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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, 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

Introduction to water fluxes in green roof systems 1 - Ralf Walker