784
The channels of C D are carried across the street A B in a channel very much flattened, so as to cause the minimum inconvenience to vehicular traffic. Any dry- weather flow is intercepted by sewer gulleys G G G and G. Still this arrangement is far from satisfactory. The depression at the intersection of the two streets is an impediment to traffic, especially in the case of tramways. Should the gulleys get stopped, a stagnant mess is the result. To make this arrangement work well it is practically necessary to concrete or asphalt the whole area at the intersection of the crossing streets.
Assuming that scavenging-lanes are recognised, as a necessity, then the difficulty may be got over, by accepting them as the main storm-water drains.
The area to be drained should be sub-divided into alternate streets and narrow scavenging-lanes.
The alignment of these should follow, approximately, the greatest slope of the ground. These would be intersected at right angles by other streets. Then all that is necessary to make the said scavenging-lanes serve as storm-water drains, is to lower their surface some 2 to 4 feet below the level of the floors of the adjacent buildings, and of the streets. The following diagram gives
'an idea of this arrangement :-
200.0
_800
·7010
80.0
7010-
When the combined scavenging-lane and drain passes under a cross street, it would obviously take the form of a bridge or culvert, which would, however, be large enough to admit a man for the purpose of scavenging, access to each length of lane being gained by a flight of steps. The lane would have a channel or chan- nels formed at its centre or sides. These channels would conduct the sewage to trapped sewer gulleys, communicating with a sewer laid under the scavenging-lane. Thus in dry weather or even during moderate rain, the scavenging passage would serve its normal purpose, namely, the removal of excreta and dry refuse, and could always be scavenged and kept clean. In heavy rain it would serve as a storm- water channel. Care, however, must be taken to proportion the width of the scaveng- ing passage and its depth, below the adjacent building lots to the maximum quantity of water that it may have to carry during heavy rain. This arrangement has the great merit that it reduces the lengths of covered drains to mere bridges or culverts. At the same time all street obstructions at crossings are avoided. Such arrange- ment has been adopted in the case of some land recently laid out for building purposes in Trinidad. It is, I am aware, one that cannot be carried out everywhere; but I give it as a suggestion, for it may be applicable to the Eastern Reclamation, Kow- loon, and in, the New Territory. Where applicable, it will offer many advantages over the present system of covered drains.