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Components of drainage systems (pipe drains (fundamentals (drain falls…
Components of drainage systems
Field drainage
open drains/ditches
pros
aesthetically pleasing
environmentally friendly
traps surface runoff
ditches which can be piped
interceptors of underground water
outfalls for underdrains
boundaries
minor carriers
minor water table controls
wet fences
stock watering dtches
ditches which cant be piped
interceptors of surface runoff
major carriers
storage ditches
ditch construction
sloped sides
gives stability
walls can be lined with clay
prevent erosion from drains entering ditch and flow of water
must have adequate fall
somewhere to outlet to
main drain
another ditch or stream
cons
require alot of maintenance
debris collecting
mowing grass banks
damage repair from erosion
Auxiliary drainage
French drains
wide tapering trenches
used along the bottom of banks
intercept runoff
pipe drains
herringbone
greens
Grid
football
tennis
bowling greens
Fan shaped
Natural
follows existing contours
fundamentals
mains
function
collect water gathered by laterals
move water to outfall
in a grid system
main drain will not be a perforated pipe
no requirement for a trench backfill
laterals
function
intercept water moving across the surface or through the ground
combined system
perforated pipe
permeable backfill
improves efficiency of interception
guides water in the trench towards the pipe
banks
intercept surface runoff before it reaches the playing surface
one interceptor at the bottom
bank remains wet
one interceptor at the top and at intervals down the slope
dryer bank
outfalls
where to send the water
storm-drain
ditch / stream
outfall pipe must be at least 150mm above highest water level
prevent backflow
non-return valves are recommended on outflows
prevent backflow
prevent vermin + frogs getting in
water storage for irrigation
soak away
not effective if there are non-porous conditions under the soak away
pump water away from a sump
expensive
drain falls
pipe drains should not be laid to a fall of less than 0.5% (1:200)
steeper fall preferred
maindrains should be steeper than laterals
pipe drain falls should be uniform
same rate of flow throughout
reduction in fall at any point can lead to a slowing of flow
leads to collection of sediment
sharp bends should be avoided
sediment build up
unless a silt trap or inspection chamber is placed at that point
all surfaces should be set to fall
surface run off
paths / small areas
1:50 - 1:80
larger areas
1:80 - 1:200
Designing drainage systems
