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ES-12¶

Purpose:¶

Apply rational equation model process to size conduits for a storm drain system.

Problem Data¶

Three drainage areas that drain to the inlets connected to the pipes as shown in Figure 1. A stormwater drainage system is being designed to carry the flow from the three areas.

Figure 1. Drainage System Layout

Table 1 lists drainage area information.

Table 1. Contributing Area Hydrologic Properties

Table 2 is a list of pipe connectivity, flow lengths, design slopes, and pipe roughness data.

Table 2. Pipe Connectivity, Lengths, and Roughness

Equation 1 is the 10-year ARI intensity equation for the area, where $I$ is intensity in inches-per-hour, and $T_c$ is the averaging time, in minutes. Depending on the location in the system it may be just the local inlet time, or a time of concentration that includes upstream contributions and pipe travel time.

The allowable velocity at design flow is between 2 and 10 feet-per-second. The pipes are to be sized so they flow $\frac{1}{2}$ full at the design discharge.

Problem Statement¶

Using the supplied problem data, and assuming the 10-year ARI is the design standard for the system:

Determine the design flow rates in cfs for each pipe
Determine the associated pipe diameters in inches for both pipes.

Deliverables:¶

A brief report with your solution, showing the requested values, any intermediate calculations, any additional data required, and its source.

References¶

Gupta, R. S. (2017). Hydrology and Hydraulic Systems. Waveland Press, Inc. pp. 711-733
Mays, L. W. (2011). Water-Resources Engineering. Wiley. pp. 613-635 http://54.243.252.9/ce-3372-webroot/3-Readings/Mays613-635/RationalMethodStormSewerDesign.PDF