Fig. 9.—Density, Area, and Population, Cincinnati, Ohio. 1850 to 1950.
| TABLE 5 | |||
|---|---|---|---|
| Densities of Population | |||
| City | Character of District | Area, Acres | Density per Acre |
| Philadelphia | Thomas Run. Residential. Mostly pairs of two and three-story houses. 1204 acres settled. | 1,840 | 59 |
| Pine Street. Residential. Mostly solid four to six-story houses. 156 acres settled. | 160 | 97 | |
| Shunk Street. Residential. Mostly pairs of two and three-story houses. 539 acres settled. | 539 | 119 | |
| Lombard Street. Tenements and hotels, 145 acres settled. | 147 | 113 | |
| York Street. Residential and manufacturing. 354 acres settled. | 358 | 94 | |
| New York City | Residential. Three-story dwellings with 18–foot frontage, and four-story flats with 20–foot frontage. | 100 | |
| Residential. Five-story flats. | 520–670 | ||
| Residential. Six-story flats. | 800–1000 | ||
| Residential. Six-story apartments. High class. | 300 | ||
| Chicago | 1st Ward. Retail and commercial. The “Loop”. | 1,440 | 20.5 |
| 2d Ward. Commercial and low-class residential solidly built up. | 800 | 53.5 | |
| 3d Ward. Low-class residential. | 960 | 48.1 | |
| 5th Ward. Industrial. Some low-class residences. Not solidly built up. | 2,240 | 25.51 | |
| 6th Ward. Residential. Four and five-story apartments. A few detached residences. | 1,600 | 47.0 | |
| 7th Ward. Same as Ward 6. Not solidly built up. Contains a large park. | 4,160 | 21.7 | |
| 8th Ward. Industrial. Sparsely settled. | 13,624 | 4.8 | |
| 9th Ward. Industrial and low-class residential. Solidly built up. | 640 | 70.0 | |
| 10th Ward. Same as Ward 9. | 640 | 80.8 | |
| 13th Ward. Low-class residential. Solidly built with three and four-story flats. | 6,100 | 36.7 | |
| 16th Ward. Middle-class residential. Some industries. Well built up. | 800 | 81.5 | |
| 19th Ward. Industrial and commercial. Some low-class residences. | 640 | 90.7 | |
| 20th Ward. Low-class residential. Some industries. Entirely built up. | 800 | 77.1 | |
| 21st Ward. Industrial. Entirely built up. | 960 | 49.9 | |
| 23d Ward. Industrial and residential. | 800 | 55.4 | |
| 24th Ward. Residential apartment houses and middle-class residences. | 1,120 | 46.8 | |
| 25th Ward. Residential. High-class apartments. Wealthy homes. Contains a large park. | 4,160 | 24.0 | |
| 26th Ward. Residential. Middle-class homes and apartments. Fairly well built up. | 4,640 | 16.1 | |
| 27th Ward. Residential. Sparsely settled. | 20,480 | 5.5 | |
| 29th Ward. Low-class residential. Two-story frame houses. “Back of the Yards”. | 6,400 | 12.8 | |
| 30th Ward. The Stock Yards. | 1,280 | 40.1 | |
| 32d Ward. Scattered residences. | 8,480 | 8.3 | |
| 33d Ward. Scattered residences. | 12,944 | 5.5 | |
| 35th Ward. Scattered residences. | 4,960 | 12.0 | |
| General average | The most crowded conditions with five-story and higher, contiguous buildings in poor class districts. | 750–1000 | |
| Five and six-story contiguous flat buildings. | 500–750 | ||
| Six-story high-class apartments. | 300–500 | ||
| Three and four-story dwellings, business blocks and industrial establishments. Closely built up. | 100–300 | ||
| Separate residences, 50 to 75–foot fronts, commercial districts, moderately well built up. | 50–100 | ||
| Sparsely settled districts and scattered frame dwellings for individual families. | 0–50 | ||
The density of population in Cincinnati from 1850 to 1913 with predictions to 1950 is given in Fig. 9.[[18]] This shows the densities for the entire city and is illustrative of the manner in which future conditions were predicted for the design of an intercepting sewer. The data given in Table 5 are of value in estimating the densities of population in various districts. The Committee on City Plan of the Board of Estimate and Apportionment of New York City obtained some valuable information on this point, especially in Manhattan. Three-story dwellings with 18–foot frontage, or four-story flats with 20–foot frontage, presumably contiguous, were found to hold 100 persons to the acre. Five-story flats held 520 to 670 persons per acre. Six-story flats held 800 to 1,000 persons per acre, and high-class six-story apartments held less than 300 per acre.
22. Changes in Area.—In order to determine the probable extent of a proposed sewerage system it is important to estimate the changes in the area of a city as well as the changes in the population. With the same population and an increased area the quantity of sewage will be increased because of the larger amount of ground water which will enter the sewers. Predictions of the area of a city are less accurate than predictions of population because the factors affecting changes cannot be so easily predicted. An area curve plotted against time would be helpful in guiding the judgment, but its extension into the future based on past occurrences would be futile. A knowledge of the city, its political tendencies, possibilities of extension, and other factors must be weighed and judged. The engineer, if he is ignorant of the city for which he is making provision, is dependent upon the testimony of real estate men, business men and others acquainted with the local situation.
23. Relation between Population and Sewage Flow.—The amount of sewage discharged into a sewerage system is generally equal to the amount of water supplied to a community, exclusive of ground water. The entire public water supply does not reach the sewers, but the losses due to leakage, lawn sprinkling, manufacturing processes, etc., are made up by additions from private water supplies, surface drainage, etc. The estimated quantity of water used but which did not reach the sewers in Cincinnati is shown in Table 6. The amount shown represents 38 per cent of the total consumption. Unless direct observations have been made on existing sewers or other factors are known which will affect the relation between water supply and sewage, the average sewage flow exclusive of ground water, should be taken as the average rate of water consumption. Experience has shown that water consumption increases after the installation of sewers.
| TABLE 6 | |
|---|---|
| Estimated Quantity of Water Used but not Discharged into the Sewers in Cincinnati | |
| Expressed in gallons per capita per day, and based on a total consumption of 125 to 150 gallons per capita per day. | |
| Steam railroads. | 6 to 7 |
| Street sprinklers. | 6 to 7 |
| Consumers not sewered. | 9 to 10½ |
| Manufacturing and mechanical. | 6 to 7 |
| Lawn sprinklers. | 3 to 3½ |
| Leakage. | 18 to 21 |
The public water supply is generally installed before the sewerage system. By collecting statistics on the rate of supply of water a fair prediction can be made of the quantity of sewage which must be cared for. The rate of water supply varies widely in different cities. It is controlled by many factors such as meters, cost and availability of water, quality of water, climate, population, etc. In American cities a rough average of consumption is 100 gallons per capita per day. Other factors being equal the rate of consumption after meters have been installed will be about one-half the rate before the meters were installed. Low cost, good quantity and good quality will increase the rate of consumption, and the rate will increase slowly with increasing population. Statistics of rates of water consumption are given in Table 7.
24. Character of District.—The various sections of a city are classified as commercial, industrial, or residential. The residential districts can be subdivided into sparsely populated, moderately populated, crowded, wealthy, poor, etc. Commercial districts may be either retail stores, office buildings, or wholesale houses. Industrial districts may be either large factories, foundries, etc., or they may be made up of small industries housed in loft buildings.
In cities of less than 30,000 population the refinement of such subdivisions is generally unnecessary in the study of sewage flow, all districts being considered the same. The data given in Tables 8 and 9 indicate the difference to be found in different districts of large cities. The Milwaukee data are presented in a form available for estimates on different bases. These data are shown in Table 10.