Coastal Watershed Assessment Procedure Guidebook (CWAP)

[Coastal Watershed Assessment Procedure Guidebook Table of Contents]

The level 1 analysis procedure

Map work

The information described below should be compiled on a topographic base map before any attempt is made to fill out the data tables. If at all possible, all of this information should be digitized and entered on an appropriate GIS using 1:20 000 Terrain Resource Information Mapping (TRIM) as a base.

On one TRIM base map or an overlay, identify and map the following information (sources for all of these data are provided in Appendix 1):
- the watershed boundaries of the main watershed of concern (see Appendix 2), and all sub-watersheds to be assessed. This will usually include sub-basins drained by streams that are one stream order less than than that at the POI. The minimum stream order size to be mapped is a second-order basin.
- the stream network
- the 300- and 800-m contours of the main basin
- areas of potential slope instability (see Appendix 3 for methodology)
- areas of fine-textured soils (see Appendix 4 for methodology)
- location of fish-bearing stream reaches (see the Fish-stream Identification Guidebook for information on fish stream mapping)
- road networks and stream crossings
- cutblocks and regeneration information
- private lands.
Overlay this information on an updated forest cover map.

All of the map-related data requirements for a level 1 analysis should be available from this base map. If the analysis is to include future development activities, then the information provided on a forest development plan should also be included on the base map.

Data compilation

For each sub-basin of interest, Forms 1 to 9 should be filled out. (Detailed information on how to do this is provided in the appendices.) The data recorded on these forms will be used to derive a score (page 15) and develop a watershed report (page 17) which will provide the basis for establishing watershed constraints and developing recommendations (page 19).

Peak flow

A discussion of the effects of forestry activities on stream flow regimes and detailed information for calculating equivalent clearcut area are presented in Appendix 5.

Consult Appendix 5 and then fill out Forms 1 to 3 below.

Form 1. Area measurements by elevation band and sub-basin

Form 2. Peak flow index (indicator #1) calculations by sub-basin

Form 3. Road inventory and density (indicators #2 and #3) (see Appendix 6)

Surface erosion

An explanation of how forestry activities affect surface erosion and, in turn, how that can affect watershed integrity is provided in Appendix 6. Details on how to fill out Form 4 and measure road lengths are also provided in Appendix 6.

See Appendix 4 for the definition of erodible soils.

Form 4. Roads adjacent to streams (indicators #4, #5 and #6)

Riparian buffers

See Appendix 7 for a discussion about the effects of forestry activities on stream channels and an explanation of how to fill out Form 5.

See the Fish-stream Identification Guidebook for a definition of fish-bearing reaches.

Form 5. Riparian buffer impacts (indicators #7, #8 and #9)

Landslides

See Appendix 3 for a definition of unstable terrain. Appendix 8 contains a discussion of the impacts of forestry activities on unstable terrain and an explanation of how to fill out Form 6.

Form 6. Landslide hazard (indicators #10, #11, #12 and #13)

Headwaters

Headwater streams are defined as first-order or second-order streams, with a gradient over 60%, as shown on a 1:20 000 contour map. Such streams drain “potentially unstable terrain units,” as described in the Mapping and Assessing Terrain Stability Guidebook.

See Appendix 10 for a discussion of forestry activities on headwater streams and guidance on filling out Form 7.

Form 7. Headwaters

Watershed characteristics

The watershed characteristics listed in Forms 8 and 9 are either required to derive one of the 15 impact indicators, or are otherwise easily acquired from a GIS analysis of digital watershed and forest cover data. The indicators are not directly used to assess cumulative impacts in a watershed, but are valuable for the round table committee to use in assessing the impact results.

Form 8. Watershed characteristics by sub-basin

Form 9. Watershed characteristics by sub-basin

CWAP conversion table

As a result of filling out all of the preceding forms, you will end up with a set of raw data. The range of raw data for each indicator varies greatly from one indicator to another. Therefore, to make the indicators easier to interpret, the data are rescaled to fit between 0 and 1.0, with increments of 0.1. Scores less than 0.4 mean low impact, 0.4–0.6 means potential moderate impact, and greater than 0.6 means potential high impact.

Table 1 provides the conversions from raw data to scores for all coastal watersheds, grouping the indicators into five categories of impact. This table was developed from the results of 20 test watersheds representing the two coastal forest regions. If you use the electronic spreadsheet, these calculations are done automatically.

Example:: To get the peak flow index score from the raw data, find the column next to peak flow index that is closest to its raw score, then go up that column to the top of the table and read the score. Enter this score in Form 10. If a value from the raw data falls right between two shown on the table, use the higher score. Therefore, if your peak flow index is 0.33 (from Form 2), then your score for that indicator would be 0.6.

Table 1. Coastal watershed assessment conversion table

Watershed report card

The final step in summarizing the raw data for the CWAP is to compile all of the conversion scores onto a watershed report card for each sub-basin of the watershed looked at. Along the top line of the report card (Form 10), enter the names of each of the sub-basins of interest. Then, for each sub-basin, enter the scores obtained from Table 1 for each of the 15 indicators.

This report card will be used as the basis for identifying watershed constraints and developing management recommendations, as described in “Interpretations and recommendations.”

Form 10. Watershed report card

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