This section presents the results of the application of the Interior Watershed Assessment Procedure to the Nazko River watershed. The tabular manner in which the results are presented is intended to allow the reader to easily compare the results of individual watersheds. Most useful are the density measurements, which allow for fair comparison of individual watersheds.

An extremely useful product of the IWAP is the mapping products which are produced as an integral part of the final product. These maps facilitate intuitive comparison of watersheds and visual analysis of the many phenomena which cumulatively result in the hazard impact scores. Small scale maps of the study area watersheds showing roads, rivers, wetlands, lakes, slopes greater than 60 percent, H₆₀ lines and the tree stand heights used in the equivalent to clear-cut area (ECA) calculations are contained in Appendices D through P. With each watershed map is the completed IWAP calculation sheets. These sheets summarize the measurements, indicators, scores and hazard indices in each of the four hazard analysis areas (i.e. Peak Flow, Surface Erosion, Riparian Buffer and Landslides).

The watersheds under consideration vary greatly in relative areal extent. Table 4 gives the area breakdown for each watershed. Of note is the relative consistency of the elevations of the H₆₀ lines, which range over 200 metres only. The purpose of the H₆₀ line is to indicate the likely location of the snowline at spring freshet. It is designed to be applied over all Interior watersheds. Like all generalizations, it compromises specificity for general applicability. Consequently, there are exceptions. The Nazko study area watersheds are exceptions. They are low relief watersheds and the snow melts both earlier and more rapidly. The hydrograph peaks in early May and descends rapidly through June and July achieving baseflow in mid to late August (Rood and Hamilton 1995).

Table 4. Areal measurements of the study area watersheds by elevation.

The Peak Flow index score results from the weighted combination of equivalent clear cut area (ECA). The ECA is calculated to estimate the hydrological recovery of a watershed following harvesting. As such, burn areas , slides and hydro-cuts are considered clear-cuts with 0% recovery. Private land of less than 15% of the total watershed area is excluded from these calculations. In the ECA calculations, tree height is used as a surrogate to estimate the extent of hydrologic recovery. The lower the tree height, the more hydrological equivalent the area is to a clear cut. The relative importance of the ECA is weighted according to whether it is above or below the H₆₀ line. The ECA above the line is given 50% more weight in the summary calculation of the Peak Flow index score. Below, table 5 presents the ECAs for each watershed.

Table 5. Peak Flow index measurements and results

Road lengths for the watersheds were measured digitally directly from the relevant TRIM maps. In general, these maps do not show the full extent of roads within the watershed. It is often then preferred that the forest cover maps be used for calculations involving roads. However, the positional accuracy of these maps is significantly less than that of the TRIM maps. As this directly affects the hazard calculations, the TRIM data was preferentially used.

Table 6. Road inventory and density

Digital terrain maps are not available for the Nazko study area. It was consequently not possible to use these maps in the delineation of sensitive or erodible soils. For the purpose of the calculations, erodible soils were considered to be all slopes of greater than 60 percent. This is in adherence to the guidebook (pg. 59), but given the relatively flat nature of the watersheds it is not a satisfactory surrogate measurement. There are thick surficial deposits of glacial materials over the study area. Some of these materials are potentially erodible. The spatial union of erodible soils, roads and streams is shown in table 7. With respect to their genesis, the erodible soils density measurements are likely underestimates.

Table 7. Roads adjacent to streams

Table 8 compares the length of streams logged to total stream length. These numbers are used to calculate the Riparian Buffer hazard index.

Table 8. Riparian Buffer impacts

The full extent of fish bearing stream through the watersheds is not accurately known. The results indicate that it is not the portion of the fish bearing stream logged that is driving the riparian impact hazard scores, but it is more simply the portion of the stream logged. As this was the case in all of the thirteen watersheds, total length of fish bearing stream was made equal to the total length of stream.

In the IWAP, unstable terrain is defined as slopes greater than 60%. Which, in the case of this analysis, is the same criterion used to determine the extent of erodible soils. Although the measurements are in some cases the same, they are attributed different impact hazard scores because they are reported in a different context. In other words, 1 km of road on a slope greater than 60% is given a different hazard potential than 1 km of road on erodible soil. Table 9 shows the length of roads on unstable terrain in the context of mass movement potential. It also gives the density of streams whose banks have been logged on slopes greater than 60% in km per square km. Again, the relatively flat nature of the study area is reflected in these measurements.

As mentioned previously, the lack of assurance in the forest cover data quality means that caution should be used when interpreting these results. It is possible too that while the total areal extent of logging is correct, the exact location of the cut may be incorrect. As an additional caution, it should be pointed out that the positional accuracy of the forest cover maps is significantly lower than the TRIM maps. So that even if the area adjacent to a stream is typed correctly as a logged area, it may not necessarily be in the indicated location. Some forest cover maps show positional inaccuracies exceeding 100 m.

Table 9. Mass Wasting hazard measurements

Although forestry is the principle landuse activity in the study area, the area is also used for unrelated activities. Among these is agriculture. The area, particular in the northern part of the study area and around the village of Nazko, is used for both crops and cattle. The area is also used for game hunting, and many of the roads are open to recreational use. Some other relevant landuses are found detailed below.

Table 10. Other landuses

Data quality problems precluded the possibility of accurately determining the area ownership characteristics for the watersheds. This notwithstanding, the area is overwhelmingly crown land, most of which is used for timber supply. Although, there is some private land, predominantly in the northern portion of the study area.

Table 11. Watershed ownership characteristics

*both FIPDBF and FME were unable to translate the ownership layers with a certain degree of accuracy.

Table 12 provides physical descriptions of the watersheds, including hydrological zone, bedrock geology and area with unstable slopes. As described earlier, unstable areas are defined as those areas with slopes greater than 60%. In the Nazko study area, there is a small percentage of area which meets this criteria due to the relatively flat to rolling nature of the landscape. Appendices D through P contain individual overlays which illustrate the extent of these areas within each watershed. Dominant bedrock geology is numerically coded to a table contained in the IWAP guidebook. Class "9" is described as "volcanic (basalt) - flows/breccias/porphyries/greenstone" (page 79). As such, it best describes the bedrock geology of the Nazko study area. However, the area was glaciated repeated during the Pleistocene (at least three times). In some areas, then, there exists deep deposits of surficial materials of glacial origin.

Table 12. Physical characteristics by watershed

The watershed report card, table 13, summarizes the hazard index scores in each of the impact categories for each watershed. The index scores were calculated from the data derived from the digital database which was described in detail in sections 3.2.1, 3.2.2 and 3.2.3. The calculations were completed using a combination of the IWAP Excel data entry and calculations spreadsheets, and long-hand checks. The measurements and calculations undertaken as part of this assessment followed closely the procedure described in the guidebook. The results were thus obtained in the intended manner, and as such represent bone fide IWAP results. However, as previously discussed, the digital forest cover data does not appear to satisfactory. The hazard impact index numbers displayed below provide only coarse indications regarding watershed hydrological impacts. As a coarse filter, the numbers simply point to potential concerns. It is the interpretation of the impact number which contextualizes the concerns.

Table 13. Watershed Report Card.

Alone, the hazard impact scores provide a gross indication of potential hydrological impacts. The purpose of this section is to interpret the numbers within the context of the data quality and limitations described. As with all scientific endeavors, the results are only as reliable as the data from which they are calculated. As previously described (see sections 3.2.2 and 3.2.3), the quality of the forest data used in this assessment appears to be compromised, and random errors are not uncommon. While affecting the results, this does not nullify them. The ramifications of the data deficiencies can be predicted and accounted for. Once accounted for, the impact index numbers can then be viewed in a more appropriate manner.

Without exception, the forest cover data (FC1s) represents the weakest link in the assessment process. The errors, when they exist, are manifest in the calculation of logged areas. The data comes directly from the forest cover spatial database. There is not a calculation step or conversion associated with the FIP to DBF file conversion or FME. This conversion is necessary in order to view the attribute data associated with each polygon (an area with homogenous characteristics). The errors are most likely connected with the addressing of attribute data. This is further verified by the use of the Ministry of Environment’s FME software which produced similar results. Emphasis then must be placed on interpretation, not on the hazard numbers themselves.

In summary, the forest cover errors affect the hazard index numbers only for those indexes which rely on the logged data. That is, the lack of data quality logging data only affects the Total Peak Flow Index, Portion of stream logged, Portion of fish bearing stream logged, and Streams on slopes >60% and banks logged. With respect to the study area watersheds, the two greatest affects are on Total Peak Flow Index and Portion of stream logged.

The following section will review and the interpret the specific assessment results on a watershed by watershed basis. The individual watershed data entry and calculations sheets, together with the watershed maps, should be used to augment the understanding of the results and aid interpretation. The sheets and maps are to be found in Appendices D through P. All of the information referenced in the following watershed sections comes directly from either the sheets or the maps. It will be noted that all of the watersheds have Riparian Buffer scores of 1.00. As discussed above, this is a function of the forest cover data difficulties encountered. In many cases the high IWAP scores are not driven by data mined from the FC1s. In these cases, the potential hydrological hazard is independent, thought likely exacerbated, by logging activities and thus the logging data.

The calculation sheet for Aneko Creek indicates that the portion of stream logged is driving the high scores found on table 14. As mentioned in the section above, this Riparian Buffer score is typical of all of the watersheds. However, the intersection of roads and high ECA areas indicates that a significant portion of the high ECA areas are typed correctly. The high Riparian Buffer score is most probably a true reflection of the buffer condition. That is, the Riparian Buffer zone has been depleted through forest harvesting.

Table 14. Aneko Creek watershed report card

Depending on the specific distribution and type of surficial materials in the watershed, it is possible that the total road density may represent an emerging concern with respect to Peak Flow. The number of stream crossings in the watershed is not contributing significantly to the hazard index numbers. However, the specific placing and condition of the 67 stream crossings will, to a great extent, determine the magnitude of potential concern.

High hazard indexes for Brown Creek are the result of harvesting activity and the density of roads within 100 m of streams. The map of Brown Creek clearly indicates that logging has taken place. The high Peak Flow and Riparian Buffer scores reflect this activity.

Table 15. Brown Creek watershed report card

The moderate Surface Erosion score is the result of road lengths within 100 m of streams. Although the score is moderate, the road lengths are, as mentioned previously, underestimates. The actual road lengths are probably greater, thus the score is in fact low.

The high Peak Flow and Riparian Buffer scores for Canyon Creek are the exclusive result of high ECA numbers. The amount of apparent logging is the only concern in the watershed. However, there are very few roads and stream crossings indicated in the data. It is difficult, therefore, to verify the significant amount of logging activity shown on the map.

Table 16. Canyon Creek watershed report card

The high Surface Erosion and Riparian Buffer scores indicated for the Clisbako River watershed are the result of high ECA numbers and the portion of streamsides logged. Rood and Hamilton (1995) cite the lower Clisbako as an area of potential hydrological concern due the amount of current and planned logging activity.

Table 17. Clisbako Creek watershed report card

Road densities in the watershed are very low and not of concern. The total road density score is 0.11 and there are, effectively, no roads within 100 m of streams.

Of particular concern in the Gruidae watershed is the depletion of the Riparian Buffer zone and the length of roads within 100 m of streams. Given the low road densities, the percentage of total roads in the watershed within 100 m of streams must be relatively high. And indeed this appears, from the maps, to be the case. All other indicators are low.

Table 18. Gruidae Creek watershed report card

Peak Flow, Surface Erosion and Riparian Buffer all appear to be areas of concern for the Michelle Creek watershed. However, for Peak Flow, it is the road density above the H₆₀ line which is driving the moderate score. Total road density for the watershed is 0.38, which, given that it is an underestimate, still low to moderate. Michelle is a relatively flat landscape and the H₆₀ line has little relative significance.

Table 19. Michelle Creek watershed report card

Surface Erosion and Riparian Buffer, however, are significant indicators. The maps clearly indicate both harvesting and road building. As such, the maps appear to accurately reflect the condition of the watershed.

The single greatest concern in the Redwater Creek watershed is the depletion of the Riparian Buffer by timber harvesting activities. The Riparian Buffer indicator, together with the map, show harvesting adjacent to the creek, which is, in turn, reflected in the high score.

Table 20. Redwater Creek watershed report card

A secondary concern in the watershed is the length of roads within 100 m of the stream. Again, the map shows the road close to and parallel with the creek.

The high Riparian Buffer score for Ross Creek is being driven by potential stream-side logging. If verified, this would represent the chief hydrologic concern in the watershed. Secondarily, the length of roads within 100 m of the stream is also high. Together with the density of road crossings

Table 21. Ross Creek watershed report card

Secondarily, the length of roads within 100 m of the stream is also high. Together with the density of road crossings it is this which resulted in the moderate Surface Erosion score.

The Snaking River watershed has undergone significant logging activity. This is reflected in the high Peak Flow and Riparian Buffer scores. The high ECA in the watershed results in the high Peak Flow index score. Related to this is the density of stream-side harvesting, which depletes the Riparian Buffer.

Table 22. Snaking River watershed report card

Ancillary to the logging is road building. And it is roads within 100 m of a stream and the number of stream crossings which is driving the moderate Surface Erosion score.

There is little evidence to verify the hazard index scores shown below for the Summit Creek watershed. The high Peak Flow score is the result of a high Peak Flow indicator which is, in turn, derived from the ECA numbers. However, the map and road length measurements show little sign of the road building which would accompany the extensive logging illustrated by the map.

Table 23. Summit Creek watershed report card

Similarly, the high Riparian Buffer indicator is driven by the high portion of the stream logged. Again, this is dependent upon the verification of logging activity.

There appears to be a reasonable correlation between the occurrence of roads and areas of varying ECA. It is probable that the data is relatively accurate. Given this, the concern areas are Peak Flow, Surface Erosion and Riparian Buffer.

Table 24. Tautri Creek watershed report card

The high Peak Flow score is the result of a high Peak Flow index indicator. Both the Peak Flow and Riparian Buffer scores are the direct result of harvesting activities. Surface Erosion is the result of roads within a 100 m of a stream.

The roads and linework indicate that the Udy Creek watershed has undergone substantial logging. Table 25 shows the effects of this in high Riparian Buffer and Peak Flow scores. These are driven by stream-side harvesting in particular and harvesting in general. The high Peak Flow score is the result of a high total Peak Flow index indicator and score.

Table 25. Udy Creek watershed report card

The primary concern in the Wentworth Creek watershed is the depletion of the Riparian Buffer zone. The map shows coincidental logging and roads, which would appear to indicate greater data accuracy.

Table 26. Wentworth Creek watershed report card

This assessment was hampered by the apparent quality of the forest cover data or the misworkings of the Ministry of Forests’ FIPDBF translation program. A subsequent attempt to translate the data using the Ministry of Environment’s FME program proved unsuccessful also. The problem stems directly form the quality of the forest cover data. Notwithstanding this, however, the results of the Nazko River watershed assessment are valuable. The stochastic errors characteristic of the FC1 data required that much more in-depth secondary analysis be undertaken. In normal circumstances, the data would have been accepted. Instead, the data was analyzed numbers times and checked against air photos, five-year forest development plans and hardcopy TRIM maps. Table 22, which follows, summarizes the interpreted and calculated results.

The Interior Watershed Assessment Procedure is a general assessment tool designed for application throughout the interior of British Columbia. As a general diagnostic filter, it measures many important hydrological and landuse parametres. The hazard index calculations used to determine the scores are formulated to be used in an average interior watershed. When considered from this point of view, the Nazko watershed is arguable not an average interior watershed. Its geological and geomorphological history conspire to make the IWAP too general to result in a completely accurate assessment. And this should be taken into consideration when interpreting the results and considering future assessments. The flat to rolling topography of the study area works to, at least partially, defeat the purpose of the H₆₀ line. The low relief means that rather than having a snowpack which lasts further into the spring, it undergoes snowment earlier and more rapidly. That is, there is not a significant higher elevation snowpack which remains later into the spring to be affected by clearcutting. Instead, it melts earlier due to the relatively low elevations. Thus the differential ECA weighing for areas above and below the H₆₀ line does not accurately estimate the actual situation.

Another anomaly of the study area is the glacial history. The area was glaciated numerous times. Most recently, it was glaciated during the late Wisconsinan Fraser glaciation. Pre-existing thick deposits of surficial materials and relatively soft volcanic bedrock combined to create a heavily incised landscape which has a drainage density which exceeds that necessary to balance hydrological inputs. This is illustrated by the large number of wetlands within the study area. In the context of the IWAP procedure, the affect is to establish an equally high density of riparian zones. In some watersheds, the drainage density is so high that any landuse activity would affect a Riparian Buffer area as defined by British Columbia’s Forest Practices Code. This too should be considered when assessing the Nazko River IWAP results.

Table 22. Summary of Results

All of the watersheds assessed in this analysis proved to contain potential significant hydrological concerns. As such they are all eligible for additional Level 2 (Channel Assessment Procedure). As a watershed assessment and inventory project, this analysis has shown the forest harvesting and associated activities, such as road building, have potentially affected the hydrological regimes of the thirteen watersheds included in this study.

The application of the Channel Assessment Procedure (CAP) to selected watersheds within the study area would further define the location and magnitude of the hydrological impacts. Following this, restoration prescriptions may be appropriate. The decision to apply the CAP should be dependent on both the value of the stream and its prospects for restoration.

It is recommended that prior to any further assessments the findings of this IWAP be verified by a detailed overflight of the study watersheds. In particular, Riparian Buffer depletion in Canyon, Ross and Summit Creeks and over harvesting in Canyon, Gruidae, Summit and Wentworth Creeks should be verified.

Provided that the data and assessment prove adequately accurate, then it is suggested that the recommendations given in Table 23 be implemented.

Table 23. Summary of Recommendations