Across the world millions of slum residents suffer the hazards and misery of frequent flooding of their streets and homes. How can we define the performance of a storm drainage system? What should it be designed to cope with? How can a community judge whether a system has improved residents’ lives?

A report from the World Bank and Imperial College explores the development of performance indicators for urban storm drainage. The field of producing indicators is still quite new and the authors stress that indicators reflect a trade-off between validity in representing performance, ease of measurement and utility in making decisions.

Interviews with slum residents in Indore, India indicate that they see flooding as an inevitable consequence of living in areas with advantages such as low rent and proximity to livelihoods. Residents say that drainage would be less of a problem if flooding occurred less often, affected fewer houses, was shallow and slow rather than deep and fast and was over quicker. They value predictability, to give them time to put coping strategies into action. Engineers, however, are not equipped to measure such a complex objective as ‘predictability’.

Engineering textbooks define ‘performance’ in terms of the frequency of flooding rather than the impact it has on the lives of those affected. Disruption caused by a centimetre of flooding above a single stretch of road for five minutes is not as grave as 30 centimetres of water sitting on the surface for six hours even if both types of event are reported to occur ten times a year.

Techniques engineers can use include:

• carrying out participatory evaluations to find worst-affected areas: leading questions should be avoided and interviewers should start by asking about the previous year’s flooding rather than a general question about the heights floods can reach
• using pre-painted rulers coated with chalk on poles or walls for useful comparisons between storms: although they require reading and re-painting after each storm, they are an invaluable check on the validity of computer models for drainage performance
• using pressure transducers connected to data recording equipment to get complete data on flood depths: however, they are too expensive and complex for routine use in low-income communities
• observing the degree of inlet blockage on kerbs and gutters and the solids in open drains; typically the mean weight of each object clogging poor countries’ drains is ten times that of the UK.

The study reminds planners that:

• Process indicators that describe the state of the drainage system can be more practical than performance indicators.
• Links between performance and decisions are often unclear.
• While the idea of indicators is appealing, it does not follow that good indicators exist for all aspects of performance.
• They should think how indicators will be used before undertaking monitoring – often far more data is collected than can ever be used.
• Performance indicators do not measure performance, or success in promoting values, but are a substitute for performance measurement.

Source(s):
‘Performance indicators for urban storm drainage in developing countries’ by P. Kolsky and D. Butler, Urban Water 4, pp 137-144, 2002
‘Solids size distribution and transport capacity in an Indian drain’ by P. Kolsky and D. Butler, Urban Water 2, 4, pp 357-362, 2000
‘Modelling drainage performance in the slums of developing countries: how good is good enough?’ by P. Kolsky, D. Butler, S. Cairncross and U. Blumenthal, Water Science and Technology 39, 9, 285-292, 1999

Funded by: DFID R5477A

id21 Research Highlight: 4 March 2004

Further Information:
Pete Kolsky
Senior Water and Sanitation Specialist
Water and Sanitation Program
Mail Stop F4K-407
World Bank
1818 H Street NW,
Washington DC 20433

Tel: +1 (202) 473 5764
Fax: +1 (202) 522 3228
Contact the contributor: pkolsky@worldbank.org

World Bank

David Butler
Imperial College London
South Kensington Campus
London SW7 2AZ
UK

Tel: +44 (0) 207 594 6099
Fax: +44 (0) 207 594 6144
Contact the contributor: d.butler@imperial.ac.uk

Imperial College London, UK

Other related links:
'Disasterproofing: reducing the impact of natural disasters'

Flood disasters in India’s West Bengal: are roads and railways to blame?

'Stimulating innovative performance and supporting world bank operations in water management' World Bank report

Report on an urban drainage workshop in Uganda