Introduction to water fluxes in green roof systems 4 - Ralf Walker

Marie-Curie IAPP ‘Green Roof Systems’ Project

The Green Roof Research Conference 18-19 March 2013, Sheffield

Introduction to water fluxes in green roof systems:

4. Evaporation from substrate Ralf Walker1, Jörg Werdin2, 1

ZinCo GmbH, ralf.walker@zinco-greenroof.com, 2 ZinCo GmbH, joergwerdin@gmail.com

Introduction When we looked at plant available water and possible tests which can be applied we found there wasn’t much easily applicable for green roofs. PF-tests have been adapted and carried out as well as a standardised Phytometer Test. But both showed limitations. Furthermore both tests do take a long time and make a quick screening and overview almost impossible.

Especially the direct evaporative losses from course material (especially during the establishment of a green roof) seemed to be important to us. Also depth related information about water losses was sought for. So a complementary test was developed.

Overview of Methodology Acrylic glass cylinders were used at 50, 100 and 150 mm depth. Surrounded by insulation material it was ensured to avoid uncontrolled heating of the sides. In order to be able to check also for drain water, a setup using trivets was chosen. Layers of drainage (without storage capacity) in between the different layers ensure movement of water as on green roofs. Sheets of Styrodur in between were used for the ease of handling.

Figure 1: Test setup/monitored characteristics + arrangement in lab with grow lamps and fan

Marie-Curie IAPP ‘Green Roof Systems’ Project

The Green Roof Research Conference 18-19 March 2013, Sheffield

Key Findings It’s interesting to see the materials evaporating at +/- the same high level on day 1. One remarkable outcome is MCS 100 + Zincolit 150. A capillary break linked to depth can explain why at day 9 there is more water content in the Zincolit 150 sample as compared to the shallower MCS 100 sample. Substrate depth of only 50 mm lose water rather rapidly and can be seen as only suitable in climates where regular rainfall recharges the build-up.

Compared to the water holding according to the FLL-guideline (which is represented approx. at day 0) we can furthermore characterise a substrate and its behaviour depending on depth by this test.

Figure 2: Remaining water content / decreasing wet horizon over the course of 9 days

When looking at the horizon between dry and wet it can be easily seen that the shallow build-ups are entirely dry and that there is no capillary break whilst the deeper build-ups seem to stabilise towards the end of the experiment. The test can be used to further investigate amended substrates which have been used in the Phytometer Test in order to find out whether in future a pre-selection of materials with potential can be made by this rather quick test.

Further Reading https://sites.google.com/a/sheffield.ac.uk/green-roof-research/