Rainfall and runoff depths were examined for 763 storms on 26 urban basins located in 12 countries. For 17 of the basins, impervious surfaces were the major contributors to storm runoff. These basins were generally smaller than 25 ha and had small to medium storms in the data set. Nine basins had significant amounts of runoff from pervious as well as impervious surfaces. Eight of these basins are located in Australia. For all 26 basins, plots of rainfall and runoff depths were used to estimate the effective impervious area and the impervious area initial loss. The data plotted close to a single straight line on all basins, indicating that the effective impervious area remained constant for all storm sizes. The effective impervious fraction was related to total impervious area and the directly connected impervious fraction estimated from maps. For the basins with pervious runoff, the depth of rain in the storm was the most important factor in determining pervious runoff for rainfalls less than 50 mm, while for larger storms other factors including rainfall intensity and antecedent wetness were also found to be significant. Ecoulement d'averses sur des surfaces perméables et imperméables dans des bassins hydrographiques urbainsRésumé Cette étude est consacrée aux précipitations et aux écoulements relatifs à 763 averses observés sur 26 bassins hydrographiques urbains situés dans 12 pays différents. Pour 17 bassins, les surfaces imperméables apportent la majeure partie de l'écoulement; la superficie de ces bassins est généralement inférieure à 25 ha et les averses observées d'importance faible ou moyenne en comparaison de l'ensemble des données recueillies. Dans neuf bassins les surfaces perméables apportent, comme les surfaces imperméables, une contribution significative à l'écoulement; huit de ces bassins se trouvant en Australie. Pour l'ensemble des 26 bassins hydrographiques, les graphiques des précipitations et des écoulements ontpermis d'estimer la surface imperméable efficace et la perte initiale de la surface imperméable. Le tracé des données pour chaque bassin est proche d'une ligne droite, indiquant que la surface imperméable efficace reste constante quelle que soit l'importance de l'averse. On a étudie les corrélations existant entre les surfaces imperméables efficaces estimées d'après les données et les surfaces imperméables totales d'une part, les surfaces imperméables drainées par les réseaux d'assainissement d'autre part, ces dernières surfaces étant estimées d'après les plans urbains. Pour les bassins à écoulement perméable, la hauteur de l'averse est le facteur principal de l'écoulement perméable pour les précipitations de moins de 50 mm, tandis que pour les averses plus importantes, d'autres facteurs, dont l'intensité pluviale et l'humidité antérieure du sol, se sont révélés importants.

Rainfall and runoff depths were analysed for 47 storms recorded on three urban drainage basins in Canberra, Australia. Three runoff mechanisms have been identified: runoff generated on effective impervious surfaces in all storms; runoff from pervious areas of small storage capacity during both large and small storms; and runoff from pervious areas of large storage capacity for larger storms. The data indicate that pervious surface runoff is generated on only a small part of the total basin area.

A study of four nested drainage basins has been used to measure relations between lag time, stream order, and network magnitude for basins within a larger watershed. Solution of the stream order laws produced a relation between lag time and drainage area which had the same form as the relations developed between different watersheds. A relation between lag time and drainage area was used to allocate storage parameters to the elements of a storage-routing model based on the stream channel rletwork. When it was applied to the most probable stream networks for a given channel magnitude, the model was shown to reproduce relations between lag time and stream order, channel magnitude, and drainage area, having the same form as was observed for the actual drainage basins used in the study.

The sanctuary on the island of Keros takes the form of deposits of broken marble vessels and figurines, probably brought severally for deposition from elsewhere in the Cyclades. These acts of devotion have now been accurately dated, thanks to Bayesian analyses of the contemporary stratigraphic sequence on the neighbouring islet of Dhaskalio. The period of use—from 2750 to 2300 cal BC—precedes any identified worship of gods in the Aegean and the site is among the earliest ritual destinations only accessible by sea. The authors offer some preliminary thoughts on the definition of these precocious acts of pilgrimage.

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