S34 REPORT — 1875. 



district, and .also the outlet for the St. George's district, lying outside the Borough 

 of Bristol, hut which hy arrangement has heeu allowed to pass through the 

 borough to this point ; and the new sewer has been constructed of sufficient size 

 and at such levels as to receive the sewage from these two districts by means of 

 iron siphons, to be laid under the river ; the sewer then continues along the side 

 of the river until arriving opposite to Myhie's culvert and Prince-Street sewer ; it 

 then continues along Coronation Road, passing the outlet for the Bedminster 

 district and Mr. Drake's tan-yard, continuing underneath the fields at the back of 

 Clift II(?use, and discharges into the tidal river for the present through the outlet 

 described as Parsons-Street sewer, thus intercepting the whole of the sewage on 

 the south side of the river Avon, and providing for the conveyance of all the 

 sewage now discharging into the river above Cumberland Basin. 



From the foregoing it will be seen that these drainage works have been designed 

 and constructed for the delivery of the whole of the sewnge now discharging into 

 the river above Cumberland Basin, at one point near Clift House, by means of three 

 iron siphons, to be laid under the bed of the river from the outlets of the following 

 districts, viz. 1st, St. Philip's and St. George's districts ; 2nd, Redcliif Hill; and 3rd, 

 Mylnes or Prince-Street district ; the only points of discharge will then be the 

 Clifton outlet on the north side, and the outlet near Clift House on the south side 

 of the river. 



Plaving brought the sewage of the borough to these two outlets, the question to 

 bo determined is, In what manner shall the same be dealt with ? and until this 

 point is settled the writer has recommended that all the present five outlets be 

 retained, viz. four on the north side, and one on the south side of the river. 



The sizes of the several sewers in each district are calculated to can-y 5 cubic 

 feet or 31f gallons per head per diem, for a variable population of from 30,000 to 

 60,000 per square mile, according to the district, and ^ inch of rainfall in twenty- 

 fovu' hours, storm overflows being formed in all cases where possible to provide for 

 any greater rainfall. 



The question of ventilation, after many years' consideration and discussion, and 

 after the experience of other localities, has been left in the same position as found 

 by the writer, viz. the sewers are without any external openings or means of 

 ventilation, the whole of the street gullies are trapped, and the manholes are all 

 closed doAvn, in which particulars the sewers of Bristol differ from those of nearly 

 all other towns, all external air being excluded. The several districts have for the 

 most part separate outlets into the tidal river, as before described, in all of which 

 districts, with one exception (that of the High Level of Clifton), j^'ovision has been 

 made for flushing from the floating harbour or watercourses discharging into the 

 harbour ; but in no case has it been found necessary to have recourse to artificial 

 flushing, there being no deposit in any of the new sewers ; nor has it been found 

 necessary to provide other means of ventilation. But in the High-Level district 

 of Clifton, it was found that during low water, when the outlet was exposed, the 

 draught in these sewers was sufficient to drive the sewer-air into some of the 

 houses, and an air-valve was placed at the top of the incline to the outlet, which 

 has prevented such draught. • The whole of the other sewers, being low-level 

 sewers, have double tidal valves fixed at their outlets. These valves are self-acting, 

 of cast iron, and oval in form ; they are hung with chains and bedded on india- 

 rubber. 



In February 1871 tlie wiiter reported on a proposal for dealing with the sewage 

 of the borough by discharging it only on the ebb of the tide. 



The outlets of the present sewers being provided with self-acting valves, which 

 open with the receding tide and close with the rising tide, it was proposed to 

 provide means for preventing the discharge of the sewage during the up-flow of 

 the tide, previous to the closing of the valves, by means of penstocks and storage 

 tanks. 



From a series of float experiments it was found that during spring-tides the 

 sewage would be carried down the Bi'istol Channel nearly as far as Portishead, 

 and would return in such a diluted form as not to be in any way offensive, but that 

 duriug neap-tides and all tides below 22 feet in height, no portion of the sewage 

 would pass out of the river, but would flow backwards and forwards with each tide, 



