────────────┬─────────┬─────────┬─────────┬────────┬──────── │Predicted│Predicted│Predicted│Measured│Measured │ Mean in │ Dry │Max. Dry │Avg. Dry│Max. Dry District │ Million │ Weather │ Weather │Weather │Weather │Gals. per│ Flow, │ Flow, │ Flow, │ Flow, │Acre per │ c.f.s. │ c.f.s. │ c.f.s. │ c.f.s. │ Day │per Acre │per Acre │per Acre│per Acre ────────────┼─────────┼─────────┼─────────┼────────┼──────── Hotel and │ .20 │ .29│ .34│ 1.04 │ .146 midtown. │ │ │ │ │ Midtown and │ .12 │ .18│ .23│ .078│ .110 financial.│ │ │ │ │ East and │ │ │ │ │ West of │ .074│ .12│ .15│ .057│ .097 midtown. │ │ │ │ │ Apartment, │ │ │ │ │ 59th to │ .043│ .06│ .09│ │ 155th Sts.│ │ │ │ │ Manhattan │ │ │ │ │ north of │ .031│ .05│ .08│ │ 155th St. │ │ │ │ │ ────────────┴─────────┴─────────┴─────────┴────────┴──────── Midtown district consists of department stores, large railroad terminals, industrial and loft buildings, and sky-scraper office buildings. It is difficult to set any definite figure for the percentage which the maximum rate of flow is of the average. Fluctuations above and below the average are greater the smaller the tributary population. This relation can be expressed empirically as _M_ = 500⁄_P_^⅕, in which _M_ represents the per cent which the maximum flow is of the average, and _P_ represents the tributary population in thousands. The expression should not be used for populations below 1,000 nor above 1,000,000. Having determined the expected average flow of sewage by a study of the population, water consumption, etc., the maximum quantity of sewage is determined by multiplying the average flow by the per cent which the maximum is of the average. In this connection W. G. Harmon[20] offers the relation _M_ = 1 + 14⁄(4 + √(_P_)), which was used in the design of the Ten Mile Creek intercepting sewer at Toledo, Ohio. For rough estimates and for comparative purposes the ratio of the average to the minimum flow can be taken the same as the ratio of the maximum to the average flow, unless direct gaugings or other information show it to be otherwise. [Illustration: Fig. 10.—Daily and Hourly Variations of Sewage Flow. ] 1. Toledo, O.; Manufacturing average. 2. Toledo, O.; Manufacturing, Monday. 3. Toledo, O.; Manufacturing, Sunday. 4. Toledo, O.; Residential, average. 5. Toledo, O.; Residential, Monday. 6. Toledo, O.; Residential, Sunday. 7. Cincinnati, O., Industrial, average.