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Main drainage of Bristol
April,1899]
Non.Ventilation oI Bristol Sewers
499
weather when the water seal evaporates. It is generally accepted that the inhalation of sewer air is detrimental to health, and that sewer air may give rise to certain forms of sore-throat and to diarrhoea, and may lower the resisting power of the individual to the action of pathogenic organisms. In unventilated sewers there is risk of sewer air getting into houses by the traps of house drains being forced, and if this take place there is no guarantee that it will all pass up the soft-plpe ventilator, and some sewer air may find its way into the house, causing detriment to health. In Bristol it is held by Mr. Crimp that if a house is properly drained, and the house-drain is provided with an intercepting trap and with a soil-pipe carried above the level of the roof, the sewer air would escape up the soil-pipe rather than force its way through the traps and sanitary appliances into the houses. It is well to bear in mind that offensive gases mainly occur in badly constructed sewers where deposits take place, owing to decomposition of such deposits, but if there are well laid sewers with smooth surfaces, good fall and flow, and free from objectionable trade refuse, steam, etc. (see Discussion, Public Health, No. 8, May, 1897), then the sewage is carried away at once; and the need is hardly apparent for the numerous openings, some acting as inlets and others as outlets, at present to be seen in ventilated towns. Should it be necessary for sewer men to enter the sewers for cleansing purposes, it is essential that the sewers be cleared of foul gases before the men enter them.
I?IAIN DRAINAGE OF BRISTOL. ~/~R. SANTO CRIMP has reported to the Corporation of Bristol on a new sewerage system for that city~ and discusses fully the various methods which might be adopted, specially recommending the " Avonmouth scheme, ' and giving his reasons for and against the adoption of other proposals. It is assumed that eventually the area covered by buildings will be 9,750 acres, and that in forty-five years' time the population will be 500,000. I t is therefore necessary to design work capable of dealing with the amount of sewage from such a population. At the present time the water-supply averages 22 gallons per head .per diem, and adding to this the amount of water required for trade purposes, the total may be put at 30 gallons per head per diem. The future daily average flow of sewage may be taken at 30 gallons per head; this with a population of 500,000 will mean 15,000,000 gallons per 24 hours to be got rid of, or 1,666 cubic feet per minute. The proportion of rainfall to be carried off is 7,868 cubic feet per minute. This, added to the daily flow of 1,666 cubic feet per minute, gives a total of 9,53¢ cubic feet, or 85½ million gallons, per 24 hours. The following schemes have been suggested :
2. 3. 4. 5.
~
1. Sand Bay. 2. Kennmore. I 3. On banks of Avon. Chemical works at Pill. Charlcombe Bay scheme. Black Nore scheme. Above Avonmouth.
1. Land treatment
500
Main Drainage of Bristol
~buc He~t~
1. It is pointed out that the lands at Sand Bay and Kennmore are both low-lying, in close proximity to Weston and Clevedon, and that there is no water-course of sufficient capacity to carry off the effluent. An area of 5,000 acres of land on the Avon bank has been suggested as a suitable site for the sewage farm, but there are other places less expensive, in ~[r. Crump's opinion, and better than the land treatment. 2. Chemioal.--Works could be erected below Pill, w h e r e 15 acres of land can be acquired for the purpose, the same principle being used as in the London method (lime and protosulphate of iron). The effluent could be discharged into the river, the sludge carried out to sea by steamers. The estimated outlay on this scheme is £366,000, the annual cost, which includes repayment and interest, being £94,628. 3. Charlcombe Bay Scheme.--The sewer not being able to discharge until some hours after high-water, the sewage would be carried along the shore to the detriment of Clevedon if this scheme were adopted. Cost, 4769,272 ; annual, 431,376. 4. Black Nero Scheme.--Ou~fall near Portishead. The sewer would be at a higher level than in the Charlcombe Bay scheme, and the sewers in the city would not be tide.locked. Cost, ~522,100; annual, ~23,695. 5. Recommended O~etfall : above Avonmo~th.--In this scheme a large tank would be provided at the tidal end of the sewer for storage of the sewage from about two hours after high-water till the tide had turned and again reached high-water; then on the turn of the tide the sewage should be discharged with great rapidity, so that it might be carried off outside the Avonwater.
By this scheme the sewage is discharged in such a manner that it is carried into the Channel clear of the shore. Appended to the report are twenty-one maps of float experiments, made with a view of finding out the direction in which floats would be carried with the wind in various quarters, and when lowered at different states of the tide. Experiments 1 to 17 deal with that part of the Bristol Channel known as King Road, and the maps show clearly that the floats in these seventeen experiments, lowered in most varying conditions of tide and wind, were all carried in the Channel far from low-water mark, and well clear of Portishead Point. Two float experiments (18 and 19) made at the Black Nore were not so satisfactory as those made at King Road. Experiments 20 and 21 were made with surface floats at King Road. These floats were carried well clear of Portishead Point. These float experiments all tend to show that by adopting the scheme recommended the sewage will be carried well away from the land without any risk of its touching the shore. The effects of doekization of the Avon on this scheme, and the effects of the scheme on dockization, are also dealt with.
Non.Ventilation oI Bristol Sewers
499
weather when the water seal evaporates. It is generally accepted that the inhalation of sewer air is detrimental to health, and that sewer air may give rise to certain forms of sore-throat and to diarrhoea, and may lower the resisting power of the individual to the action of pathogenic organisms. In unventilated sewers there is risk of sewer air getting into houses by the traps of house drains being forced, and if this take place there is no guarantee that it will all pass up the soft-plpe ventilator, and some sewer air may find its way into the house, causing detriment to health. In Bristol it is held by Mr. Crimp that if a house is properly drained, and the house-drain is provided with an intercepting trap and with a soil-pipe carried above the level of the roof, the sewer air would escape up the soil-pipe rather than force its way through the traps and sanitary appliances into the houses. It is well to bear in mind that offensive gases mainly occur in badly constructed sewers where deposits take place, owing to decomposition of such deposits, but if there are well laid sewers with smooth surfaces, good fall and flow, and free from objectionable trade refuse, steam, etc. (see Discussion, Public Health, No. 8, May, 1897), then the sewage is carried away at once; and the need is hardly apparent for the numerous openings, some acting as inlets and others as outlets, at present to be seen in ventilated towns. Should it be necessary for sewer men to enter the sewers for cleansing purposes, it is essential that the sewers be cleared of foul gases before the men enter them.
I?IAIN DRAINAGE OF BRISTOL. ~/~R. SANTO CRIMP has reported to the Corporation of Bristol on a new sewerage system for that city~ and discusses fully the various methods which might be adopted, specially recommending the " Avonmouth scheme, ' and giving his reasons for and against the adoption of other proposals. It is assumed that eventually the area covered by buildings will be 9,750 acres, and that in forty-five years' time the population will be 500,000. I t is therefore necessary to design work capable of dealing with the amount of sewage from such a population. At the present time the water-supply averages 22 gallons per head .per diem, and adding to this the amount of water required for trade purposes, the total may be put at 30 gallons per head per diem. The future daily average flow of sewage may be taken at 30 gallons per head; this with a population of 500,000 will mean 15,000,000 gallons per 24 hours to be got rid of, or 1,666 cubic feet per minute. The proportion of rainfall to be carried off is 7,868 cubic feet per minute. This, added to the daily flow of 1,666 cubic feet per minute, gives a total of 9,53¢ cubic feet, or 85½ million gallons, per 24 hours. The following schemes have been suggested :
2. 3. 4. 5.
~
1. Sand Bay. 2. Kennmore. I 3. On banks of Avon. Chemical works at Pill. Charlcombe Bay scheme. Black Nore scheme. Above Avonmouth.
1. Land treatment
500
Main Drainage of Bristol
~buc He~t~
1. It is pointed out that the lands at Sand Bay and Kennmore are both low-lying, in close proximity to Weston and Clevedon, and that there is no water-course of sufficient capacity to carry off the effluent. An area of 5,000 acres of land on the Avon bank has been suggested as a suitable site for the sewage farm, but there are other places less expensive, in ~[r. Crump's opinion, and better than the land treatment. 2. Chemioal.--Works could be erected below Pill, w h e r e 15 acres of land can be acquired for the purpose, the same principle being used as in the London method (lime and protosulphate of iron). The effluent could be discharged into the river, the sludge carried out to sea by steamers. The estimated outlay on this scheme is £366,000, the annual cost, which includes repayment and interest, being £94,628. 3. Charlcombe Bay Scheme.--The sewer not being able to discharge until some hours after high-water, the sewage would be carried along the shore to the detriment of Clevedon if this scheme were adopted. Cost, 4769,272 ; annual, 431,376. 4. Black Nero Scheme.--Ou~fall near Portishead. The sewer would be at a higher level than in the Charlcombe Bay scheme, and the sewers in the city would not be tide.locked. Cost, ~522,100; annual, ~23,695. 5. Recommended O~etfall : above Avonmo~th.--In this scheme a large tank would be provided at the tidal end of the sewer for storage of the sewage from about two hours after high-water till the tide had turned and again reached high-water; then on the turn of the tide the sewage should be discharged with great rapidity, so that it might be carried off outside the Avonwater.
By this scheme the sewage is discharged in such a manner that it is carried into the Channel clear of the shore. Appended to the report are twenty-one maps of float experiments, made with a view of finding out the direction in which floats would be carried with the wind in various quarters, and when lowered at different states of the tide. Experiments 1 to 17 deal with that part of the Bristol Channel known as King Road, and the maps show clearly that the floats in these seventeen experiments, lowered in most varying conditions of tide and wind, were all carried in the Channel far from low-water mark, and well clear of Portishead Point. Two float experiments (18 and 19) made at the Black Nore were not so satisfactory as those made at King Road. Experiments 20 and 21 were made with surface floats at King Road. These floats were carried well clear of Portishead Point. These float experiments all tend to show that by adopting the scheme recommended the sewage will be carried well away from the land without any risk of its touching the shore. The effects of doekization of the Avon on this scheme, and the effects of the scheme on dockization, are also dealt with.