Baseflow as a hydrograph component is discussed with special reference to Hall's [1968] paper 'Base-Flow Recession--A Review'. Additional references with particular emphasis on the baseflow problem are given. A three parameter baseflow partition functional is shown to give substance to the concept of 'group persistence' and to suggest an underlying mechanism to the Hurst statistical phenomenon.

Research) wrote that the experiments reported by Ackers and Harrison had provided very useful knowledge of the behaviour of flood waves in partly filled pipes, and marked another stage in the rapid advance now being made into a more scientific approach to the problems of surface water drainage. The Authors did not comment on what impact they thought their experiments might have on current development of new methods of designing surface water sewers, in particular the R.R.L. Hydrograph method. It could be inferred from 3 of the Paper that a recorded retension curve was essential when the R.R.L. Hydrograph method was employed in the examination of an existing system. This is not SO; with the aid of a digital computer the approximate retention relation can be readily calculated.40. To assess the relative accuracy of the Authors' method of calculation and of the reservoir retention technique used in the R.R.L. Hydrograph method the trapezoidal input hydrograph shown in Fig. 2 has been routed through pipe retention by the R.R.L. method, for the four positions along the pipe illustrated. The values of maximum instantaneous depth then obtained were compared in Table 1 with the values given by the characteristics solution. 41.The agreement between the two methods was remarkably good. It was problematical, however, whether the method of characteristics could be applied, possibly as modifications to the R.R.L. method, to the more complex case of a sewer *

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