The Urban Hydrologics approach considers all urban surfaces as an interconnected network that receives, captures, detains, and conveys rainwater from the top of roofscapes and façade surfaces down to the ground level and ultimately to downstream waterways and river corridors. This reinterpretation and redefinition of the city as not a series of objects but of a series of surfaces defines the Urban Hydrologics approach. Each surface has a role to play in managing rainwater on it’s way to rivers and streams – giving light to the phrase – “your building is the river” UHS, 2015. This idea concept was articulated by Pedro Santa during explanations of the Urban Hydrologics approach to diverse contacts in tropical cities.

Each surface of the city plays a role in modulating runoff flow rates and attenuation. Hardscape surfaces and smooth urban manmade surfaces speed up runoff as there’s less roughness coefficient and a higher runoff coefficient. Hardscape surfaces also completely eliminate the infiltration into the soil and force surface flows to move to lower elevations, towards discharge points, inlets, and outlets. Green surfaces, on the other hand, do the opposite. When a building is retrofitted or designed to incorporate intensive and extensive green roofs, façade planters, podium level gardens, and planting zones with vegetation and soil media, the runoff coefficient of those areas is significantly reduced. This is because all the leaves of greenery, flora, and forested zones lead to an increase in surface roughness coefficients, and the soil slows down water through infiltration and hydraulic conductivity – leading to a compounded effect that reduces the average runoff coefficients of a plot. The result of the weighted runoff coefficient of a building, from the roof to the ground, is a water-sensitive urban plot.

The description of this idea is embedded in the Urban Hydrologics summary phrase – Your Building is the River / Your Roof is the River. Narratives are essential to create a sense of community that can rally behind a common goal, and this phrase unlocks the power of people’s imagination to remind oneself that the urban surfaces are under your control – e.i. your roof and your building/plot surfaces – are directly impacting the well-being of your watershed, its streams, and its river. By collectively taking action as rivershed communities, we can impact how our entire city responds to weather extremes, both extreme rainfall and extreme drought periods. At Urban Hydrologics, we are committed to this mental paradigm shift, and we look forward to working with communities, governments, and industry leaders to make this collective transformation happen. All our buildings are the river.