An Improved Bedload Sampler

Improvements upon the Birkbeck bedload sampler (Reid et al., 1980) were implemented in the North Fork of Caspar Creek, a gravel-bedded stream draining 383 ha in northern coastal California. Bedload sediment falls through a slotted plate covering a .125-m steel box set within a formed concrete pit in the streambed. In the original Birkbeck design, a water-filled pressure pillow beneath the box responded to the weight of accumulating sediment and the overlying water column. The hydraulic pressure was communicated via tubing to a pressure-bulb transducer, which was in turn connected via a set of mechanical linkages to a chart recorder. In two seasons of experimentation at Caspar Creek, the pillow and hydraulic and mechanical linkages of a Birkbeck-like sampler were replaced with an electronic load cell and an electronic data logger, resulting in more trouble-free operation, greater precision, and reduced background noise. Low-profile fences were erected along the cover plate slots to prevent material from entering traps across the lateral slot boundaries. Data were collected at 2-minute or 5-minute intervals from four bedload pits and recorded on non-volatile memory chips. Because of rapid filling of the boxes, a suction dredge was used to empty sediment from boxes during storms.