Relation of Rainfall and Run-Off to Cost of Sewers: Fid-Bau Portal

Relation of Rainfall and Run-Off to Cost of Sewers

Rousculp, John A.

The preliminary design of storm sewer systems often requires a number of laborious studies involving various plans and perhaps various combinations of the two design factors-rainfall frequency rates and run-off percentage. It is the purpose of this paper to describe the development of a method, using time-saving charts, based on a study of relative costs of a system, which can be a valuable aid in preliminary design work.

The relative costs of storm sewers, as studied herein for various combinations of design factors, are based on the application of such combinations to an assumed district. The selection of this assumed district was based upon a study of the concentration of area of a number of actual districts.

The rational method of estimating run-off was used in computing the various cases. Explanation is made of the method of determining the assumed district, and a sample computation is given to illustrate the method of determining the run-off, Q, for one of the cases. The results of the run-off Q-computations for all cases are plotted on charts showing the run-off, Q, for corresponding area. These charts are used as the basis for computing relative sewer-capacity requirements in connection with the study of cost relations. A discussion of results is given, together with examples suggesting some practical uses of a study of this nature.

The writer does not intend that the charts, as developed, should cover the full range of design stipulations that may be encountered, or be of widespread applicability. Rather, it is hoped that the development, as a method, may be helpful to other engineers in making similar studies to satisfy various special requirements.