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What are sponge cities?

Simply put, a sponge city "is a city that is designed to passively absorb, clean and use rainfall in an ecologically friendly way that reduces dangerous and polluted runoff".

Sponge cities not only reduce the risks of flooding but allow for water to be used within the cities and to be filtered back into the ground under the cities. As the effects of climate change become more prevalent, the need to manage our freshwater resources becomes more urgent. Rapid urbanization and increasing city populations put strain on currently water management systems leading to water shortages and a need for quick alternative water sources such as aquifers and underground springs. Draining groundwater isn’t a viable solution as it takes millions of years for groundwater to be replenished to adequate usage levels once it is gone. Using groundwater also poses a risk to the infrastructure of cities, as the probability of sinkholes and shifting earth is greater due to there now being a space where the water used to be.

In traditional cities the ground is covered with concrete and tar, and all rain water is funnelled into gutters and stormwater pipes which take the water away. The ground beneath cities doesn’t get any rainfall as the natural water absorption system is blocked by roads and buildings. This means cities get hotter and the ground gets drier. Berlin has started changing how its city manages rainwater and China wants 20% of their urban areas to have sponge features by 2020.

Incorporating green spaces, green roofs, blue spaces (ponds and rivers), swales and new drainage systems into cities will allow water to be absorbed naturally and evaporation will help to cool the cities. Sustainable management and storage of stormwater will allow water scarce cities to supply water without negatively affecting the immediate environment around the city. The benefits of sponge cities include clean water for the city to use, cleaner groundwater, reduced flooding and reduced strain on drainage systems.

Urban farming is a wonderful use of green spaces in sponge cities as it not only provides the green space but it also feeds the local community and creates jobs. Our Urban Farming project is situated in the heart of Cape Town and has grown into one of the best organic markets in the city.

Yours,
The Good Hope Volunteer Team

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