roof gardens guidelines for monitoring the hydrologic

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Guidelines for Monitoring the Hydrologic

and Water Quality Performance of Green

Roofs in the Greater Seattle, Washington

Region

Final

April 2006

Prepared for

Seattle Office of Sustainability and Environment

and

Seattle Public Utilities

Prepared by

Taylor Associates, Inc.

Funding Acknowledgements

King Conservation District


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Taylor Associates, Inc. City of Seattle

TABLE OF CONTENTS

Table of Contents........................................................................................................................................... i

List of Tables................................................................................................................................................ iii

List of Figures .............................................................................................................................................. iv

Executive Summary...................................................................................................................................... v

1.0 Introduction.................................................................................................................................... 1

2.0 Background..................................................................................................................................... 1

2.1 What is a Green Roof? ................................................................................................................ 2

2.2 Benefits of Green Roofs.. ........... .......... ........... .......... ........... .......... ........... .......... ........... .......... .... 2

2.3 Use of Green Roofs in the Cascadia Bioregion........................................................................... 2

2.4 City of Seattle Sustainability Program Goals and Objectives for Monitoring Green Roofs ....... 4

2.4.1 Hydrologic Monitoring Objective for Green Roof Monitoring.............................................. 5

2.4.2 Water Quality Monitoring Objective for Green Roof Monitoring.......................................... 7

3.0 Measuring the Hydrologic Cycle and Water quality on Green Roofs....................................... 7

3.1 Overview of the hydrologic cycle on green roofs........................................................................ 73.2 Overview and Monitoring of Typical Green Roof Drainage System Meteorology and Runoff. 9

3.2.1 Monitoring Existing Green Roof Structures ........................................................................... 9

3.2.2 Designing Green Roof Structures for Ease of Monitoring.................................................... 11

3.2.3 Review of Monitoring Instrumentation and Installation for Green Roof Hydrology ........... 12

3.2.3.1. Quality Assurance and Quality Control (QAQC) Considerations............................... 13

3.2.3.2. Desired Data File Format............................................................................................ 13

3.2.3.3. Rainfall........................................................................................................................ 14

3.2.3.4. Air Temperature.......................................................................................................... 14

3.2.3.5. Humidity ..................................................................................................................... 15

3.2.3.6. Wind Speed................................................................................................................. 16

3.2.3.7. Solar Radiation............................................................................................................ 16

3.2.3.8. Flow Runoff ................................................................................................................ 17

Final Report Guidelines for Monitoring the Hydrologic andApril 2006 Water Quality Performance of Green Roofs

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3.3 Overview and Monitoring of Typical Green Roof Drainage System Water Quality ............ .. 19

3.3.1 Water Quality Monitoring Approach for Green Roof Monitoring ....................................... 20

3.3.2 Green Roof Monitoring Sampling Design............................................................................ 20

3.3.3 Green Roof Water Quality Monitoring Installation and Instrumentation............................. 21

3.3.4 Green Roof Water Quality Monitoring Parameters............................................................. 22

References ................................................................................................................................................... 25

Appendix A: EXAMPLES OF AVAILABLE MONITORING EQUIPMENT ................................... 29


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LIST OF TABLESTable 1. Recommended monitoring parameters for green roof monitoring compared to

parameters for cistern monitoring, and related water quality standards................... 23


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LIST OF FIGURESFigure 1. Diagram of generic green roof layers and stormwater runoff pathways

(Hutchinson 2003). ..................................................................................................... 3

Figure 2. Parameters for green roof data collection and related modeling goals using the

collected data. ............................................................................................................. 6

Figure 3. Green roof cross section and hydrologic processes. From Taylor and Gangnes

(2004).......................................................................................................................... 8

Figure 4. Green roof showing gravel-filled low point drainage path to roof drains (Ballard

Public Library). ......................................................................................................... 10

Figure 5. Green roof at Seattle City Hall with roof drains distributed in soil................... 11

Figure 6. Typical tipping bucket rain gauge. .................................................................... 14

Figure 7. Typical air temperature thermister and hygrometer with solar shield............... 15

Figure 8. Typical (directional) anemometer. .................................................................... 16

Figure 9. Typical pyranometer for measuring solar radiation. ......................................... 17

Figure 10. Typical (A). tipping bucket flow meter, (B). compound weir insert, (C). weir

box, and (D). in-line magnetic resistance flow meter............................................... 18


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EXECUTIVE SUMMARYThe City of Seattle is evaluating a variety of innovative methods to manage stormwater

within the city. One of these possible methods is the increased use of green roofs. To

assist the City of Seattle in learning more about the potential stormwater management

benefits of green roofs, this document provides monitoring guidelines and information to

support a uniform approach for monitoring green roofs.

The monitoring guidelines presented here address both the hydrology (water quantity)

and water quality aspects of green roofs. The guidelines follow: (1) a mass balance

approach for monitoring the hydrologic performance of green roofs, and (2) a flow-

weighted, storm event based approach for water quality parameters on both green and

conventional roofs. The instrumentation needed for this monitoring and the available

equipment are described in the report. Users of the guidelines should develop their own

individual Quality Assurance Project Plan (QAPP) and institute Quality

Assurance/Quality Control (QA/QC) procedures to assure data quality. Users should also

consult building architects and engineers when installing instrumentation.

The data collected from the hydrologic monitoring should include continuous electronic

records of rainfall, temperature, humidity, solar radiation, wind speed, and runoff. The

hydrologic data will be used to calibrate the Western Washington Hydrology Model

(WWHM) for individual green roofs. The calibrated model can then provide simulated

long-term hydrologic records to evaluate the performance of different green roof design

conditions and their potential contribution to storm water management.

Data collected from the water quality monitoring effort should be from at least 12 annual

storm events distributed over all seasons. The sampling criteria for minimum storm size,

antecedent rainfall conditions, and rainfall start and end times follow those developed in

the Washington State Department of Ecology TAPE guidelines (WDOE, 2004). The

mean storm event concentrations and loads for green and conventional roofs can then be

compared to each other and to water quality criteria to evaluate their potential effects onreceiving waters.

With uniform monitoring approaches, the effects of green roofs on stormwater runoff

hydrology and water quality can be more accurately compared from site to site. These

comparisons can then support generalizations about green roof performance to inform

policy and regulatory development in the City of Seattle.


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1.0 INTRODUCTIONThe City of Seattle encourages sustainable methods of growth and redevelopment.

Sustainable building will enhance the citys long-term livability and reduce

environmental impacts and resource consumption. The use of green roof technologies is

one of a number of these sustainable development strategies.

Green roofs are an attractive sustainable technology, especially in densely developed

areas where space in public rights-of-way for other stormwater management alternatives

is limited. Yet, uncertainty remains regarding their benefit in reducing and attenuating

roof water runoff or their effects on water quality.

To help the city learn more about the stormwater benefits of green roofs, this document

provides monitoring guidelines and information to support a uniform monitoring

approach for green roofs. With uniform monitoring approaches, the effects of green roofs

on stormwater runoff hydrology and water quality can be compared more accurately from

site to site. These comparisons can then support generalizations about green roof

performance that can inform policy and regulatory development in the City of Seattle.

This document aims to provide monitoring guidelines and information for both water

quantity and quality monitoring. It should be noted, however, that each application of

monitoring will need its own monitoring plan that addresses the unique conditions of

each site. These conditions include the existing roof and downspout infrastructure,

supporting utilities, technical staff availability, and overall monitoring budget.

This document is intended to provide (1) a conceptual understanding of overall green

roof monitoring objectives and (2) ideas for monitoring equipment and data analysis

resources available for the user to conduct their monitoring. As an additional resource,

the user should also consult the Washington Department of Ecology Guidelines for

Preparing Quality Assurance Project Plans (QAPPs) for Environmental Studies for

guidelines to support preparation of a project specific QAPP (WDOE 2004).

2.0 BACKGROUNDBackground information on green roofs is provided in this section. This background

includes defining a green roof and their associated benefits, examples of regional use of

green roofs, and listing of local project goals and objectives.


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2.1 WHAT IS A GREEN ROOF?A green roof is a layered system of synthetic roofing and drainage layers underlying a

layer of soil and plants on a building roof. These systems are typically vendor proprietary

systems installed either during the original building construction or as part of a roof

replacement or retrofit during the life of the building. A typical structural design of a

green roof is presented in Figure 1. The two types of soil and vegetation systems

commonly used are termed extensive and intensive green roofs. Extensive green roofs

generally have shallower soil depths (1 to 6 inches) that support low lying and drought

tolerant plants. Intensive green roofs comprise deeper soil depths and can have a wide

range of plant types. The later generally requires more irrigation and overall landscape

maintenance.

2.2 BENEFITS OF GREEN ROOFSStormwater reduction and attenuation are not the only recognized benefits of green roofs.

Other prominent benefits of green roofs include (see Dunnet and Kingbury [2004] and

Peck and Goucher [2005] plus the references below for summary of benefits):

1. Architectural and landscape aesthetics (Earth Pledge 2005)

2. Ecological benefits (Moran 2004)

3. Reduction of the heat island effect (Moran 2004)

4. Energy cost savings (Peck et al. 1999)

5. Air quality improvements (Peck et al. 1999)6. Social benefits (e.g. new economic sector, health benefits; Peck et al. 1999)

Each of these benefits supports the value of using green roofs. This report only addresses

the water quantity and quality benefits of green roofs.

2.3 USE OF GREEN ROOFS IN THE CASCADIA BIOREGIONMany green roofs have been built in Europe. In Germany, by 2001, green roofs covered

14 percent of the total flat roof surface or 13.5 million square meters. Of these figures,

extensive green roofs make up 85 percent of the market share and most of theinstallations (60 to 65 percent) were done as roof renovation or repair projects (Herman

2003). Many of these roofs have been monitored for their performance in reducing and

attenuating stormwater runoff. A summary of their generalized performance is provided

by Mentens et al. (2003).


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Figure 1. Diagram of generic green roof layers and stormwater runoff pathways (Hutchinson 2003).

In contrast to Europe, relatively few green roofs have been constructed in the greater

Puget Sound or Cascadia Bioregion. In the City of Seattle, green roofs have been

constructed on buildings at the Ballard Public Library, the Seattle City Hall, Justice

Center, Woodland Park Zoo, Boeing field, two transfer stations for King county, and

several private residences. None of these newly constructed roofs have been monitored

although monitoring plans are in progress. Green roofs have recently been designed for

the Seattle Fire Station 10 and the Ross Park Shelter House in anticipation of subsequentperformance monitoring.

Other known constructed green roofs that have been monitored in the region include the

City of White Rock, B.C. Operations Center (Johnston, unpublished data), and the

Vancouver, B.C. City Library (Johnston et al. 2003). The City of Portland has monitored


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the Hamilton Apartments in Portland for several years (Hutchinson, et al. 2003).

Monitoring has also taken place at the Multinomah Oregon County Building (Spolek,

2005). In addition to these constructed green roof buildings, research on the stormwater

runoff from experimental green roof plots is being conducted in Seattle by Magnusson

Klemencic Associates (Taylor 2004; Taylor and Gangnes 2004) and British ColumbiaInstitute of Technology (Connelly and Liu 2005). Several residential roofs have been or

will be monitored over the next year (Dick Lilly, personal communication). Additionally,

Herrera Environmental Consultants (2005) prepared another related summary of green

roof flow and pollutant characteristics for SPU.

2.4 CITY OF SEATTLE SUSTAINABILITY PROGRAM GOALS ANDOBJECTIVES FOR MONITORING GREEN ROOFS

The principal goal for monitoring green roofs in Seattle is to provide a local base of

knowledge that will:

1. Support Seattle Public Utilities policy development regarding the use and

performance of green roofs in meeting flow-control requirements in connection

with changes planned for 2006 in the Stormwater, Grading, and Drainage

Control Code,

2. Support Seattle Public Utilities development of drainage rate credits and other

incentives for the installation of green roofs as part of SPUs Rainwise Strategies.

3. Provide a methodology for determining potential water quality impacts from

green roof runoff to guide policy development regarding location of green roofs

(relative to combined or separated sewer systems and creek-served drainage

areas) and drainage code and design criteria to minimize harmful runoff.

4. Assist policy makers to make informed decisions about optimum green roof

performance when recommending specifications for green roof design, or permit

review guidelines

5. Provide educational opportunities using monitoring case studies to educate Seattle

city staff and the citys development community to better understand and

encourage the use of green roofs.

The scientific objectives of the monitoring guidelines to support these goals include: (1)

to conduct a hydrologic mass balance analysis and modeling of the effect of green roofs

on stormwater runoff (quantity) and (2) to evaluate their effect on water quality.


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2.4.1 Hydrologic Monitoring Objective for Green Roof MonitoringThe mass balance data set collected from monitored green roofs will be used to calibrate

the Western Washington Hydrology Model (WWHM, a form of Hydrologic Simulation

Program Fortran [HSPF]). The WWHM is used to create a simulated hydrologic runoff

record. This simulated record would then provide a prediction of how green roofs wouldperform (hydrologically) in the City of Seattle. A green roof modeling element has

already been developed for use in the WWHM (Beyerlein 2005). Data collected from

future monitoring efforts would then be used to calibrate this model element more

accurately. Figure 2provides a schematic representation of the parameters for flow data

collection and related modeling goals using the collected data for a green roofs. The

importance of each of these parameters to the calibration process is discussed in section

3.0.

The most important objective of the green roof monitoring guidelines is to collect

continuous rainfall, flow, and meteorological data over a long enough period to support

calibration of the WWHM (optimally at least one continuous year). The duration of a

continuous data set is the most important element influencing the quality of the

calibration of the WWHM (Doug Beyerlein, personal communication,). The calibrated

model can then be run utilizing a long-term historic rainfall and climatolological data set

to simulate the potential long-term performance of the monitored green roofs. The

collected data and the subsequent modeling will allow evaluation of the affects of

between-storm (antecedent) dry period durations, humidity, temperature, and wind speed

on antecedent soil moisture conditions, and thereby the performance of green roofs to

reduce and attenuate runoff during subsequent storm events. This kind of long-term

simulation to characterize green roof performance has not to date been found in the

literature.

The continuous model of green roof performance is important when evaluating the effects

of the highly seasonal rainfall patterns observed in the Seattle region. Much of the

monitoring literature on green roofs utilizes data collected over single storm events or

short periods and report apparent rainfall water loss as a percent of these short periods

(e.g. Rowe et al. 2003 ) or as a function of annual total rainfall, irrespective of seasonal

distribution (Mentens et al. 2003). These authors do recognize that differing antecedent

moisture conditions and different seasons will likely have a large effect on the resulting

reduction in runoff. Recently, Mentens et al. (In press) reported on several studies that

showed much less runoff reduction during winter months than for summer months.

Pacific Northwest temperate climate has a high proportion of rainfall occurring during the


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Figure 2. Parameters for green roof data collection and related modeling goals using the collected

data.


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winter months when between-storm dry periods are short and the climate and growing

conditions do not promote a significant amount of evapotranspiration.

Clear representation and modeling of these conditions characteristic of Western

Washington will help local policy makers make better-informed decisions about the bestspecifications to use in green roof design. With this initial modeling, based on

continuously collected monitoring data, the city will be able to evaluate the relevant

hydrologic response characteristics of different green roofs (especially reduction in total

runoff volumes, peak flow rates, and shifts in peak flow timing) in relation to specific

stormwater management questions.

2.4.2 Water Quality Monitoring Objective for Green Roof MonitoringThe water quality data collected following these guidelines will be used to evaluate the

expected runoff quality from green roofs in relation to the potential impacts on receivingwater. The water quality monitoring design is intended to provide the city with an

indication of the potential change in stormwater quality runoff if green roofs are

promoted throughout the city. Many design factors may affect water quality runoff from

green roofs: soil composition, depth, seasonality, vegetation success, age, and

maintenance practices of green roofs. Monitoring water quality on both conventional

roofs and green roofs will help the city: (1) identify the magnitude of the potential

changes on water quality between conventional and green roofs, and (2) identify design

recommendations for green roofs that optimize water quality conditions in green roof

runoff. The most important step in the water quality monitoring effort is to follow a

common sampling approach as described in section 3.3.2 below.

3.0 MEASURING THE HYDROLOGIC CYCLEAND WATER QUALITY ON GREEN ROOFSThis section provides an overview of the hydrologic cycle on green roofs and monitoring

requirements of a typical green roof drainage system. The overview of the monitoring

requirements includes both meteorological and runoff components.

3.1 OVERVIEW OF THE HYDROLOGIC CYCLE ON GREEN ROOFSConducting a hydrologic mass balance analysis of green roofs as described above means

measuring or estimating the elements of the hydrologic cycle on green roofs; that is,

measuring incoming rainfall and the resulting roof runoff, evapotranspiration, and short-

term retention in the soil. As an equation, the mass balance approach means we are


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attempting to account for all the rainfall as the total of roof runoff, evapotranspiration,

and soil retention:

Total rainfall volume = roof runoff volume + evapotranspiration + soil retention

Rainfall (including run-on from adjacent roof surfaces) and roof runoff rates and volumes

can be measured directly by electronic instrumentation (described below).

Evapotranspiration is not typically measured directly but is instead calculated based on

measured solar radiation, air temperature, humidity, and wind velocity. Figure 3provides

a graphical representation of a typical green roof cross section and the associated

hydrologic processes.

It should be noted that some green roofs utilize irrigation to help sustain the growing

plants during dry periods. Use of irrigation water on green roofs adds a significantcomplication to the hydrologic analysis presented in these guidelines. If irrigation exists

on a green roof to be studied, irrigation quantities and timing must be monitored and

incorporated into the model.

Figure 3. Green roof cross section and hydrologic processes. From Taylor and Gangnes (2004).


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3.2 OVERVIEW AND MONITORING OF TYPICAL GREEN ROOFDRAINAGE SYSTEM METEOROLOGY AND RUNOFF

A typical green roof system involves both synthetic material layers and overlying soil and

vegetation layers. Figure 1provided an example of a typical green roof cross section

showing the various layers used in the construction. Most of the green roofs expected to

be used in the Pacific Northwest are of the extensive variety.

Drainage systems on green roofs can utilize runoff collection at a downstream location on

the roof such as occurs with the Ballard Public Library design (Figure 4), or can be

collected at distributed downspout locations as occurs with the Seattle City Hall design

(Figure 5). In either case, downspouts or rain leaders collect the roof water flow to a

common discharge points that either daylight at the street level or connect below ground

to storm drainage systems.

The following discussion provides some initial guidance for monitoring green roofs. The

user is reminded that the selection and installation of monitoring instruments involves

evaluation of built structures. It is highly recommended that the building architects and

structural and mechanical engineers are involved when evaluating how to incorporate a

monitoring system into an existing green roof. Proper professional oversight will be

required to avoid potential damage or compromise of the original building design because

of monitoring site installation. When possible, monitoring design should be incorporated

with the overall design of the roof or building prior to construction.

3.2.1 Monitoring Existing Green Roof StructuresIn many cases, it will be necessary to install monitoring equipment on existing green roof

structures. In these cases, the monitoring will need to be adapted to the roof drainage

pattern already in place. These drainage patterns may or may not be conducive to actual

monitoring. The difficulty in monitoring existing green roof structures is that the drainage

from the roof is typically not collected in a single rain leader but rather in multiple

downspouts, thus requiring multiple monitoring sites (and replication of equipment and

maintenance, data files, and so on) to fully characterize the quantity and qualityassociated with the roof runoff. Rain leaders may also be difficult to access within the

building (for example, pipes located within walls or in work areas) or may pose a safety

hazard (for example, pipes located in electrical utility rooms). Additionally, existing

green roof structures may not be designed to segregate green roof runoff from

conventional roof runoff. That is, the flow measured at downspout locations may have


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Gravel-filled drainage path

Roof drain

downspouts

Figure 4. Green roof showing gravel-filled low point drainage path to roof drains (Ballard Public

Library).


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both conventional and green roof surfaces flowing to the same location thus commingling

different runoff types within that roofs drainage system. Retrofitting the drainage system

of existing roofs, where feasible, is a preferable option to installing multiple monitoring

sites.

Indicates grouped

downs outs.

Figure 5. Green roof at Seattle City Hall with roof drains distributed in soil.

3.2.2 Designing Green Roof Structures for Ease of MonitoringThe optimal green roof monitoring scenario is where all the green roof drainage is

collected to one or two downspout locations within a safe work locale in or adjacent to

the building. Experience has shown that it can be difficult, costly and in some cases

impossible to monitor a green roof if there are multiple downspouts. This site should

include a safe AC power source, data communications ports, and an adaptable piping

configuration that allows easy retrofit of the pipe system to accommodate the ultimate

flow conditions and monitoring equipment needs. This space should also be large enough

to provide a work area for periodic repair and maintenance of flow monitoring equipment


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as needed and, if desired, the installation of water quality monitoring equipment. Planners

should keep in mind adequate work area around the instrumentation will be needed for

installation, operation, and maintenance.

3.2.3

Review of Monitoring Instrumentation and Installation for GreenRoof Hydrology

As described above, the purpose of instrumentation on the green roof is to measure the

mass balance components of the hydrologic cycle. Total rainfall on the roof will

necessarily need to equal the amount of runoff, plus the amount evapotranspiration and

storage in the soil. Evapotranspiration is not measured directly but is calculated as a

function of measured solar radiation, air temperature, humidity, and wind velocity. Soil

moisture storage is calculated as the remaining unaccounted rainfall (i.e. not necessarily

directly measured) and will generally trend back to zero over the course of a full years

data cycle.

All of the parameters to be monitored are best done so using vendor supplied electronic

meters. A variety of technologies are available and vendors are constantly bringing new

instruments to market. Users of these guidelines will need to shop for and evaluate those

instruments that they believe will best serve their needs and budget. Examples of

available instruments are listed in Appendix A. The meteorological instruments in

particular can be obtained as a package of instruments from some vendors However,

many of these instruments can be obtained individually by the user resulting in both

lower cost and or better performance.

As a final comment on the overall green roof monitoring effort, the user should anticipate

that all the needs for conducting monitoring will require at best a number of months of

administrative and logistical preparation before data will be successfully begin to be

collected. The relatively long schedule required for writing a sampling plan, equipment

acquisition, installation, field shake down, infrastructure retrofit for utilities and

communications, and obtaining authorization from building owners should be

anticipated. For the shake down period, our experience has shown that at least two or

three storm events will be needed to confirm proper operation of the equipment. Periodic

maintenance and repair through the life of the monitoring program should also be

expected. Frequent tracking of instrument performance and data quality should also be

done on a regular basis to ensure long data gaps or poor quality are avoided.


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3.2.3.1. Quality Assurance and Quality Control (QAQC) ConsiderationsThese guidelines do not promote any particular vendors of monitoring instruments as

more or less dependable. Nor do they review the overall QAQC or instrument-specific

requirements for the installation of each of these instruments. Researchers installing

monitoring equipment should follow vendors recommendations for calibration andinstallation and refer to other guidelines such as USEPA (2000) Meteorological

Monitoring Guidance for Regulatory Modeling Applications.

While vendor-provided and EPA QAQC recommendations are useful, the user of these

guidelines should be aware that the recommendations may not apply to their particular

rooftop. Meteorological conditions may be affected by local obstructions or

environmental conditions (for example, adjacent buildings affecting rainfall or local

temperature). Even with these obstructions or environmental conditions, the goal is to

measure the actual conditions on the roof as they exist. As with all scientific datacollection efforts, it is the responsibility of each user to assure the quality and accuracy of

the data collected for their own project.

In addition to data QAQC, it is recommended that a Quality Assurance Project Plan

(QAPP; WDOE 2004) is written and followed for each case of monitoring. A QAPP will

ensure consistent protocols are followed by all the parties involved. As previously noted,

it is recommended that the project manager/researcher involve the building architect and

relevant engineers and building operations staff during the planning and installation of

any equipment on the roof.

3.2.3.2. Desired Data File FormatThe data collected should be as comma delimited files. These data files are typical

formats for most instruments, and are logged either internally to the instrument meter or

in a separate logging module. Comma delimited files can be manipulated for later use

during modeling efforts or in spreadsheet tabular presentations.

In addition to reporting data in comma delimited file formats, calibration of the WWHM

is best achieved with continuous records of the measured parameters (i.e. minimal data

gaps) and kept in separate files. The minimal data gaps helps maintain the consistency of

the antecedent conditions during the model calibration process, and the use of separate

files facilitates data management and handling by the modeler.


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3.2.3.3. RainfallRainfall information is important to collect as it represents the total influx of rainfall to

the green roof system. Rainfall is commonly collected in funnel-type, tipping-bucket rain

gauge instruments (Figure 6). These instruments collect rainfall as a frequency of tips

in a calibrated small tipping bucket beneath a collecting funnel. Rain gauges should beplaced to avoid large obstructions (e.g., other buildings or trees) but minimize exposure

to excessive wind (USEPA 2000). The objective is to measure rainfall occurring on the

roof being monitored and therefore some local obstructions that affect rainfall at the site

are warranted.

Figure 6. Typical tipping bucket rain gauge.

3.2.3.4. Air TemperatureAir temperature is important to measure because it is one of the parameters needed to

calculate evapotranspiration. As such, temperature measurements for green roof

evapotranspiration should be measured on the project roof surface, typically within a few

feet of the roof surface. Sensors used for monitoring ambient air temperature include:

wire bobbins, thermocouples, and thermistors. Platinum resistance temperature detectors


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(RTD; Figure 7) are among the more popular sensors used in ambient monitoring

(USEPA 2000). Continuously collecting thermometers are available inexpensively and

from many vendors. Appendix A provides typical available instruments for measuring

temperature.

Figure 7. Typical air temperature thermister and hygrometer with solar shield.

3.2.3.5. HumidityHumidity is again important to measure because it is one of the parameters needed to

calculate evapotranspiration and should be measured on the test roof surface.

Hygrometers (Figure 7) are the most commonly used instruments for measuringhumidity. Psychrometers are also still used in many meteorological stations, however

their use is generally not suitable for routine monitoring programs (USEPA 2000). If

possible, humidity sensors should be housed in the same aspirated radiation shield as the

temperature sensor. The humidity sensor should be protected from contaminants such as

salt, hydrocarbons, and other particulates as these will affect performance of the

instrument. The best protection is the use of a porous membrane filter, which allows the


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passage of ambient air and water vapor while keeping out particulate matter (USEPA

2000).

3.2.3.6. Wind SpeedWind speed data are needed for green roof modeling to calculate evapotranspiration.While wind direction is not required for the WWHM calculations of evapotranspiration,

the roof orientation relative to wind direction especially on peaked roofs may affect

evapotranspiration. The most common devices to measure wind speed are anemometers

(Figure 8) which are generally directional propellers or spinning cup meters connected to

logging units.

Figure 8. Typical (directional) anemometer.

3.2.3.7. Solar RadiationAs with air temperature, humidity and wind speed, solar radiation is needed for green

roof modeling to calculate evapotranspiration. Energy supplied by the sun and

surrounding air is the main driving force for the vaporization of water (FAO, 1998).


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Correspondingly, solar orientation of green roofs has been documented to affect

evapotranspiration substantially from green roofs (Mentens et al. 2003).

Solar radiation is typically measured using pyranometers. Pyranometers (Figure 9) should

be located with an unrestricted view of the sky in all directions during all seasons(USEPA, 2000). However, as with the other parameters, the objective of measuring solar

radiation on a green roof is to measure the true amount reaching the roof. Shadows from

adjacent buildings will in many cases be unavoidable. Depending on the size of the roof

and the extent of shadows, more than one pyranometer may be warranted. Correction of

data to account for shadows may also be needed.

Figure 9. Typical pyranometer for measuring solar radiation.

3.2.3.8. Flow RunoffRainfall runoff from the roof is the final and most important hydrologic parameter to be

measured as part of monitoring green roof hydrology. Measuring the flow from the roof


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is also potentially the most difficult since a wide range of flows must be measured and

the flow may need to be measured in multiple downspout locations.

Two general approaches have been used to monitor flow from green roofs: (1) calibrated

primary flow devices (weir boxes, flumes, weirs, or orifice restrictor devices) and (2) in-line flow meters. For the lowest of flow rates, tipping bucket meters (Figure 10) can be

used in conjunction with the calibrated weir boxes. A combination of these instruments

will help measure both low flow and high flows on the same roof accurately.

A B

C D

Figure 10. Typical (A). tipping bucket flow meter, (B). compound weir insert, (C). weir box, and (D).

in-line magnetic resistance flow meter.

In calibrated weir boxes or weir inserts (Figure 10), the water level is electronically

monitored using a pressure transducer or other level monitoring device in a box or pipe

behind a weir. The weir geometry selected for the site (i.e. the angle of the V and

whether a compound weir is used) must match the anticipated range of flows from the

green roof. The upper end of the potential flow range should be calculated from local

rainfall records using a local extreme design storm.


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A V notch weir with a geometric angle that accurately measures low and high flows

has been used in several projects (Moran 2004, 2005 and Carter and Rasmussen 2005).

One researcher found the use of V notch weirs was compromised by nuisance algal

growth (Chris Johnston, personal communication,). Flumes were used at downspouts tomeasure flow in Portland (Hutchinson et al. 2003) and orifice restrictor devices were used

by Taylor and Gangnes (2004).

One concern raised by architects and building owners in the use of weir boxes is the

potential for damage to a secondary conventional roof surface if the weir box is located

on the roof and not at the ground level or inside the building. The mass of water in the

weir box may cause impingement damage to a roofing material and compromise the

warranty.

In-line flow meters are water meters similar to those used to meter residential water

usage. These meters can be impeller, nutating, or electromagnetic type meters (Figure

10). In all these cases, downspout plumbing must be replumbed to form a P-trap (fully

submerged) section of pipe where the meter is located. While the impeller and nutating

meters can be used, they may be susceptible to clogging since their moving parts are

internal to the pipe. Electromagnetic meters utilize the principal that voltage of a

conductive fluid moving across a magnetic field is proportional to the velocity. This

principal allows mounting of the meter external to the pipe flow. Green roof monitoring

projects that have utilized electromagnetic meters include Spolek (2005) and Liu andMinor (2005).

When sizing an in-line flow meter for a particular roof, the meter may not adequately

measure the lowest flows if the selected meter is oversized. Johnston et al. (2005) solved

this problem by using two flow meters the first flow meter being larger thus allowing

the lowest flows to pass through to a second, smaller, flow meter that accurately

captured low flow rates. Liu and Minor (2005) found that high flows never reached the

highest possible extremes anticipated in initial calculations and thus the flow meter size

could be safely reduced to better measure the lowest flow rates.

3.3 OVERVIEW AND MONITORING OF TYPICAL GREEN ROOFDRAINAGE SYSTEM WATER QUALITY

The water quality from green roofs has been monitored much less than the water

quantify. Water quality from conventional roofs has been monitored to some extent in the


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literature, and findings show both conventional roofs and green roofs can be a source of a

variety of water quality constituents. The degree and nature of pollutant production

depends on the roofing (and gutter) materials used in conventional roofs, and the soil

composition and fertilization practices on green roofs (Hutchinson et al. 2003). Minton

(2005) provides a summary of findings from the literature on stormwater pollutants fromconventional roofs.

The principal categories of pollutants investigated in the literature and of significance to

the City of Seattle are nutrients and metals (e.g. phosphorus, nitrogen, copper, and zinc).

Nutrient concentrations from green roofs have consistently been shown to increase over

conventional roof runoff (Hutchinson et al. 2003, Berndtsson 2004, Moran 2005).

Related conventional parameters will also be valuable to monitor in conjunction with

these parameters (e.g. total suspended solids, pH, conductivity, hardness). All of these

conventional parameters also appear to rise as rainfall passes through a green roof (DeCuyper et al. 2005).

It should be noted that while some water quality parameters may show an increase in

concentrations, the reduction in total flow from green roofs especially during the summer

will reduce the total load of pollutants washing off. Many small summer storms may even

have zero runoff when a conventional roof would be producing runoff.

3.3.1 Water Quality Monitoring Approach for Green Roof MonitoringThe goal for the City of Seattle in monitoring green roof water quality is to evaluate the

potential changes in roof runoff water quality in green roofs compared to conventional

roofs, and to help identify design considerations that lead to the best water quality

conditions in receiving waters. In order to reach this goal it is important to collect data

from conventional and green roofs within the City of Seattle that follows a common

monitoring approach and parameter list. This data set will then allow city staff to identify

potential water quality impacts and design criteria to guide development of green roof

incentives and building codes for their use.

3.3.2 Green Roof Monitoring Sampling DesignThe proposed approach is to collect flow-weighted samples to evaluate water quality

event mean concentrations for both a conventional roof and green roof following the

procedure set forth in the Washington State Department of Ecology Guidance for

Evaluating Emerging Stormwater Treatment Technologies: Technology Assessment

Protocol Ecology (TAPE; WDOE, 2004). These procedures have been developed to


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evaluate stormwater treatment technologies statewide, but provide a good common basis

to follow for green roofs as well.

Storm events should be collected from all seasons for each green and conventional roof

monitored. Sample size for number of storms should be at least 12 storms distributedacross the four seasons. Because local pollutant sources may affect different areas of the

city differently, an effort should be made to select conventional roofs representing these

different areas.

While the water quality sampling is best conducted in conjunction with the flow

monitoring, continuous flow monitoring is not required. Flow monitoring is required,

however, during collection of the water samples to run the automated water sampling

instruments. Specifically, flow monitoring during sampling enables collection of flow

weighted composite samples (i.e. sample volumes are collected proportional to flow rate).

The sampling criteria for minimum storm size, antecedent rainfall conditions, and rainfall

start and end times follow those developed in the Washington State Department of

Ecology TAPE guidelines (WDOE, 2004). Sample handling and analytical protocols

should follow common protocols such as those provided in (APHA 1995) or similar field

and laboratory procedure protocols.

The data collected under these TAPE guidelines will result in a set of data for seasonal

storm events showing water quality concentrations and loads for individual conventionaland green roofs. These data can then provide a qualitative comparison of the seasonal

mean storm event concentrations and total loads between green and conventional roofs.

New comparisons and insights can be made as results from newly monitored green and

conventional roofs accumulate.

3.3.3 Green Roof Water Quality Monitoring Installation andInstrumentation

Both green roof and conventional roof monitoring is best conducted using automated

water sampling devices. These samplers are able to pump and collect samples from a

water source based on either time or flow rate. Flow meters are electronically connected

with these samplers to enable programmed automated collection of the water samples.

Time paced samples can be collected and later composited based on the runoff

hydrograph but this approach requires additional manual handling of the water samples

and still requires collecting flow measurements. In addition, some automated water


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22

quality samplers are able to connect to and log data from electronic water quality meters

in the field. Appendix A provides example vendors that provide commonly used

instruments for sampling. Detailed explanations of automated flow monitoring

procedures can be found in Teledyne ISCO (2000) and WDOE (1995).

3.3.4 Green Roof Water Quality Monitoring ParametersThe water quality parameters for green roof monitoring are those most likely to be

significant to receiving waters, and have shown a substantial presence in green or

conventional roofs. In addition, some judgment has been made here to narrow the

parameter list to be more manageable by users of these guidelines.

Table 1 provides a summary of these recommended parameters together with parameters

previously recommended for cistern water collected from roofs for use in gardens and

related water quality parameters. Seattle Public Utilities should be particularly attentiveto the effect of green roofs on nutrients (phosphorus and nitrogen) and metals (zinc and

copper) as these may have deleterious effects on receiving waters and have been reported

to increase in the roof runoff relative to conventional roofs (De Cuyper 2005, Forster and

Knoche 1999, Minton 2005).


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REFERENCESAmerican Public Health Association (1995). Standard methods for the examination of

water and wastewater. Washington, DC, American Public Health Association.

Berndtsson, J. C. (2004). The influence of extensive vegetated roofs on runoff quality.

Lund, Sweden, University of Lund.

Beyerlein, D. (2005). Western Washington Hydrology Model 3 Eco-Roof

Documentation. Seattle, WA, Seattle Public Utilities.

Beyerlein, D. Clear Creek Solutions. Personal communication.

Carter, T. L. and T. C. Rasmussen (2005). Use of green roofs for ultra-urban stream

restoration in the Georgia Piedmont (USA). Proceedings of the 2005 Georgia

Water Resources Conference, Athens, GA, Institute of Ecology, The University ofGeorgia.

Connelly, M. and K. Liu. (2005). Green roof research in British Columbia an overview.Greening Rooftops for Sustainable Communities, Washington, D.C., Cardinal

Group, Inc.

De Cuyper, K. Dinne, and L. Van De Vel. (2005). Rainwater discharge from green roofs.Plumbing systems and design.

Dunnett, N. and N. Kingsbury (2004). Planting Green Roofs and Living Walls. Portland,

OR, Timber Press.

Earth Pledge. (2005). Green Roofs: Ecological Design and Construction. Atglen, PA,Schiffer Publishing, Ltd.

Food and Agriculture Organization of the United Nations. (1998). Crop

evapotranspiration. Guidelines for computing a crop water requirements. FOAirrigation and drainage paper 56. Food and agriculture organization of the united

nations, Rome.

Forster, J. and G. Knoche (1999). Quality of roof runoff from green roofs. Eighth

International Conference on Urban Storm Drainage, Sydney, Australia.

Herman, R. (2003). Green roofs in Germany: yesterday, today, and tomorrow. Greening

Rooftops for Sustainable Communities, Chicago, Il, Cardinal Group, Inc.

Herrera Environmental Consultants (2005). Summary of pollutant removal and flow

attenuation capability of green roofs. Seattle, WA, Seattle Public Utilities.


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Hutchinson, D., P. Abrams, et al. (2003). Stormwater monitoring two ecoroofs in

Portland, OR. Greening Rooftops for Sustainable Communities, Chicago, Ill,Cardinal Group, Inc.

Johnston, Chris. Kerr Wood Leidal Associates. Personal communication.

Johnston, C., K. McCreary, et al. (2004). Vancouver Public Library green roof

monitoring project. Greening Rooftops for Sustainable Communities. Second

North American Green Roof Infrastructure Conference Awards and Trade Show,Portland, OR, Cardinal Group, Inc.

Kohler, M. and M. Schmidt (2003). Study of extensive green roofs in Berlin. Berlin,Germany.

Lilly, D. Seattle Public Utilities. Personal communication.

Liu, K. and J. Minor. (2005). Performance evaluation of an extensive green roof.Greening Rooftops for Sustainable Communities, Washington, D.C., Cardinal

Group, Inc.

MacMillan, G. (2004). York University rooftop garden stormwater quantity and quality

performance monitoring report. Greening Rooftops for Sustainable Communities,Portland, OR, Cardinal Group, Inc.

Mentens, J., D. Raes, et al. (2003). Effect of orientation on the water balance of greenroofs. Greening Rooftops for Sustainable Communities. The First North

American Green Roof Infrastructure Conference Awards and Trade Show,Chicago, Il, Cardinal Group, Inc.

Mentens, J., D. Raes, et al. (In Press). "Green roofs as a tool for solving the rainwaterrunoff problem in the urbanized 21st century?" Landscape and Urban Planning.

Minton, G. (2005). Stormwater Treatment: Biological, Chemical and Engineering

Principals. Seattle, WA, Sheridan Books.

Moran, A. (2004). A North Carolina field study to evaluate green roof runoff quantity,

runoff quality, and plant growth. Department of Biological and AgriculturalEngineering. Raleigh, NC, North Carolina State University.

Moran, A., B. Hunt, et al. (2004). A North Carolina field study to evaluate green roofrunoff quantity, runoff quality, and plant growth. Greening Rooftops for

Sustainable Communities, Portland, OR, Cardinal Group, Inc.

Moran, A., B. Hunt, et al. (2005). Hydrologic and water quality performance from greenroofs in Goldsboro and Raleigh, North Carolina. Greening Rooftops for

Sustainable Communities, Washington, DC, Cardinal Group, Inc.


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Peck, S. W. and C. Callaghan (1999). Greenbacks from Green Roofs: Forging a NewIndustry in Canada. Toronto,ON, Peck and Associates.

Peck, S. W. and D. Goucher (2005). Overview of North American policy development

and the policy development process. Greening Rooftops for SustainableCommunities. The Third North American Green Roof Infrastructure Conference

Awards and Trade Show, Washington, DC, Cardinal Group, Inc.

Peck, S.W., C. Callaghan, B. Bass, and M.E. Kuhn (1999). Greenbacks from green roofs:

forging a new industry in Canada. Prepared for Canada Mortgage and Housing

Corporation. Peck and Associates, Toronto, ON, Canada.

Rowe, D. B., C. L. Rugh, et al. (2003). Green roof slope, substrate depth, and vegetation

influence runoff. Greening Rooftops for Sustainable Communities. The First

North American Green Roof Infrastructure Conference Awards and Trade Show,

Chicago, IL, Cardinal Group, Inc.

Spolek, G. (2005). Multnomah County building ecoroof performance. Portland, OR, Cityof Portland, Office of Sustainable Development.

Taylor, B. (2004). Model calibration and validation using Portland green roof monitoringdata. Seattle, WA.

Taylor, B. and D. Gangnes (2004). New method for quantifying runoff reduction of greenroofs. Greening Rooftops for Sustainable Communities, Portland, OR, Cardinal

Group, Inc.

Teledyne Isco (2000). Instruction Manual, 6700 Portable Samplers. Lincoln, NB,

Teledyne Isco.

U.S. Environmental Protection Agency (2000). Meteorological monitoring guidance for

regulatory modeling applications. Research Triangle Park, NC, U.S.

Environmental Protection Agency.

Washington State Department of Ecology (1995). Stormwater quality monitoring

guidance manual. Olympia, WA, Washington State Department of Ecology.

Washington State Department of Ecology (2004). Guidance for evaluating emerging

technologies: Technology assessment protocol - Ecology (TAPE). Olympia, WA,Washington State Department of Ecology publication no. 02-10-037.

Washington State Department of Ecology (2004). Guidelines for preparing quality

assurance project plans for environmental studies. Olympia, WA, Washington

State Department of Ecology publication no. 04-03-030.


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APPENDIX A: EXAMPLES OF AVAILABLE

MONITORING EQUIPMENT

Packaged Weather Stations

Campbell Scientific, Inc. (CSI) ET106 Evapotranspiration Monitoring Station. Measures

rainfall, solar radiation, air temperature, relative humidity, wind speed/direction. Soil

moisture and temperature probes can also be integrated.

www.campbellsci.com/et106

RainBird Maxicom

2

Weather Station WS-PRO. Same sensors as the CSI ET106, butintegrates into the Maxicom

2irrigation controller.

www.rainbird.com/pdf/turf/ts_WSPRO.pdf

HOBO

Weather Station Starter System. Temperature, relative humidity, and wind

speed/direction.

www.onsetcomp.com/Products/Product_Pages/weatherstation/wsindex.html

Rain Gauges

Hydrological Services PTY, LTD.

http://www.hydrologicalservices.com/

Novalynx Corporation

http://www.novalynx.com/products-rain-gauges.html

Campbell Scientific, Inc.

http://www.campbellsci.com/precipitation

Geneq, Inc.

http://www.geneq.com/frames.html#
http://www.campbellsci.com/et106http://www.onsetcomp.com/Products/Product_Pages/weatherstation/wsindex.htmlhttp://www.hydrologicalservices.com/http://www.novalynx.com/products-rain-gauges.htmlhttp://www.campbellsci.com/precipitationhttp://www.geneq.com/frames.htmlhttp://www.geneq.com/frames.htmlhttp://www.campbellsci.com/precipitationhttp://www.novalynx.com/products-rain-gauges.htmlhttp://www.hydrologicalservices.com/http://www.onsetcomp.com/Products/Product_Pages/weatherstation/wsindex.htmlhttp://www.campbellsci.com/et106


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Flow Meters

UniData Tipping Bucket flow gauge. www.unidata.com.au/products/water/6506gh

DataGator

flow meter. Partial and full-pipe flow.

www.yestech.com/renaissance/app&ben.html

Teledyne Isco. www.isco.com

HACH/Sigma.

www.hach.com/hc/static.template/templateName=HcBridgePage.HcSigma.htm

Campbell Scientific, Inc. www.campbellsci.com

USA BlueBook. Various flow meters and equipment. www.usabluebook.com

In-Situ Inc. Pressure transducers. www.in-situ.com/default.html

Endress + Hauser. Magnetic flowmeters. www.za.endress.com

ABB. Magnetic flowmeters. www.abb.com

Advanced Flow Technology Company UniMag DP Series Magmeter (for PVC)

www.advancedflow.com

Primary Flow Devices

PlastiFab FRP weirs and flumes. www.plasti-fab.com

Free Flow

, Inc. Primary flow devices weirs and flumes. www.freeflowinc.com

Thel-Mar compound weirs.

Water Quality

Teledyne Isco. www.isco.com
http://www.unidata.com.au/products/water/6506ghhttp://www.isco.com/http://www.hach.com/hc/static.template/templateName=HcBridgePage.HcSigma.htmhttp://../bryan/Local%20Settings/Temporary%20Internet%20Files/OLK3/www.campbellsci.comhttp://www.abb.com/http://www.advancedflow.com/http://../bryan/Local%20Settings/Temporary%20Internet%20Files/OLK3/www.plasti-fab.comhttp://www.freeflowinc.com/http://www.freeflowinc.com/http://../bryan/Local%20Settings/Temporary%20Internet%20Files/OLK3/www.plasti-fab.comhttp://www.advancedflow.com/http://www.abb.com/http://../bryan/Local%20Settings/Temporary%20Internet%20Files/OLK3/www.campbellsci.comhttp://www.hach.com/hc/static.template/templateName=HcBridgePage.HcSigma.htmhttp://www.isco.com/http://www.unidata.com.au/products/water/6506gh


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HACH/Sigma.

www.hach.com/hc/static.template/templateName=HcBridgePage.HcSigma.htm

YSI. www.ysi.com/index.html

HACH/Hydrolab. www.hydrolab.com

In-Situ Inc. Water quality meters. www.in-situ.com/default.html
http://www.hach.com/hc/static.template/templateName=HcBridgePage.HcSigma.htmhttp://www.ysi.com/index.htmlhttp://www.hydrolab.com/http://www.in-situ.com/default.htmlhttp://www.in-situ.com/default.htmlhttp://www.hydrolab.com/http://www.ysi.com/index.htmlhttp://www.hach.com/hc/static.template/templateName=HcBridgePage.HcSigma.htm


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roof gardens guidelines for monitoring the hydrologic

Documents