Assessing urban soil unsealing constraints and potential for water regulation: a framework and case study of Brussels-Capital Region

Abstract

After a functional and immaterial reduction of urban soil to a two-dimensional surface, dominating the urbanism of the 20th century, over the last decades, soil has been progressively restored as a material, urban, and living element.

This study proposes a comprehensive framework for assessing soil thickness within urban environments, emphasizing its threedimensional and multidisciplinary nature. The proposed framework conceptualizes soil as comprising three distinct strata: (1) the land surface, which underpins urban planning and zoning practices; (2) the living soil, a dynamic and biologically active stratum composed of various horizons and domains of pedology; and (3) the deep underground, comprising parent materials and geological formations typically studied by geologists. In urban contexts, these strata are subject to significant anthropogenic interference. In particular, the urban underground is often heavily constructed, accommodating basements, mobility networks, and technical infrastructure.

The proposed framework is applied to the case study of Brussels and aims to foster a soil-sensitive approach among urban designers and planners, thereby enabling site-specific unsealing and soil restoration practices. The application to Brussels reveals key insights into the benefits and constraints of soil unsealing, particularly concerning the soil's function in water regulation. This study underscores the importance of considering soil in urban planning and offers a model for assessing the potential effectiveness of soil unsealing projects, ultimately promoting more resilient and sustainable urban environments.