WFH #DRAINAGE

 Drainage at Slab:

-when estimating depth above slab for decking, walkway, planting. whether 150, 200mm, is related to 

-Length of run to the rwdp. Eg: length of slope ( eg 16m) to fall at gradient 1:200, will need min 80mm for slanting of screed, if it is a straight line.

-Summit point is usually 100mm below top level. thickness for scupper drain neeeded

- this allowance of depth also determines the ponding affect allows before flooding, and the intervals of rwdp needed. hence if too shallow depth, more rwdp is needed at closer intervals.

-for rwdp penetration, as it is usually along columns, note penetration through beam

-note on siphonic drainage. usually pipe is smaller, no need for gradient , but because of tournedo effect if it is a leafy area, twigs and leaves may affect it

-rwdp, estimated 150mm dia pipe covered 200m2 area of rain water

-Every vertical pipe needs a sump. BIG/HDB only allows one 1 penetration per beam

Drainage for site:

-M&E: in charge of IC invert level

-C&S:  in charge of MH invert  lvl

** when MH/IC is more than 1.5m height difference, need a M&E tumbling bay detail

Drainage Tanks: 2 main systems: gravity vs pump drainage system

There are many types of tanks, detention tanks, RW harvesting tank, storm water tank.

1)Firstly, note Rainwater---> Harvesting Tank--->overflow--->Detention Tank

Usage Harvesting Tank--->Treatment room--->water use to wash void decks. ( not irrigation)

*to note pipe length required to run to the void deck, unless 1 treatment rm per block?

Detention Tank requires 2 access hatch, for air ventilation

2)House Drains/ CE drains---> Detention Tank--->External drain

3)Stormwater Tank: is for capturing basement water. the detail is same as detention tank. Location is below MPL

* Do note that because it is in basement, requires a pump to bring the water out. A swan neck/goose neck is necessary as it prevents backflow as there is usually electricity from the pump

4)Tank depths:

If Tank is 3m deep, water quantity collected, is 2m, as 1 m for access

5) Rain Garden as a bio swale, contributes to the catchment of the site. Eg, Catchement of 25% is needed for Detention Tank,