Revision of the Churchill Reservoir Trap Efficiency Curves Using Smoothing Splines¹

The trap efficiency of a reservoir is the percentage of incoming sediment which is trapped by the reservoir. The standard predictor of trap efficiency is the Brune curve, expressing trap efficiency as a function of the capacity‐inflow ratio of the reservoir. If in addition the average velocity of water in the reservoir is known, then the sedimentation index of the reservoir can be calculated, and the less well known but more descriptive Churchill curves can be used to predict trap efficiency. Churchill's curves have not been revised since their introduction in 1948, even though more data are available than were used originally. We revise Churchill's curves using the method of smoothing splines to obtain a best fit to these data and Churchill's original data.