Plain,
sloping roofs can collect up to 50% more rainwater than flat roofs
with gravel. This water is also of higher quality. These are the
conclusions of a study conducted by researchers from Autonomous
University of Barcelona (UAB, Spain) which suggests the incorporation
of systems to collect rainwater in urban planning. The water
collected can be used to water streets and gardens, wash floors or
vehicles and fill cisterns.
Ramon
Farreny
UAB
Co-Author
 "It
is important to consider the collection of rainwater when planning
and designing cities, as this is an alternative water source with
many different uses, it can even be used to save drinking water. One
such project, published in the journal Water Research, indicates that
roofs "are the first choice for collecting rainwater in urban
areas, but not all roofs function in the same way and it is necessary
to select the most appropriate ones."Farreny explains: "The
inclusion of criteria related to the slope and roughness of roofs in
urban planning may be useful in promoting the harvesting of rainwater
as an alternative water source. This could also contribute to
preventing flooding and water shortages."
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The
results show that plain, sloping roofs, such as those made of metal
or plastic, make it possible to collect up to 50% more rainwater than
flat, rough ones. The information was obtained between 2008 and 2010
using four types of roofs on the university campus: three sloping
roofs (tiled with metal and polycarbonate sheets) and one flat gravel
roof.
To
analyse the information, the authors developed a model which
estimates the runoff volume (quantity of water that runs over a
surface) and initial losses of each roof which were greater in the
gravel roof, due to its roughness.
Water
obtained from the sloping roofs was better in terms of physical and
chemical quality compared to the water collected from the gravel
roof. This can be seen in practically all the parameters
(conductivity, total organic carbon and carbonates). In the water
from gravel roofs, greater meteorisation, depositioning of particles
and colonisation by plants were observed.
According
to the study, the results are of "importance" for local
governments and urban planners in designing buildings and cities from
the perspective of sustainable rainwater management. With the
appropriate filtering and treatment, the resulting water can be used
to wash floors and vehicles, water gardens, streets and even for
filling cisterns or washing machines.
Making
the most of this resource requires the installation in buildings of a
collection and filtering system, pipes and tanks that should be
separate from the drinking water system, to prevent the risk of cross
contamination. Installations of this kind are being tested on the
university campus, and in pilot projects promoted by some local
governments, such as Barcelona City Council.
Tito
Morales-Pinzón
Author
of the study
Researcher
at UAB and
Pereira Technological University (Colombia)
 "However,
the costs and environmental impact of these systems have yet to be
assessed, because although one material may be efficient in
collecting or storing the rainwater, it may also be too expensive or
cause contamination. Under the Water Framework Directive, local water
prices will increase to include the real supply costs and this could
lead to an interest in rainwater-collection strategies from the
economic point of view.”
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The
team has evaluated the most 'cost-effective' strategy for collecting
rainwater in a estate of the town of Granollers in the province of
Barcelona, as an example of a densely populated urban environment
(600 inhabitants/ha) in the Mediterranean area and an average
rainfall of 650 mm per year.
The
results of this study, published in the journal Resources,
Conservation and Recycling, show there are doubts about the economic
feasibility of this type of project considering current water rates.
However if the price reached €1.86/m3 it could be profitable.
Regarding
the environmental impact of these systems, scientists from the team
have conducted a third study which shows that the best
infrastructures are those which have a covered rainwater tank on the
roof.
The
conclusions, published in The International Journal of Life Cycle
Assessment, also recommend including these rainwater devices in urban
planning, but adapting the design to the purpose intended for the
water. This would prevent subsequent impacts in building renovation.
Source:
Plataforma SINC
Journal
References:
Ramon
Farreny, Tito Morales-Pinzón, Albert Guisasola, Carlota Tayà, Joan
Rieradevall, Xavier Gabarrell. Roof selection for rainwater
harvesting: Quantity and quality assessments in Spain. Water
Research, 2011; 45 (10): 3245 DOI: 10.1016/j.watres.2011.03.036
R.
Farreny, X. Gabarrell, J. Rieradevall. Cost-efficiency of rainwater
harvesting strategies in dense Mediterranean neighbourhoods.
Resources, Conservation and Recycling, 2011; 55 (7): 686 DOI:
10.1016/j.resconrec.2011.01.008
Sara
Angrill, Ramon Farreny, Carles M. Gasol, Xavier Gabarrell, Bernat
Viñolas, Alejandro Josa, Joan Rieradevall. Environmental analysis of
rainwater harvesting infrastructures in diffuse and compact urban
models of Mediterranean climate. The International Journal of Life
Cycle Assessment, 2011; DOI: 10.1007/s11367-011-0330-6
EXPERTS RECOMMEND THE INCLUSION OF RAINWATER-COLLECTION SYSTEMS IN CITIES - WATERWAYS NEWS - 20 NOVEMBER 2011
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