WATER SENSITIVE URBAN DESIGN
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INTRODUCTION:
The objective of this paper is to give overview
of various technologies available to integrate, for sustainable site development.
This approach is commonly called as water Sensitive Urban design widely being practiced
in Australia. In USA similar technologies are called as Low Impact Storm water Design
(LID) Technologies i.e., making less impact on existing storm or drainage system,
increasing the sustainability of the sites. This is also being used in European
countries.
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What is WSUD?
Worldwide urban planners and engineers are looking for ways to make better use of
storm water in expanding cities. A best practical approach to urban storm water
management is rapidly evolving Water Sensitive Urban Design
that provides for sustainable management and improvement of water quality entering
waterways. WSUD contributes to urban sustainability and provides conditions for
attractive human scale living environment through integration of urban planning
and design with the management protection and conservator of whole water cycle.
Principles of WSUD:
Key Principles of WSUD from storm water management and planning perspective are
Why is it necessary?
WSUD provides range of measures to help address the environmental degradation that
flows from traditional practices of stormwater management. WSUD is designing urban
environment to more closely match the predevelopment stormwater runoff both quality
& quantity.
Optimizing the use of rainwater that falls on urban areas.
Reducing the amount of water we transport between catchment both in water supply
import and waste water export.
WSUD Measures:
Various WSD measures are given below .However function of each WSUD measures and
its role in treatment train should be understood with their application, limitation,
and pollutant removal efficiency & construction issues.
1. Vegetated swales
2. Vegetated filter strips
3. Sand filters
4. Bio retention system
5. Permeable pavement
6. Infiltration trenches
7. Infiltration basins
8. Rain water tanks
9. Landscape development.
WSUD measures can be chosen based on treatment requirement like Primary, secondary
& tertiary. WSUD measures appropriate to each category is summarized below
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Table 3.1 WSUD Treatment Measure Categories
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Category
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Definition
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Typical-Retained pollutant
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Typical-WSUD measures
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Primary
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Physical screening or rapid sedimentation techniques
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Gross pollutants and litter, coarse sediments, free oil/grease
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Gross pollutant traps(GPT’s), sediment traps, oil/grit separators
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Secondary
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Finer particle sedimentation and filtration techniques
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Fine particles and attached pollutants
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Sand filters, permeable pavements, vegetated filter strips, vegetated swales, infiltration
systems.
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Tertiary
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Enhanced sedimentation and filtration, biological uptake, absorption onto sediments
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Nutrients and heavy metals
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Constructed wetlands, bioretention systems, natural stream systems
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Relationship between various WSUD measures:
A fundamental feature of WSUD philosophy is the restoration of natural resources
in the hydrological system. This is typically achieved by series of hydrological
design responses at four distinct treatment control levels or stages in urban hydrological
system. The description & various WSUD measures that can be applied at each
level of the four levels are summarized below.
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Table 3.2 Control Levels in the Urban Hydrological
System
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Level
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Description/Location
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Typical WSUD Measures
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Source Control
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At the individual building allotment
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Rainwater tanks, infiltration trenches, vegetation filter strips, planting beds,
permeable pavements
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Conveyance Control
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Conveyance of stormwater to streets and channels
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Vegetated filter strips and swales, on-line bioretention systems, natural channels,
streetscapes
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Discharge Control
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At the point where water leaves the lot, estate or catchment
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Bioretention and infiltration basins, sand filters, constructed wetlands, detention
ponds
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Natural Systems
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Throughout the urban catchment
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Natural water courses, creeks, floodplains, wetlands and vegetation
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SUD selection & treatment train:
A fundamental feature of the WSUD Philosophy is the restoration of natural features
in the hydrological system by forming a hierarchy at smaller level, larger level
& large catchment level.
Table 3.4 Scale of WSUD application in urban catchments:
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WSUD Measure
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Smaller scale
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Medium Scale
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Larger Scale
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Vegetated Swales
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Vegetated Filter Strips
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Y
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Y
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Y
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Sand Filters
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Y
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Y
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Bioretention Systems
-Off-line (planting beds)
-Online (conveyance)
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Y
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Y
Y
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Y
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Permeable Pavements
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Y
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Y
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Infiltration Trenches
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Y
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Y
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Y
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Infiltration Basins
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Y
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Rainwater Tanks
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Y
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Landscape Developments
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Y
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Y
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Y
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Each WSUD measures should not be considered in isolation, but an element forming
continuous TREATMENT TRAIN through the urban development catchment.
The assembly of the treatment train is often based on achieving the desired outcomes
within a system of stormwater management measures for e.g. gross pollutant, coarse
to medium sediment, fine sediment removal.
The optimal WSUD measure incorporated in the system is dependent on the following.
a) The style of development and the type of pollutants likely to be generated.
b) Pollutant reduction objectives
c) Location within the development catchment
d) Role, function and effectiveness of the treatment measure.
e) Individual site assessment, physical constraints and design issues such as soils,
slopes, ground water and space available.
f) Operation & maintenance issues and life cycle cost considerations.
Typical Combination of WSUD treatment processes that are recommended for various
developments (subject to site constraints) are provided below:
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wsud measure
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water quality treatment
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flow attenuation
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reduction in runoff volume
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vegetated swales
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h
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m
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l
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vegetatedfilter strips
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h
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m
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l
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sand filters
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h
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m
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l
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bioretention systems
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h
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m
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l
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permeable pavements
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m
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h
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h
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infiltration trenches
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h
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h
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h
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infiltration basins
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h
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h
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h
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rainwater tanks
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l
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h
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h
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landscape developments
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m
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m
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l
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Residential lot:
Rainwater tank (with first flush device) for reuse for toilet flushing with overflow
to detention /retention trench.
Permeable pavement along driveways with overflow arrangement to street drainage
system.
Storm water runoff from impervious areas and lawns draining to landscape or garden
areas.
Excess runoff from impervious areas to detention /retention trench with overflow
to street drainage.
Roads and commercial /Industrial pavement.
Runoff from pavements draining to vegetated filter strips (replacing conventional
kerb & gutter)
With overland flow draining to bioretention or infiltration trench, via vegetated
swales.
Applicability and Function of WSUD measures:
Prior to selection of appropriate WSUD measures in the treatment train it is important
to recognize the appropriate scale of application ,the primary role and function
of each measure so that the water management issues for individual sites can be
effectively addressed.
TABLE 4.1 Role and Function of WSUD Measures
KEY: H- High level role: M-medium level role: L-Low level role
Applies to frequent events
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WSUD Measure
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Steep Site
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Shallow Bedrock
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Salinity Hazard
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Low perme-ability Soils
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High perme-ability Soils
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High Water Table
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High Sediment Input
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Land Availa- bility Limita-tion
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Hydr- aulic Head Loss Limita- tion
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Vegetated
Swales
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C
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M
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M
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Y
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Y
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M
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M
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C
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Y
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Vegetated
Filter Strips
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C
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M
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M
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Y
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Y
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M
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M
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C
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C
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Sand Filters
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M
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M
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M
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Y
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M
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C
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C
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M
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C
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Bioretention
Systems
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C
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M
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M
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Y
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M
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C
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C
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C
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C
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Permeable
Pavements
(Infiltration)
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C
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C
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C
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C
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Y
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C
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C
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C
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C
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Permeable
Pavements
(Detention)
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C
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M
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M
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Y
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M
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C
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C
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C
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C
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Infiltration
Trenches
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C
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C
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C
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C
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Y
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C
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C
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M
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C
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Infiltration
Basins
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C
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C
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C
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C
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Y
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C
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C
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C
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Y
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Rainwater
Tanks
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Y
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Y
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Y
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Y
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Y
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Y
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Y
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C
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Y
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Landscape
Developments
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Y
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M
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M
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Y
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Y
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M
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M
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C
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Y
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C -Constraints may preclude the use of this
WSUD
M - Constraint may be overcome with appropriate modifications
to design
Y -Generally not a constraint (i.e. design specification
apply)
Technologies:
Swales: Vegetated swales are used to
convey storm water in lieu of underground pipe drainage system. They provide a means
of disconnecting impervious areas from downstream waterways assisting in protecting
downstream waterways from damage by frequent storm events by reducing the flow velocity
compared with the pipe system. Swales alone cannot provide sufficient treatment
to meet the water quality objective. Swales are good at coarse sediment removal
as pretreatment for tertiary systems such as wetland and bioretention basins.Swales
can be located within parland areas along roadways corridor within foorpath or centre
medians.
Notes
1. Swales Shall Be Blended Or Smoothned
To The Natural Topography.
2. Swale Vegetation To Be Maintained
Greater Than 100 In Height.
All Dimensions In Millimeter
Unless Noted Otherwise.
Bio retention swales:
Bio retention swales provides both stormwater treatment & conveyance functions.
Combining bio retention system installed in the base of a swale that is designed
to convey stromwater as part of minor & major drainage system.
The swale component provides pretreatment of stormwater to remove coarse & medium
sediments while bio retention system removes finer particles and associated contaminants.
Bio retention provides flow retardation for frequent storm events.
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BIORETENTION SWALES |
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STREET SWALES |
Notes
1. The Bioretention System Shall Not
Be Used For Sediment Control During Construction.
All Dimensions In Millimeter Unless Noted Otherwise.
Notes
1. The Bioretention System Shall Not
Be Used For Sediment Control During Construction.
All Dimensions In Millimeter Unless Noted Otherwise.
Sedimentation basin:
Reducing sediment loads is an important component in improving storm water quality.
Sedimentation basins are storm water detention systems to provide settling of sediments
through the reduction of flow velocities & temporary detention.
Notes
1. Sand Filter Shall Not Be Used For
Sediment During Construction.
All Dimensions In Millimeter Unless
Noted Otherwise.
Storm water infiltration: This
system captures storm runoff and encourages infiltration into surrounding soil and
underlying groundwater.This has the benefit of reducing storm water runoff peak
flows and volumes and reducing downstream loading improving ground water .The purpose
of infiltration systems are the storm water management strategy
NOT the storm water treatment
Notes
1. Infilteration Trench Shall Not Be
Used For Sediment Control During Construction.
2. Trench Subgrade To Be Ripped/Tyned
Prior To Placement Of Trench Gravel
All Dimensions In Millimeter Unless Noted Otherwise.
Permeable Pavement.
Permeable pavements are alternate to impermeable pavement, allowing runoff to percolate
through hard surfaces to an underlying granular subbase reservoir for temporary
storage until the water either infiltrates to the ground or discharges to a storm
outlet. they provide functions such as
Removing sediments and attached pollutant by infiltration through underlaying sand,
gravel media, reducing runoff volumes and delaying peak runoff by providing retention/detention
storage capacity and reducing flow velocities.
Two types of permeable pavements are available.
Infiltration systems-Temporarily holding surface water for sufficient period to
allow percolation into underlying soils.
Notes
1. Subgrade To Be Ripped/Tyned Prior
To Placement Of The Reservoir Course.
All Dimensions In Millimeter Unless Noted Otherwise.
Inspection,Monitoring & maintainance:
Inspection,Monitoring & maintainance of various water sensitive technologies
briefed below.