Water retention and transfer properties of a Green roof volcanic substrate

Filip Stanic,Yu Jun Cui,Emmanuel De Laure,Pierre Delage,R Cardoso,C Jommi,E Romero

doi:10.1051/e3sconf/202019503011

Abstract

The water retention curve and the hydraulic conductivity function of a volcanic coarse granular material used as a substrate in an urban green roof in the Paris area was carried out on a newly developed device, in which low suctions were controlled. In the same cell, a hanging column system was used for controlling smaller suctions (up to 32 kPa) and the axis translation technique for larger suctions (up to 50 kPa). Water exchanges were monitored in connected tubes by using a high accuracy differential pressure transducer. The step changes in suction were also used to determine the hydraulic conductivity function by means of Gardner’s method, accounting for the impedance effects due to the high air entry value ceramic porous disk with Kunze and Kirkham’s method. van Genuchten and Brooks and Corey models were used for the water retention curve, but the hydraulic conductivity functions derived from these expressions appeared to lead to a significant under-estimation, confirming the need of operational and simple device for the experimental determination of the hydraulic conductivity function.

Highlights

IntroductionUrban green roofs are used to reduce both the urban heat island that characterize cities (thanks to the evapotranspiration of vegetation) and urban run-off
Urban green roofs are used to reduce both the urban heat island that characterize cities and urban run-off
Good comparability is observed between the section obtained with the hanging column technique (1 – 10) and with the axis translation method (11 – 13)

Summary

Introduction

Urban green roofs are used to reduce both the urban heat island that characterize cities (thanks to the evapotranspiration of vegetation) and urban run-off. Their substrates have to be light enough and present satisfactory water retention and transfer properties, which is the case of the coarse volcanic granular substrates used in the “Green Wave” of the Bienvenüe building (Versini et al 2017) [1], located close to Ecole des Ponts ParisTech, 18 km east of Paris. The size of particles smaller than 80 μm have been measured by sedimentation (NFP94-057 - 1992) [4]

Methods

Results

Conclusion