94 Floods on the River Barwon. 



to be allowed, as a rule. Without some information on the 

 above-mentioned points, no engineer can feel sure that any 

 works which interfere with a channel are safe. It is not 

 enough in such a case to know merely the highest flood 

 level; if that is all the knowledge obtainable, a channel 

 should always be kept as free as possible from obstruction. 

 And in questions of this nature, it must not be overlooked 

 that where a river in flood overflows its ordinary banks, the 

 channel to be considered is not merely the summer bed of 

 the river, but the whole width in which there is a downward 

 current. If there is not intended to be any contraction of 

 the waterway, the knowledge of the highest flood level 

 might often suffice ; though it would be always more 

 satisfactory to ascertain, if possible, the flood discharge as 

 well as the flood level. Many of these remarks may appear 

 very commonplace, but that they are not wholly unnecessary 

 is clear from the points alluded to having been overlooked 

 in the case of an important river like the Barwon. 



24. In conclusion, the author desires to state his decided 

 conviction that the whole of the trouble and expense (in the 

 late trial) resultiug from the flood of September, 1880, arose 

 from the neglect of the foregoing considerations when 

 designing the railway across the Barwon. Had a proper 

 inquiry into the action of the flood of 1852 been made 

 before the line was constructed, the iron bridge on the 

 Colac-road would not have been taken as the sole guide for 

 the waterway to be given to the railway bridge over the 

 same river, as it was admitted at the trial was done. It 

 may be further remarked that the unfavourable conditions 

 of the site fixed upon for the railway bridge (contrasted 

 with those of the iron bridge site) were not properly allowed 

 for. The iron bridge has an unobstructed waterway with a 

 clear channel below, but the railway bridge has neither of 

 these advantages. Fortunately, however, other arrangements, 

 without being designed for such a contingency, in a measure 

 counteracted some of the errors that were made. The 

 Barwon bridge was evidently intended to carry off the 

 flood waters of the River Barwon, and the Waurn Ponds 

 bridge those of the Waurn Ponds creek ; but, in reality, in 

 September, 1880, the latter bridge served the purpose of a 

 safety-valve to the Barwon; and when the flood was at 

 its height, it (with the adjoining gaps in the embankment) 

 discharged about the same quantity of water as the Barwon 

 bridge itself. Certainly, the cutting away of the railway 



