Assessment of Selected Stream Crossings in the Canfor Grande Prairie's Forest Management Agreement Area - Phase I Final Report 2003
Tyler W. P. Johns, Michael A. Doran, John P. Tchir, Paul J. Hvenegaard
Detrimental effects to aquatic environments, resulting from stream crossings, are well documented. Stream crossings such as culverts and bridges, allow for both road
crossings and connectivity of waterways, with minimal aquatic impacts when properly installed, monitored and maintained. Improperly installed culverts have been shown to encroach on stream channels. This leads to increased water velocities, scouring, sedimentation and hanging culverts, which can impact habitat connectivity resulting in reduced viability of fish populations. Prioritizing culvert crossings for remediation requires information on the status and effectiveness of culverts to provide fish passage and maintain road integrity. The information collected will form the basis for managers to make informed decisions that will provide the greatest benefit to fish populations. Canfor Grande Prairie identified 79 crossing sites for evaluation and assessment of associated fish and habitat qualities within their Forest Management Agreement Area #9900037 (FMA). Seventy-eight crossing structures were assessed for fish passage potential. Culvert assessments were performed on all sites. While, forty-five sites were deemed suitable for fish and habitat assessments. Data were collected in adjacent stream reaches upstream and downstream of the crossing structure. We defined fish passage barriers as either: outfall (distance from culvert outlet to water surface greater than jumping ability of relevant fish species), potential velocity (water velocity greater than fish passage ability), debris (logs, beaver dams, etc), and damaged pipe (physical distortion to culvert shape making the structure impassable to fish).
Potential barriers were identified at 55% (43 of 78) of sites. Of 43 potential barrier sites, outfalls accounted for 79% (34 sites), potential velocity accounted for 9% (4 sites), debris accounted for 9% (4 sites), and damaged pipe accounted for 2% (1 site). Sites assessed were prioritized for remediation based on the following criteria: Strahler Stream Order; fish presence at crossing; proximity to fish bearing water; usable upstream habitat; and type of potential barrier. Although a large proportion of culverts assessed did not accommodate potential fish passage, the majority (86%) of crossings were located on first-order and second-order reaches. There is a relatively low probability of fish occurrence in these orders, and stream crossing structures were ranked accordingly.
Given the high likelihood of culvert crossings resulting in potential fish passage barriers, it is necessary for responsible watershed stakeholders to monitor, maintain and replace culverts more frequently than other structures (i.e., open bottom arches or bridges) to provide fish passage over longer durations. Canfor’s proactive approach to dealing with culvert crossings is a step toward sustainable development and reduces the ecological footprint.