The Birmingham age-herald., 1908-05-01

lation would be the area occupied largely by boarding houses, apartment houses, etc. Then in the order of population would come the area occupied by the ordinary residences, and finally the area in which the more expensive dwellings are located, the lots being larger and con- sequently the population is smaller per acre.
 After having these areas defined and having determined the probable popula- tion per acre for each district, and hav- Ing determined the number of gallons of sewage per capita per "A hours to be taken care of, and remembering that one-half of the sewage will reach the sewers dur ing six hours of each day and assuming the percentage of ground water that will md its way into the sewers and will have to be taken care of just as if it were sewage, this percentage varying accord ing to whether the sewers are passing through low or high ground, and knowing the Tall Tor each sewer and knowing the amount of sewage that will pass through it, it is easy enough to determine the size of the sewer.
 somewhat similar procedure has to be followed in designing the storm water sewers. As an illustrations: In designing a main sewer and branches for the South side, it is necessary first to determine the area lying between the top of Red mouu- J area to be drained and between the west ern extremity of the sewer and the east ern boundary of the area to be draind Then there are a number of spurs or ridges which leave the mountain and extend dowT to the level portion of this section which divides the total drainage area into. number of smaller areas, and each of these hollows or depressions has to be taken care of by a sewer constructed in 2 it, and each of these branches has numer- ous smaller branches extending into smaller areas which make off from it. Having determined the number of acres in the entire basin and the number of acres in each of the sub basins, it is then necessary to determine the portion of the area which will be covered with business houses.
 It is obvious that the greater the per cent of roof area the greater percent of the rain water will reach the sewers dur ing a storm instead of being partially taken up by the earth, as would occur in suburban areas. This territory will have to be divided into somewhat similar sub- divisions for the purpose of calculating as was done in the case of the sanitary sewers, varying from the thiclkly built-up district to the large suburban lots which have comparatively large lawns, and con sequently retarded the progress of the water to the sewers.
 It Is also necessary to determine the area of the streets in the basin, since eventually all streets will be paved, and consequently practically all the rain water reaching them will find its way promptly to the sewers.
 Then it is necessary to- determine the slopes of the areas in these sub-basins, since it is obvious that the sleeper the slopes the quicker the rain water will flow towards the sewers, and consequently less time being allowed for percolation into the soil greater percentage reaches the sewers than occurs on comparative ly level ground.
 Having collected all this data, and hav- ing decided upon the maximum rate of rainfall that can be reasonably expected to occur at comparatively short intervals. and the percentage of the same which will reach the sewers promptly, and the fall which each sewer and branch will have. 1t is a comparatively simple prop osition to determine the sizes of the sewers.
 entire city, and is pretty well in hand Of course, in making preliminary esti- mates of the cost of the sewers, it was not necessary to have all of this data accurately determined in advance, but from the maps and data at hand and my general knowledge of the city, these pre- liminary or approximate, estimates were made.
 Trusting that the above is full reply 10 your questions, l remain, yours very truly, i JULIAN KENDRICK,
 City Engineer.