Storm Drainage System PDF

Module 10 Storm Drainage System General water and convey the same to the main storm drain. A storm drainage system convey...

Module 10 Storm Drainage System General water and convey the same to the main storm drain. A storm drainage system conveys rainwater from a building or site to points of disposal. Among these 7. Catch basin-Area drain: A device, usually a locations to be drained are roofs, courts, courtyards, fabricated box-like structure designed to collect lanais, patios, gardens, pathways or simply open areas rainwater and surface run-off from downspout and exposed to directly or indirectly exposed to rain. It also ground surface, respectively. includes parking lots, roadways, lawns, etc., In general, other than small or incidental areas, all interior and 8. Junction box: A device designed to act as a exterior storm drainage should be connected externally to connecting unit where a number of storm drainage the building storm drainage system. pipes may converge and provide a single pipe on its outlet. Definition 9. Junction box-Area drain: A junction box that Storm drainage system is a component system in also serves as an area drain in one unit, usually drainage that is designed to collect, convey and provided with open (usually grated) cover to allow discharge storm water or rainwater to a suitable or surface run-off to flow into the unit. approved location or a system of disposal. 10. Storm drain pipe: Pipe intended to collect The following are some of the commonly-used terms rainwater or surface run-off and convey the same related to storm drainage systems: to a suitable or approved means of storm water disposal. 1. Roof drain: Device installed on a roof to receive water collected on the surface of the roof and to 11. Sub-soil drain: Drainage system usually made discharge it to a point of disposal through a of perforated pipes that collects sub-surface water conductor (or downspout). and conveys it to a place of disposal. 2. Gutter: Exterior trough (installed at the lower 12. Controlled storm drainage system: Storm side or section of a roof) which collects rainwater drainage system that collects storm water on a from the roof and discharges it to the point of roof and slowly releases the flow to the drainage disposal through a leader. system to allow the load to drain within a longer timeframe. 3. Leader: Usually a horizontal portion of a rainwater or storm drainage system installed at the 13. Primary drainage system: Basic storm water exterior or a building which connects the roof drainage system designed for normal or general gutter and the downspout or conductor. use without treatment. 4. Downspout/conductor: Vertical portion of a 14. Secondary drainage system: Additional storm storm drainage system installed in the exterior or drainage system that will handle any storm water integrated within the walls or columns (interior) of overflow that may occur when heavier storms a building. occur and may involve treatment for a specific use. 5. Catch basin: A box-like device usually installed at the base of a downspout used to collect 15. Sump (storm water): Receiver/pit that receives rainwater and convey it to the storm drain pipe at liquid waste, storm water, or groundwater located ground level or at the lowest part of the storm below the elevation of a gravity system. drainage system of a building or structure. 16. Sump pump (storm water): Pump that 6. Area drain: Similar to a roof drain, except that it removes liquid or storm water from a sump. is installed in an exterior open area usually in a garden, lawn, lanai, patio, etc., paved or unpaved, 17. Projected roof area/horizontal projected roof used to collect surface run-off or ground storm area: The horizontal component of a sloping or pitched roof. The projected roof area is, in effect, equal to a flat roof at the base of the pitched roof.  When rain falls at an oblique angle, one side of intermediate branch from the roof to the ground the pitched roof will intercept more rain than the level. other side. However, the average rainfall on both sides of the roof is still no more than that of a flat Roof Drain roof. Materials Commonly-used piping materials include: Roof drains shall be of cast iron, galvanized iron, copper,  Aboveground (interior): Rainwater downspouts brass or other corrosion-resistant materials. or conductor piping placed within the interior of a building inside a vertical pipe chase or run within Strainers a vent shaft shall be of cast iron (C.I.) with caulked or mechanical joints), galvanized steel Roof drains shall be equipped with strainers extending with mechanical joints (welded joints are not not less than 102 mm above the surface of the roof permissible), copper pipes (types K or L), copper immediately adjacent to the drain. Dome-type strainers tube (Drain, Waste and Vent, DWV), brass, shall have a minimum total net inlet area of 1½ times the aluminum, plastic (ABS, Schedule 40 or Polyvinyl area of the outlet pipe to which it is connected. chloride, (PVC) Drain Waste and Vent ,DWV, Roof deck strainers for use on sun decks, parking decks, Series 1000) or other approved materials. and similar occupied areas shall be an approved flat- surface type which is level with the deck. Such drains  Aboveground (exterior): Rainwater downspouts shall have a total net inlet area not less than two (2) times or conductors for low rise buildings or structures the area of the outlet pipe to which the drain is shall not be less than 26 ga. galvanized sheet connected. metal. The bottom of the conductor draining over the catch basin of the storm drains or storm sewers Roof drains passing through the roof into the interior of a is protected from damage by connecting a stronger building shall be made watertight at the roof level by the material such as steel pipe or cast iron at its lowest use of a C.I. drain with integrally-cast waterstop rings(s) section; other materials include cast iron (C.I.) , around the outside of the body and placed at mid-depth galvanized iron (G.I.) or steel, copper leader of the concrete roof slab and the installation of a clamped (round or rectangular), aluminum leader (round or suitable flashing material around the drain. rectangular). In all cases, the outlet connections are inside-caulk or female-screwed.  Belowground (within building): Cast iron (C.I.) pipe, copper (type K), reinforced concrete, plastic Design Principle (ABS or PVC) The fundamental principle behind the design of storm  Belowground (exterior to building): Extra- water systems is to install a piping or conductor system strength vitrified clay pipe (VCP), reinforced to lead the storm water away from the building and site concrete, plastic (Acrylonitrile butadiene styrene, in a reasonable length of time to keep the surfaces dry. ABS or Polyvinyl chloride, PVC) The size of the system depends on the rate of rainfall,  Subsoil drainage: Open-jointed or perforated rather than the total rainfall in a day or in a year. The rate vitrified clay pipe (VCP), plastic, bituminized of rainfall varies with intensity and frequency of fiber, concrete pipes embedded in crushed gravel, occurrence – for example, inches of rainfall during a 15- rock, or stone. minute period as it may happen once per 100 years (15 minutes per 100-year return). (It should be understood Rainwater piping located within a medium-height that “per 100-year return” actually means “1-percent building basement area shall be of galvanized iron probability,” and “per 10-year return” means “10-percent pipe, Schedule 30; cast iron soil pipe, S.W.; Type probability”, that the stated intensity of rainfall may DWV copper tube, Schedule 40 ABS, DWV occur. As with any statistical data, the same probability Series 1000, PVC DWV or other approved may occur in consecutive years or may not occur at all materials. for many years. Downspouts for high-rise buildings shall be of Design of Storm Drainage Systems stronger pipe materials to resist the high hydrostatic pressure inside the vertical downspout In designing a storm drainage system, first determine installed within the pipe chase which has no where drainage is required. Other than roofs, areaways, driveways, and walkways toward spaces of lower elevation, entrances into and exists from buildings are all areas that should be considered. Whenever possible, all exterior storm drains should be connected to a storm sewer outside the building. Drains lower than the elevation of the sewer may have to be collected in a sump and pumped out automatically. After this, determine the roof drain locations. Roof drains should be located at lower spots or in depressed areas of the roof. The locations should be determined by the architect and structural engineer. A 0.5-percent minimum slope toward each roof drain is necessary to assure positive drainage without standing water or ponding. Where controlled discharge is desired, in order to use the roof as a reservoir, the roof structure must be designed to carry the extra weight of water (at 62.4 lb/cu ft.). In general, a minimum of two roof drains should be installed for a building, and a minimum of four for buildings over 10, 000 sq. ft. Next, determine the roof drain design criteria, based on or exceeding the code requirements for the rate of rainfall for primary and secondary roof drain systems. Secondary drainage is a safety provision during extremely heavy rainfall or in the event that drains become clogged. A secondary system may be piped separately or may be designed to spill over the roof, as is permitted by the code. Then select the appropriate drainage fittings. Numerous designs of roof and area drains are available to suit the methods of construction. General Storm Drainage System Installation Guidelines  As a general rule, storm drain is not permitted to discharge into a septic tank or to the main sanitary sewer line except in storm sewer or combination sewer line.  Rainwater piping shall not be used as soil, waste, and vent pipes.  Rainwater piping installed in locations where they may be subjected to damage shall be protected.  Roof drains, overflow drains, and rainwater piping used in a building’s construction shall be previously tested and accepted in conformity with the local code.