Landscape elements as a basis for integrated water management

Abstract

Water scarcity and flooding associated to climate variability and poor water use efficiency affect the liveability of our cities and their water security in the long term. As advocated by the Integrated Water Management (IWM) model, a transition towards arrangements that, besides centralized water infrastructures, also include onsite and efficient organization of water flows is required. A Landscape Elements Water Management Strategy (LEWMS) has been outlined to immediately guide the exploration of potential source control solutions for the recurrent spatial elements of a given urban landscape (roofs, gardens, parks, etc.) and the result of their reiteration at the catchment level. In the LEWMS, spatial configurations, water flow patterns and stakeholder’s arrangements generated by the spread of different decentralized options are drawn up to allow their comparison. Tested in the Brussels-Capital Region (BCR), the analysed macro effects of micro-scale landscape-based practices are gaining the attention of the local institutions.

Keywords:

• Integrated water management
• water sensitive urban design
• best management practices
• catchment management
• landscape elements

Acknowledgements

The author would like to thank Sybrand Tjallingii, Luisa Moretto, and the reviewers of previous drafts of this paper for their useful advice and suggestions. Gratitude is extended to Simone Conz for his kind support essential for the elaboration of GIS data.

Notes

1. The estimation of the average tank’s capacity is based on the graphic from IBGE-BIM (2010) providing the size of the tank per the ratio between the effective surface area of the roof (m²) and quantity of rainwater used (l/day). To prevent the tank remaining empty in more than 3% of cases, a maximum capacity of 4.5 m³ is required when the roof surface is just sharp to the snap of 17.5 m². Due to decreasing ratios, the capacity reduces while approaching the next snap.

2. Although a number of apartments can correspond to a single roof (e.g., high-rise buildings), in this demonstrative exploration, the amount of dwellers in a building benefitting from rainwater for cleaning and washing is limited by the amount of rainwater that, according to its surface, the roof intercepts.

3. Based on data recorded between 1898 and 2003, Brouyaux and Tricot (2006) estimated that the cumulative rainfall related to storm events of 10 days’ duration and 200 years return time amounts to 148 mm.

4. The formula used to compute is , where c are the classes displayed in Figure 4a, w is the overall yearly use of rainwater for washing and cleaning of each class, u is the number of household units of the same class. For example, for c = 1: w₁ is the average demand of water for washing and cleaning per person per day (25 litres) multiplied by the number of persons of the class 1 (2) and the number of days per year (365); u₁ is the number of units of the class 1 (16,842).

5. This simplified estimation does not take into account the overflow due to storm events with a duration longer than 10 days nor other variables such as evapotranspiration rate. Hence, the amount of rainwater potentially detained in the soft public spaces and that infiltrating from the infiltration-prone public spaces are obtained by multiplying their respective overall surface (s) (see Figure 4b) by the average annual precipitation (p): s ⋅ p.