Benefits of design modifications to the Birkbeck bedload sampler illustrated by flash-floods in an ephemeral gravel-bed channel

The benefits of three simple modifications to the design of a Birkbeck bedload slot-sampling system that has been continuously operating in Nahal Eshtemoa, Israel, since the early 1990s are demonstrated. The modifications include the deployment of a removable slot cover which delays the accumulation of sediment, so allowing sampling at late stages of a flood and, in conjunction with other samplers, extending the period of sampling during a flood wave; inclusion of a slot the size of which is adjustable so that that the probability of sampling the largest clast sizes in transit as bedload can be increased post-installation, once knowledge is gained about the bedload grain-size distribution; and a sampler side-wall door that allows stratification and textural changes within the accumulated bedload to be identified, so promoting intelligent sampling of the deposit for grain-size determination. Results from seven flash-floods are presented and discussed, with recommendations for bedload monitoring, particularly in rivers where sediment flux is high and dynamic sediment records are inevitably short because of instrumental limitations. Copyright (c) 2006 John Wiley & Sons, Ltd.