RAIN WATER MANAGEMENT&STORM DRAINAGE

Building Services 1

Reference:

Plumbing Practices: Chapter 12by-Syed Azizul Haq, PEng

Week 12: Class 25 and 26

Introduction:Rain water management is the concept of using rainwater in fulfilling the various demands of water and draining excess rainwater.

Rainwater is considered to be the potential option for using as source of water where use of surface water or ground water is either limited or costly for water supply.

Theoretically rainwater should be the purest form of water but it contains some dissolved substances taken from the atmosphere while falling. It has low content of dissolved solids and so it is tasteless.

Rainwater is slightly acidic, so its taste seems to be little bitter. Rainwater also lacks dissolved minerals and as such it is relatively aggressive.

Regular drinking of rainwater may cause deficiency of calcium and magnesium in human body.

The presence of some pathogens such as Cryptosporidium, Giardia, Campylobacter, Vibrio, Salmonella, Shigella and Pseudomonas spp has been found in rainwater.

Rainwater quality

1.      Collecting rainwater from suitable catchments areas.2. Flushing out first rain water.3.      Storing rainwater.4.      Qualifying rainwater according to the purpose of use.5.      Supplying rainwater to the points of use.6. Draining of excess rain water.

Rainwater utility technology:

Rainwater collection:

The major components in rainwater collection are as follows.

01.  Catchments

02.  Gutter

03.  Rainwater down pipe (RDP) or leader

04.  Filtration system

05.  Storage tank.

The horizontal surface area, which receives the rainwater directly and the vertical surfaces, which contributes partially to the rainwater accumulation are considered as the catchments area for rainwater discharging pipes.

Generally from following built up areas rainwater can be collected easily.

1.      Roof top areas.

2.      External walls and other vertical surfaces.

3.      Balconies.

4.      Sunshades.

5.      Artificial ground areas.

6.      Parking lots

7. Play ground etc.

Catchments areas for collecting rainwater

01. The catchments structure must be non-toxic to human life.

02 The surface should be smooth, dense (hard inorganic). Galvanized metal roof is preferable. Surface shall not be painted. Bituminous roofing material should be avoided.

03.Regular cleaning of the catchments surface. Fencing should be made around catchments surface.

04. Providing smooth, even surfaced and gentle sloped catchments.

05. Locating the catchments in a free and open area.

06. Thatched roof should be covered with polyethylene sheets.

 

Measures taken for Catchments areas

On flat surface, storm water run off into roof drains due to a slight pitch created by a roof fill, lime terracing etc.The high points are the ridges and the low points are the valleys that pitch toward the drain.

Various slope for different surfaces on flat roof.

Sl. no. Surface condition Slope

1 Smooth surface

(Polished stone, cement/ terrazzo floor, etc.) 0.50 - 0.75%

2 Normal surfaces

(Brick, rough stone/concrete blocks, tiles, etc 0.75 - 1.00%

3 Rough surfaces

( Gravel, cobbled, etc) 1.50 - 2.00%

Catchments area: Flat surface

Determining Catchments area

Measures to be taken for RDP

Following measures are taken for rainwater down pipes for economy and efficiency of the system.

01.  Number of rainwater down pipe shall be kept as minimum as possible.

02.  Adequate pipe size shall be selected.

03.  Dome shaped grating shall be provided on inlet of pipe.

04.  Minimum number of bends shall be provided.

05. Proper jointing and anchorage of pipe shall be ensured

Rainwater Down Pipe (RDP)

4”Dia RDP (Rainwater Down Pipe)

6x4 Reducer

Dome Shaped Grating

Diameter of RDP mm (in.)

Maximum Rainfall mm/hr (in/hr)

50(2) 75(3) 100(4) 125(5) 150(6)

75(3) 153 102 76 61 51

100(4) 349 233 175 140 116

125(5) 621 414 310 248 207

150(6) 994 663 497 398 331

200(8) 2137 1424 1068 855 706

250(10) 3846 2564 1923 1540 1282

300(12) 6187 4125 3094 2476 2062

375(15) 10126 6763 5528 4422 3683

Diameter of rainwater down pipe in mm based on roof area (sqm) and intensity of rain (mm/hr). Slope of horizontal portion of pipe is 100:1.

Sizing Rainwater Down Pipe

After finding the number of rainwater down pipe its position shall be well planed in accordance with the configuration of roof plan and position of the other catchment areas of the building.

Where possible rainwater down pipes should be proportionately distributed along all the sides of buildings.

There shall be at least two rainwater down pipe for a reasonably big catchment area.

Rainwater down pipes should not be too away from the ridge so that thickness of finishing layer on roof at ridge become too thick.

Positioning Rainwater Down Pipe

The quality of rainwater can be determined by the nature of the collecting sources. The required quality level is contingent on the purpose of use. Rainwater shall be treated in the following methods according to the purpose of use shown in the table.

01. Screening 02. Sedimentation, 03. Filtration and 04. Disinfecting

Qualifying Rainwater

Sl. no Rainwater uses Treatment

01 Drinking, cooking, washing utensils, bathing

Disinfecting along with filtration

02 Bathing, ablution, clothe washing, fountains

Filtration with hygienic treatment

03 Sprinkler, fire fighting, cooling water for air conditioning, floor car washing etc.

Sedimentation

04 Toilet flushing, gardening, cleaning artificial ground, parking lots etc.

Screening

Class Test: 03

01. Draw elevation of a toilet showing the fixtures- basin, water closet and a shower in a row. and 5

Results of Assignment: 03 and Class test: 03 On 13th Week

Time 30 min. Marks-10

02. Also show the drainage piping connected with a stack for those fixtures. 5

12th Week, 22.11.08,