions are a lack of runoff along road running

surfaces or a lack of continuous flow in road ditches.

• Promote rapid revegetation of ditches by seeding with native seed mixture, and using slash

and/or straw as a temporary ground cover along ditchlines until revegetation occurs. Straw

and hay are not interchangeable. Hay contains the seed heads and leafy portions of the

forage grasses that nourish animals while straw is the inedible stalk portion of forage

grasses that is best suited for bedding or mulching.

• Install sumps at culvert inflows to trap sediment.

• Armour seepage points along ditchlines and culvert outflows with coarse rock to prevent

erosion.

• Use ditchless overland road construction on gently sloped ground.

• Install culverts parallel to and 20 m to 30 m from stream crossings, so that the majority of

ditch water is dissipated onto adjacent slopes and is not directly connected to the stream.

• Use silt fences and/or straw bales during road construction to trap sediment generated

during the construction process. Straw bales have lower maintenance requirements than

silt fences.


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6.0 HYDROLOGIC RISK ASSESSMENT

In 2020, Engineers and Geoscientist BC (EGBC) and the Association of BC Forest Professionals (ABCFP) released a joint practice guideline for watershed assessments in the forest industry2. The new guidelines define an appropriate scope of work for hydrologic assessments in a forest context. Statlu followed the guidelines to assess the cumulative effects that harvesting and roadbuilding is expected to have on streamflow, sedimentation, and hydrologic risk.

6.1 Watershed Characteristics

The area around the blocks comprises several sub-basins of the North Lake watershed and

three face units that drain into Agamemnon Channel (Figure 3). These divisions were used to

determine the likelihood that the proposed harvesting could result in detectable changes to

stream hydrology.

The terrain in all the watersheds is similar, with hummocky topography with a morphology

controlled by the underlying granitic bedrock. The bedrock is covered with thin surficial

materials composed of sandy till and organic sediments. The slope gradients are mainly gentle

to moderate (10% to 50%), with short lengths and undulating morphologies.

The watersheds are drained by small streams that connect wetlands before reaching either the

ocean, North Lake, or North Creek (Table 2). The streams are shallowly incised with narrow

channels. In most locations, the streams have eroded into the sandy till, with compact sediment

forming the banks (Photo 1). Some reaches that experience higher flows have fine grained

mineral sediment in the channel. There is a large component of coarse and fine woody debris

in all the streams. Some reaches flow under thick accumulations of organic debris, especially

in wetland near headwaters of Stream EGG6-A.

2 https://www.egbc.ca/getmedia/8742bd3b-14d0-47e2-b64d-9ee81c53a81f/EGBC-ABCFP-Watershed-Assessment-V1-0.pdf.aspx


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Table 2: Streams in the blocks Stream Name Stream Class Watershed or Sub-basin

EGG3-A S4 North Creek

EGG3-B S4 North Lake North

EGG6-A S6 Face 1

EGG6-B (Comeau Creek) S6 Face 3

EGG6-B1 S6 Face 3

Stream EGG3-A is fish-bearing. Rock Quarry Road and the proposed Br. Roads EGG3-02 and

EGG3-07 will cross the stream. It flows into North Creek about halfway between North Lake

and Agamemnon Channel. No PODs are on the stream.

Stream EGG6-A is not fish-bearing. It has no existing crossings, but Br. Road EGG6-01 will

cross it. The POD mapped as being on this stream is actually located on Stream EGG6-B.

Stream EGG3-B drains a wetland that lies downslope of Block EGG3. The stream flows into

North Lake.


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Photo 1: Stream EGG3-A showing mineral and organic sediment in the channel. Note the shallow incision depth and abundant riparian vegetation. This is the typical condition of the streams flowing in the area.


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6.2 Hydrologic Risk

Hydrologic risk is a function of watershed characteristics and the proposed level of harvesting

in each watershed. In general, proposed harvesting is expected to result in a low likelihood of

detectable changes to watershed hydrology if it covers less than 30% of the watershed area,

assuming the remaining part of the watershed is unharvested. At harvesting intensities above

30%, detectable changes to the timing and magnitude of peak flows in streams and other

adverse effects are expected. At levels above 30%, the risk to valuable resources must be

considered when making forest harvesting decisions.

The blocks are located in four watersheds that either flow into Agamemnon Channel, North

Lake, or North Creek (Figure 3). The North Lake watershed was divided into three sub-basins:

north of the lake, south of the lake, and North Creek. The proposed block areas were

intersected with the watersheds to determine the proposed harvest area that lies within each

watershed (Table 3). The three watersheds that flow into Agamemnon Channel were

designated as the Face 1, Face 2, and Face 3 watersheds for this assessment. The stream in the

Face 1 watershed has no official name. Both the licensed Dawson Creek and Earl Brook water

intakes are within the Face 2 watershed. The Face 3 watershed contains one named stream,

Comeau Creek.

Table 3: Watersheds and proposed harvesting Watershed Sub-basin Watershed Area

(ha) Net Harvest Area

(ha) % Watershed

Area Hydrologic Risk

Face 1 48.0 19.7 41.0 Moderate

Face 2 (Dawson Creek and Earl Brook)

56.5 1.4 2.5 Very Low

Face 3 (Comeau Creek)

45.6 9.3 20.4 Low

North Lake

North 115.7 8.0 6.9 Very Low

South 195.8 0 0 Very Low

North Creek 114.7 12.8 11.2 Very Low

Total 576.5 52.2 9.1 Very Low


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Face 1 is a small watershed (48.0 ha) that drains directly into Sechelt Inlet. Stream EGG6-A

drains the watershed. This watershed includes the mapped streams EGG6-A and NCD-5,

which flow in a wetland between Blocks EGG3 and EGG6 and are tributary to Stream EGG6-A.

The BC government’s mapped location for the water license point of diversion (POD) on

Comeau Creek is located in this watershed but the infrastructure associated with this license is

actually located in the Face 3 watershed.

Portions of both Blocks EGG3 and EGG6 are in the Face 1watershed. A total of 19.7 ha in will

be harvested in this watershed. The harvested area will be 41% of the total watershed area. The

proposed area of harvesting will result in a moderate likelihood of detectable changes to stream

hydrology in Stream EGG6-A. Peak flows will increase after harvesting. Low flows should also

increase slightly, but the seasonal low flow period will last for longer after harvesting. Changes

in peak flow frequency and magnitude might cause detectable changes to the frequency of

sediment transport in Stream EGG6-A, although the wetland in the watershed will act as a

buffer. Water quality could be reduced if the frequency of sediment transport in the stream is

increased, even if sedimentation from blocks and roads is controlled.

The other sub-basins and watersheds, including North Lake, North Creek, Face 2, and Face 3,

are not expected to experience detectable changes to streamflow, peak flows, or water quality

as a result of harvesting because the area proposed to be harvested in each unit is well below

30% to 35% of watershed area.

6.3 Hydrologic Recovery

Hydrologic recovery is a way to describe how a forest returns to its pre-harvest hydrologic

condition after harvesting as new growth occurs. The effects of harvesting on the Stream

EGG6-A catchment will decrease over time and thus the resultant hydrologic risk is a function

of time as well as harvested area. The length of time for the watershed to return to a condition

where the effects of harvesting will no longer result in detectable changes to water availability

and water quality was estimated using hydrologic recovery using provincial forest cover data.

The result was compared to forest growth models provided by Chartwell.


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It will take approximately 8 years for the Face 1 watershed to recover to an equivalent of less

than 35% of harvested watershed area and 11 years to reach 30%. Therefore, detectable changes

to the hydrology of the stream in the Face 1 watershed (Stream EGG6-A) will persist for at least

8 years, and possibly up to 11 years after the blocks are harvested.

6.4 Hydrologic Risk

The hydrologic risk presented to Stream EGG6-A is a function of not only the expected changes

to watershed hydrology but also nature of the identified resources in the watershed. Future use

of Stream EGG6-A should not be inferred from present use alone. The hydrologic risk depends

on if, how frequently, and how much water will be used over the next eight to eleven years, not

only on the predicted changes to peak and low flow. If water from Stream EGG6-A is not being

used now and will not be used in the coming decade, then the predicted increase in peak flow

and longer low-flow period may be acceptable. If water from the stream is being used or will

be used in the short-term, then these changes may not be acceptable.

6.5 Recommendations

One way in which the hydrologic risk can be reduced is by reducing the harvested area. In the

Face 1 watershed, reducing the harvested area from the presently proposed 41% of total

watershed area to a level of 35% or less would result in a low likelihood of detectable changes

to watershed hydrology. This could be done either by placing 2.9 ha or more of the presently

proposed blocks in reserves, or by deferring the harvest of an equivalent area for eight years or

more. If water from Stream EGG6-A is being used or will be used in future, reducing the

harvested area in the watershed or deferring the harvest of some area of the planned blocks for

at least eight years will prevent detectable adverse effects on water availability and water quality

for water users.


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7.0 CONCLUSION

7.1 Terrain Stability Hazard

Terrain within Blocks EEG2, EGG3, EGG5, and EGG6 has low terrain stability hazard. No

block boundary adjustments are required. Existing and proposed roads in the area were not

assessed for terrain stability hazard because they cross terrain with gentle to moderately steep

slopes with gradients consistently less than 60%.

7.2 Sedimentation Hazard

Harvest of the blocks presents a low sedimentation hazard because of the lack of connectivity

to downslope sensitive receptors and the gentle to moderate slopes in the area.

Most of the road segments present low sedimentation hazard because of the lack of

connectivity to sensitive receptors.

The following road segments have moderate sedimentation hazard:

Where Quarry Rock Road (0+425) and Br. Road EGG3-07 (0+031) cross Stream

EGG3-A.

Where Br. Road EGG6-01 (0+649) crosses Stream EGG6-A and passes near a wetland

(0+448 to 0+649)

Quarry Rock Road (0+000 to 0+077), where it is close to Stream EGG3-A

Implementation of the general and specific remedial measures prescribed in Sections 5.2 and

5.3 will reduce the post-construction sedimentation hazard to low.


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7.3 Hydrologic Risk

The Face 1 unit will have a moderate likelihood of detectable changes to watershed hydrology

for at least 8 years after harvest. This likelihood can be reduced to low likelihood by reducing

the proposed harvest by 2.9 ha or deferring harvesting of at least 2.9 ha for 8 years or more. It

is likely that after harvesting, if no reduction in harvested area occurs, Stream EGG6-A would

see higher peak flows in fall and winter and also slightly higher low flows in late summer, but

that the low flow period in summer and fall would last for longer than it does at present. These

detectable effects would persist for up to eight years after harvesting before returning towards

pre-harvest levels.

There is one licensed water POD on Comeau Creek (Stream EGG6-B), and field investigation

indicated that it is presently unused. Therefore, there will be low risk to Comeau Creek water

users from the proposed harvesting in the Face 3 watershed.

8.0 LIMITATIONS

The recommendations provided in this report are based on observations made by Statlu and

are supported by information Statlu gathered. Observations are inherently imprecise.

Conditions other than those indicated above may exist on the site. If such conditions are

observed or if additional information becomes available, Statlu should be contacted so that this

report may be reviewed and amended accordingly.

This report was prepared considering circumstances applying specifically to the client. It is

intended only for internal use by the client for the purposes for which it was commissioned

and for use by government agencies regulating the specific activities to which it pertains. It is

not reasonable for other parties to rely on the observations or conclusions contained herein.

Statlu prepared the report in a manner consistent with current provincial standards and on par

or better than the level of care normally exercised by Professional Geoscientists and

Professional Agrologists currently practicing in the area under similar conditions and

budgetary constraints. Statlu offers no other warranties, either expressed or implied.


19-123 JUNE 22, 2020

PAGE 18

9.0 CLOSURE

Please contact me should you have any questions or if you require further clarification.

Yours truly,

Statlu Environmental Consulting Ltd.

Prepared by: Reviewed by:

Eryne Croquet, M. Sc., P. Ag., P. Geo. Drew Brayshaw, Ph. D., P. Geo.

Agrologist and Geoscientist Hydrologist

EC/DB


19-123 JUNE 22, 2020

PAGE 19

REFERENCES

APEGBC. 2010. Guidelines for Terrain Stability Assessments in the Forest Sector Association of Professional Engineers and Geoscientists of British Columbia and Association of Professional Foresters of British Columbia, Vancouver, BC

B.C. Ministry of Forests. 2002. Forest Practices Code of British Columbia Guidebook – Forest road engineering guidebook. 2nd Ed. Forest Practices Branch., BC Ministry of Forests, Victoria, BC.

BC Ministry of Environment, 2020. Water Licences Report http://a100.gov.bc.ca/pub/wtrwhse/water_licences.input BC Ministry of Forests and Range and BC Ministry of Environment. 2010. Field Manual for Describing Terrestrial Ecosystems Land

Management, 2nd Edition, Handbook Number 25. BC Ministry of Forests. 1994. A guide for management of landslide-prone terrain in the Pacific Northwest, second edition. Land

Management Handbook 18. http://www.for.gov.bc.ca/hfd/pubs/docs/Lmh/Lmh18.htm BC Ministry of Forests. 1999. Forest Practices Code of British Columbia Guidebook - Hazard assessment keys for evaluating site sensitivity

to soil degrading processes guidebook. 2nd Ed., Version 2.1. Forest Practices Branch., BC Ministry of Forests, Victoria, BC BC Ministry of Forests. 1999. Forest Practices Code of British Columbia Guidebook – Mapping and Assessing Terrain Stability Guidebook.

2nd Ed. Forest Practices Branch., BC Ministry of Forests, Victoria, BC BC Ministry of Forests. 2001. Watershed Assessment Procedure Guidebook. 2nd Ed., version 2.1. Forest Practices Branch., BC Ministry of

Forests, Victoria, BC. https://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/coastal/cwaptoc.htm BC Ministry of Forests. 2003. Estimating historical variability of natural disturbances in British Columbia. Land Management Handbook 53.

http://www.for.gov.bc.ca/hfd/pubs/Docs/Lmh/Lmh53.htm Brayshaw, D. and M. Hassan. 2009. Debris flow initiation and sediment recharge in gullies. Geomorphology 109, 122-131 Clayoquot Sound Scientific Panel (CSSP). 1995. Sustainable ecosystem management in Clayoquot Sound: planning and practices. Victoria,

BC. Environment Canada. 2020. Canadian Climate Normals 1981-2010. http://www.climate.weatheroffice.gc.ca/climate_normals/index_e.html. Google Earth. 2020. HabitatWizard. 2020. [http://maps.gov.bc.ca/ess/hm/habwiz/] Howes, D. E., and E. Kenk. 1997. Terrain Classification System for British Columbia (Version 2). BC Ministry of Environment, Lands and

Parks, Victoria, BC. Hudson, R. and Horel, G. 2007. An operational method of assessing hydrologic recovery for Vancouver Island and south coastal BC. B.C.

Research Section, Coast Forest Region, Ministry of Forests, Technical Report TR-032. Hudson, R., 2000. Assessing snowpack recovery of watersheds in the Vancouver Forest Region. Research Section, Vancouver Forest Region,

BC Ministrry of Forests, Technical Report TR-004. iMapBC. 2020. Online webmap. http://maps.gov.bc.ca/ess/sv/imapbc/. Laird, H. 2001. The current state of engineering geology, slope stability, and harvest unit plans. The International Mountain Logging and

11th Pacific Northwest Skyline Symposium. http://depts.washington.edu/sky2001/proceedings/papers/Laird.pdf Millard, T., T.P. Rollerson, and B. Thomson. 2002. Post-logging landslides rates in the Cascade Mountains, South-Western British

Columbia. Vancouver Forest Region Technical Report 23. Available at: http://www.for.gov.bc.ca/rco/research/Geompub.htm Pike, R.G., T.E. Redding, R.D. Moore, R.D. Winkler, and K.D. Bladon (editors). 2010. Compendium of forest hydrology and geomorphology

in British Columbia. B.C. Min. For.Range, For. Sci. Prog., Victoria, B.C. and FORREX Forum for Research and Extension in Natural Resources, Kamloops, B.C. Land Manag. Handb. 66. www.for.gov.bc.ca/hfd/pubs/Docs/Lmh/Lmh66.htm

Ryder, J. M., and D. E. Howes. 1986. Terrain Information: A User’s Guide to Terrain Maps in British Columbia. BC Ministry of Environment and Parks.

Soil Classification Working Group (SCWG). 1998. The Canadian System of Soil Classification 3rd ed. Research Branch. Agriculture and Agri-Food Canada, Ottawa, ON. Publ. 1646.

Wang T., A. Hamann, D. Spittlehouse, and C. Carroll. 2016. Locally Downscaled and Spatially Customizable Climate Data for Historical and Future Periods for North America. PLoS ONE 11(6): e0156720. doi:10.1371/journal.pone.0156720. http://www.climatewna.com/help/ClimateBC/Help.htm

Wise, M.P., G.D. Moore, and D.F. VanDine (editors). 2004. Landslide risk case studies in forest development planning and operations. BC Ministry of Forests Land Management Handbook 56. http://www.for.gov.bc.ca/hfd/pubs/Docs/Lmh/Lmh56.htm

Wolter, Andrea, B. Ward, and T. Millard. 2010. Instability in eight sub-basins of the Chilliwack River Valley, British Columbia, Canada: a comparison of natural and logging-related landslides. Geomorphology 120, pp 123 – 132.

EGG6-03

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LegendStreamsTraverse Route: Apr. 30, 2020RoadsReservesRiparian Areas Block Boundaries

Terrain Stability HazardVery HighHighModerateLowVery LowNot AssessedPreviously Assessed

Author: E. CroquetDate Saved: Jun 04, 2020 NAD 1983 UTM Zone 10N

0 50 100 150 200Meters´

1:5,000

Figure 1: Terrain Stability

HazardBlocks EGG2. EGG3,

EGG5, and EGG6Egmont, BC

Client: ChartwellProject Number: 20-123

Terrain stability hazard ratings are depicted for the proposed harvesting method described in the accompanying report.

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Author: E. CroquetDate Saved: Jun 08, 2020 NAD 1983 UTM Zone 10N

0 50 100 150 200Meters´

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Figure 2: Sedimentation

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Client: ChartwellProject Number: 20-123

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Client: Tsain-koProject Number: 20-123

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19-123 JUNE 22, 2020

PAGE 23

METHODOLOGY

The methods used in this assessment to evaluate and report on present or potential future geotechnical hazards, estimate their probability of occurrence, size and runout distance, and anticipate their probable consequences should they occur are based on accepted standards of professional geoscience current in the province of British Columbia. These methods follow the outline of recommended practice embodied in guidance documents, including:

• Guidelines for Professional Services in the Forest Sector – Terrain Stability Assessments (APEGBC, 2010); • Mapping and Assessing Terrain Stability Guidebook (BC Ministry of Forests, 1999); and • Similar publications.

The methods include insights for improved practice gained from current publications in peer-reviewed scientific literature.

My assessment included a consideration of the background information available for the area, including the area’s climatic condition, topographic features, vegetation, bedrock, and surficial geology. I obtained and reviewed overview images for the area, including some or all of Google Earth imagery, digital orthophotos, and/or historic aerial photography, to provide historical perspective to my ground observations.

The field traverse was located using a combination of results from overview observations, discussion with the forest professional, and professional experience to located features of interest. The field traverse passed through and beyond the area(s) of interest to include areas of steep or potentially unstable ground within and adjacent to the proposed blocks and roads.

The field traverse is augmented by observations of terrain in the general vicinity of the block(s), looking particularly for evidence of past natural or logging- or road-related instability, especially activity that might have occurred more recently than the date of the most recent imagery covering the area in question.

During my field traverse, I observed and recorded details of surficial material type, drainage, topographic expression and position, stream courses, vegetation, bedrock geology, and evidence of past instability. I considered the proposed development (logging and/or road building) as well as the proposed size and location of drainage structures and the resultant potential for changes in runoff and subsurface hydrology. I made note of existing patterns of windthrow, including whether or not past windthrow had resulted in local instability.

Based on my overview and field investigations, and my professional experience and judgment, I divided the terrain and proposed roads within the study area into homogenous polygons or segments of road. I developed qualitative estimates of the likelihood of landslides or other terrain instability for the polygons and road segments that I assessed, both for existing conditions, and for post-harvest or post-construction conditions assuming that the development occurred using the construction, harvest, and yarding methods proposed by forest professionals for the block(s) and/or road(s) in question. In areas where the post-construction or post-harvest likelihood of instability was greater than low, I provided recommendations to mitigate the hazard.

I have evaluated the potential consequences of terrain instability and described those consequences to the best of my professional ability. Ultimately, the determination of acceptable risk is outside the scope of my assessment and must be made by forestry professionals and government land managers. This assessment is intended to provide information to assist those professionals with their decisions.


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RATIONALE FOR ASSESSMENT AND DEFINITION OF HAZARD AND

CONSEQUENCE

Rationale for Assessment

The slope stability hazard ratings in this report are determined using a comparative analysis based on observations of terrain conditions near the cutblock and the results of previous logging and road building in adjacent areas. Studies of past occurrence, causes and impacts of natural and logging-related landslides in southwestern British Columbia are also taken into account, including Millard et al. (2002), Brayshaw and Hassan (2009), and Wolter et al. (2010)

Based on our professional experience and the discussion above, the main criteria leading to a moderate or high likelihood of landslides or debris flows are:

• Steep slope gradients generally greater than 75%; • Imperfect or poorer soil drainage, and/or presence of springs and seepages; • Slope morphology – gullies and slope concavities that concentrate drainage; • Thick deposits of glaciogenic surficial materials, including till, glaciofluvial, and glaciolacustrine deposits,

associated with steep slopes or gullies; • Rapidly weathering or highly fractured bedrock; and, • The presence of past landslides. These factors act in combination and may not indicate slope hazard in isolation. The probability of the hazard occurring increases as more of the factors listed above occur in combination. A rapidly drained 80% gradient open slope with thin blocky colluvial deposits may have a low likelihood of post-logging terrain instability; a moderately well-drained 80% slope in deep silty till along a gully sidewall represents a high likelihood for post-harvest instability.

For roads, the most important factors in predicting slope failure are slope gradient, road construction and maintenance methods, water management, and nature and depth of the surficial materials exposed in the cutslope. Most road related failures are associated with oversteepened fill, poor water management, a lack of maintenance, or oversteepened cutslopes.

The frequency and magnitude of large bedrock landslides are generally unaffected by forest harvesting, and prediction of such events is beyond the scope of this report. However, where we have observed evidence of bedrock instability that could result in worker or public safety hazards, we have noted it in the report.

Definition and Classification of Terrain Stability Hazard

Hazards related to terrain instability depend on the frequency and magnitude of geomorphic events such as debris flows and landslides. Event frequency and magnitude are inversely related, that is, large landslides occur less frequently than small landslides. Statlu uses a qualitative rating system, based on pre-existing standards of practice embodied in legislation and used by professional geoscientists throughout British Columbia (i.e., BC Ministry of Forests Mapping and Assessing Terrain Stability Guidebook, LMH 18, LMH 53, LMH 56), to express the probability of occurrence of landslides post-harvesting or post-road building (Table A1). These probabilities of occurrence are based on an expected magnitude for relatively small and consequently frequent landslides typical of slope instability within forestry operations – an area of 0.05 to 1.0 ha and a total failure volume of from hundreds to thousands of cubic meters of material.


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PAGE 25

Table A1: Definition of Terrain Stability Hazard Classes

Hazard Class

Expected Number of Failures Per 100 ha of Similar Terrain

Expected Probability of At Least One Failure over One Forest Rotation for 10 ha Polygon

Expected Number of Failures Per km Length of Road

Very Low <0.1 <0.8% <0.01

Low 0.1-1 0.8%-5% 0.01-0.04

Moderate 1-5 5%-40% 0.04-1

High 5-50 40%-95% 1-5

Very High >50 95%-100% >5

Consequences of Terrain Instability and Partial Risk

Land Management Handbook 56 (Wise et al. 2004) and the BC Ministry of Forests Forest Road Engineering Guidebook (2002) define risk as the product of the probability of hazard and consequence. Consequence further depends on the nature of the element(s) at risk, the exposure of those elements to the hazard, and the vulnerability of those elements to the hazard. Statlu recognizes that the evaluation of the exposure and vulnerability of elements at risk to the identified hazards is difficult and may require specialized skills or additional information not available to professional geoscientists. Since the information is available or potentially available to land managers and statutory decision makers, we have concentrated on identifying and describing the geomorphic components of the consequence of terrain instability, specifically the expected runout distance and expected areas of deposition for landslides and their likelihood of reaching downslope identified elements and resources at risk. This is a partial risk analysis since it identifies the geomorphic components of a risk analysis without addressing the vulnerability of the elements at risk to the hazard.

As an example, consider a theoretical 10 ha cutblock planned for clearcut harvest on a steep mountain slope. There is a forest service road 400 m downslope and a S3 fish stream 600 m downslope. Statlu estimates that the post-harvest hazard of landsliding from the cutblock is low, and that if landslides occur, they are likely to reach and cross or deposit on the forest service road, and will likely deposit on the low-gradient terrain between the road and the stream, but could potentially reach the fish stream below the road.

To extend this geomorphic analysis to a full evaluation of the consequence of the potential landslide and the resultant risk requires information on the value of timber on the slopes below the block, the nature and frequency of use of the forest service road by industrial and recreational traffic, the quality of riparian habitat, species present and seasonality of use of the fish stream by those species, and other information beyond the purview of geoscience but available or potentially available to land managers and statutory decision makers.

Broadly speaking, the estimations of probability for runout and deposition determined by Statlu correspond to the following classes of consequence from the Forest Road Engineering Guidebook (Table A2). These correspondences are approximate and are provided only to help with decision-making.

Table A2: Definition of Probabilities of Consequence Qualitative Probability of

Consequence Range of Quantitative Probabilities

of Occurrence Approximate Qualitative

Consequence Class

Certain; Will Occur >50% Very High

Likely to Occur 25-50% High

Probable; Could Occur 10-25% Moderate

Unlikely to Occur 1-10% Low

Remote or Will not Occur <1% Very Low


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DEFINITIONS

Statlu follows the Terrain Classification System for British Columbia, 2nd Version when describing terrain attributes (Howes and Kenk, 1997) and the Canadian System of Soil Classification, 3rd Ed. (SCWG, 1998) when describing soil drainage and forest soils.

Sensitive receptor: any natural or human-constructed feature that may be adversely affected by a hazardous material. Hazardous material includes sedimentation, contamination, or other forms of pollution.

Slope morphology: the shape of the slope, both along contour and in profile.

Term Along Contour In Profile

Concave The contour converges Slope gradient decreases downslope

Convex The contour diverges Slope gradient increases downslope

Irregular No pattern to slope changes Slope changes gradient with no pattern

Uniform/straight Consistent shape Slope has consistent gradient

General Slope Descriptors

Benched A series of flat bench tops broken by steeper steps between benches, similar to terraces but not formed by fluvial processes

Terraced Slope pattern of step-like forms composed of flat tops or treads separated by shorter, steep pitches (risers); formed by fluvial processes

Undulating An assemblage of multidirectional slopes; regular slope variation along contour

(From LMH 18)


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Soil Drainage: the rate at which saturated surficial material reaches field capacity, the moisture content remaining after removal of water by gravity (usually 24 hours after saturation)

Soil Drainage Class Description

Very rapid Water removed rapidly in relation to supply. Water source is precipitation.

Rapid Water removed rapidly in relation to supply. Water flows downward if material is pervious. Water source is precipitation. Soils are generally coarse textured.

Well-drained Water readily removed from soil. Water flows downward or laterally.

Moderately well-drained Water is removed from soil somewhat slowly in relation to supply.

Imperfect Water is removed from the soil slowly. The soil remains wet for a significant portion of the growing season. Soils may be mottled.

Poor Water is removed so slowly in relation to supply that the soil remains wet when it is not frozen. Soils may be mottled or gleyed.

Very Poor Water is removed so slowly in relation to supply that the water table remains at or near the surface for most of the time the soil is not frozen. Associated with wetlands.

(From LMH 25)

Surface expression: the form and pattern expressed by a surficial material at the land surface. Figure B1 provides a general summary of terms commonly used to describe surface expression. In addition to common terms, we describe sediments thicker than approximately 5 m as “deep.”

Figure B1: Common surface expression terms (Ryder and Howes, 1986)

Surficial materials: non-lithified, unconsolidated sediments that are classified by mode of deposition (i.e., till, colluvium, glaciofluvial).


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Surficial material texture: the size, shape, and sorting of particles in clastic sediments.

Single Particles Mixtures

Class Name Particle Size and Shape Class Name Particle Size and Shape

clay < 0.002 mm gravel > 2 mm, mix of round particles; pebbles, cobbles, boulders

silt 0.002 mm – 0.0625 mm rubble 2 mm to 256 mm, mix of angular particles

sand 0.0625 mm - 2 mm mud mix of clay and silt; may include sand

pebbles 2 mm - 64 mm, round angular fragments > 2 mm, mix of angular particles; blocks and rubble

cobbles 64 mm - 256 mm, round mixed fragments > 2 mm, mix of round and angular particles

boulders > 256 mm, round diamicton mix of materials with two or more distinct particle sizes

blocks > 256 mm, angular

Harvesting Methods

Harvesting systems include four phases: falling and bucking, yarding, loading, and hauling. Timber yarding methods have the greatest effect on terrain stability and are often modified to reduce the likelihood of increased post-harvest terrain instability (CSSP, 1995).

Ground-based yarding uses skidders, hoe forwarders, or other equipment to bring timber to the landing. Skidders drag timber on the ground, hoe forwarders carry timber or lift and swing it to a yarding or skidding corridor, landing, or roadside. Application of ground-based methods is limited by slope gradient, slope shape, soil sensitivity to erosion, and weather. Ground-based yarding with rubber tired or tracked machines is limited to slope gradients <40%. Restricted ground-based yarding uses ground-based machines on slope gradients between 40% and 60% by running machinery on cut and fill skid trails or from roads.

Cable yarding uses stationary yarders to move logs along cables from where they were felled to the roadside or landing. Cable yarding reduces soil disturbance and can be used on steep slopes. Skyline and highlead are two cable yarding methods.

Helicopter yarding is used to yard logs in sensitive or inaccessible terrain. Helicopters are used to fly logs from where they were felled to an accessible drop site. Helicopter yarding is both expensive and slow compared to other yarding methods.


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Road Construction Terms

Conventional Construction: cut and fill is balanced; fill is sidecast on the downslope side of the road and will form a portion of the load-bearing road surface. Where conventional construction is described as a low-hazard option, other construction techniques that use more fill than cut, such as overlanding and full fill, are also low-hazard options unless otherwise specified.

Conventional Reconstruction: conventional reconstruction of an existing road consists of resurfacing the road, re-establishing a functional ditch line, and installing drainage structures with appropriate capacity and spacing.

Conventional Reconstruction with no sidecast is identical to regular conventional reconstruction, but prescribed in areas where existing roads cross steep slopes and where sidecast would result in oversteepened or unstable perched fills. Material which cannot be incorporated into the road surface during reconstruction operations must be endhauled to an appropriate spoil site.

Full Bench: the cut width is equal to the road width; none of the road prism is supported on fill. Sidecast may be hauled to a dump site, used for road ballast, or fully sidecast, as prescribed in the report and as defined below. Ditches are constructed on full bench road segments and where specifically recommended in the report.

Partial Bench (Sliverfill): 3/4 to full bench construction where fill is supported on rubbly material draped down hillslope. Used only in rock or coarse colluvium, or in locations where thin veneers of sidecast material will disperse downslope stably. Do not place material over organic material, soil, logs, etc.

Full Sidecast: Excavated material may be cast downslope but must not form a portion of the load-bearing road surface. Full bench with full sidecast is typically prescribed in locations where the slope is too steep for load-bearing fill to be stable but topographic features downslope of the road prism will capture and stabilize sidecast material.

No Sidecast: The sideslopes are too steep to support sidecast; therefore, all sidecast material must be hauled to a spoil site or spoiled in grade on adjacent road segments.

Keyed Fill: The ballast is composed of coarse pieces of angular rock placed on, and supported by, an excavated bench. The toe of the bench should be wide enough to support the lowest course of placed rock (generally 1.0 m to 1.5 m wide) and should be gently outsloped to facilitate drainage.


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SEDIMENTATION HAZARD ASSESSMENT METHODOLOGY

Statlu uses the Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook, 2nd Ed. (Ministry of Forests, 1999) to determine sedimentation hazard. The following keys have been modified from the guidebook.

Sedimentation hazard is the chance that eroded sediment will reach sensitive receptors. It depends on erosion potential and sediment delivery potential. Erosion potential is the ability for sediments to be eroded and it depends on precipitation, topography, sediment thickness and texture, etc. Sediment delivery potential describes the connectivity between sediment sources and sensitive receptors.

Erosion Potential

Erosion potential uses site factors to classify blocks and roads. The classification assumes that the soil is exposed to intense rainfall events. The erosion potential classification considers only the likelihood of sediment being displaced. It does not address the likelihood of eroded sediment reaching sensitive receptors.

Soil Erosion Hazard Key

Site factors

Degree of contribution of factors

Low Moderate High Very High

Climate precipitation factor (points)

Low 2

Moderate 4

High 6

Very high 8

Slope Gradient (%) (points)

0-10 1

11-20 3

20-50 6

>50 9

Slope Length/Uniformity (points)

Short, broken 1

Short, uniform 2

Long, broken 3

Long, uniform 4

Depth to water-restriction (cm) (points)

>90 1

61-90 2

30-60 3

<30 4

Surface soil texture (0-15 cm)a (points)

SC, C, SiC 1

SiCL, CL, SCL 2

SL, L 4

Si, SiL, fSL, LS, S 8

Surface coarse fragments % (0 to 15 cm)a (points)

>60 1

31-60 2

16-30 3

<16 4

Subsoil texture (16 cm to 60 cm)a (points)

S, LS, SL, fSL 1

L, SiL, Si 2

CL, SCL, SiCL 3

C, SC, SiC 4

Soil erosion hazard rating b

(point total)

Low

<16

Moderate

16-22

High

23-31

Very High

>31

a If two contrasting textures or coarse fragment contents occur in the depth, use the one with the highest point rating. b Gently sloping areas with long, uniform slopes may rate as high soil erosion hazard since substantial erosion can occur, under the right

conditions.

The climate precipitation factor is very high for southwest BC except for specific very dry ecosystem subclasses. All other site factors are classified according to field observations.


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Sediment Delivery Potential

Sediment delivery potential describes the probability of displaced sediment reaching creeks with moderate or high sediment transport capacity. It is a classification that assumes sediment has been displaced by erosion, creeks are capable of transporting sediment to sensitive receptors, and the forest floor and understory vegetation remain relatively intact.

Sediment Delivery Potential Keys

Risk of sediment delivery to streams

Proximity and size of stream

No stream in or adjacent Minor stream¹ in or adjacent

Major stream² in or adjacent

Low >70% slopes³ < 25% slopes

Moderate 25 to 70% slopes < 25% slopes

High > 70% slopes 25 to 70% slopes ¹

² Perennial streams with channel widths > 1.5 m, or Class S1, S2, or S3 streams. ³ Slope steepness downslope to stream channel.

Sedimentation Hazard

Sedimentation hazard is defined as the product of soil erosion potential and sediment delivery potential. The hazard is based on the probability of eroded sediments reaching a sensitive receptor.

Sediment Delivery Potential

Low Moderate High

Ero

sio

n

Po

ten

tial

Low Low Low Low

Moderate Low Moderate Moderate

High Low Moderate High

Very High Moderate High Very High


19-123 JUNE 22, 2020

PAGE 32

HYDROLOGIC RISK AND RISK ASSESSMENT METHODOLOGY

Peak flow is the maximum flow rate that occurs within a specified period, usually on an annual or event basis. Generally, melting of the snowpack in spring and/or heavy rainstorms or rain-on-snow events generate peak flows. Tree removal and road building by forestry can affect peak flow timing and volumes. By removing trees, not only is more precipitation able to reach the ground and infiltrate the soil, but the timing of the delivery may be altered. Timber harvesting reduces interception and evapotranspiration, and increases the winter snowpack. This can result in an earlier and more rapid snowmelt, and higher flow resulting from the deeper snowpack. It can also result directly in higher runoff during rainfall events and/or higher groundwater levels. By changing the longwave and shortwave radiative balance, logging can also change the timing of snowmelt, although this depends on aspect and other shading as well as forest canopy removal.

Construction of logging roads can affect the pathway and the timing in which precipitation or snowmelt reaches the stream channel. Subsurface flow may be intercepted and directed down ditches as surface flow, reaching stream channels at an accelerated rate. Compacted surfaces of roads reduce infiltration, transferring surface flow to ditches, which also means that surface water reaches stream channels at an accelerated rate.

Cumulative hydrologic effects are commonly expressed as the likelihood that logging will result in increases to peak flow magnitude or frequency. Cumulative hydrologic effects are evaluated by considering the net area logged over time and determining the equivalent clearcut area (ECA) for each logged area, which consists of the initially clearcut area modified by a recovery term that accounts for the restoration of forest canopy, root structures, transpiration, and interception as new trees grow. For instance, an area of 10 ha, originally clearcut, fully restocked, and with vigorous new growth 20 years old, might be calculated to have recovered 30% of the original hydrological effectiveness of the previous forest in terms of rainfall and snowfall interception and ground shading. The ECA is calculated as clearcut area times the recovery factor (percent clearcut minus percent recovered). In this example, the ECA is 10 ha * (100%-30%) = 7 ha. Therefore the 10 ha, 20-year-old block would be determined to be hydrologically equivalent to a 7 ha fresh clearcut. ECA is summed for each past block harvested in a watershed to determine cumulative hydrologic effects. Intermediate categories (such as very low to low) are included in the table to indicate the range of watershed sensitivities, which depend on woody debris abundance, channel substrate, geology, hydrograph type (snowmelt or rainfall dominated) and other factors.

In addition to peak flow changes, cumulative hydrologic effects can result in changes to mean annual or low flow, and to changes in the timing and duration of flow. Flow might become less variable if melt from different aspects and elevations is synchronized. The timing of low flow might be altered, and its duration lengthened, if snowmelt occurs earlier in the year. Conversely, by reducing transpiration, forest harvesting might increase low flow levels or decrease the duration of summer low flows.


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ECA Range (percent of total watershed area)

Hydrologic Risk Qualitative Interpretation

0% to 15% Very low Detectable changes to peak, mean and low flow will not occur

15% to 20% Very low to low

20% to 25% Low Detectable changes to peak or flow are unlikely to occur. Small variations might be detectable using statistical analysis.

25% to 30% Low to moderate

30% to 35% Moderate Detectable changes to peak flow might occur for some flow magnitudes and return periods. Flow durations might be altered.

35% to 40% Moderate to high

40% to 45% High Detectable changes to peak flow frequency and magnitude will occur. Floods will become larger and more frequent. Low flows might increase or decrease. Mean annual flow might change.

45% to 50% High to very high

50% or higher Very high Watershed hydrology will be significantly changed. Peak flow frequency and magnitude will undergo large changes. Floods will be much larger and much more frequent. Low flow and mean annual flow frequency and duration will change.

Risk is a function the likelihood of an event occurring and the exposure of downslope or downstream resources to the event, and vulnerability of the downslope resources, which together determine the consequences should the event occur. Land Management Handbook 56 (Wise et al. 2004) and the BC Ministry of Forests Forest Road Engineering Guidebook (2002) define risk as the product of the probability of hazard (likelihood of occurrence) and consequence. Consequence further depends on the nature of the element(s) at risk, exposure, and vulnerability.

Statlu recognizes that the evaluation of the exposure and vulnerability of elements at risk is difficult and may require specialized skills or additional information not available to professional geoscientists. Since the information is available or potentially available to land managers and statutory decision makers, we have concentrated on identifying and describing the geomorphic components of the consequences, specifically their likelihood of reaching downstream identified elements and resources at risk. This is a partial risk analysis since it identifies the geomorphic components of a risk analysis without addressing the vulnerability of the elements at risk.

As an example, consider a theoretical watershed of 1000 ha. The existing ECA is 150 ha, and another 100 ha are planned for logging, with associated road construction, which will raise the watershed ECA to 25%. The main stream in the watershed flows into a lake and has built a fan at its mouth; there are cabins on the lake, with a community water license intake near the head of the fan, and fish present in stream reaches on and near the fan, while higher stream reaches are too steep for fish habitat. Statlu estimates that the post-harvest likelihood of peak flow changes is low, and that if changes to peak flow regimes do occur they are likely to be transient and persist for less than five years. Small changes to the timing of flow are likely: spring snowmelt may occur up to a week earlier, and the summer low flow period may be extended by a similar length of time, but summer low flows may be slightly higher for up to ten years due to reduced evapotranspiration. Changes to channel pattern in the stream and on the fan are unlikely and changes to water quality are unlikely if all roads are built as planned and incorporate site-specific erosion and sediment control measures, and if old roads are deactivated.

To extend this hydrogeomorphic analysis to a full evaluation of the consequence of the potential harvesting and road building and the resultant risk, requires information on the frequency of use, and designated flood construction level and flood control measures incorporated into the design of the cabins on the fan, the nature and frequency of use of the forest service roads by industrial and recreational traffic, the quality of riparian habitat, species present and seasonality of use of the fish stream by those species, the water diversion and treatment methods used at the water intake, and other information beyond the purview of geoscience but available or potentially available to land managers and statutory decision makers.


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Broadly speaking, the qualitative estimations of probability determined by Statlu correspond to the following classes of consequence from the Forest Road Engineering Guidebook (Table A2). These correspondences are approximate and are provided only to help with decision-making.

Qualitative Probability of

Consequence Range of Quantitative Probabilities of

Occurrence Approximate Qualitative

Consequence Class

Certain; Will Occur >50% Very High

Likely to Occur 25-50% High

Probable; Could Occur 10-25% Moderate

Unlikely to Occur 1-10% Low

Remote or Will not Occur <1% Very Low


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RATIONALE FOR HYDROLOGIC ASSESSMENT

Rationale for Assessment

Forest harvesting can affect hydrology in many ways. The assessment of hydrologic impacts in a CWAP focuses on the potential for:

Changes to peak stream flows, Accelerated surface soil erosion, Accelerated landslide activity, Changes to riparian zones; and, Changes to channel morphology.

The following section describes the potential effects of changes to these five indicators resulting from forestry and forestry-related activities.

Changes to Peak Stream Flow

Peak flow is the maximum flow rate that occurs within a specified period, usually on an annual or event basis. Generally, melting of the snowpack in spring and/or heavy rainstorms or rain-on-snow events generate peak flows. Tree removal and road building by forestry can affect peak flow timing and volumes. By removing trees, not only is more precipitation able to reach the ground and infiltrate the soil, but the timing of the delivery may be altered. Timber harvesting reduces interception and evapotranspiration, and increases the winter snowpack. This can result in an earlier and more rapid snowmelt, and higher flow resulting from the deeper snowpack. It can also result directly in higher runoff during rainfall events and/or higher groundwater levels.

Construction of logging roads can affect the pathway and the timing in which precipitation reaches the stream channel. Subsurface flow may be intercepted and directed down ditchlines as surface flow, reaching stream channels at an accelerated rate. Compacted surfaces of roads reduce infiltration, transferring surface flow to ditches, which also means that surface water reaches stream channels at an accelerated rate.

Accelerated Surface Soil Erosion

Surface soil erosion is defined as the detachment, entrainment, and transport of individual sediment particles due to falling or running water, or wind. It is a function of surface cover, mineral soil type, slope gradient, slope length and shape, and rainfall intensity.

The principal effect of forest practices on surface soil erosion results from road building. Sediment generated from ditches, cut and fill slopes, and road surfaces is introduced to stream channels through ditches and at stream crossings. Higher road densities indicate higher potential for sediment delivery to streams. High quantities of sediment can clog ditches and stream channels, accelerate stream bank erosion, deposit fine sediments in reservoirs, cover fish spawning grounds, and reduce downstream water quality. Timber harvesting can also cause accelerated surface soil erosion due to exposing soil as a byproduct of removal of vegetation. However, roads, particularly old pre-Forest Practices Code roads that have not been deactivated, pipeline and powerline access roads, and other similar roads, are a far greater potential source of sediment than conventional harvesting done to current Forest and Range Practices Act (FRPA) standards.


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Landslide Activity

Landslides are a natural process on steep terrain, and occur over time at a natural rate. Forest practices can accelerate this natural rate through road construction and logging on unstable or potentially unstable terrain.

The alteration of natural drainage patterns through road building can lead to unusual concentrations of water on hillslopes, road fillslopes, and road beds, leading to a higher likelihood of landsliding. Timber harvesting can alter slope hydrology. Removal of forest cover results in a reduction of transpiration and interception losses, leading to increased soil saturation, subsurface flow, and surface runoff. In addition, when trees are harvested, the roots of the stumps decay and begin to lose their soil binding strength, reducing their reinforcing capacity. This makes slopes more susceptible to landsliding until new growth re-establishes deep root systems.

The harvesting method can also lead to slope instability. Log yarding can disrupt natural pathways for water drainage, and create new pathways. Yarding logs across slopes and using heavy machinery can damage the soil surface and the roots that help hold the soil.

FRPA requires that logging not cause landslides, adverse gully processes, or fan destabilization. The frequency of landsliding from logged terrain has been reduced by identifying and avoiding harvesting on unstable slopes, and by applying mitigation measures that promote stability on harvested slopes.

Changes to Riparian Zone

The riparian area, or land adjacent to the high water line in watercourses and standing bodies of water, is important to stream ecosystems and stream morphology. Riparian areas help maintain water quality by controlling sedimentation, supplying nutrients and large woody debris, and maintaining stream channel morphology. Excessive harvesting within riparian areas can destabilize stream banks, increase bank erosion and stream sedimentation, diminish the supply of woody debris to the channel, and increase the size of sediment wedges of some stream reaches.

Changes to Stream Channel Pattern

Analysis of stream channel patterns can indicate that changes to sediment supply, riparian vegetation, or peak flow indices may have influenced a watershed because these variables influence changes to stream channel pattern. For instance, increased flooding can lead to increased bank erosion or overbank deposition as well as changes in bed material texture. Increased sediment supply can result in increased sediment deposition in-channel and a consequent widening of the channel or changes in the texture and composition of channel bedforms. Changes to riparian vegetation can change coarse woody debris inputs to the channel, altering the frequency and size of logjams as well as the bed texture.

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