STREET SEWERS (o. p.)
DISTRICT SEWERS (c. d.)
MAIN SEWERS (A. B.)
Fig. 1.
Fig. 2.
With respect to the form of the drains, when bricks are used as building materials, the bottoms of the drains will be best formed of inverted arches of blue bricks, as forming a cheap, hard, and durable surface, and giving every facility from the form, for the scouring force of the water to remove the filth brought into the drain; but whether the curve of the bottom shall be a semicircle or a segment will, I apprehend, depend on the size of the drain. For very small drains a circular form would be the cheapest and best; the next size would be more advantageously constructed of an oval or egg shape, but still of bricks. Drains of a still larger size, viz. the second class, may be conveniently made either of brick or stone, arched and counter-arched at top and bottom with battered sides, either straight or curved; the counter-arches or curved bottoms will conveniently become flatter as the drains increase in capacity to afford greater room for the accumulated water to pass without rising and flooding back into the feeders. The first and second-class sewers must be deep seated to receive their respective tributaries or feeders, with some overfall; and though a sufficient width for large drains may generally be procured, it is difficult in many cases to command enough of depth, another circumstance that can best be obviated by flattening the arches both at top and bottom; but in large drains, where there is a body of water, the scourage will be sufficient, without resorting to deeply curved bottoms.