Page 288 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SITE UTILITY SYSTEMS

6.10 CHAPTER SIX

While the piping system is being designed, after the storm water drainage inlet struc-
tures have been located, the type and size of inlets and grates must be selected. In most
cases, the authority having jurisdiction has design standards available for such purposes. If
no standards are available, the following can be used as a guide. Storm water drainage inlet
structures are classified according to their functions as follows:
1. Drainage inlets (DIs) are structures that admit storm water into the piping system. They
are generally located in areas that are reasonably free from sediment or debris such as
paved, lightly vegetated, or unimproved areas. The bottom of a DI is leveled with the
invert of the outlet pipe. A shallow DI is illustrated in Fig. 6.7 and a deep DI is illustrated
in Fig. 6.8.
2. Catch basins (CBs) are similar to drainage inlets, except that there is a space below
the inlet and outlet pipes for retention of debris or sediment. A CB is usually located
in paved areas where debris can be easily washed in. Experience has indicated that
inadequate maintenance negates their benefits, and catch basins are not generally used
unless good maintenance can be assured. A typical CB is illustrated in Fig. 6.9.
3. Manholes (MHs) do not allow surface rainfall to enter but are provided for ease of pipe
connections for cleaning purposes. Drop manholes provide for pipe connections where a
difference of more than 2 ft in elevation exists between inlet and outlet pipe. A precast MH
is illustrated in Fig. 6.10 and a drop connection into an MH is illustrated in Fig. 6.11.

Gratings
Gratings allow water to enter the drainage structure, and some gratings will prevent the entrance
of debris into the piping system. Gratings are classified as plain, curb, or combination.
• A plain grate (or gutter grate) is flat and allows water to enter from all unobstructed sides.
Bars prevent the entrance of debris.
• A curb grate has a single vertical opening in the side of a curb. Water enters only from
the front. Debris can enter freely.

FIGURE 6.7 Typical shallow drainage inlet.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com)
Copyright © 2009 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.