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:

1. Runoff + Evapotranspiration out of substrate- + plants-layer

Ralf Walker

ZinCo GmbH, ralf.walker@zinco-greenroof.com

Introduction

The proceeding for runoff-measurements according to the German FLL Green Roof

Guideline suggests to apply rain on pre-saturated green roof build-ups. Pre-saturation is of

course not always the case in a real weather situation, as there usually is an antecedent dry

weather period (ADWP) before storms. The research focuses on extensive vegetation using

standard green roof substrate and includes plants in order to get a better understanding of

runoff under more realistic conditions. In order to be able to define future proceedings a

better understanding of quantities of Evapotranspiration in summer months was sought.

Overview of Methodology

Containers with a stainless steel grid at the bottom, a filter sheet and substrate were

developed and pre-cultivated with Phedimus-species. Once the vegetation was fully

developed (from sedum cuttings) it was only periodically irrigated (once a week).

Evapotranspiration was measured once a day and for some containers continuously (for

better understanding of the mechanism).

Figure 1: Container set-up / pre-cultivation / hanging + ready for storm event

Tests regarding storm events used a standardised block rain of 15 min duration and an

intensity of 300 l/(s*ha). With the containers hanging during the rain event it was possible to

register their weight continuously.

Marie-Curie IAPP ‘Green Roof Systems’ Project

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

Key Findings

The Evapotranspiration of the vegetation complex is highest on day 1. This is due to wet

leafs and the substrate surface which dries out as well. The highest Evapotranspiration rates

are achieved during the daytime (in our experiment between 4 am and 12 pm). After 2.5

days about 10 mm of water capacity have been restored.

Figure 2: Evpotranspiration over a 2.5 day period

With different antecedent dry weather periods there are huge differences in water-uptake.

The release after a rain event looks almost the same, whenever the rain was applied.

Figure 3: Runoff-characteristics after an ADWP of 1 or 5 days.

Further Reading

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