SANITARY DRAINAGE OF WASHINGTON. 11 



out of the city and removed to a point where it will do no harm. 

 It has been assumed iu the construction of work hitherto executed, 

 that the drainage of the streets and the drainage of the houses is 

 to pass off through the same channels. Whatever the objections 

 to this, there are undoubtedly practical reasons why this existing 

 system ought not to be, or at least why it certainly will not be 

 entirely abandoned, but it is an objectionable system, and it surely 

 should not be extended. It seems to me that its objections are so 

 simple and palpable that they must convince all who will consider 

 them. They are largely as follows : Any sewer, as sewers are 

 ordinarily constructed, with the rate of inclination required by the 

 usual slope of the ground, depending upon the simple constant flow 

 of the unassisted household wastes, and having the roughness and 

 irregularity unavoidable in such work, must inevitable retain a 

 deposit along its course, especially toward its upper end, where the 

 amount of flow is slight, and where the solid matters are sure to 

 be stranded for want of sufiicient stream to move them forward. 

 This condition is pretty nearly constant while house-drainage alone 

 flows into a channel too wide for it to wash clean.- It is aggravated 

 whenever a light rain or a short heavy shower carries into the 

 sewer horse-droppings, papers, and all manner of nameless rubbish 

 from the surface of the street. Now and then there comes a heavy 

 down-pour, or a long and strong rain, which gives every sewer a 

 thorough scouring out from end to end, but the gradual flow at 

 the end of every such a storm too often leaves behind it a deposit 

 of earthy matters which its waning volume and velocity have 

 been insufficient to carry along. Even where this does not happen,' 

 the storm once over and its flow subsided, the houses along the 

 route begin again their work of dejiosit, and we must wait until 

 another heavy rain for the thorough removal of the accumula- 

 tions. It is during this waiting that the mischief occurs. 



It will surely be accepted by all sanitarySjngineers as very desir- 

 able that all waste organic matter should be delivered at the mouth 

 of the sewer at least within twenty-four hours after its production. 



