Component Test/Process Methodology Preliminary results

Vege

tatio

n

Plant Screening

Programme ü  2 climatic conditions (maritime, Sheffield, UK

and continental, Stuttgart, DE) ü  46 plant species in UK (29 forbs, 10 grasses, 7

succulents) and 144 species in Germany (90 forbs 10 grasses, 44 succulents) - 32 common with UK

ü  3 irrigation regimes ü  3 depths of growing medium

Vege

tatio

n-Su

bstra

te

Evapotranspiration ü  3 substrates and 3 vegetation options

ü  Saturated samples drained to field capacity ü  Weight of each microcosm recorded at 1 hour

intervals using calibrated load cells ü  Temperature, Humidity & Light controlled to

replicate spring (5.01-9.76 °C, 12 hours sunlight) & summer (13.76-19.84 °C, 17 hours sunlight) conditions

ü  2 iterations of 14 days & 1 of 28 days for each condition

Phytometer Test

ü  8 synthetic/inorganic and 6 organic amendments ü  3 plant species at greenhouse condition set at

22 °C and relative humidity 70% (OECD 2006)

Subs

trate

Moisture retention/ Pressure

plate extraction (pF curves)

ü  Substrates and amended substrate tested from -0.35 to -15 bar pressure (specific method)

Physical/Chemical

Characteristics (FLL 2008)

ü  Granulometric distribution ü  apparent density ü  total pore volume ü  Max. water holding capacity ü  Permeability ü  Organic content ü  pH, nutrients

Pore space distribution

ü  Image analysis of sections of substrate cores solidified in resin

ü  4 substrate options

Detention ü  Small-scale laboratory rainfall simulator

ü  detention process vs substrate depth, organic content, rainfall intensity, presence of moisture mat

Subs

trate

- Dr

ainag

e lay

er

Moisture vertical flux from drainage layer to substrate

ü  Moisture balance observation in controlled climatic condition (35 °C and 20% relative humidity) through specifically designed trays

Drain

age l

ayer

Detention ü  5×1 m rainfall simulator to test 4 drainage layer

components vs rainfall intensities, roof length, roof slope.

Retention/detention of novel component

ü  Hydraulic tests of different detention enhancing

devices

Climate Chamber

WP1 AND WP2: GREEN ROOF COMPONENTS PERFORMANCE STUDY

COLLABORATIVE RESEARCH TO ENHANCE GREEN ROOF SYSTEMS Christian Berretta1, Tobias Emilsson2, Zoë Dunsiger1, Ralf Walker2, Nigel Dunnett1, Virginia Stovin1

1University of Sheffield, Green Roof Centre, United Kingdom 2 ZinCo GmbH, Germany

Marie Curie Industry Academia Partnership Programme (IAPP)

The demand for extensive green roofs that are less resource and maintenance-intensive systems and which have high aesthetic value is increasing.

This ecological view demands that extensive green roofs become biologically more diverse whilst also offering improvements in delivery of ‘ecosystem

services’ such as stormwater retention, carbon sequestration, energy conservation and nutrient cycling.

In this context, there is the need to broaden the available plant palette that can be used under different climatic regimes and growing medium

thickness. There is an increasing pressure to include native species and to investigate alternative plant species according to their optimal growth

requirements and their tolerance limits to environmental stress. A new focus on evapotranspiration and inter-event moisture balance and transfer within

components of the system is required. This relates to a better understanding of the plant physiology and growing medium physical properties.

As for the hydrological performance of green roofs, the existing knowledge is derived from field or laboratory experiments in which observations of

rainfall and runoff have been used to derive empirical ‘black-box’ performance functions. The predictive value of these relationships is, however,

restricted to each study’s specific system configuration and climatic influences. As the individual influence of each system component (plant, substrate,

drainage layer) is lost in the overall system performance, it is difficult to optimise the design of either individual components or complete systems to

meet specific performance objectives. There is the need for single component based understanding of performance linked to fundamental physical

properties of the system, to enable modelling and system design.

INTRODUCTION

The project is divided into three Work Packages (WP).

In WP1 a standardized plant screening protocol has been developed and used to investigate plant performance for a range of species in relation to

growing media depth and moisture availability. The protocol has been tested in two climatic contexts: continental (Stuttgart, DE) and maritime climate

(Sheffield, UK). A cross factorial experimental design is used, which involves 3 different levels of water availability obtained by different irrigation

regimes (low, moderate and abundant) and three different depth of the growing medium (5, 10 and 15 cm). A growing medium composed of 55%

crushed brick, 30% pumice, 10% coir fibre and 5% composted bark was specifically adopted for the project as a reference substrate not containing

peat. 46 plant species (29 forbs, 10 grasses, 7 succulents) have been tested. Spaces of sowing was 10 cm to permit plant interaction at an early stage.

The arrangement of plant species in each module was determined randomly. At this stage of the project data have been collected for two growing

seasons (2010 and 2011) in the University of Sheffield site and one growing season (2011) at ZinCo in Germany. The following data were collected:

percentage germination, shoot extension, maximum height of flowering stem, mean diameter, number of inflorescence or flowering stem, species

survival and percentage dieback of vegetative growth.

WP2 focused on investigating the hydrological processes occurring in a green roof system.

Prior to a rainfall event the substrate is characterized by an initial moisture content MC0. The maximum moisture content that a substrate can hold is

referred to as its field capacity, WHCmax. Any excess rainwater is temporarily stored within large air pores, but will typically drain from the roof under

gravity within two hours. This temporary storage effect is referred to as detention, and it provides an important stormwater management function

through delaying and reducing the impacts of storm peaks on sewer systems or watercourses. It depends on substrate physical characteristics

(‘vertical’ detention) and drainage layer characteristics (‘horizontal’ detention). During dry periods, the substrate will then lose moisture gradually as a

result of plant evapotranspiration. The rate at which moisture content decreases depends on the plant physiology, the substrate characteristics and the

climatic conditions. The moisture level in the substrate can decrease to the level that that plants experience drought-stress. The soil structure and the

pore size distribution characterize its moisture release behaviour or pF curve (Kasmin et al., 2010; Stovin et al., 2012).

WP2 aimed at understanding and quantifying the influence of each component of green roof systems on the described hydrological processes. For this

purpose specific experimental methodologies aimed at characterizing and enhancing green roofs components have been developed in this study.

These methodologies are described on the right.

WP3 focused on studying the complete green roof system by using the knowledge developed in the previous phases of the project and data from the

continuous monitoring of 9 external test beds installed at the University of Sheffield. In particular, three vegetation options (Sedum, meadow flower

mixture, no vegetation) and three substrates were selected for investigation. The field installations include weather stations, and selected beds

incorporate water content reflectometers for moisture content vertical gradient measurement.

Furthermore, in WP3 we are implementing a physically-based hydrological model specific for green roofs, validated on experimental data acquired

through the field tests. The model will also be used for simulating the impact of green roofs on a catchment scale. Finally, novel drainage layers that

enhance retention and detention and novel substrate enhanced with amendments have been tested in this phase of the project.

METHODOLOGY

The University of Sheffield Green Roof Centre, together with ZinCo GmbH, is involved in the project “Collaborative Research and Development of Green Roof

Systems Technologies” that aims at enhancing traditional intensive and extensive green roof systems by revisiting the fundamental basis of green roof system

design. The objective is to provide a profound understanding of green roof system performance that will enable the optimization of stormwater attenuation and

plant performance during drought, with a renewed focus on aesthetics. The project is funded under the European Union People programme as a Marie Curie

Industry Academia Partnerships and Pathways (IAPP) project. It is the largest international green roof project to date, involving 11 researchers from an

academic institution and a commercial partner and has a long time span, running over 4 years.

WP3: MONITORING AND MODELLING THE COMPLETE SYSTEM

INTEGRATED RESEARCH APPROACH

3 plant strategies: •  Non-vegetated; •  Meadow Flower; •  Sedum Mat. 3 substrates: •  Heather with Lavender (HwL) •  Sedum Carpet

manufactured by Alumasc - crushed brick and selected mineral aggregates, enriched with a small amount of mature compost

•  Lightweight Expanded Clay Aggregate (LECA) - 80% of LECA, 10% of loam (John Innes No. 1) and 10% of compost

Data Collected continuously since January 2010: •  Rainfall: tipping bucket rain gauges (ARG100, 0.2 mm resolution) •  Runoff: collected in tanks - measured with pressure transducers

PDCR1830; •  Climatic conditions (wind speed, temperature, solar radiation,

relative humidity, barometric presure): Campbell Scientific; •  Soil moisture content: CS616 Water Content Reflectometers

installed in 4 test beds at 3 different substrate depths

Test Bed Characteristics Size: 3 m x 1 m Slope: 1.5° Drainage Layer: ZinCo FD25 Filter Sheet: ZinCo SF Substrate Depth: 80 mm

ZinCo , DE Univ. of Sheffield, UK

The main result is the rigorous characterization of plant species and their performance. Preliminary analysis of the data collected during the first growing season in the UK showed that leaf extension growth response is influenced by depth of the rooting medium. However there is clear differentiation at this growth stage between horticultural plant groups.

•  Summer ET losses are greater than spring •  ET rates decay exponentially with respect to time / moisture content •  Initial daily ET rates of 2 and 3.5 mm (spring and summer

respectively); •  After 10 days, ET losses total 14 and 22 mm (spring and summer

respectively) •  Substrate composition and permeability affects ET; variably

influenced by climate •  Plant cover initially limits ET rates, but after time, ET losses are

greater

-  Moderate detention effect with no significance difference between different drainage layers

-  An increased detention effect was observed with the use of a moisture mat combined with the drainage layer.

-  A runoff model based on storage routing and a power-law relationship between storage and runoff and incorporating a delay parameter was developed. A sensitivity analysis showed the influence of roof slope and drainage material.

•  Detention in green roof substrates increases as a function of depth and organic matter content.

•  A modified reservoir routing model was used to simulate the detention process. The model parameters are largely independent of rainfall intensity, and it appears feasible to predict them from known physical characteristics of the substrate, specifically its depth and permeability.

 

0

5

10

15

20

25

30

35

40

ET  Losses  (m

m)

ADWP  (Days)

Sedum  on  HLS

Sedum  on  SCS

Sedum  on  LECA

MF  on  HLS

MF  on  SCS

MF  on  LECA

Non-­‐vegetated  HLS

Non-­‐vegetated  SCS

Non-­‐vegetated  LECA

  •  Amended substrates with 10 to 15% organic material (peat, composted bark or biochar) increased

WHCmax, but no statistical difference in between the three amendment rates •  The permeability was significantly effected by amendment type and all substrate mixes with biochar had

significantly higher permeability than all the other substrates •  No correlation was found between the FLL WHCmax values and the pressure plate extraction

measurements •  Dramatic loss of water from the substrates during the first week. Plant aesthetics decreased in a similar

fashion and all non‐succulent plants were dead after 35 days following onset of the drought treatment •  A higher FLL WHCmax was not reflected in prolonged plant survival or increased aesthetics

LECA

MCS

Sedum Substrate

HwL

The rate of moisture flux from the synthetic layers to the substrate was observed to be approximately 0.12-0.14 mm/day, in the absence of plants. A greatly improved experimental design was developed to provide definitive, repeatable results.

A deeper knowledge of each element’s performance, as well as of the combination of elements (complete system), allows interpretation

and understanding that can result in enhancing the system by new product development or more effective combination of traditional

elements. The described process restarts from the testing of the new or more effective solutions. The adopted approach requires a

combination of expertise including horticulture, plant ecology, plant physiology, hydrology, civil engineering and the collaborative

partnership between academia and the industry. Also the duration of the project allows the possibility to collect representative data and

when needed to repeat series of tests after more promising solutions have been determined.

Berretta, C., Emilsson, T., Dunnett, N., Stovin V. and Walker R. (2012). Towards an Enhanced Green Roof System. Proceedings of the World Green Roof Congress. 18-21 September 2012, Copenhagen, Denmark

Emilsson, T., Berretta, C., Walker, R., Stovin, V., and Dunnett, N. (2012) Water in Green Roof Substrates – Linking Physical Measurements to Plant Performance. Proceedings of the World Green Roof Congress. 18-21 September 2012, Copenhagen, Denmark

Kasmin, H., Stovin, V. and Hathway, E. (2010) Towards a generic rainfall-runoff model for green roofs. Water Science & Technology, 62, 4, pp. 898-905.

Poë, S., Stovin, V., and Dunsiger, Z. (2011) The Impact of Green Roof Configuration on Hydrological Performance, Proceedings of the 12th International Conference on Urban Drainage, Porto Alegre/Brazil, 11-16 September, 2011

Poë, S., and Stovin, V. (2012) Advocating a Physically-based Hydrological Model for Green Roofs: Evapotranspiration during the Drying Cycle. Proceedings of the World Green Roof Congress. 18-21 September 2012, Copenhagen, Denmark

Stovin, V., Vesuviano, G. and Kasmin, H., (2012) "The hydrological performance of a green roof test bed under UK climatic conditions", Journal of Hydrology, 414-415, pp. 148-161.

Vesuviano G and Stovin V. (2012) A Generic Hydrological Model for a Green Roof Drainage Layer, Proceedings of the 9th International Conference on Urban Drainage Modelling (9UDM), Belgrade, Serbia, 3-7 September, 2012.

Yio, M.H.N., Stovin, V., and Werdin, J. (2012) Experimental Analysis of Green Roof Detention Characteristics, Proceedings of the 9th International Conference on Urban Drainage Modelling (9UDM), Belgrade, Serbia, 3-7 September, 2012.

REFERENCES

Orifice Filter

Enhanced detention device Two components have been tested to optimize detention in green roof systems. -  The proposed system is alternative to traditional drainage systems and consists of a

shallow tank under the substrate layer that collect runoff through a perforated top surface and store temporarily runoff with a slow release to the drainage network regulated by hydraulic devices.

-  A novel drainage layer designed to enhance temporary storage and detention is at the moment under test.

(Vesuviano and Stovin, 2012)  

(Yio et al., 2012)  

(Emilsson et al., 2012)  

(Poë et al., 2012)  (Poë et al., 2011)  

Forbs Grass Succulent

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