SANITARY DRAINAGE OF WASHINGTON. 21 



constitute together a source of disease and deatli compared with 

 which your sewers and your river bottoms are insignificant. The 

 improvement of these is very essential to the welfare of the city, 

 but however complete it may be made, you will be in far from a 

 good sanitary condition until your houses are put into proper 

 plight. 



It is no part of my purpose to criticise the many recommenda- 

 tions of those who have preceded me in the discussion of the 

 "Washington problems, but I must make an exception in the case 

 of one recommendation of the Board of Survey of 1872, which is 

 of radical importance. That Board advises, with reference to the 

 sewage of the region discharging through the Rock Creek valley 

 and to the discharge of the B-street sewer, that these be allowed 

 to flow into an outlet, presumably a sewer, in which the tide will 

 rise and fall ; the theory being that the volume of the tidal flow 

 will be so great as to nullify any bad effect otherwise to be 

 apprehended. 



This conclusion is not in accordance with the opinion of the best 

 engineers in England, where the question of tidal outlets has 

 always been prominent. It is found that the checking of the 

 current by the set-back of tide-water causes deposits which are a 

 fruitful source of trouble. 



With the great constant flow from the Upper Potomac it would 

 probably be safe, at least for a long time to come, to discharge the 

 sewage in a fresh state into the open river, after its channel shall 

 have been rectified as proposed ; though sooner or later the deposit 

 on the flats at Gravelly Point would doubtless make it necessary 

 to reclaim them also, carrying the rectified main channel farther 

 down. It is not impossible that it will be found necessary, in time, 

 to dispose of the dry-weather flow of the sewers by agricultural 

 irrigation, at a safe distance below the city. 



I have now sketched in a rapid manner the main features of a 

 comprehensive scheme which seems to me adequate to the improve- 

 ment required. Let me, in closing, restate its essential points : 



