GAR 2015 Main Report

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Box 11.2 The influence of urban layout on sustainability and flood risk

For any given set of social and economic requirements, there is always an optimum urban layout. Different urban layouts have vastly different percentages of land utilization and unit circulation lengths (Caminos and Goethert, 1978

Caminos, Horacio and Reinhard Goethert. 1978,Urbanization Primer: Project assessment, site analysis, design criteria for site and services of similar dwelling environments in developing areas, Collection of photographs on urbanization. MIT Press.. .

). This affects both the initial cost of urbanization as well as its future sustainability. Given that the costs of circulation and storm drainage are normally five times the cost of electricity and street lighting and 18 times the cost of water supply, adopting an efficient urban layout directly influences the local government’s capacity to provide and maintain this basic element of flood risk-reducing infrastructure (ibid.).

Studies have found that the cost of infrastructure networks per hectare, including storm drainage in a typical modern suburban layout with square plots (see Figure 11.4), is approximately double the cost of an efficient grid layout with rectangular plots. At the same time, the proportion of land required for roads in the suburban layout is 38 per cent, compared to 21 per cent in the grid layout. Thus the suburban layout nearly doubles the area of impermeable paved surfaces, which in turn has critical implications for storm run-off. The length of roads per hectare in the suburban layout is approximately double that in the grid layout, meaning that services such as waste disposal and product delivery have to travel twice the distance to achieve the same result, increasing both costs and carbon emissions. In addition, the wasteful use of land means that there is less safe, well-located land that could be made available for low-income housing.

The implication is that an efficient layout reduces the cost of land per inhabitant by making more efficient use of that land. It also dramatically lowers the cost of installing and maintaining infrastructure, particularly storm drainage, which has a critical impact on the capacity of local governments and utility providers to provide such infrastructure. Moreover, efficient layouts decrease the impermeable paved area, mitigating flood hazard, and they shorten the distance that vehicles have to travel to provide basic services. Unfortunately, the influence of urban layout on these factors is too often ignored, even in low-income countries. This increases costs for both residents and their local governments, reduces sustainability, increases flood risks and contributes to climate change.

Figure 11.4 Urban layouts

(Source: Google Earth.)

	217 Box 11.2 The influence of urban layout on sustainability and flood risk For any given set of social and economic requirements, there is always an optimum urban layout. Different urban layouts have vastly different percentages of land utilization and unit circulation lengths (Caminos and Goethert, 1978 x Caminos, Horacio and Reinhard Goethert. 1978,Urbanization Primer: Project assessment, site analysis, design criteria for site and services of similar dwelling environments in developing areas, Collection of photographs on urbanization. MIT Press.. . ). This affects both the initial cost of urbanization as well as its future sustainability. Given that the costs of circulation and storm drainage are normally five times the cost of electricity and street lighting and 18 times the cost of water supply, adopting an efficient urban layout directly influences the local government’s capacity to provide and maintain this basic element of flood risk-reducing infrastructure (ibid.). Studies have found that the cost of infrastructure networks per hectare, including storm drainage in a typical modern suburban layout with square plots (see Figure 11.4), is approximately double the cost of an efficient grid layout with rectangular plots. At the same time, the proportion of land required for roads in the suburban layout is 38 per cent, compared to 21 per cent in the grid layout. Thus the suburban layout nearly doubles the area of impermeable paved surfaces, which in turn has critical implications for storm run-off. The length of roads per hectare in the suburban layout is approximately double that in the grid layout, meaning that services such as waste disposal and product delivery have to travel twice the distance to achieve the same result, increasing both costs and carbon emissions. In addition, the wasteful use of land means that there is less safe, well-located land that could be made available for low-income housing. The implication is that an efficient layout reduces the cost of land per inhabitant by making more efficient use of that land. It also dramatically lowers the cost of installing and maintaining infrastructure, particularly storm drainage, which has a critical impact on the capacity of local governments and utility providers to provide such infrastructure. Moreover, efficient layouts decrease the impermeable paved area, mitigating flood hazard, and they shorten the distance that vehicles have to travel to provide basic services. Unfortunately, the influence of urban layout on these factors is too often ignored, even in low-income countries. This increases costs for both residents and their local governments, reduces sustainability, increases flood risks and contributes to climate change. Figure 11.4 Urban layouts (Source: Google Earth.)	Page 1 Page 10 Page 20 Page 30 Page 40 Page 50 Page 60 Page 70 Page 80 Page 90 Page 100 Page 110 Page 120 Page 130 Page 140 Page 150 Page 160 Page 170 Page 180 Page 190 Page 200 Page 207 Page 208 Page 209 Page 210 Page 211 Page 212 Page 213 Page 214 Page 215 Page 216 Page 217 Page 218 ->Page 219 Page 220 Page 221 Page 222 Page 223 Page 224 Page 225 Page 226 Page 227 Page 228 Page 229 Page 230 Page 231 Page 240 Page 250 Page 260 Page 270 Page 280 Page 290 Page 300 Page 310