Low Impact Thinking of the Spongy City Construction in Built-Up Areas from the Perspective of Sustainable Urban Design

Sponge city construction can improve cities’ ability to adapt to the environment change and the ability to cope with floods, and it can also prompt cities’ development to be more healthy and sustainable. However, the process itself of sponge city construction may also has impact on the environment especially in built-up areas, to reduce the impact, the rainwater landscape design needs to integrate sustainable thoughts as follows: (1) balancing earthwork on site. Borrowing the traditional Chinese concept of "dig lake and pile mountain", providing earthwork balance on site by adjusting the micro-topography. (2) Protecting trees and bushes on site. When introducing bio-retention ponds to the built-up area with new plants which will be drought-resistant and wet-resistant, perennial, and with low maintenance, the designers need to think about how to protect and rearrange the existing plants especially trees and bushes at the same time which are relatively stable and mature in green spaces of old town. (3) Recycling the existing paving materials. Impermeable paving material on sidewalk, square, pedestrian area, parking area, etc. will be replaced by permeable concrete, permeable bricks, gravel, other permeable materials, and waterway kerbs. These abandoned materials could be recycled on site, such as use of the old concrete slabs, bricks building short stone walls to divide space or seats for people to rest, and it will reduce a lot of construction waste and avoid the pollution of new material consummations to the environment. (4) Taking the opportunity of spongy city construction to improve urban non-motor vehicle traffic environment, raising bike lanes along roads outside blocks and small roads inside blocks with permeable asphalt to improve walking and biking environment in cities. (5) Making public open spaces such as squares and green spaces support more staying activities with the opportunity of introducing rain garden to these areas. This is a kind of sustainable urban design point of view. Following the principle of minimum energy and material consumption and reducing the impact of sponge city construction itself on the environment will avoid a new round of environmental problems and resource waste. It has important significance to the construction of ecological city.