1. ABC Waters Design Handout
INTRODUCTION | ABC WATERS FEATURES | MUSIC | SPREADSHEET
TOK ZHAO CHIN
UNIVERSITY INTERN

2. ABC Introduction
Active :
Create new community spaces, bring
people closer to water
Beautiful :
Transform waterway and reservoirs
into aesthetically pleasing attractions
that integrate with parks, estates and
commercial development
Clean :
Improve water quality, minimize water
pollution
Google Image
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3. Water Quality Indicators
TSS: Total Suspended Solids
Particles that are sized 125µm or larger that are found in water.
TP: Total Phosphorus
causes many water quality problems including increased purification costs,
decreased recreational and conservation value of an impoundments, loss of
livestock and the possible lethal effect of algal toxins on drinking water.
TN: Total Nitrogen
Lack of oxygen in water bodies, drinking water can be harmful to young infants
or young livestock. Excessive nitrate can result in restriction of oxygen
transport in the bloodstream
PUB Design Requirement:
TSS – 80%
TP – 45%
TN – 45%

4. BUILD A PEOPLE-WATER
RELATIONSHIP

5. Features Functions Remarks
Sedimentation Basins • Remove 70-90% of coarse to medium sediments from
runoff
• Provide temporary retention
• Protect downstream elements
• Pretreatment
• Used for small and large
catchment
Bioswales
Bioretention Swales
• Remove coarse to medium sediments from runoff
• Protect waterway from damage – slow flow velocity
• Bioretention used to partially treat water quality, attenuate
flooding potential and convey stormwater
• Pretreatment
• Max contributing area <1ha
Bioretention Basins • Maximize volume of runoff treated through the filtration
media
• Treat pollution, recharge groundwater
• Does not convey stormwater
• Require Pretreatment
Cleansing Biotopes • Artificially constructed wetland with recirculation
• Consist of wetland plants that are known for their water
cleaning capacity
• Connected to sedimentation
basin
• Recirculation Function
Bioengineering • Used in slope and bank stabilization
• Protect slope from erosion during storm events
Surface Flow
Wetlands
• Remove stormwater pollutants associated with fine to
colloidal particulates and dissolved contaminants
• Increase in detention time,
more efficiency pollutant
removal
Infiltration Systems • Reduce runoff peak flows and volumes (reduce flooding)
• Improve groundwater recharge
• Pretreatment
• Best use in moderately to
highly permeable in-situ
soils
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6. 6
ABC Features
1. Sedimentation Basins
2. Bioswales
3. Bioretention Basins
4. Cleansing Biotopes
5. Bioengineering
6. Surface Flow Wetlands
7. Infiltration Systems

7. Sedimentation Basins
Do not need special handling and disposal as
pollutants usually attached to finer sediment
and colloidal particles.
Rule of thumb: The size of a sedimentation basin
is calculated to match the settling velocity of a
target sediment size (125µm or larger) for a given
design flow (1 year ARI). Size of sedimentation
basin must not be reduced even if there is space
constraint.
Planting along the littoral zone: Prevent scouring and
erosion as well as to inhibit public access to the open
water body.
Terrestrial planting: recommended to screen areas
and provide access barriers to uncontrollable areas.
Water quality here is very poor as it is the first
“treatment” where polluted water go through.
Design Procedures
ABC FEATURES

8. Bioretention swales (Bioswale)
Four function for stormwater
management: collection, conveyance,
filtration and infiltration
• Reduce and delay peak runoff
volume
• Treat stormwater quality
If slope is too steep, install check dams
Dry – provides water quality benefit by
facilitating stormwater infiltration
Wet – uses residence time and natural
growth to treat stormwater prior to
discharge to a downstream surface
water body
Design Procedures for Bioretention swales
Design Procedures for Bioswales
ABC FEATURES

9. Bioretention Basins (Rain Garden)
• Protects water quality and reduces storm water runoff – esp in developed areas
• Ponding above a bioretention surface to maximize the volume of runoff treated
through the filtration media
3 types of Key Design Configurations:
 Lined Bioretention System
 Unlined Bioretention System
 Unlined Bio-infiltration System
STRONGLY RECOMMEND TO USE BIORETENTION SYSTEMS WHICH
INCLUDE SUBMERGED ZONES – to maintain a healthy plant community
throughout long dry spells
Most preferred design configuration:
UNLINED BIORETENTION
SYSTEMS DUE TO INCREASED
NUTRIENT REMOVAL
Design Procedures
ABC FEATURES

10. Lined Bioretention System
• Prevents Exfiltration and Minimizes losses through system
• Best used in situation where:
-Exfiltration is not possible
-For removal of Nitrogen
-Where receiving waters are highly sensitive to Copper or Zinc
BACK TO BIORETENTION BASINS

11. Unlined Bioretention System
• Simplest configuration of bioretention system to design and build
• Best used in situations where:
- Minimal infiltration is allowed [hydraulic conductivity of the surrounding soils
should be an order of magnitude lower than the filter media to ensure minimal
infiltration]
- Systems that are not designed for stormwater harvesting
Submerged zone must be lined to maintain saturation
BACK TO BIORETENTION BASINS

12. Unlined Bio-infiltration System
• Hybrid system, combining a standard
bioretention system and an infiltration
system
• Used in area where:
- Exfiltration is allowed
- Both water quality improvements and
runoff reduction is required
- Systems that are not designed for
stormwater harvesting
No collection pipes in drainage area
BACK TO BIORETENTION BASINS

13. Cleansing Biotopes
Key Words:
1. Detention
2. Filtration
3. Biological Uptake
• Effective in removing organic load, phosphate, nitrogen
composites, pathogenic bacteria – improving water quality
standards
• Connected to sedimentation basin because cleansing biotopes work
best when there are no suspended solids in the inflow as they tend
to clog the substrate
Top-flow : Water is introduced from the top of the bed
Side-flow : Water is piped into the cleansing biotopes from one end of
the side of the bed, such that the pipe submerged in the substrate –
effective for treating black water
Distribution Plate
Design Procedures
ABC FEATURES

14. Bioengineering Using the qualities and capabilities of
natural materials to provide structural
integrity while being ecological and
aesthetically pleasing – stabilizing river
embankments as well as prevent soil
erosion
The various techniques are:
• Log cribwall with brush layers
• Rip Rap with cuttings
• Brush mattress with live fascine
• Geotextile wrapped soil lift
• Fascine with geotextile
• Multiple fascine
• Reed roll
• Stone wall with cuttings
• Gabion Wall
• Vegetated reinforced soil
• Tree stumps with cutting
• Rock sill
• Rock Gabion Mat
The type of technique used would
depends on site conditions such as:
 Gradient of slope
 Soil Type
 Water velocity along waterways Design Procedures &
various techniques
ABC FEATURES

15. Surface Flow Wetlands
Inlet zone – sedimentation basin to remove coarse sediments
Macrophyte zone – heavily vegetated area to remove fine particulates and
update of soluble pollutants
High flow bypass channel – protect the macrophyte zone
Design Procedures
ABC FEATURES

16. Infiltration Systems
• Reduce stormwater runoff peak flows and volume
• Reduce downstream flooding
• Managing the hydrologic regime entering downstream aquatic ecosystems
• improving groundwater recharge
• Require pre-treatment to avoid clogging and to protect groundwater quality
• Best suited to moderately to highly permeable in-situ soils
There are four basic types of infiltration systems:
• Leaky Well
• Infiltration Trench
• Infiltration ‘soak-away’
• Infiltration Basin Design Procedures
ABC FEATURES

17. When and where to use infiltration system
Selection of type of
infiltration system is
determined by the size of the
contributing catchment
Level 1 Pre-treatment - To prevent blockage of the infiltration system media,
stormwater should be treated to remove coarse and medium sized sediments and
litter.
Level 2 Pre-treatment - To protect groundwater quality, pre-treatment is required
to remove fine particulates and dissolved pollutants, such as nutrients and metals.
Level 2 pre-treatment applies to leaky wells, infiltration trenches and infiltration
soak-aways. It also applies to most infiltration basin applications.
Can be designed to function as a
bioretention system

18. Unsuitable:
• in areas with poor soil conditions, in particular sodic/ saline and dispersive soils, and
shallow saline groundwater
• on steep terrain as in can increase the risk of slope instability.
• locations where soils are underlain by rock or a soil layer with little or no permeability
(i.e. Ksat < 0.36 mm/hr).
• near building footings to avoid the influence of continually wet sub-surface or greatly
varying soil moisture content on the structural integrity
Suitable:
• Soils with a saturated hydraulic conductivity of 3.6 mm/hr to 360 mm/hr
Maybe:
• fractured or weathered rocks
• Soils with a low hydraulic conductivity (0.36 - 3.6 mm/hr)
might work but the required infiltration/ storage area may become prohibitively large.
However, soils with lower hydraulic conductivities will be more susceptible to clogging and will therefore
require enhanced pre-treatment to remove sediment.

19. Leaky Well
• Used in small scale residential
applications
• Consist of a vertical perforated pipe
(concrete or PVC) and an open base
How it works?
• Pretreated stormwater enters via an inlet
pipe at the top of the well and when
detention volume is full, an overflow pipe
delivers excess waters to the downstream
drainage system
BACK TO INFILTRATION SYSTEMS

20. Infiltration Trench
• Consist of a 0.5-1.5m deep trench
• Filled with gravel or modular plastic
cells lined with geotextile (non-
woven) and placed under 300mm of
backfill
How it works?
• Pretreated runoff enters the trench
either directly or via an inlet control
pit, with excess waters delivered
downstream via an overflow pipe
• If the trench contains gravel fill then a
perforated distribution pipe is
incorporated into the system to ensure
effective distribution of stormwater
into the detention volume.
BACK TO INFILTRATION SYSTEMS

21. Infiltration Soak-Away
• Larger plan area, typically rectangular and shallower depth
• Similar to trenches in operation
• Can be applied across a range of scales from residential allotments through
to open space or parklands
BACK TO INFILTRATION SYSTEMS

22. Infiltration Basin
• Used in larger scale applications where space is not a constraint
• Consist of natural or constructed depressions designed to capture and store
stormwater runoff on the surface prior to infiltration into the in-situ soils
• Best suited to sand or sandy-clay in-situ soils and can be planted out with a range of
vegetation to blend into the local landscape
How it works?
• Pretreatment of stormwater entering infiltration basin is required with the level of
pretreatment varying depending on in-situ soil type and basin vegetation
BACK TO INFILTRATION SYSTEMS

23. Model for Urban Stormwater
Improvement Conceptualization
(MUSIC)

24. Limitations of MUSIC
• Not a detailed design tool – does not contain the algorithms necessary for
detailed sizing of structural stormwater quantity and/or quality facilities
• A conceptual design tool
• Music must not be the only tool used in the design as other factors such as
land and soil characteristics are important
• The assumptions used in MUSIC might not be the actual site conditions –
recalibration needed
NOTE: MUSIC MODELLING IS NEEDED FOR BIOSWALES, BIORETENTION
BASINS, SURFACE FLOW WETLAND – CONCEPTURAL DESIGN FOR THE AREA
OF BASIN
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25. Design Toolkit
Check
0 ha
0 ha
4 ha
0 -
0 -
1 -
1 -
1 year ARI
100 year ARI
1
500 m
2 m/s
40 m
8 minutes
Singapore -
110 mm/hr
283 mm/hr
1 -
1 -
- -
1.2 m3
/s
3.1 m3
/s
2
90 %
3
300 m2
Refer to fig1
32 m
8 m
4 L:W (1) Time of concentration?
0.5 - Refer to fig2
2 m
2 V:H (1)
2 m
2 m2
115 m2
58.5 m3
3 m3
/ha/year
- -
54 m3
YES -
10.8 years
4
YES -
5
0.5 -
Volume of Accumulated Sediment over 5 years (Vs,5year)
Vs > Vs,5year
Sediment Clean-out Frequency, given Vs
Design Inflow Systems
-
Scour Protection and/or energy dissipation provided
Design Outlet Structures
- Overflow Pit
Cross Section Batter Slope (Below Permanent Pool Depth)
- Sediment Storage Volume
Blockage Factor
Permanent Pool Depth
Area of Basin at half the permanent pool depth
Depth of Permanent Pool
- Internal Batters
-
Area of Basin at the Base
Sediment Loading Rate
- -
- Fraction Impervious
SEDIMENTATION BASIN : DESIGN CALCULATION SUMMARY
CALCULATION SUMMARY
Outcome
Catchment Characteristics
- Land Uses
Residential
Commercial
Roads
Calculation Task
Pipe Length
Pipe Width
Drain Flow Velocity
Basin Length
Basin Width
Design Operation Flow (1 year ARI)
Above Design Flow (100 year ARI)
Peak Design Flows
Design Rainfall Intensity for Design Operation Flow
Design Rainfall Intensity for Above Design Flow
Time of Concentration - Estimate from Flow Path Length and Velocities
Identify Rainfall Intensities - REFER TO IDF CURVE
Station used for IFD Data
Design Runoff Coefficient
Design Operation Flow
Above Design Flow
Refer to the Singapore Code of Practice on Surface Water Drainage (2000)
Sediment Storage Volume (Vs)
Design Operation Flow
Residential
Commercial
Above Design Flow
Estimate Design Flow Rates
Time of Concentration
Roads
Weighted Average
Identify Design Criteria
Confirm Treatment Performanace and Concept Design
Capture Efficiency of Sedimentation Basin (90%)
Confirm Size and Dimensions of Sedimentation Basin
- Inlet Design
Area of Sedimentation Basin
Aspect Ratio
Hydraulic Efficiency (desired if its 0.5 and above but less than 1)
Job No.
Member/Location
Made by
Job Title
Chd.Date
Drg. Ref.
Sheet No. Rev.
Calculation
Fig1
Fig2:
Inflowand outflow of channel,with 'o' as islandsin the water body and doublelineas
weir, singlelineas a dividers
Highlighted sections in
spreadsheet are the
sections to input values.
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26. QUESTIONS?