In this section are instructions on how to summarize the results in each of the impact categories and how to produce a hazard index for each category. Instructions are also provided on how to interpret and apply these results to the watershed development plan.

Determining hazard index scores

Peak flows

The peak flow hazard index is equal to the greater value of either the:

• the peak flow index (indicator #1)
• the average of peak flow index (indicator #1), road density above H60 line (indicator #2), and road density for entire sub-basin (indicator #3).

Surface erosion

The surface erosion hazard index is equal to the greater of:

• roads on erodible soils <100 m from a stream (indicator #6)
• the average of density of roads on erodible soils (indicator #4) and density of stream crossings (indicator #7)
• the average of density of roads <100 m from a stream (indicator #5) and density of stream crossings (indicator #7)
• the average of density of roads <100 m from a stream (indicator #5) and road density for entire sub-basin (indicator #8)
• the average of density of roads on erodible soils (indicator #4) and road density for entire sub-basin (indicator #8)
• the average of density of roads on erodible soils (indicator #4), density of stream crossings (indicator #7), and road density for entire sub-basin (indicator #8).

Riparian buffers

The riparian hazard index is equal to the greater value of:

• the portion of stream logged (indicator #9)
• the portion of fish-bearing stream logged (indicator #10).

Mass wasting

The mass wasting hazard index is equal to the greater value of:

• the density of landslides (indicator #11)
• the average of the density of roads on unstable slopes (indicator #12) and the streambanks logged on slopes > 60% (indicator #13)
• the average of the density of landslides (indicator #11), the density of roads on unstable slopes (indicator #12), and the streambanks logged on slopes >60% (indicator #13).

Form 11. Hazard index

Level 2 watershed assessment (channel assessment procedure)

At this point in the level 1 assessment, it must be decided whether further analyses on a particular watershed are required. As a rule of thumb:

• If all hazard indices (Form 11) are less than 0.5, there are no or limited perceived cumulative impacts and no further IWAP analysis is required to assess impacts of past forestry activity. However, if a forest development plan is proposed for the area, a second level 1 analysis must be completed to assess the potential impacts that may result from that forest development. The assessment can thus be used strategically to alter the plan, as necessary, to minimize watershed impacts.

• If the surface erosion hazard index is greater than or equal to 0.5, but all other hazard indices are less than 0.5, no further IWAP analysis is required.

• If any of the peak flow, mass wasting, or riparian buffer hazard indices are greater than or equal to 0.5, then a level 2 analysis (that is, a channel assessment) must be completed before the interpretations, as described, are developed. The results of the level 2 analysis should be used in the interpretation worksheets in the section “Making interpretations and recommendations,” under “channel instability.”

As noted earlier, this assessment is best performed by an individual with at least basic experience in hydrology and/or geomorphology. The level 2 WAP is presented only in summary form here, and is described in detail in a separate document titled the Channel Assessment Guidebook.

Stream channel assessment contains both air photograph analysis and field analysis components. Each component can be done in two levels of detail, an initial, overview level or a more rigorous and comprehensive level.

Air photograph analysis

In the general assessment:

• qualitatively assessing the aerial photographs, from before and after logging, for any obvious, gross changes in channel morphology
• summarizing the spatial and temporal extent of channel change associated with forest harvesting activities as inferred from the aerial photograph analysis
• determining the channel impact value for the level 1 matrix.

Then, if required, in a detailed analysis:

• delineating all reach breaks, using the most recent air photograph series that pre-date logging
• describing the morphology of each reach according to the appropriate system
• comparing the morphological features over time (before and after logging), by corresponding reach
• summarizing the spatial and temporal extent of channel change associated with forest harvesting activities, as determined by the aerial photograph analysis
• determining the channel impact value for the level 1 matrix (refer to the section, “ Interpretation matrices”).

Field assessments

To determine the degree of channel disturbance associated with forest practices, the condition of the stream channel before it was subjected to altered streamflow discharge or sediment supply must be estimated. In the absence of historical information or robust theoretical descriptions, it is assumed that the original, or undisturbed, channel state would have been the “typical” morphology for the particular stream size and type. The generalized sequence of channel changes are described in the Channel Assessment Procedure Guidebook.

Three levels of assessment can be undertaken in the field:

• The first level is qualitative and relies on visual observations of the channel condition in comparison with keys indicating a typical, or expected, channel state.

• The second level is more quantitative and compares detailed stream survey data with theoretically predicted values and/or current condition in comparable channels.

• The third level of analysis is completed by a fluvial geomorphologist.

The objective of the field assessments is to determine if past forest practices have caused channel impacts. Therefore, the challenge in level 2 is to correctly and consistently identify both the impacts and their causes. The obvious field indicators of channel disturbance are:

• eroding banks (freshly eroded or noticeable lack of under-cut or over-hung banks)
• extensively scoured zones (most channel bars and bed material are absent due to scouring flows)
• elevated mid-channel bars (bar tops are at elevations equal to or above the adjacent bank tops)
• extensive channel bar amount (predominantly bed material with minimal flowing water during low flows. In extreme cases this can be a de-watered channel).
• relative abundance of small sized large woody debris (LWD) (commonly logs with saw cut-ends and detached root wads and branches)
• most LWD is lying parallel to the channel banks (very little LWD lying perpendicular to the channel and spanning from one bank to the other)
• presence of recently formed LWD debris jams
• extensive riffle zones (extensive braided zones are the extreme)
• limited frequency and extent of pools
• minimal sediment texture variability (sediment sorting is influenced by changes in LWD characteristics).

From the field procedures (described in detail in the Channel Assessment Procedure Guidebook) an estimate of the level of channel disturbance associated with forest practices is determined for the most sensitive channel type within each watershed or sub-basin. The resultant channel impact score is then used in the interpretation matrices, where required, in the following section.

Making interpretations and recommendations

It is important to emphasize at this point, the pivotal role of the round table in using the interpretations and recommendations developed through this procedure. Both should be viewed as the basis for discussion amongst the stakeholders at the round table, not as firm requirements. They are guidelines only and can be over-ridden by a detailed level 3 assessment or, where a consensus is reached, by a decision of the round table.

Interpretation matrices

The following five matrices provide a means of considering these interrelated effects. Each matrix considers a combination of two hazard indices, grouping the results into three categories: low, medium, and high. These categories are defined as follows:

The combination of two hazards in each matrix results in an interpretation value of 1 to 4. Associated with each value are interpretations and recommendations, described beneath each matrix.

Interaction matrix 1. Peak flow vs. channel instability

Recommendations:

Value = 1:

There are no harvesting or equivalent clearcut area (ECA) implications.

Value = 2:

Do not increase the current ECA levels unless a level 3 analysis indicates site-specific opportunities.
Do not allow logging in high landslide hazard zones.
Limit ECA to 20% in areas that drain onto high landslide hazard zones.

Value = 3:

Do a detailed channel assessment to confirm channel stability rating.
Allow very limited additional logging (emergency salvage) until ECA levels are reduced to at least a medium hazard category.
Initiate channel (and slope) rehabilitation if appropriate.

Recommendations:

Value = 1:

There are no harvesting or equivalent clearcut area (ECA) implications.

Value = 2:

Initiate an assessment of sediment sources (refer to Moore 1994[1]).
Do not allow additional harvesting above and around sensitive soils.
Rehabilitate roads near streams, and avoid construction of more roads on sensitive soils or adjacent to riparian management areas.
Minimize additional stream crossings.
Where the peak flow hazard score is high, do not increase ECA .

Value = 3:

Initiate an assessment of sediment sources (refer to Moore 1994).
Do not increase current ECA levels, particularly above and around sensitive soil types.
Do not allow additional roads to be constructed before a rehabilitation/ deactivation program is developed and initiated.

Value = 4:

Initiate an assessment of sediment sources (refer to Moore 1994). Permanently deactivate as many roads as possible, consistent with access management requirements.

• Reduce ECA over the entire watershed.
• Do not allow additional roads in sensitive areas.

Interaction matrix 3. Peak flow vs. mass wasting

Recommendations:

Value = 1:

There are no harvesting or equivalent clearcut area (ECA) implications.
A detailed site assessment is required on any potentially unstable slope.

Value = 2:

A detailed site assessment is required on any potentially unstable slope.
Initiate an assessment of sediment sources (refer to Moore 1994).
Assess roads as sources of landslides and initiate a road deactivation and landslide rehabilitation program as required.

Value = 3:

Restrict harvesting to a maximum of 20% on areas draining onto or above Class IV or V slopes.
Complete terrain mapping at a 1:20 000 scale for all areas of proposed forest development, and complete detailed field assessments on any Class IV or V slope before approving harvesting or road building.

Value = 4:

Reduce ECA in the watershed to at least a moderate hazard level.
Complete terrain mapping at a 1:20 000 scale for all areas of proposed forest development.
Do not allow any logging on or above Class IV or V slopes.
Initiate a landslide rehabilitation program.

Interaction matrix 4. Mass wasting vs. channel instability

Recommendations:

Value = 1:

There are no harvesting or equivalent clearcut area (ECA) implications.

Value = 2:

Initiate a detailed channel stability assessment.
Complete terrain mapping at a 1:20 000 scale for all areas of proposed forest development, and complete detailed field assessments on any Class IV or V slope before approving logging or road building.

Value = 3:

Assess roads and investigate causes of mass wasting in the watershed, and develop and initiate a rehabilitation and road deactivation program as required.

Value = 4:

Allow no further logging until a detailed channel stability assessment is complete.
Assess roads and investigate causes of mass wasting in the watershed, and develop and initiate a rehabilitation and road deactivation program as required.
Complete detailed terrain mapping and do not allow logging on or above any Class IV or V slope.
Reduce the ECA in the watershed to ensure the peak flow hazard score is not greater than moderate.

Recommendations:

Value = 1:

There are no harvesting or equivalent clearcut area (ECA) implications.
There are no WAP restrictions on logging in the management zones of riparian management areas.

Value = 2:

Do not conduct logging in active floodplain areas.
Investigate whether individual, site-specific, landslides are impacting the stream channel, requiring rehabilitation.
Investigate causes of channel instability by completing a detailed channel assessment.

Value = 3:

Retain higher tree retention in the management zones of riparian management areas along S2, S3, and S4 streams, consistent with windthrow management requirements.
Do not conduct logging in active floodplain areas.

Value = 4:

Complete a detailed channel assessment. Initiate a stream channel rehabilitation program as necessary.
Do not conduct logging in active floodplain areas.
Ensure that 10-metre reserve zones are retained in the riparian management areas along all S4 and S5 streams, consistent with windthrow management requirements.
Retain higher timber volumes in the management zones of riparian management areas along S2, S3, S4, S5, and S6 streams, consistent with windthrow management requirements.

Interpretation worksheet