[Coastal Watershed Assessment Procedure Guidebook Table of Contents]

Interpretations and recommendations

The CWAP produces numerical scores in five impact categories—peak flows, surface erosion, riparian buffers, landslides, and headwaters—each of which has two to four indicators.

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

One hazard index score between 0 and 1 should be determined for each of the five impact categories according to the following procedures:

Peak flows

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

Enter the peak flow hazard index in Form 11.

Surface erosion

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

Enter the surface erosion hazard index in Form 11.

Riparian buffers

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

Enter the riparian hazard index in Form 11.

Landslides

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

Enter the landslide hazard index in Form 11.

Headwaters

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

Enter the landslide hazard index in Form 11.

Form 11. Hazard index

Level 2 watershed assessment (channel assessment)

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:

The level 2 WAP provides an overview assessment of stream channels in the watershed, and estimates the level of channel disturbance associated with forest practices for the most sensitive channel type within each watershed or sub-basin. An impact score between 0.0 and 1.0 is assigned, where:

Low <0.5
Medium 0.5–0.7
High > 0.7
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 Procedure 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

Stream channel impacts, both within individual channel reaches and at a watershed scale, can be assessed on air photographs. This level of assessment involves:

In the general assessment:

And then, if required, in a detailed analysis:

Field assessments

 If the results of the air photograph analysis warrant it, field assessment of stream channels is required.

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 three levels of field assessments are completed successively, from first to third, as required. Not all levels of assessment are required in all cases.

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:

The first level of channel assessments uses channel keys that have incorporated most of the field indicators listed above. The keys attempt to show in pictorial format the properties that would need to be measured, compiled, and analyzed to determine the level of channel disturbance.

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

Once the level 1 and, if required, level 2 analyses have been completed, the interpretations and recommendations presented in the following pages must be considered.

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

Each hazard index by itself does not provide the optimum information. Because most of the impact categories are inter-related, they must be interpreted that way. For example, a high value for the peak flow hazard index is not very informative unless you relate it to the condition of the riparian area. Similarly, the landslide hazard index is much easier to interpret when it is combined with the riparian buffers index.

The following seven 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:

Hazard category

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 landslides 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.

Interaction matrix 2. Peak flow vs. surface erosion

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. landslide

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. Landslide 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 landsliding 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 landsliding 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.

Interaction matrix 5. Riparian vs. channel instability

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.
Interaction matrix 6. Headwaters vs. channel instability

Recommendations:

Value = 1:
There are no harvesting or equivalent clearcut area (ECA) implications.
Value = 2:
Investigate causes of channel instability by completing a detailed channel assessment.

Identify individual headwater streams that might have experienced accelerated erosion from past logging and that might require rehabilitation.
Value = 3:
Assess S4, S5, and S6 headwater channels for erosion.

Assess road crossings of streams for stability. Investigate culvert and drainage system integrity. Increase the frequency of culvert and drainage system maintenance where necessary.

Retain higher timber volumes in the management zones of riparian management areas along S4, S5, and S6 headwater streams.
Value = 4:
Complete a detailed channel assessment of S4, S5, and S6 headwater channels and develop and initiate a stream channel rehabilitation program as necessary.

Reduce ECAs to no more than 20% on areas tributary to logged S4, S5, and S6 headwater streams.

Retain higher timber volumes in the management zones of riparian management areas along S4, S5, and S6 headwater streams.

Complete an assessment of road stream crossings on S4, S5, and S6 headwater channels, and initiate a road rehabilitation program.

Interaction matrix 7. Headwaters vs. peak flow

Recommendations:

Value = 1:
There are no harvesting or equivalent clearcut area (ECA) implications.
Value = 2:
Retain higher tree retention in the management zones of riparian management areas along S4, S5, and S6 headwater streams.
Value = 3:
Do not increase ECA to more than 20% on areas draining into gullied S5 and S6 channels.
Value = 4:
Complete a detailed channel assessment of S4, S5, and S6 headwater channels and develop and initiate a stream channel rehabilitation program as necessary.

Reduce ECAs to no more than 20% on areas flowing into logged S4, S5, and S6 headwater streams.

Retain higher timber volumes in the management zones of riparian management areas along S4, S5, and S6 headwater streams.

Complete an assessment of road-stream crossings on headwater channels, and initiate a road rehabilitation program.

Interpretation worksheet

 The interpretation worksheet shown below should be used to synthesize the results of the interpretation matrices, and to document the recommendations for each sub-basin analyzed in the watershed. The interpretation value for each of the seven interactions, listed in the worksheet, are obtained from the seven interpretation matrices shown in the previous section.

Interpretation worksheet

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