The Urban Project as an Incremental Operation Part 2 Project 2002 Juan Patricio Poblete Pontifical Catholic University of Chile Santiago | Chile Rainwater Park: An Incremental programme for Cerrillo’s Bicentennial’s Masterplan The celebration of the bicentennial of the independence has originated a series of urban Government initiatives the most important of which is the conversion of a former airfield into a model urban sector. Cerrillo’s 245 ha aerodrome is the biggest, single ownership, vacant site within Santiago’s Metropolitan Urban Area (15 minutes to downtown). The airfield has been surrounded by low-density settlements (U$ 197 monthly income media) in a process that has triggered its functional obsolescence. The removal of the main international operations to a new airport in 1967 settled the fate of the site.The scheme complies with the guidelines of an international ideas competition organized by the housing ministry which state a compulsory use of 30 % of the site as public areas .Its strategy combines this requirement with the programme of a rainwater infrastructure linking this way diverse requirements and obtaining by means of this operation increased resources .The scheme is devised as a small size intervention which can promote further developments.Stretching along the lowest elevation of the site a public park catches the increased amount of surface rainwater taking care of the expected urbanization of the area .Its water collecting capacity also solves the problem of local floods. The water park comprises a series of ponds and lagoons based on a modular dimension of 140 x 20 meters. Its layout follows an orientation 16 degrees north west that is set by an equation between the topography of the terrain and its predominant slope of 1,5 %. This way an average water storage depth of 5 centimetres is attained. In so far as a large scale prediction of very complex urban scenarios, the master plan is a discredited instrument: much of the best urban discourse research and design of the recent decades has revolved around alternative modes of urban design. The studio assumed a progressive emergence of the urban project as represented by the principle of incremental occupation. Students had to discern from the site, the city, and their knowledge about the urban project, such clues for a first occupation of the site as to guarantee an efficient possession of the site, open enough to invite multiple interventions and enlightened enough to stimulate unforeseen developments in the future.The first occupation could be seen then as a combination of certain key projects intent on opening the site to urban use and the possibility of the ample spaces as a commons.Patricio´s scheme draws its fundamental clues from environmental considerations .The site is seen as an important urban resource for the management of rainwater. Such task is combined with the amenities of an urban park, a water park that behaves quite differently in each season registering the weather patterns that characterize this semi arid region where rain falls copiously only during a short period of winter. Rain replenishes the various water basins, many of which are designed such as to devolve rainwater to the soil slowly. Thus water contracts or expands within the scheme.Large and idiosyncratic enough to leave an urban imprint in the plan of Santiago, the water park becomes a new urban reference, meeting in equal terms a demand for leisure spaces and the betterment of the environmental behavior of the city’s basin.