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,