Physical stream feature assessments using aerial videographic surveys

The accuracy of aerial videographic surveys to identify and locate physical stream features was compared to ground-identified physical stream features. A portion of the Mackenzie Timber Supply Area, in northern British Columbia, was surveyed using aerial videographic survey techniques to identify selected stream features. The features were identified visually and recorded on a computer with their corresponding GPS locational positions. In addition, a super VHS video recording was made using a camera mounted to the undercarriage of the helicopter. A Watershed Restoration Program Levell fish habitat assessment was developed using this video recording to investigate the information that may be collected using a video-only approach. The accuracy of identification and location of both the visual and video-only survey data were determined by conducting ground stream assessments on a stratified random sampling of aerial ~ - surveyed stream segments. The visual aerial stream feature information had an overall accuracy of less than eight percent with an average locational error of~ 3 7 metres for each stream feature. Aerial identification accuracy was affected significantly by the type of stream feature identified and the order of the stream surveyed. Larger, easily interpreted features such as "Bridges" or "Culverts" that were associated with openings in the crown closure were successfully identified with 100% accuracy, while smaller, more complex features such as "Backwater Channels" were not successfully identified during the course of the aerial survey. The identification of detailed stream features from the air was not possible on any size of stream using the current aerial video graphic methodology and therefore the technique should not be used for gathering detailed stream habitat information. However, aerial videographic surveys appear to be a cost-effective tool for assessing overview information such as large, easily interpreted features and general stream descriptions. The preliminary investigation of a video-only approach indicated that qualitative stream habitat assessments may be performed with a high success rate on streams larger than 4thorder. However, the successful identification of quantitative stream parameters might decrease as stream complexity increases. Detailed physical information on larger streams might be obtainable visually and recorded with higher resolution video with changes to the aerial videographic survey technique.