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:
2. Flow path + travel time of water through green roof drainage Ralf Walker ZinCo GmbH, ralf.walker@zinco-greenroof.com Introduction It was a question which was discussed and came up during our research about how the water flows and how we could really split the different processes up in single ones in order to make future examinations easier, not always having to look at the entire system. Therefore it was important to look at the non-substrate components and prove that the water flowing onto the drainage can be drained away without rising into the substrate layer.
Overview of Methodology Some calculations with given drainage capacities were done but also some visual tests with the drainage layers, looking at the flow paths of water. At ZinCo the 1 x 5 m Rain Simulator which has a capacity of up to 1000 l/(s*ha) was used in order to visualize the water flow in different drainage layers and also get a first understanding of travelling time.
Figure 1: Floradrain® 25 / Floraset® 50 prepared with a fluorescent tracer (Uranin) @ 2% slope
Table 1: Drainage capacities (tested at SKZ in Germany, acc. to EN ISO 12958)
Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Key Findings Calculations show how much water needs to be dealt with at the drainage level. Assuming the worst case, the rain intensity will equal runoff out of the substrate. This means that there can be quite huge amounts of water to be dealt with. In the given example there are about 5 m of drainage required @ 2 %, if all the water shall stay in the drainage plane.
Figure 2: Calculations for a model roof with a central outlet
With fluorescent tracers it’s quite easy to see how water flows. The figure below shows 2 drainage elements compared to a blank roofing membrane. Flow time depends largely on drainage design and the spot where the tracer is applied.
Figure 3: Travel time for 5 m flow length
Further Reading https://sites.google.com/a/sheffield.ac.uk/green-roof-research/