Non-Permanent Stream Crossing Assessments in the Notikewin River Watershed
Mike A. Doran, Tyler W.P. Johns and John P. Tchir
In Alberta there are numerous detrimental effects on aquatic ecosystems from access infrastructure. These impacts can pose risks to the distribution, abundance and subsequent viability of fish stocks. Aquatic habitat degradation through sedimentation, physical habitat alteration and fragmentation, are impacts directly attributable to some industrial activities. The effects of non-permanent stream crossings on aquatic habitat quality in the Notikewin River watershed were examined during summer of 2003. Stream crossings were identified through spatial analysis of hydrological and linear disturbance attribute data collected in 1998. Stratified random sampling was used to select sites for assessment. Stream crossings were qualitatively and quantitatively assessed for habitat degradation and potential sediment contributions.
From GIS queries there were 10,062 linear disturbances (cutlines, pipelines, winter roads, etc) that crossed streams in the Notikewin River watershed. Stream length was proportionate to the number of crossings per order. First order streams represent 50.2% of the total stream lengths within the watershed and are crossed by 63.5 % of the linear disturbances.
In this relatively low gradient watershed 93% of rights-of-way (ROW) slopes had gradients less than 20%. Soils were found to be highly erodible at 50% of sites. Approximately 60% of sites assessed had greater than 90% vegetative cover on ROW’s. Grasses were the dominant vegetative cover recorded and appeared to provide suitable root mass to prevent erosion or sediment delivery into the stream. Sediment delivery potential ranking corresponds to this determination with 81% of sites having low to no sediment delivery potential. It is believed that the condition of non-permanent stream crossings in this watershed is largely a result of the low frequency of off-high-way vehicle (OHV) use. There were 51% of sites with little to no visible use. It is believed that in a watershed with more frequent OHV use, sediment delivery potential and impacts would be greater due to the disturbance to vegetative cover and sedimentation from mechanical disturbance and surface runoff. As a result of low use, low gradient and high vegetative cover there appears to be a low risk of impact on a site-specific basis. In-stream effects of sedimentation should be quantified and these results applied to the watershed level to gain a better understanding of cumulative effects. Continued improvement in integrated resource management with regard to access infrastructure is critical to minimizing terrestrial and aquatic habitat fragmentation and degradation.