Yarra Floods. 149 



above Prince's Bridge to the lower side of the Falls, a suit- 

 able channel must be formed for passing those waters from 

 the Falls to the Bay, and an efficient outlet into the Bay 

 must also be constructed. Neither of these agencies exists 

 at present. This is evident from the fact, that during heavy 

 floods the waters after passing the obstructions in their 

 course between their source and the Falls, instead of escap- 

 ing at once into the Bay, as they would do if the river channel 

 were equal to its requirements are checked in their out- 

 flow until they inundate the low-lying lands about Mel- 

 bourne, and rise to such a level as to drown a large extent of 

 property. A considerable amount of injury is, doubtless, 

 occasioned to land adjoining the river above Prince's 

 Bridge, but the injury is small as compared with that 

 done below. The main difficulty to be dealt with is 

 manifestly that of providing for the escape of the flood- 

 waters into the Bay. The difference of level between the 

 river at the Queen's Wharf and the water in the Bay during 

 floods is so slight, through the water in the Bay being driven 

 up to a high level by the southerly winds which prevail dur- 

 ing those periods, that the escape of the upland waters into 

 the Bay becomes seriously checked, and the backwater, thus 

 formed, spreads over the low lands. To meet this difficulty 

 it is imperatively necessary to construct a wide channel and 

 outlet. A deep narrow channel is evidently useless, as it 

 could possess no outward current below the line at which the 

 force of the down flowing waters ceased to overpower the 

 opposing mass of water in the Bay. The channel should 

 then be of such a width and depth that throughout the whole 

 extent of its sectional area the water would be in motion in 

 an outward direction. Knowing as we do, the height to 

 which the waters rose in the Yarra above Prince's Bridge 

 during the December floods, and knowing also the level of 

 the southern approach to that bridge, we have absolutely 

 reliable data as to the quantity of water for the passage of 

 which provision has to be made. With this information to 

 guide us, combined with existing records as to the height of 

 the water in Hobson's Bay, as registered by the tide-gauge 

 at the time of the late floods, the requisite width and 

 depth of the flood channel can be arrived at with positive 

 certainty. 



It is obvious, that a channel of sufficient discharging 

 power to accommodate the exit of the flood-waters without 

 injury to property about Melbourne, cannot be constructed 



