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A number of predictive bed-load sediment transport equations are rated against a unique set of field data collected by automatic slot samplers during flash floods in a desert wadi. The Meyer-Peter and Muller equation is shown to perform well, providing a median ratio of calculated to observed (C/O) bed-load flux of 1.18. The Bagnold equation is shown to underpredict considerably, with a median C/O of 0.44. The Parker equation performs better, though it still underpredicts with a median C/O of 0.78. The apparent success of the Meyer-Peter and Muller formula is attributed to the ready supply of sediment to the channel system in desert and semidesert environments. This ensures that the channel bed remains unarmored, in contrast to supply-limited, armored, perennial rivers of humid zones. It also ensures that bed-load flux responds to changing hydraulic conditions in a comparatively simple fashion.