Chapter 10: Storm Drains

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Section 1: Introduction

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Overview of Urban Drainage Design

The objective of urban storm drainage is to optimize safe passage of vehicle traffic by collecting stormwater from the roadway, and to convey it safely to an adequate receiving body without undue risk to pedestrian traffic or contributing to damage of adjacent private properties during the design storm event.

The flow of water along a roadway can interfere with or halt highway traffic. The most destructive effects of an inadequate drainage system are damage to surrounding or adjacent properties, deterioration of the roadway components, and hazard or delay to traffic caused by excessive ponding in sags or excessive flow along roadway grades.

Proper drainage of a roadway in an urban region can be more difficult than draining roadways in sparsely settled rural areas for the following reasons:

These conditions require sound and consistent engineering principles and the use of all available data to achieve an acceptable drainage design.

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Overview of Storm Drain Design

Although the design of a storm drain system entails many conventional procedures, the design also requires engineering judgment. The proper design of any storm drainage system requires accumulation of basic data, familiarity with the project site, and a basic understanding of the hydrologic and hydraulic principles and drainage policy associated with that design.

The development of a storm drain design requires a trial and error approach:

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  1. Analyze a tentative storm drain system.
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  3. Compare the system to design criteria.
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  5. Evaluate the system economically and physically.
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  7. Revise the system if necessary.
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  9. Analyze the revised system.
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  11. Make the design comparisons again.
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  13. Repeat the process until a storm drain system has been developed that satisfies the technical function of collecting and disposing of the runoff within budgeted allowances.

The hydraulic designer must establish design parameters and criteria, decide component location and orientation, determine appropriate design tools, and ensure comprehensive documentation.

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