Rainwater management techniques
A review of rainwater management techniques
and their integration in planning
Roland Burkhard, Colenco-Hounger Ag, Mellingerstrasse, Baden, Switzerland
Ana Deletic, Engineering Department, University of Aberdeen [email protected]
Anthony Craig, SEARCH, The Robert Gordon University, Aberdeen
This paper presents a review of rainwater management and a discussion as to how they can
be integrated in future water-planning issues. Each approach is reviewed from a technical
perspective with a further commentary on economic and social factors that underpin the
different techniques that each approach has to offer. This is followed by a discussion on
how integrated assessment can lead to the design and implementation of more sustainable
approaches to wastewater management.
Key Words: Wastewater Management, Rainwater, Sustainability, BMPs, SUDS,
1
Rainwater management techniques
Introduction
If future generations are not to be constrained even further, we must develop a coherent ‘holistic’ approach to
the planning, specification, costing and evaluation of water and wastewater options in the domestic context,
such as where the demand for new housing developments is forecast to have significant and widespread
environmental impact. It requires a balance of technical, economic, environmental and social goals, while
satisfying the demands of developers, planners, environmental protection agencies and customers. The
techniques used in water management which may satisfied these needs are called sustainable management
solutions.
According to Otterpohl et al. (1996), the World Commission on Environment and Development (WCED 1987,
also known as Brundtland Report) made the most popular definition of sustainability. Sustainable development
is defined as ‘development that meets the needs of the present without compromising the ability of future
generations to meet their own needs.’ According to Tages-Anzeiger (1995), the word sustainability has long
been used in forestry where it means that volume and mass taken out is replaced and hence the mass
balance accounts to zero. This is nowadays known as ‘natural sustainability’, whose criteria are based on
mass flux and the ability of a technique to recycle nutrients and other valuable resources from wastewater
before they are lost. A different aspect is ‘financial sustainability’. It can be argued that the success and
survival of business follows natural laws as well, i.e. money spent on production, wages and interest has to be
replaced by money earned for services or goods. However, the costs and use of raw materials included in the
processes to produce the goods or deliver a service may seriously affect the mass balance. The instability that
can thus be created by applying different economic criteria is one of the principal reasons why the issue of
sustainability is raised at all. Hence, the quest for sustainability is intimately linked to the quest for economic
models, which take the natural mass fluxes into account. A third and important factor in sustainability
considerations are the potential users of a system. Their behaviour and commitment to participate in the water
management process make a method sustainable, because the occurrence of pollution in the water cycle is
mostly due to human behaviour. This third factor may be called ‘social sustainability’. In this review, sustainability
will be discussed in the context of the above three distinct interpretations.
Of the many criteria which may be used to assess the feasibility of water and wastewater systems, it is likely
that ‘the social aspects will be the most difficult issues’ (Harremo_s 1997). This oft-neglected ‘social’ side of
2
Rainwater management techniques
systems can provide a wealth of information regarding the appropriateness of a technology in a given setting,
along with any potential barriers to its implementation.
Review Methodology
Three aspects have been analysed in rainwater management regarding efficiency, economic, and social aspects
of present techniques, as listed below.
Techniques: Both traditional and novel will be presented with a brief description of their design requirements.
Efficiency: For all techniques, the efficiency is presented with respect to their purpose (e.g. suspended solids
and heavy metals removal).
Economics: Cost data are hard to find. Whenever possible, real costs were used, but in all cases qualitative
cost were systematised. They may include values, which are subjective to the user, e.g. environmental benefits.
Social aspects: The social impact of the different techniques will differ largely. The subjective importance of
various social-sustainability criteria (based on Balkema et al. 1998) will be discussed briefly for systems affected
by that criterion.
Techniques
1 Traditional storm drainage systems consist of inlet structures (inlets with gully-pots or catch-basins), and
drainage pipes which transport water to the nearest outfall. A number of ancillary structures may be included
in such systems, such as silt traps, storage tanks and controllable structures. This form of drainage is still the
most widely used technique. A distinction between combined and separate drainage systems (Escritt 1984)
needs to be made:
1(a) CSS: Combined sewer systems convey both wastewater (domestic/industrial) and storm runoff.
1(b) SSS: Separate sewer systems collect and convey the wastewater and runoff in separate
collection systems. This requires two parallel pipe systems.
3
Rainwater management techniques
Table 1: Input Requirements for Infiltration Systems
q [m/h]
AD [m2]
n [m3/m3]
i [m/h], D [h]
Infiltration
coefficient from
test. (> 0.001)
Area to be
drained
Porosity of fill
Intensity and
material (0.2 – 0.5) duration of
rainfall events
Ad [m2]
Drainage area
of infiltration
system
Click here to go to enlarged view
Table 2: Design Criteria of Permeable Block Pavement
Base Layer
Depth [mm],
Material,
Porosity
Top Layer (Filter) Pavement
Depth [mm],
Material,
Porosity
n/a, Porous Fill
Material, n/a
50-100, Filter or
Geotextile, n/a
Literature
Distance to
Source
Groundwaterlevel [m]
Porous
Macadam,
Concrete blocks
2 Infiltration and collection systems have been used in urban drainage for centuries, however they were
almost forgotten in the era of high urbanisation. These methods are now experiencing a renaissance and
are being increasingly used in the planning of new developments. Infiltration systems help break peak
runoff in sewer systems and can thus reduce overflow from combined systems. Extensive literature exists
in several countries (Watkins, 1995; Bettess 1996, Bettess et al. 1996, Hydro Research 1993; AGW 1991,
1996; AfU Luzern 1994; WEF 1998, ATV, 1997). Bettess et al. (1996) distinguish between plane infiltration
Bettess 1996
n/a
systems and 3-D infiltration systems. To design infiltration systems, the required inputs are listed in Table 1.
300, Coarse
100, Fine Graded Modular block,
>0.9
Gravel (3.5 – 5.0 Gravel (0.3 – 2.0 blocks of lattices
etc
cm), 0.3 – 0.4
cm), 0.2 – 0.3
WEF 1998
200-300, clean
stone (25-150
mm), 0.3-0.4
Leonard and
Sherriff 1992
50, geotextile,
50 mm
n/a; 50, gravel
Macadam, 80
15 - 25 mm; n/a mm concrete
block
The design procedures vary from country to country. The main requirement is the establishment of enough
n/a
storage for a specified storm event. Safety factors attempt to minimise risks and result in larger systems.
2(a) PP: Permeable pavement is used for surfaces on parking lots and residential roads. Permeable
macadam is also an option, but very expensive and tends to clog after 1 to 3 years. It also needs considerable
Click here to go to enlarged view
maintenance effort. Also in widespread use are lattices of blocks with the infiltration surface below the
load-bearing surface. In some countries, surface infiltration does not need any hydraulic design
Figure 1
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considerations when rainfall is infiltrated. Table 2 shows some guidelines in the selection of PP’s.
Table 3: Design Criteria of Infiltration Basins
Max depth [m] Distance to
Groundwaterlevel [m]
Layout
Vegetation
Literature
Source
0.3
Several small
basins instead of
one large
Grasses that will
survive prolonged
inundation
WEF 1998
>1.2
Click here to go to enlarged view
Table 4: Design Criteria of Swales
Minimum Min/Max Min÷Recom Max Flow Roughness Max Depth
k [m1/3s-1] of Flow
Velocity
m÷Max
Length [m] Bottom
Width [m] Slope [%]
[mm]
[ms-1]
5/4.17
75
WEF 1998
n/a
n/a
n/a
Bettess
1996
n/a
n/a
n/a
250-1000
Leonard,
(total depth) Sherriff
1992
< 6.0
< 0.5
n/a
n/a
30
0.6/2.4
0.5÷2.0÷6.0 <0.3
n/a
n/a
< 4.0 without berms
n/a
1
n/a
n/a
Literature
Source
FRPB 1995
2(b) IB: Infiltration basins (Figure 1) are allocated grassed areas that can be flooded at times of rain when
water can slowly drain into the ground. During dry weather intervals, the infiltration basins are empty and
can be used for other purposes. Table 3 shows some general design considerations. Bettess (1996)
suggests that attention should be paid in handling the soil, as this is important for the support of the plants
growing in the basin as well as the infiltration capacity. Plant selection and plant community according to
local microclimate is also an important issue. Cutting grass prevents shrub invasion.
2(c) Sw: Swales are grassed ditches, taking up runoff from roads or parking lots. The runoff slowly runs
through the grass swale and infiltrates into the ground. There is no stagnant water in a carefully designed
swale. Table 4 shows some design guidelines and their figures.
Click here to go to enlarged view
2(d) So: Soakaways or infiltration trenches (Figure 2) are underground structures, which normally are
circular shafts or trenches. They are filled with a gravel medium into which runoff is discharged. Circular
soakaways normally consist of precast concrete manhole elements filled with gravel. The concrete elements
Figure 2
Click here to go to enlarged view
4
often are solid on top and perforated at the bottom. However, this varies from guideline to guideline (AGW
Rainwater management techniques
1996; WEF 1998; Bettess 1996). Combinations of circular soakaways with trenches are used, and
soakaways can be linked which enlarges the infiltration area (Bettess 1996). Table 5 shows some design
Table 5: Design Criteria of Soakaways and Infiltration Trenches
Porosity of
Maximum
Filling [m3m-3] Depth
Layout
Configuration
Dist to Seasonal
High Groundwaterlevel [m]
Literature
Source
figures.
0.15÷0.30
f(Wall stability,
groundwaterlevel)
Long and Deep
>1.2
WEF 1998
3 Detection systems have been used to control runoff peaks and for treatment of combined-sewer overflows
n/a
3-6 m
Depth excavation < 3 *
depth to invert
of drain
Mention of
caution
Leonard and
Sherriff
1992
(CSO) for a number of years, usually at the outlet of a conventional system. However they are now
increasingly used for catchment management.
3(a) P: Ponds act as detention or retention structure where the rainfall runoff enters straight from the
drained surface. The pond also acts as a settlement structure. Any overflow from the pond can be directed
via an outlet structure, into a receiving watercourse, a soakaway, or drainage pipe. The pond can easily be
integrated into the landscaped surrounding of a new housing estate and can serve as a habitat for wildlife.
Table 6 shows some design data for a dry pond. Wet detention ponds also exist.
3(b) CW: Constructed wetlands can act as detention and purification ponds. They can also be used for
cleaning wastewater spilled through CSO’s. Table 7 shows some design data.
3(c) OR : On site retention systems may consist of grassed roofs or other roof areas where runoff can
temporarily be stored. These may be parking lots, sports grounds and other suitable areas.
Efficiency
For rainwater control systems efficiency of water quality control (qualitative efficiency) and the efficiency of
Click here to go to enlarged view
Table 6: Design Criteria of Ponds
Storage Volume
Layout
Basin Side
Slopes
Literature
Source
Capture volume + 20%
Expand from inlet,
contract toward outlet, top
stage 0.6 – 1.8 m deep,
bottom slope 2%; bottom
stage 0.5 – 0.9 m
< 4:1
WEF 1998
Detain storm runoff for
a few hours, capture of
first foul flush
Careful inlet and outlet
design to prevent
scouring, orifice control for
outlet
n/a
FRPB 1995
n/a
Off- and on-line detention
tanks, flow storage
n/a
Luker and
Montague 1994
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Table 7: Design Criteria of Constructed Wetlands
DWF depth
variation [m]
Wet weather storage
Open water
area
Length to
width ratio
Literature
Source
0.1 – 1.2
Design as detention
pond, surcharge
depth 0.6 m above
DWF depth,
drawdown 24 h
< 50 % total
wetland area
> 3:1, 2:1
recommended
WEF 1998
Click here to go to enlarged view
Figure 3
flood control (quantitative efficiency) were examined. The qualitative efficiency of these systems is assessed
with regard to the removal of suspended solids (SS) and heavy metals (HM) from the runoff.
Suspended Solids
Data from literature on removal efficiency of SS for the presented techniques are shown in Figure 3. The
minimum efficiency recorded in the literature for a certain technique is presented as ‘low’, while the highest
figures is presented as ‘high’. The following remarks concern each studied technique.
1(a) CSS: Depending on the inlet structure and the particle size, sediment traps need maintenance to be
efficient (Luker and Montague 1994; Bettess 1996)
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5
Rainwater management techniques
1(b) SSS: As above (Luker and Montague 1994; Bettess 1996)
2(a) PP: Removal efficiency is high and amounts to almost 100%, removal = f (infiltration media) (FRPB 1995)
2(b) IB: As above (FRPB 1995; Luker and Montague 1994)
2(c) Sw: Research restricted on lab conditions, no interaction between natural environment and sediment
studied (FRPB 1995; Deletic 1998; White 1987; Gray 1989; Escritt 1984)
2(d) So: As PP and IB (Mehler and Ostrowski 1998; FRPB 1995)
3(a) P: From low to very high, depending on design and hydraulic loading of ponds (Mehler and Ostrowski
1998; FRPB 1995; Bettess 1996; WEF 1998; Luker and Montague 1994). Long term wet detention pond
performance was found to be very good according to Maristany (1993), suggesting consistent removal
of particulate constituents.
3(b) CW: Most extensive data, removal efficiency depending heavily on hydraulic loading and hence
design of system (Bettess 1996; WEF 1998; Luker and Montague 1994; Knight et al. 1993; Sapotka and
Bavor 1994; Kadlec and Hey 1994)
3(c) OR: No data found, OR techniques are combination of different techniques, hence good removal
efficiency likely.
Heavy Metals
Other significant pollutants include heavy metals (HM). There is research on HM removal, but this is mainly for
heavily polluted runoff from special mining and industrial processes (Eger 1994). Data on removal of HM in
urban runoff can be found in Luker and Montague (1994) and FRPB (1995).
For all techniques, the removal efficiency is governed by design.
Maintenance is also crucial for the effective functioning of a technique. The performance of almost all techniques
with regard to SS removal can be improved by using sediment traps (AGW 1996) and generously designed
inlet structures (Ellis and Revitt 1991). It is not possible to draw from literature whether low performing techniques
were badly designed.
6
Rainwater management techniques
Land Use
The quantitative removal of storm water runoff in urban areas is determined by the design return period (RP)
storm, imperviousness of the catchment, slope of the catchment, the surface/underground on/in which the
technique will be applied, the vegetation cover, the use of the catchment and the available space. A simple
example is presented to illustrate the typical land use of each technique as a percentage of a newly developed
Table 8: Design Constraints BMP’s
site. A hypothetical catchment was located in Aberdeen. The parameters for the design storm were chosen for
the Aberdeen area (NERC 1974; Bettess 1996; Leonard and Sherriff 1992), and the site specifications were
1
adopted according to literature. The chosen site and storm characteristics are presented in Table 8.
Soil Type, k2 Dwelling
Type3
Runoff
coeff.3
Site
Rainfall
Event1
Aberdeen,
UK
10 Year RP Loamy sand, Detached,
0.45
0.3 m/h
Semidetached
Estate size
Distance
GWL
2 ha
2m
Bettess 1996, 2Data from AGW 1996; 3Data from Heierli 1991
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The following was assumed for each technique:
1(a) CSS: Assumed all underground structures under access roads
1(b) SSS: Assumed all underground structures under access roads
2(a) PP1: Permeable pavement with sub-grade material of porosity n = 0.325
2(a) PP2: Permeable pavement without subgrade material, hence porosity n = 1
2(b) IB: Infiltration basin with maximum water depth of 0.4 m
2(c) Sw: Swales with base width of 2.4 m, embankment slope of 1:4 and base slope of 0.5 %
2(d) So: Soakaway with filling material of porosity n = 0.35
3(a) P: Detention pond with length:width ratio 2:1
3(b) CW: Constructed wetland with length:width ratio 2:1
3(c) OR: Other retention measures with an average depth of 0.2 m
Using the recommendations from Bettess (1996), AGW (1996), WEF (1998), NERC (1974) and Leonard and
Figure 4
Sherriff (1994), the data on land use presented in Figure 4 were obtained. The figure shows that the detention
BMP techniques use most land. OR seems to be particularly problematic. However, if we take into account
that the OR techniques include roof and parking lot retention, allocation of new land for their construction
becomes less than for P and CW. Infiltration techniques are from a land-use point-of-view least problematic,
but they hardly contribute to amenity value.
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7
Rainwater management techniques
Table 9: Economic Aspects of Rainwater Management
Technique Capital Cost Operation & Environmental Remarks
Maintenance Benefit
costs
1(a) CSS
High
Low-Med
negative
***
1(b) SSS
High
Low-Med
negative
***
2(a) PP
High
High
positive
High maintenance costs,
sweeping. Also, may have a
limited life (10 years)
2(b) IB
High
Low-Med
positive
Require periodic
refurbishment.
2(c) Sw
Low-Med
Med
positive
Cost high when land has to
be acquired. Require
periodic refurbishment.
2(d) So
Med
Med
positive
High maintenance and
refurbishment costs.
Require periodic
refurbishment.
High
3(a) P
Low
Cost high due to land
acquisition, lower
maintenance costs, wet
ponds cheaper than drier
positive
3(b) CW
High
Med
positive
***
3(c) OR
Low-High
Low-High
positive
***
Economic Aspects
Economic comparisons exist in several CIRIA publications (Luker and Montague 1994; Bettess 1996). While
Luker and Montague valued the BMP’s for highway drainage only qualitatively, Bettess saw the necessity of
an appraisal of costs. He proposed to compare the prices of the conventional drainage system with the on-site
infiltration schemes. Costs for the conventional system include construction costs and enhancement of
downstream systems, whereas costs for infiltration systems comprise construction costs and lower enhancement
costs of downstream systems. Bettess also stresses the distinction between economic and financial appraisal.
Economic appraisal is often difficult, as many aspects cannot be measured in cash terms, such as the impact
of infiltration on groundwater levels. Financial appraisal concerns only the flow of money, which arises from
the system.
Table 9 shows a qualitative economic comparison of the various rainwater management techniques (based on
Click here to go to enlarged view
Figure 5
18
Luker and Montague 1994). It should be noted that such a comparison is inherently subjective and therefore
hard to generalise from. A qualitative assessment however does provide the means to balance conflicting
criteria.
16
14
McKissock (1999) gathered information on capital costs of rainwater control techniques. These are presented
in Figures 5 and 6.
12
10
8
6
4
2
0
1(a)
CSS
1(b)
SSS
2(a) 2(b)
PP
IB
2(c)
Sw
2(d)
So
3(a)
P
3(b) 3(c) Comb
CW OR
Click here to go to enlarged view
Social Aspects
The social science literature on of rainwater management is extremely limited and would clearly benefit from
further quantitative research. Nevertheless, some qualitative analysis can be helpful. The different criteria and
degree of interdependence are listed below:
Figure 6
800
• Social Acceptance of rainwater management systems will generally be high, as there is usually little
awareness of such systems. However, in the case of ponds, perceived safety to children might influence
700
600
500
400
acceptance, and thus deter their use (McKissock et al. 1997). Acceptance may be influenced by a perception
of flood risk for swales and infiltration basins, as they may be designed to flood public areas. Acceptance
300
200
100
0
1(a) 1(b) 2(a)
CSS SSS PP
2(b) 2(c) 2(d) 3(a)
IB
Sw
So
P
3(b) 3(c) Comb
CW OR
Click here to go to enlarged view
8
of constructed wetlands could be influenced if people have similar safety worries, or think there might be
a problem with insects. Perception of tighter land use control may also influence acceptance (WEF 1998)
Rainwater management techniques
• The added Amenity Value of a rainwater management system will depend largely on how well landscaped
the systems are (e.g. how much involvement landscape architects have). In a recent study where a range
of people involved with BMP’s were questioned, it was found that only 12% believed that runoff control
could have amenity objectives (McKissock et al. 1997). Houses that are built near to water tend to be
preferred by the public. Emmerling-DiNovo (1995) found that the residents in her study valued wet detention
basins significantly higher than dry detention basins. EPA (1995) found that well designed runoff controls
can provide significant economic benefits in the form of increased property values.
• Community Participation is important, especially for those systems that might affect the amenity and
landscape value of an area. People tend to be especially concerned about landscape changes that might
affect the value of their property (EPA 1995). However, public education is a prerequisite to public
participation (see WEF 1998; Pateman 1970).
• Awareness of rainwater management systems is generally rather low. Educational interventions are
required to increase awareness, such as storm drain stencilling (this is where community groups stencil
slogans on storm drains or nearby signs, such as “when you rubbish the streets, you rubbish the river”
(Melbourne Water 1997) which makes potential polluters aware of the connection between the drain and
the river.
• Institutional Requirements will vary from site to site, depending on the size of the development in
question and the land availability. By and large, however, the developer will be responsible for providing
the land, meeting the capital costs, and landscaping costs of BMP’s. Legal arguments around who is
responsible for long term maintenance are common (Maxwell 1997). Lack of guidance, rather than general
ignorance seems to be the cause of a lack of uptake of BMP’s by developers, who prefer to stick to
traditional drainage structures (McKissock et al. 1997). Monitoring of discharge standards will require the
same institutional involvement (from the relevant environmental protection agency) for each of the different
systems.
• Local Development potential of the different systems will depend largely on who is responsible for
installation and maintenance (i.e. are local people employed).
9
Rainwater management techniques
There is potential for Stimulation of Sustainable Behaviour, especially for ponds and wetlands, to which
visits could be incorporated into school curricula. Various examples exist in Australia of such educational
programmes (e.g. Melbourne Water 1997)
Reference
1.
AfU, Amt für Umweltschutz Luzern (1994) Versickerung und Retention im Liegenschaftsbereich. Kantonales Amtfür
Umweltschutz Luzern.
2.
AGW, Amt für Gewässerschutz und Wasserbau (1991) Retention und Versickerung von Meteorwasser im Liegenschaftsbereich.
Baudirektion des Kantons Zürich.
3.
AGW, Amt für Gewässerschutz und Wasserbau (1996) Today Amt für Wasser, Energie und Luft des Kantons Zürich (AWEL),
Die Versickerung von Regenabwasser auf der Liegenschaft, Baudirektion des Kantons Zürich.
4.
ATV (Abwassertechnische Vereinigung e.V.) (1997) Versickerung von Regenwasser, Gesellschaft zur Förderungder
Abwassertechnik, Hennef.
5.
A.J. Balkema, S.R. Weijers, F.J.D. Lambert, On Methodologies for Comparison of Wastewater Treatment Systems with Respect
to Sustainability, Proc. of Conference ‘Options for closed water systems’, Wageningen, the Netherlands, 1998.
6.
R. Bettess Infiltration Drainage, Manual of Good Practice, CIRIA Report 156, London, 1996
7.
R. Bettess, A Davis and D Watkins Infitration Drainage – Hydraulic Design, CIRIA Project Report 23, London, 1996.
8.
A Deletic ‘The First Flush Load of Urban Surface Runoff’, Water Research, 1998, 32(8), 2462 - 2470.
9.
J. Ellis, D. Revitt Drainage from Roads: Control and Treatment of Highway Runoff, National Rivers Authority, Reading, 1991.
10. C. Emmerling-DiNovo, Stormwater Detention Basins and Residential Locational Decisions, Water Resources Bulletin, 1995
31(3), 515-521.
11. EPA (U.S. Environmental Protection Agency) (1995) Economic Benefits of Runoff Controls,
website: http://www.epa.gov/owowwwtr1/NPS/runoff.html.
12. L.B Escritt Sewerage and Sewage Treatment, Wiley Interscience Publication, Chichester 1984.
13. FRPB (Forth River Purification Board) (1995) A Guide to Surface Water Best Management Practices, Edinburgh.
14. N.F. Gray Biology of Wastewater Treatment, Oxford Science Publications, Oxford, 1989.
15.
P. Harremo_s Integrated Water and Waste Management, ‘Water Science Technology’ 1997, 35(9), 11-20.
16. R. Heierli Lecture notes: Überblick über die Abwassertechnik, Swiss Federal Institute of Technology, Zürich, 1991.
17. Hydro Research Urban Drainage – The Natural Way, Hydro Research and Development Ltd, Clevedon, 1993, UK,
10
Rainwater management techniques
18. O.J Leonard J.D.F Sherriff Scope for Control of Urban Runoff: Guidelines, CIRIA Report 124, Vol 3, 1992 London.
19. K. Luker M, Montague Control of Pollution from Highway Drainage Discharges, CIRIA Report 124, 1994 London.
20. A.E. Maristany Long Term Performance of Wet Detention Ponds, Water Management in the 90’s, Proc. of the 20th Anniversary
Conference, Editor: Hon K, ASCE, 1993.
21. J. Maxwell Scotland’s First “BEST MANAGEMENT PRACTICE” Surface Water Treatment: The Developers Perspective, Proc. of
an Engineering Foundation conference ‘Sustaining Urban Waters in the 21st Century’, Malmo, 1997, Sweden..
22. G. McKissock, University of Abertay Dundee, Personal communication, June 1999.
23. G. McKissock , C Jeffries C, B. D’Arcy An Assessment of rainage Best Management Practices in Scotland, CIWEM, 1997 13(1), 47 – 51.
24. R. Mehler, M.W. Ostrowski, Comparison of the Efficiency of Best Stormwater Management Practices in UDS, Proc. of the Fourth
International Conference on Development in Urban Drainage Modelling, UDM ’98, London, Eds. D. Butler & _. Maksimovi_, 1998
25. Melbourne Water (1997) Website: http://www.greenweb.com.au/melbwater/html/drains_to_the_ bay.html.
26. NERC Flood Studies Report, Publisher: Natural Environment Research Council. 1974 London
27. R Otterpohl, A Albold, M Grottker Integration of Sanitation into Natural Cycles: A New Concept for Cities, Environmental Research
Forum Vols. 5-6, Editors: Etnier C, Staudenmann J, Schönborn A, Transtec Publications, 1996 Switzerland.
28. C. Pateman Participation and Democratic Theory, (970 Cambridge, Cambridge University Press.
29. Tages-Anzeiger (1995) Was ist Nachhaltigkeit?, Tages-Anzeiger, edition of Wednesday, 21. September 1995. Zürich.
30. D.C. Watkins Infiltration Drainage – Literature Review. CIRIA Project Report 21. 1995 London.
31. WEF (Water Environment Federation) (1998) Urban Runoff Quality Management, Alexandria, USA.
32. J.B. White Wastewater Engineering, Third Edition, Edward Arnold, 1987.
11
Rainwater management techniques
Table 1: Input Requirements for Infiltration Systems
q [m/h]
AD [m2]
Infiltration
coefficient from
test. (> 0.001)
Area to be Porosity of fill
Intensity and
drained
material (0.2 – 0.5) duration of
rainfall events
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12
n [m3/m3]
i [m/h], D [h]
Ad [m2]
Drainage area
of infiltration
system
Rainwater management techniques
Table 2: Design Criteria of Permeable Block Pavement
Base Layer
Depth [mm],
Material,
Porosity
Top Layer (Filter) Pavement
Depth [mm],
Material,
Porosity
Literature
Distance to
Source
Groundwaterlevel [m]
n/a, Porous Fill
Material, n/a
50-100, Filter or
Geotextile, n/a
n/a
Porous
Macadam,
Concrete blocks
Bettess 1996
300, Coarse
100, Fine Graded Modular block,
>0.9
Gravel (3.5 – 5.0 Gravel (0.3 – 2.0 blocks of lattices
etc
cm), 0.3 – 0.4
cm), 0.2 – 0.3
WEF 1998
200-300, clean
stone (25-150
mm), 0.3-0.4
Leonard and
Sherriff 1992
50, geotextile,
50 mm
n/a; 50, gravel
Macadam, 80
15 - 25 mm; n/a mm concrete
block
n/a
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13
Rainwater management techniques
Figure 1
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14
Rainwater management techniques
Table 3: Design Criteria of Infiltration Basins
Max depth [m] Distance to
Groundwaterlevel [m]
Layout
Vegetation
Literature
Source
0.3
Several small
basins instead of
one large
Grasses that will
survive prolonged
inundation
WEF 1998
>1.2
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15
Rainwater management techniques
Table 4: Design Criteria of Swales
Minimum Min/Max Min÷Recom Max Flow Roughness Max Depth
k [m1/3s-1] of Flow
Velocity
m÷Max
Length [m] Bottom
Width [m] Slope [%]
[mm]
[ms-1]
16
5/4.17
75
WEF 1998
n/a
n/a
n/a
Bettess
1996
n/a
n/a
n/a
250-1000
Leonard,
(total depth) Sherriff
1992
< 6.0
< 0.5
n/a
n/a
30
0.6/2.4
0.5÷2.0÷6.0 <0.3
n/a
n/a
< 4.0 without berms
n/a
1
n/a
n/a
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Literature
Source
FRPB 1995
Rainwater management techniques
Figure 2
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17
Rainwater management techniques
Table 5: Design Criteria of Soakaways and Infiltration Trenches
Maximum
Porosity of
Filling [m3m-3] Depth
Dist to Seasonal
High Groundwaterlevel [m]
Literature
Source
0.15÷0.30
f(Wall stability,
groundwaterlevel)
Long and Deep
>1.2
WEF 1998
n/a
3-6 m
Depth excavation < 3 *
depth to invert
of drain
Mention of
caution
Leonard and
Sherriff
1992
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18
Layout
Configuration
Rainwater management techniques
Table 6: Design Criteria of Ponds
Storage Volume
Layout
Basin Side
Slopes
Literature
Source
Capture volume + 20%
Expand from inlet,
contract toward outlet, top
stage 0.6 – 1.8 m deep,
bottom slope 2%; bottom
stage 0.5 – 0.9 m
< 4:1
WEF 1998
Detain storm runoff for
a few hours, capture of
first foul flush
Careful inlet and outlet
design to prevent
scouring, orifice control for
outlet
n/a
FRPB 1995
n/a
Off- and on-line detention
tanks, flow storage
n/a
Luker and
Montague 1994
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19
Rainwater management techniques
Table 7: Design Criteria of Constructed Wetlands
DWF depth
variation [m]
Wet weather storage
Open water
area
Length to
width ratio
Literature
Source
0.1 – 1.2
Design as detention
pond, surcharge
depth 0.6 m above
DWF depth,
drawdown 24 h
< 50 % total
wetland area
> 3:1, 2:1
recommended
WEF 1998
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20
Rainwater management techniques
Figure 3
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21
Rainwater management techniques
Table 8: Design Constraints BMP’s
1
Rainfall
Event1
Aberdeen,
UK
10 Year RP Loamy sand, Detached,
0.45
0.3 m/h
Semidetached
Bettess 1996, 2Data from AGW 1996; 3Data from Heierli 1991
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22
Soil Type, k2 Dwelling
Type3
Site
Runoff
coeff.3
Estate size
Distance
GWL
2 ha
2m
Rainwater management techniques
Figure 4
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23
Rainwater management techniques
Table 9: Economic Aspects of Rainwater Management
Technique Capital Cost Operation & Environmental Remarks
Maintenance Benefit
costs
1(a) CSS
High
Low-Med
negative
***
1(b) SSS
High
Low-Med
negative
***
2(a) PP
High
High
positive
High maintenance costs,
sweeping. Also, may have a
limited life (10 years)
2(b) IB
High
Low-Med
positive
Require periodic
refurbishment.
2(c) Sw
Low-Med
Med
positive
Cost high when land has to
be acquired. Require
periodic refurbishment.
2(d) So
Med
Med
positive
High maintenance and
refurbishment costs.
Require periodic
refurbishment.
3(a) P
High
Low
positive
Cost high due to land
acquisition, lower
maintenance costs, wet
ponds cheaper than drier
3(b) CW
High
Med
positive
***
3(c) OR
Low-High
Low-High
positive
***
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24
Rainwater management techniques
18
16
14
12
10
8
6
4
2
0
1(a) 1(b) 2(a) 2(b) 2(c) 2(d) 3(a) 3(b) 3(c) Comb
CSS SSS PP
IB
Sw
So
P
CW OR
Figure 5
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25
Rainwater management techniques
800
700
600
500
400
300
200
100
0
1(a) 1(b) 2(a) 2(b) 2(c) 2(d) 3(a) 3(b) 3(c) Comb
CSS SSS PP
IB Sw So
P
CW OR
Figure 6
26
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