The UNBC bedload movement detector: calibration, initial results and analysis

In September 1997 the UNBC Bedload Movement Detector was installed in O'Ne-ell Creek, a mountain gravel bed river in the northern headwaters of the Fraser River. The device is designed to measure coarse sediment flux by passive induction as bedload material (> 1 mm), containing natural ferrous minerals, passes over an array of electromagnetic sensors. The device consists of a series of 82 sensors, housed in an aluminum beam and placed across the stream, inserted such that its surface is flush with the gravel bed. The device can be raised or lowered to compensate for bed aggradation and scour. A data acquisition system collects signals from the device at 100 Hz, providing a continuous, high-resolution record of any bedload transport event. The device is sensitive enough to record the movement of most volcanic, metamorphic, granitic, and ultramafic clasts larger than a few millimeters. The installation and operation of the device is described, as well as the calibration and development of signal processing routines for estimating transport rates. Nival event transport records are presented and discussed. Some of the phenomena apparent in the records include: a pulsating pattern of activity, discrete 'sweep transport' events, lateral movement of the transport zone, and a sudden onset ofbed movement with a tapered cessation. An initial estimate of transport volumes compares favourably with existing measurements taken at the study site. It is anticipated that more sophisticated calibration work will continue in the future.