Transcript Filter Strips and Swales - Bakkala Consulting Engineers

Is civil engineering a necessary encumbrance involving
considerable cost but no visible or tangible benefit?
Because it goes largely unseen, engineering tends to matter to
people only when things go wrong and fail to function properly.
A tendency exists to commit the minimum required resource to
obtain the minimum required result. As a consequence,
marginal infrastructure can result. We believe the way to avoid
costly and marginal infrastructure is to aim for a result that
people can appreciate, like…
…Pretty Nice Looking Drains
Filter Drain with filter strip
• Surface runoff from road drains
to median
• Runoff passes through grass
vegetation planted on edge of
filter drain, removing pollutants
• Stone medium slows and filters
the water
• Larger rocks and variety
planting adds to the aesthetic
value while slowing the flow of
water
Filter Drain with filter strip
Filter Drain with filter strip
Grassed Swale
Grassed Swale
Infiltration Detention Basin
Detention Basin
Permeable Carpark
Permeable Carpark
• Surface runoff from
impermeable carpark
surface drains over grass to
filter drain
• Infiltration only achievable
for small carpark areas or if
highly permeable soils exist
on site
• Otherwise, filter drain will
treat and attenuate surface
water before discharge
The following slides illustrate the application of SuDS
principles to civil engineering designs carried out by
Chris Bakkala’s team at Buro Happold.
Ballyshannon Model Village
FKL Architects
A new Place
Place = Location + Identity
Accommodation = Place for Living
• 1 x 5 classroom primary
school
• 1 crèche
• Village hall
• 4 commercial units
• Enterprise units
• 9 Office/ work units
• 1 stables building
• 128 houses
• Allotments
• Football pitch
• Age-specific playgrounds
• Bridle path
• Wetlands, ponds – biodiversity habitats
• Kick around space
• Open green space
Streetscape room walk, grow and drive
Streetscape shaping topography
to drain without pipes
Natural Effluent Treatment Systems
A Proposed Reed Bed and Wetland System
To provide full treatment for 500P.E from the Ballyshannon Model Village and tertiary treatment to ~1000P.E
from surrounding developments in Calverstown. It is proposed to achieve this through the use of a gravity
fed natural treatment system having the benefit of increasing biodiversity habitats for many bird, animal and
invertebrate species, in keeping with the rural aspect of the development.
Primary Treatment – Settlement Tank
Secondary Treatment – Horizontal Flow Reed Bed
The primary and secondary systems have been designed
according to the EPA Wastewater Treatment Manuals,
“Treatment Systems for Small Communities, Business,
Leisure Centres and Hotels”
Secondary and Tertiary Treatment – Integrated
Constructed Wetland (ICW)
The tertiary system has been designed according to the
ICW concept developed by the National Parks and
Wildlife Service, Department of Environment, Heritage
and Local Government.
Reed Bed Wastewater Treatment Systems
Very Low Maintenance
Horizontal Flow Reed Bed and Integrated Constructed Wetlands
• Weekly
- Log flow rates from continuous flow monitor to and from the wetland
- Examine distribution pipes for blockages
- Water level management and flow maintenance
- Visual monitoring of final effluent, vegetation progress and initial fencing
• Monthly
- Surface water quality monitoring of influent, effluent and receiving water course
- Ground water monitoring
• Yearly
- Maintenance of embankments
- Sediment/sludge management
The Village,Cloughjordan
Solearth Ecological Architects
Layout
Boreens and meandering streams
SOAKAWAYS
Filter Drains
Swales and Detention Ponds
Paving over soft ground
Traditional Drainage Systems
(‘Traditional’ is a word whose meaning will change in the future)
Aims:
• Remove surface water from streetscape (conveyance)
• Reduce potential downstream flooding (storage)
• Remove heavy particulates and hydrocarbons – more recent addition
(treatment)
Methods:
• Road Gully Traps connected to an underground pipe network
• Attenuate stormwater on-site – via underground tanks or ponds – with
discharge from site restricted via a hydrobrake or orifice plate etc
• Surface water from carparks and large road areas passing through a
Catchpit and Petrol and Oil Interceptor
Sustainable Drainage Systems (SuDS),
or, Sustainable Urban Drainage Systems (SUDS)
Focuses decisions about drainage on the environment and on people
• Takes account of the quantity AND quality of runoff
• Takes account of the amenity value of surface water in the urban
environment (work with Landscape Architects)
Requires a philosophy shift from previous design techniques used
• Aim to mimic natural (greenfield) drainage processes, albeit in a
controlled, engineered manner
- Infiltration; volume of infiltration should ideally match greenfield rates
- Slow runoff
- Runoff to pass through vegetation
- Good water quality
Sustainable Drainage Systems (SuDS)
• Surface Water Management Train
- Source Control (street level)
- Site Control (estate/developed site)
- Regional Control (receiving waters – local authorities)
• SuDS features also achieve the three main aims of the traditional
drainage system, broadly summarised as:
- Conveyance
- Storage
- Treatment
SuDS Techniques
Filter Strips and Swales
• Mimics natural drainage patterns; surface flow
• Surface Runoff passes through vegetation, slowing and filtering the flow
• Can be designed to achieve conveyance, infiltration, storage and
treatment
• Suitable for roads, carparks and small residential developments
• Very economical, however flow path may be easily blocked by parked
cars, construction materials etc
Filter Drains and Permeable Surfaces
• Encourages subsurface flow
• Contains permeable material below ground to convey and store surface
water
• Provides treatment by slowing, filtering and storing the flow
SuDS Techniques
Infiltration Devices
• Subsurface – Soakaways, infiltration trenches/filter drains
• Surface – Swales, landscaped basins/fields
• Remain dry (except during heavy rainfall periods) allowing public use,
such as playing fields, recreational areas, public open space etc
• Help to recharge groundwater, thereby mitigating development impacts
on rivers and streams by maintaining base flows
Detention Basins and Retention Ponds
• Basins are utilised during heavy rainfall to provide flood attenuation and
can be incorporated to fulfill a number of SuDS aims such as treatment
and infiltration
• Ponds retain water in dry weather, providing treatment and amenity value
(with an allowance for flood attenuation) and include wetlands and
lagoons
Opportunities from SuDS
• Many engineers are used to treating surface water as a ‘nuisance’
• Chance to be seen as leading thinkers and designers for holistic drainage
design – quantity, quality and amenity
• Work closely with Landscape Architects:
- SuDS can play a vital role in the landscaping of a development. It is highly
advantageous to work together early in the planning/design phase to
understand the possibility of achieving common goals through SUDS.