P. Beaudry and Associates Ltd. Integrated Watershed Management

Transcription

1 P. Beaudry and Associates Ltd. Survey of Small and Large Sediment Sources Within the Watershed Dawson Forest District Prepared for: Chetwynd Forest Industries A Division of West Fraser Mills Ltd. P.O. Box 330 Chetwynd, B.C. V0C 1J0 Prepared by: P. Beaudry and Associates Ltd S. Nicholson Prince George, B.C. V2N 1V8 February 2003 P.Beaudry and Associates Ltd. Phone: (250)

2 EXECUTIVE SUMMARY This project was initiated in 2002 by Chetywnd Forest Industries (CFI) in an effort to quantify and describe the nature of sediment sources within the watershed. The primary objective of this work was to better understand how forest activities may be impacting water quality. Both large and small sources of sediment were inventoried and described by this project. Large sources (greater than approx.0.05 ha) were inventoried using digital air-photos and a helicopter overflight of the watershed. Small sources were inventoried using a procedure called the Stream Crossing Quality Index (SCQI) survey, which was initially developed for Canfor s forest certification programme. The SCQI value is obtained by surveying all of the stream crossings within a given watershed and qualitatively assessing the potential for erosion and the delivery of sediment to the stream at each crossing. The SCQI method focuses on evaluating the addition of fine sediment to streams at stream crossing locations. SCQI scores for individual crossings (referred to as individual crossing scores ) range between 0 and 1, depending on the potential impact the crossing may have on water quality. A score of 1 indicates that the crossing has the potential for a substantial negative impact on water quality. As the potential impact is reduced, the score decreases until it eventually reaches 0. The SCQI for the watershed is calculated by adding the individual crossing scores and dividing this value by the watershed area. The resulting overall watershed SCQI score provides an index of the cumulative impact that the crossings are having on the introduction of sediments to the stream network at a watershed level. This score can then be translated into a Cumulative Watershed Effects Hazard Rating based on surface erosion and delivery potential, ranging from very low to very high. The SCQI is a refinement of the stream crossing density index (SCDI), an office based exercise that has traditionally been used to assess the potential impact that stream crossings have on water quality within a watershed. The individual crossings scores are a valuable tool in identifying specific areas where there may be localized negative impacts to water quality. Each crossing was assigned a Water Quality Concern Ratings (WQCR) of either None, Low, Medium, or High based on the individual crossing score. During the 2002 field season we surveyed a total of 419 stream crossings in the watershed. Slightly under half of these crossings had WQCRs of low or none. Approximately 29% of the crossings received medium WQCR s and the remaining 24.5% of the crossings received high WQCR s (Table 1). Most of these crossings with high WQCR s were associated with small streams (i.e., less than 1.5 meters in width). Detailed maps are included in the report which provide the identification and the WQCR for each surveyed stream crossing. Many of the crossings surveyed in 2002 had high WQCRs and some common problems were identified. These include: 1) long ditchlines with exposed soil connected directly to streams, 2) sediment from the road surface directly entering streams at crossings and 3) poorly deactivated crossings. Most of the problems were associated with new roads, either recently constructed or recently deactivated, that had poorly implemented Erosion and Sediment Control (ESC) measures or none at all. P. Beaudry and Associates Ltd. ii February, 2003

3 Table 1 illustrates the key results found in each sub-basin or area surveyed in the 2002 season including the SCQI for the sub-basin, the SCQI Watershed Cumulative Effects Hazard Rating, and the percentage of crossings in the sub-basin with a high water quality concern rating. Table 1. Summary of SCQI Results for Sub-basins Surveyed in Watershed in Sub-basin or area identification Entire Watershed Upper Size of sub-basin (km 2 ) Number of crossings surveyed Stream crossing density index (number of crossings/km 2 ) SCQI for subbasin (sum of individual crossing scores/km 2 ) SCQI Watershed Cumulative Effects Hazard Rating 1 % of individual crossings surveyed classified as High water quality concern Low Very Low 0 Shangweshi Very High Highrise Very High Hulcross High Dokie Low 0 Lower Residual N/A 2 N/A 2 N/A This hazard rating relates to the potential for negative impacts to water quality caused by watershed cumulative effects of erosion and sediment delivery to streams at road crossings. 2 The stream crossing density index (SCDI), stream crossing quality index (SCQI) and the SCQI Watershed Cumulative Effects Hazard Rating do not apply to Lower Residual since this area is not a stand-alone watershed such as the others listed in the table. An assessment of the large sediment sources in the watershed was also conducted for the entire watershed. The survey of large sediment sources was completed using digital airphotos and an overflight that was conducted in September These have been described and mapped and the results are provided in the report and the appendices. The large sediment source survey found many large natural sediment sources within the watershed, including large ravelling streambank terraces, extensive gravel bars, accelerated bank erosion and mass wasting which may be attributed to natural bank erosion, past forest fire activity, and the major flood of Mass wasting type sediment sources (e.g., slumps and debris avalanches) caused by riparian forest harvesting and roads were also depicted in the P. Beaudry and Associates Ltd. iii February, 2003

4 watershed. In addition, it was found that riparian agriculture, including the removal of riparian vegetation and livestock grazing, caused many large land-use related sediment sources (e.g., accelerated bank erosion) within the watershed. Overall, natural sediment sources encompassed 66% and land-use related sediment sources comprised 34% of the large sediment sources documented in the watershed. Of the large land-use related sediment sources, forestry related large sediment sources comprised 46% and riparian agriculture related sediment sources comprised 39%. The remaining 5% of the large land-use sediment sources were caused primarily by transmission lines in the watershed. Table 2 provides a summary of the density and number of large sediment sources, including both natural and land-use type sediment sources. P. Beaudry and Associates Ltd. iv February, 2003

5 Table 2. Summary of Large Sediment Sources identified in the River Watershed in Watershed or Sub-basin within watershed Large Sediment Sources number density (#/km 2 ) Large natural sediment sources number density (#/km 2 ) Large natural sediment sources directly connected to a stream number density (#/km 2 ) Large land-use related sediment sources number density (#/km 2 ) Large land-use related sediment sources directly connected to a stream number density (#/km 2 ) Entire Watershed Upper Shangweshi Highrise Hulcross Dokie N/A 0 N/A Lower Residual P. Beaudry and Associates Ltd. v February, 2003

6 ACKNOWLEDGMENTS We would like to thank Mr. Brian Pate, Forestry Supervisor at Chetwynd Forest Industries (CFI), for initiating the project and providing invaluable assistance throughout the project. We would like to thank Ray Huscroft, GIS coordinator at CFI, for his help in acquiring the necessary GIS data in a timely fashion. Mr. Bill Floyd, B.Sc., and Ms. Becky L Hirondelle B.Sc. of P. Beaudry and Associates Ltd. (PBA) completed the stream crossing surveys. Ms. L Hirondelle and Ms. Natalie Newman, R.P.Bio, of PBA, completed the data analysis and the reporting. Mr. Pierre Beaudry, M.Sc, R.P.F. also of PBA was the project manager, completed the aerial survey of the large sediment sources and provided technical guidance and quality assurance throughout the project. Funding for this project was provided by the B.C Forest Investment Account (FIA). P. Beaudry and Associates Ltd. vi February, 2003

7 Table of Contents EXECUTIVE SUMMARY... ii ACKNOWLEDGMENTS... vi 1.0 INTRODUCTION METHODOLOGY General Description of SCQI Survey SCQI Sampling Individual Crossing Scores and the SCQI SCQI vs. SCDI Hazard Rating Associated with Road Related Sediments Water Quality Concern Rating Survey of large sediment sources RESULTS AND INTERPRETATIONS Entire Watershed Stream Crossing Quality Index Survey Survey of Large Sediment Sources Upper Stream Crossing Quality Index Survey Survey of Large Sediment Sources Shangweshi Stream Crossing Quality Index Survey Survey of Large Sediment Sources Highrise Stream Crossing Quality Index Survey Survey of Large Sediment Sources Hulcross Stream Crossing Quality Index Survey Survey of Large Sediment Sources Dokie Stream Crossing Quality Index Survey Survey of Large Sediment Sources Lower Residual Water Quality Concern Rating Survey of Large Sediment Sources SELECTED PHOTOGRAPHS FROM FIELD ASSESSMENTS Selected Photographs of a High WQCR Selected Photographs of a Medium WQCR Selected Photographs of a Low WQCR Selected Photographs of a None WQCR P. Beaudry and Associates Ltd. vii February, 2003

8 5.5 Selected Photographs from the Overview Flight (Large Natural Sediment Sources) Selected Photographs from the Overview Flight (Large Land-Use Related Sediment Sources) LITERATURE CITED APPENDIX 1. SCQI SCORING RATIONALE APPENDIX 2. EROSION, DRAINAGE AND SEDIMENT CONTROL TECHNIQUES APPENDIX 3. POTENTIAL SCQI TARGETS APPENDIX 4. OVERVIEW MAP OF ALL CROSSINGS SURVEYED IN THE MOBERLY WATERSHED APPENDIX 5. OVERVIEW MAP OF LARGE SEDIMENT SOURCES IDENTIFIED IN THE MOBERLY WATERSHED APPENDIX 6. DATABASE OF LARGE SEDIMENT SOURCES APPENDIX 7. SCQI DATA SHEETS AND SCORE SHEET P. Beaudry and Associates Ltd. viii February, 2003

9 Survey of Small and Large Sediment Sources within the Watershed Watershed Dawson Forest District 1.0 INTRODUCTION The main objective of this project was to quantify and describe the nature of sediment sources within the watershed in an effort to understand how forest activities may be impacting water quality. Sediment sources can be divided into two broad categories. The first of these categories includes large sources that are clearly visible from air-photos and helicopter reconnaissance, e.g. landslides, slumps, large failing stream banks and avalanche tracks. The second category includes small sources that can only be detected and documented from the ground, e.g. eroding ditch lines, road running surfaces and cut and fill slopes. To document the large sources we completed a helicopter flight on the 9 th of September 2002 and mapped all of the sources from digital orthophotos. The small sediment sources were surveyed using the stream crossing quality index (SCQI) methodology which assesses the amount of erosion and sediment delivery that occurs in the vicinity of stream crossings. The SCQI survey was developed in 2000 for Canfor s sustainable forest management plan and has been used throughout a number of areas in central B.C. (e.g., TFL #30, TFL#48, Fort St. John District, Horsefly Watershed, Bulkley District, Prince George T.S.A.). A decline in water quality can have major impacts on the water resources in an area. It is also widely accepted that improper forestry practices can have negative impacts on water quality (Government of BC 1995). Sediment generation from forestry practices comes from the following three main sources: roads, landslides and stream bank instability. Significant increases in sediment concentration in streams over natural levels can have a negative effect on fish and fish habitat (Slaney et al. 1977; Government of BC 1995; Hall et al. 1987; Hartman and Scrivener1990; Phillips 1971; Scrivener and Tripp 1998.). Sediment can also reduce the value of water for domestic, industrial and agricultural use (Government of BC 1995). In areas where rainfall precipitation is dominant and harvesting occurs on steep slopes, landslide processes can be a major contributor of sediment to streams. In areas such as the Watershed where the landscape is dominated primarily by rolling to moderately steep topography and wide valley bottoms, landslides are generally not a dominant sediment producing process (at least not compared to steep coastal watersheds). In watersheds such as the, the main source of forestry related accelerated erosion is generally associated with road building and road use. The scale of cumulative impacts at the watershed level is generally related to the density of stream crossings because this is where eroded material from roads has the potential to be delivered to the stream network. Sediment yields from logging and roads can show a 2 to 50 fold increase over historical levels (Reid 1993). The main point of road sediment delivery to streams is at crossings such as culverts and bridges (Brownlee et al. 1988; Government of BC 1995). While it is recognized that roads are not the only source of sediment related to forestry practices, they are considered to be the most significant causes of increased sedimentation (Beschta 1978; Brownlee et al. 1988; Government of BC 1995; Reid and Dunne 1984). Through the proper layout, P. Beaudry and Associates Ltd. 1 February, 2003

10 construction, deactivation and use of erosion and sediment control (ESC) measures, the impact that roads have on water quality can be significantly reduced (Beaudry 1998; Government of BC 1995). The SCQI survey is based on the concept of the stream crossing density index (SCDI) used in the Watershed Assessment Procedure (WAP) (Government of BC 1999). The assumption in the WAP is that the risk to water quality increases as the density of stream crossings within a watershed increases. The stream crossing density index assumes that every crossing is a problem from the point of view of erosion and sediment delivery. Although this is a useful index to highlight potential for cumulative effects, it does not consider the actual quality of erosion and sediment control (ESC) or effective de-activation measures that may have been implemented at a particular stream crossing. Consequently, the numerical value of such an index will always increase with increasing activity within a watershed. Thus, such an index cannot evaluate progress towards the achievement of a specified goal, this being an explicit requirement of many forest management certification schemes (e.g. CSA). Consequently, it became necessary to develop an index that would document and evaluate problems as well as successes. The index must provide an incentive to improve practices by documenting those practices that achieve the desired goals. The SCQI method was designed to be such an index. The SCQI method is based on the concept that the impact of stream crossings on water quality can be reduced through effective erosion and sediment control practices, and that this can be evaluated and scored. As with the SCDI, each crossing within a watershed is, at priori, assumed to be having a negative impact on water quality. However, the theoretical negative impact of this stream crossing can be reduced if the crossing is evaluated in the field and does not show any signs of erosion and sediment transport to the stream. Using this method of evaluation a crossing that shows substantial problems receives an individual crossing score of one (1). As the quality of a crossing improves, the score is reduced, eventually reaching zero (0). This can effectively eliminate the crossing from the erosion and sediment producing inventory. As the scores for the individual crossings are reduced so is the SCQI for that watershed. This mechanism provides an incentive to implement good ESC measures. The SCQI method also provides valuable data that can be used to identify specific problem sites or areas. This enables the forest manager to implement proper ESC measures in areas where it is required. By addressing specific problems, the negative impact on water quality will be reduced and the overall SCQI score for that watershed will also be reduced. It also enables forest licensees to focus their resources to areas that will receive the greatest benefits. Specific problem crossings were identified in sub-basins with a high or very high SCQI and a summary of the problems were also provided in the report. In addition, the SCQI method provides a way to monitor progress in regards to water quality. The SCQI values calculated in this report could be used as a baseline to monitor the relative improvement of forest practices within the Watershed. P. Beaudry and Associates Ltd. 2 February, 2003

11 Williston Lake Hudson Hope Chetwynd Forest Industries A Division of West Fraser Mills Watershed M O B E R L Y L A K E Watershed Cr ee k Legend Hu lcr os s Roads maintained by Ministry of Transportation PI Chetwynd NE City Streams British Columbia VE R Lakes R IV E R RI PI NE Watershed Boundary SU KU NK A R IV E R Watershed Kilometers Base Map From Government of BC Watershed Atlas NAD83 February 2003 Figure 1. Location map for the Watershed. 8

12 Pete Lake Watershed M O B E R L Y L A K E Chetwynd Forest Industries A Division of West Fraser Mills Watershed: Sub-basins M O B E R L Y Benson Pys Dokie Ck Ck Shangweshi Hulcross Dokie Roy R i v e r Carl Wildmare Hulcross Bissett Carl Wildmare Lake Fur Stone Ck R I V E R Young C r e e k C r e e k C a r o n Goodrich H a s l e r Ck Fur Bickford Lake P I N E Cleveland Big Boulder Ivorline Beaudette C R I V E R Commotion Commotion P I N E Walton Bowlder Bowlder Johnsen R I V E R Alvin Rocket Rocket Johnsen Pete Highrise M O B E R L Y Highrise Shangweshi Fred Thief Thief Nelson R I V E R Browns Willow F a l l i n g C r e e k Crassier Fisher Frank Upper Lower Residual Highrise Shangweshi Hulcross Dokie M o b e r l y R i v e r M o b e r l y Doonan Little Coyote Boulder Doonan Little Boulder Silver Sands Cairns Figure 2. Sub-basins selected for the sediment source survey in 2002 Legend Roads maintained by Ministry of Transportation City Streams Lakes Watershed Boundary Kilometers Base Map From Government of BC Watershed Atlas NAD83 February McNairn

13 SPECIAL NOTE The above information is an excerpt from the final report titled Survey of Small and Large Sediment Sources within the Watershed. A complete version of the final report is available with Mr. Brian Pate, Forestry Supervisor with Chetwynd Forest Products. P. Beaudry and Associates Ltd