This research will present opportunities and limitations of rooftop rainwater harvesting within Glasgow Avenues Project area. Potential potable water savings will shed light on other environmental benefits, such as greenhouse gasses emissions and energy consumption. All findings of conducted research will be detailed within subsequent chapters of this paper.
Estimations predict that, due to current freshwater shortages, water will replace petroleum as the liquid gold of the 21st century. Even though some regions, such as Scotland, have an abundance of water, it can be argued that due to the trends of growing population, which inevitably leads to greater consumption, and the relentless increasing of the Earth's temperature, which translates into triggering more rapid evaporation rates, this situation may not be sustainable in the future. Supplying water leads to many environmental changes, such as decreasing groundwater levels in aquifers or air pollution from water collection, treatment and pumping over long distances. Air pollution significantly contributes to the global climate change, which in turn will intensify the water shortage problem. Rainwater harvesting as a capture, storage and supply of rainwater at the point of use may be a viable solution for these issues. Properly designed and supplied by renewable energy these systems may enhance the city’s resilience to climate change and help tackle environmental issues.
In urbanised areas, the least contaminated rainwater can be collected from the rooftops. Rainwater contamination impacts on the system's efficiency and longevity, which is important in financial and maintenance aspects. Rainwater collected at the building rooftop can be utilised for non-potable purposes within that building, and any excess water can be stored for future use during dry periods. No water treatment is required for such use of water; thus, energy is saved and carbon emissions reduced. In situ rainwater harvesting also precludes energy consumption for transportation. However, a certain amount of energy is needed for pumping rainwater from the main storage tank to the points of use.
Table of Contents
Abstract
1. Introduction
1.1 Background
1.2 Importance of this study
1.3 Aim and objectives
1.4 Sample Methodology
2. Literature review
2.1 Rainwater harvesting
2.1.1. Rainwater harvesting from the rooftops
2.1.2 Roofs in the research area
2.1.3 Frequency use of the system
2.2 Components of a rooftop rainwater harvesting system
2.3. Rainwater harvesting systems
2.3.1 Gravity Feed Systems
2.3.2 Pump Feed Systems
2.4. Rainwater harvesting system to be considered for Glasgow Avenues Project area
2.5. Summary
3 Methodology
3.1 Theoretical study
3.2 Glasgow Avenues Project as a Case Study
3.3 Computer programs
3.3.1 Google Earth
3.3.2 Microsoft Excel
4 Results and discussion
4.1 Water used by residents living in the study area
4.2 Water end-uses by residents in Glasgow
4.2.1 Based on Scottish Water emailed data
4.2.2 Based on the Scottish Government data
4.2.3 Total water end-uses
4.3 Rainfall data
4.3.1 Short-term analysis for 2010 (1 year)
4.3.2 Short-term analysis for 2011
4.3.3. Long-term analysis (10 years)
4.4 Rainfall catchment area
4.5 Potential potable water savings
4.5.1 Short-term potable water savings for 2010
4.5.2 Short-term potable water savings for 2011
4.5.3 Long-term potential (10 years)
4.5.4 Short- and long-term drinking water savings comparison
4.6 Potential operational carbon footprint reductions
4.6.1 Potential carbon footprint reductions in a short-term of 2010
4.6.2 Potential carbon footprint reductions in a short-term of 2011
4.6.3 Potential carbon footprint reductions in a long-term
4.6.4 Operational carbon footprint comparison
4.7 Discussion
5 Conclusions and recommendations
5.1 Summary of key findings
5.2 Recommendation for future research
5.3 Recommendation for future practice
References
Appendices
Abstract
Estimations predict that, due to current freshwater shortages, water will replace petroleum as the liquid gold of the 21st century. Even though some regions, such as Scotland, have an abundance of water, it can be argued that due to the trends of growing population, which inevitably leads to greater consumption, and the relentless increasing of the Earth's temperature, which translates into triggering more rapid evaporation rates, this situation may not be sustainable in the future. Supplying water leads to many environmental changes, such as decreasing groundwater levels in aquifers or air pollution from water collection, treatment and pumping over long distances. Air pollution significantly contributes to the global climate change, which in turn will intensify the water shortage problem. Rainwater harvesting as a capture, storage and supply of rainwater at the point of use may be a viable solution for these issues. Properly designed and supplied by renewable energy these systems may enhance the city’s resilience to climate change and help tackle environmental issues.
In urbanised areas, the least contaminated rainwater can be collected from the rooftops. Rainwater contamination impacts on the system's efficiency and longevity, which is important in financial and maintenance aspects. Rainwater collected at the building rooftop can be utilised for non-potable purposes within that building, and any excess water can be stored for future use during dry periods. No water treatment is required for such use of water; thus, energy is saved and carbon emissions reduced. In situ rainwater harvesting also precludes energy consumption for transportation. However, a certain amount of energy is needed for pumping rainwater from the main storage tank to the points of use.
This research will present opportunities and limitations of rooftop rainwater harvesting within Glasgow Avenues Project area. Potential potable water savings will shed light on other environmental benefits, such as greenhouse gasses emissions and energy consumption. All findings of conducted research will be detailed within subsequent chapters of this paper.
Acknowledgements
During the process of creating this report, a number of people took part in it by providing advice, guidance, or information. These people are those who I would like to thank. As a first is Professor Vernon P., from whom I had the opportunity to research such topic. Appreciations are owed also to the Scottish Water team who provided me with significant data and other organisations such as SEPA and Scottish Government.
1. Introduction
1.1 Background
Rainwater harvesting is known as collection, storage and use of the rainfall. Collection can be done before rain reaches the ground (rooftop collection), or from the surface runoff. It is an ancient concept utilized to provide water resources for potable and non-potable uses, as well as agriculture (Sisuru Sendanayake, 2016). Rainwater harvesting has been practised for thousands of years during seasonal rain events as a way of water preservation for future uses. Collected rainwater was usually stored in natural basins or man-made cisterns (Heather Kinkade-Levario, 2007).
The amount of rainwater available for harvested highly depends on the rainfall intensity within the area, catchment area size and surface type (Rani Devi et al., 2012). Additionally, surroundings of the catchment area, its location, temperature and evaporation rate are also important. Rainwater reuse seems to be appropriate for arid regions of the World, where water resources are scarce. Although, cooler places with higher rainfall can also benefit from this technology. Water savings as the main reason for rainwater harvesting can also lead to other benefits.
Different sources inform about different dates of rainwater harvesting emergence. According to one of them, technology was already used in 4500 BC by people of city-state named Ur in Mesopotamia, today’s Iraq (Syed Azizul Haq, 2017). Rainwater runoff was also harvested 4000 years ago in Israel, where rainfall from desert hills was collected for agriculture and human use (Syed Azizul Haq, 2017). The first rainwater harvesting system in a building is believed to be discovered in Palace of Knossos on Crete. Archaeological works discovered sophisticated rainwater harvesting within the wider water management system (Gorokhovivch et al., 2011). Different technologies were used for water distribution and drainages, such as aqueduct, cisterns, sedimentation tanks and wells. Drainage canals, like the one presented in Figure 1, were also playing a significant role in the whole system (Gorokhovivch et al., 2011).
In north-west of Knossos in ancient Rome many residences were equipped with cisterns and paved areas for rainwater collection (Syed Azizul Haq, 2017). Romans were making great work in developing this technology. They have built beautiful Yerebatan Palace, known as a Basilica Cistern, which was a completely underground storage tank collecting rain runoff from streets of Istanbul. Construction, presented in Figure 2, survived until today and was the largest of the ancient cisterns with a water capacity of about 100,000 tons (80000m³) (Yilmaz Emre, 2014). Romans used rainwater for drinking, washing, bathing, agricultural irrigation and for animals.
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Figure 2. Palace/Basilica Cistern in Istanbul (Electrum Magazine, 2012)
Underground cisterns for rainwater collection were also found in Middle America. Captured rainfall was transported by drainage structures into the cisterns and from them conveyed further by pipes. Natural mountain runoff was also used for rainwater collection (Mays et al., 2013). The dense network of rainwater harvesting systems connected to the peoples’ settlements was used in north-west ancient Egypt. With minimal disruptions to the environment's scarce water resources utilisation was maximised to preserve water and soil resources of the region. Many of these systems are still in use (Vetter et al., 2009).
Nowadays, rainwater harvesting is still used in many countries around the world, despite the climate and water accessibility (Yannopoulos et al., 2019). Both basic rainfall capture systems and modern, more sophisticated ones are in use. Rainfall reuse is often an addition to the whole water management system to support shrinking resources and address increasing environmental issues. Usually used to satisfy non-potable water needs, in some cases rainwater treatment may be a response to reduce the number of people without access to drinking water. This objective is paramount for the Global Rooftop Rainwater Harvesting Movement, which is behind rainwater harvesting to deliver drinking water to the schools in rural communities around the World, especially those who are confronted with a severe water shortage
The Building Standards technical handbook 2019 issued by the Scottish Government provide guidance on rainwater harvesting in Scotland. System design, installation, maintenance and water end-uses quality requirements have to comply with British Standards for rainwater harvesting systems (BS8515:2009). Water reuse systems that contain a public mains water back-up supply must comply with the WaterSupply (WaterFittings) (Scotland)Byelaws2014 to ensure suitable backflow safety at the point where back-up is supplied. Additionally, all pipework must be appropriately identified to reduce the risk of cross-connection (Scottish Water, 2020). Prior to the storage rainwater has to be filtered to eliminate organic material and dirt. In case of heavier contamination like faeces or oil disinfection might be essential.
This research will try to assess the benefits and drawbacks of this ancient technology, along with the ways in which it can be developed to provide the greatest advantage for human activity and the environment. Subsequent parts of this Chapter will discuss why it is important to do such research, how it will be carried out and what are the ways to answer the research question. Rainwater harvesting technology with a focus on rainwater collection from the rooftop will be discussed in detail in Chapter 2.
1.2 Importance of this study
Scotland is considered to be a wet country that possesses abundant water resources in comparison with arid regions of the World. However, estimations predict that drought periods in Scotland will double up by 2050 (Gosling, 2014; Waajen, 2019). In summer 2018 no rainfall period led to 30% water demand increase (Scottish Water, 2019). Dry periods occurrence has been recognised and appropriate steps have been taken to address this, such as producing Scotland’s National Water Scarcity Plan, which is the first document of its kind (SEPA, 2015). Additionally, SEPA prepares Water Scarcity Situation Reports since the beginning of 2019, which informs that north-east and south-west parts of Scotland are in the biggest risk of water scarcity during the summer months (SEPA, 2019). Estimations state that by 2050 people from over 570 World’s cities will face at least 10% decline in freshwater availability due to climate change (UNESCO, 2020). Even though Glasgow’s population growth, with 626000 people now, is slowing down (National Records of Scotland, 2018, 2019), rising water demands, and drier summers can still overwhelm the main water supply. Therefore, rainwater harvesting is being widely introduced across the World, to reduce climate change impact on water supply (Thamer et al., 2006). Additionally, the United Kingdom recognises rainwater harvesting as one of the key infrastructures in reducing surface water flooding (Quinn et al., 2020). According to SEPA annual average damages from flooding in Glasgow can account for 2.11 to 4.10 million pounds and in some cases even between 10 and 16 million pounds, with the risk of flooding up to 2900 properties (SEPA, 2016). North and south-east parts of Glasgow Avenues Project area are at high risk of flood from surface water (SEPA, 2020). Diverting rainfall from the sewer system to the households, as a non-potable water resource, reduce and delay storm water discharges to the watercourses. Water pollution is dispersed in time, erosion and sediment concentration in the storm water runoff reduced, and flooding risk minimised. Additionally, rainwater harvesting in a cold and humid climate with frequent rainfall, like in Glasgow, present the highest rainwater storage potential (Palla et al., 2012).
Copenhagen Accord of 2009 recognised reduction in greenhouse gas emissions as a way of tackling climate change (UNFCCC, 2009). The European Union intends to reduce CO2 emissions by 20% on 1990 levels by 2020 as does the UK. Furthermore, in the Climate Change Act (2008) the UK declare to reduce emissions by at least 80% by 2050 (Environment Agency, 2010). Rainwater harvesting could support this fight by eliminating raw water abstraction, which may lead to reductions in energy use and carbon footprint (Valdez et al., 2016).
Scottish Water, as one of the largest electricity users in Scotland spent a significant amount of energy into making water safe to drink, while half of it is flushed down the drain (Scottish Water, 2019/2020). If non-potable water demand could be covered by captured rainwater greenhouse gasses emissions would be significantly reduced, as the energy required for water treatment, abstraction and transportation over long distances would be eliminated. Kinkade-Levario (2007) argues that rooftop rainwater harvesting saves energy, as an increase of 1m in groundwater level can save 0.40 kWh in groundwater abstraction. As roofs constitute of around half of the total sealed surface of the cities, they offer significant potential for rainwater harvesting (Farreny et al., 2011). The biggest problem in supplying water comes from energy consumption during the operational phase. The efficiency of the water supply system increases when energy intensity and thereby carbon footprint decrease (.
1.3 Aim and objectives
This research aims to establish if rooftop rainwater harvesting within Glasgow Avenues Project area can lead to potable water savings, which could potentially result in a reduction of energy consumption and support a downturn trend in greenhouse gas emissions.
To achieve the aim of this research following objectives were considered.
Objectives:
- Establishing the rooftop surface available for rainwater harvesting with the assistance of the Glasgow Avenues Project and computer programmes (Microsoft Excel, Google Earth).
- Obtaining ten years daily rainfall data specific for Glasgow to carry out rainwater yield potential simulations on a short- and long-term time series.
- Determining runoff coefficient to be used for rainwater harvesting yield calculations.
- Estimating a number of residents living within a fixed area along the Glasgow Avenues Project to help calculate potential drinking water savings.
- Obtaining data on water consumption per person and water end-use for Glasgow to define possible drinking water savings.
- Obtaining data on Scottish Water energy used per water supplied (abstracting, treatment to drinking standards and pumping of water to the customers).
- Obtaining data on Scottish Water carbon footprint from drinking water supply.
- Establishing the best rainwater harvesting system for energy efficient non-potable water supply.
- Estimating energy use and carbon footprint of rooftop rainwater harvesting system proposed for Glasgow Avenues Project area.
1.4 Sample Methodology
This study’s introduction outlines the rainwater harvesting process and describes its relevance to the ongoing research in the field. The Glasgow Avenues Project will be used as a case study to determine the potential of rainwater harvesting in urban areas. Therefore, the data used in this study will be gathered in Glasgow. Quantitative and qualitative research methods will be used to answer the research question and achieve the established objectives. The data will be processed using mathematical calculations and computer software. The rainfall data, rooftop surface areas, and runoff coefficients will be used to determine the potential harvesting yield. These results will be compared with water consumption and the end uses of water to estimate the potential potable water savings. In turn, the potential water savings will be compared against the local energy consumption and carbon footprint to determine if rainwater harvesting in Glasgow Avenues can successfully reduce the carbon footprint and save water.
Next, the study will discuss the rainwater harvesting systems that could be used in the Glasgow Avenues area. The system that saves the most energy and potable water and thus has the greatest environmental benefits will be identified. Also, the study will examine existing urban rooftop rainwater harvesting systems in the UK and around the globe. The advantages and disadvantages of these harvesting systems will be determined. Based on all of these results, the best harvesting system can be conclusively identified. The system with the smallest carbon footprint will be chosen.
The methodology used in this study will be discussed in detail later in the appropriate section. The rationale behind the research methods used in the study will also be explained. Once all results with conclusions are presented, along with the answer for the research question with all pros and cons, recommendations for the future options for further investigation in the same area will be provided.
2. Literature review
2.1 Rainwater harvesting
Rainwater harvesting technique to capture and store rainwater for the future uses is an important unconventional water resource. Commonly used around the World, in countries such as Brazil, United States, Australia, United Kingdom, Sweden, proved to be effective in saving potable water resources (Hayssam Traboulsi, 2017). Rainwater can be collected from the ground or roof top level and stored in below or above the ground storage tanks. Shape and size of the catchment surface are important in terms of designing suitable system (adequate components). While surface material is important in terms of water quality appropriate for the end use (Syed Azizul Haq, 2017). Land use adjacent to the catchment surface is also important in terms of creating reliable and safe water resource (Eslamian, 2016).
Urbanised areas with big population, such as Glasgow, impose huge pressure on water resources. Fresh water conveyed from appreciable distances, as Loch Katrine located 55 kilometres north from Glasgow, involve a significant amount of energy for transportation, treatment and supply (Engineering Timelines, 2020). Harvested rainwater could be utilised for non-potable water purposes, such as toilet flushing, laundry, plant watering, and outdoor washing (e.g. cars, building facades, pavements, roads, etc.) which in Glasgow accounts for as much as 50% of water usage (Scottish Government, 2019). Rainwater is a source of high-quality soft water that is low in mineral content and thus it requires less detergents which makes it attractive for laundry or cleaning (Heather Kinkade-Levario, 2007).
Physical and chemical characteristics of rainwater usually do not pose substantial health risk when used as a non-potable water resource. Nevertheless, raised concentrations of such parameters can have an adverse impact on rainwater harvesting system itself. Some roofing materials can lead to pollution which might cause serious issues for the system's operation (Khayan, 2019).
Rainwater captured from specific areas vary in terms of content. Some microbial contamination from the rooftop can be beneficial for garden use, while water collected at the ground level of urban area will contain much more car pollution or pesticides from the run-off (Health Facilities Scotland, 2015).
2.1.1. Rainwater harvesting from the rooftops
For the best results in achieving valuable water resource in terms of quality and energy efficiency rooftops seems to be more attractive than the ground surface catchments (Farreny et al., 2011). Rainwater harvesting from the rooftop seems to be preferable to rainwater captured on the ground (especially in urbanised areas). Despite that contaminants present on the roof surface can also be of concern, they can influence rainwater quality and system longevity. Rainwater harvested from the rooftop usually contains microorganic contamination (Salmonella, Aeromonas, Cryptosporidium), heavy metals (lead, zinc, copper). Additionally, organic matter, animals and birds’ faeces, inert solids and complex organic compounds. However, levels of these contaminants decrease significantly as collection continues. No legal obligations standards are set for collected rainwater (Health Facilities Scotland, 2015). Usually pure rainwater is low in pollutants depending on the quality of the atmosphere. Atmospheric pollutants in urban areas consist of particles, heavy metals and organic substances (Helmreich, 2008).
Tar roofs, with higher concentrations of polycyclic aromatic hydrocarbon (PAH), can impair pollution-reducing devices effectiveness (filters) and are carcinogenic. Roofs made of zinc and copper, can increase concentrations of heavy metals and cause aquatic toxicity. (Helmreich, 2008). Additionally, heavy metals accumulating in sediments of rainwater harvesting system storage tanks can pose a problem for disposal of sediments after routine tank cleaning. Also, on the bottom of the storage tanks contaminants and sediments settle. Thus, the roof material should be considered in terms of system design and the intended deployment of the rainwater. (Ward et al., 2010). Additionally, rainwater harvested from roofs made of zinc, copper and lead are not suitable for potable uses (Heather Kinkade-Levario, 2007). Chemically inert roofing materials are the most desired ones as they exclude toxic pollution. Additionally, rooftop rainwater can contain urban pollution particulate matter, dust, mosses, lichens, pesticides, bird and other animal excrements and sea originating inorganic ions (Ca, Na, Mg, K, Cl, SO4), and dissolved gases, such as CO2, NOx, Sox (Kus et al., 2013).
Roof slope angle is also important in rainwater harvesting design, as it affects rainwater runoff during a rain event. Tilted roofs represent higher runoff velocity than flat roofs and clean roof surface contamination more easily. Slow rainwater flow on a flat roof poses a higher risk of contamination and collects rainwater more slowly and less efficiently than a sloping roof. (Lai et al., 2018).
Rainwater harvesting for non-potable uses can be done on any type of the roofing material (Heather Kinkade-Levario, 2007). For non-potable uses, such as gardens, toilet flushing, general cleaning, filter backwashing and laundry low or medium water quality is required. Where water is not used for consumption and there is a very low risk of contact (Health Facilities Scotland, 2015). Water must be clean and odour free, but not necessarily sterile. Thus, water oxygenation would be sought to prevent the water from smelling. Before rainwater reaches the storage tank it should be filtered. The mesh filters applied on the pipes are necessary, as is the first flush diverter device (Celtic Water, 2020).
2.1.2 Roofs in the research area
Roofs in Glasgow Avenues Project area are made of slate and such metals as lead, zinc, copper and stainless steel (Glasgow City Council, 2018) (Greene, 2014). Slate is a strong, very long-lasting material (can even last more than 100 years) with verygoodweather resistance and lowwaterabsorption. Its hardness and smooth surface make perfect conditions for a rainfall catchment. The runoff factor on them is relatively high, which benefits in higher rainwater collection (Syed Azizul Haq, 2017). Slateroofsare relatively heavy and must be considered while designing a system with a header tank installed at the top layer of the building. The header tank will add a weight to the overall building construction that might exclude some buildings which could be unable to support extra weight. Additionally, rainwater from slate roofs presents low or zero pollution (Helmreich, 2008). While not very important in the provision of water for non-potable uses, it could become beneficial if potable water demand were to be considered.
Roofs with zinc and copper can increase concentrations of heavy metals (Helmreich, 2008). It is not recommended to harvest rainwater from roofs made of zinc, copper and lead, for potable uses (Heather Kinkade-Levario, 2007). Glasgow Avenues Project area rooftops are located in an area of high traffic density. Cars emit lead, Particulate Matter (PM), Volatile Organic Compounds (VOCs), Nitrogen oxides (NOx) , Carbon monoxide (CO) , Sulphur dioxide (SO2) and greenhouse gases . Additionally, the roofs of Glasgow’s Avenues Project area are partially made of lead, copper and zinc which can bring potential hazards for rainwater harvesting system operation. However, rainfall collected from Glasgow’s roofs would be used as a non-potable water resource. Non-potable rainwater uses include flushing toilets, landscape and garden watering, car and floor washing and for such uses treatment of rainwater is not required (Thamer et al., 2006).
2.1.3 Frequency use of the system
Rainwater harvesting can be used with varying frequency, as those stated below:
- On an irregular basis when rainwater captured during the rainy season can satisfy all water needs, but through the dry season water demands are supplied from the mains water.
- Occasionally, with rainwater being stored for just a couple of days. Good to be used in regions with a moderate rainfall pattern, with very short no rain periods and with a reliable substitute water source.
- Partially, where collected rainwater is used to satisfy only a part of the water demand during the year. Rainwater can be used only for non-potable water needs like laundry, toilets flushing, cleaning or plant watering. Drinking water is then supplied from mains water.
- To cover full water demand through the year. This usually happens where an alternative water source does not exist. It requires good rainwater management practice and sufficient storage tanks to overcome dry periods (Malu, 2018).
2.2 Components of a rooftop rainwater harvesting system
There is no general agreed upon definition of a rainwater harvesting system. The basic rooftop system consists of a rooftop with an adjacent storage tank (Giesen, 2015). In this study we will consider six component groups between the rooftop and the distribution of rainwater to the outlets of the RWH system.
- Catchment Area (Rooftop), is the surface where rainfall is initially collected and directed to the storage tank. It should be taken into consideration that in this stage the rainwater will pick up any debris and/or contaminants present in the catchment area. Prior evaluation of the rooftop and immediate environment may be necessary. The roof may be flat or sloping. Within the Glasgow Avenues Project area, a majority of the rooftops are flat (Giesen, 2015).
- Conveyance systems, Enable the carriage of rainwater from the rooftop to where it's needed through pipes, gutters and drains. Water pipes should be of required capacity. The inlet of each drain at the rooftop should have wire mesh to restrict floating material (Malu, 2018).
- First flush devices. These are systems which flush off rainfall received in the first shower to avoid contaminating rainwater by potential atmospheric and roof contaminants. They also help to remove material deposited on the roof (e.g. silt) during the dry period. First rain separators should be installed before the storage tank (Gikas et al., 2012).
- Filters are components which remove contaminants from the captured rainwater. The rainwater can be filtered in different stages along the harvesting system, for example, before and/or after the storage tank. Disinfection, such as chlorination, ultraviolet or solar, might be needed to control microbial growth (Medina, 2016).
- Storage Tank is used to store the water that is collected from the roof after it has been filtered for debris and dust. Tank with cylindrical, rectangular or square shape. The tank should be covered on the top to avoid the contamination of water from external sources. The storage tank must be equipped with pipe fixtures to draw the water to sanitise it and to dispose of excess water. Dimensions of the storage tank can vary depending on the requirements of the household and the amount of rainfall (Giesen, 2015). Table 1 below presents materials commonly used to produce storage tanks. According to the British Standard (BS8515:2009) for rainwater harvesting, tanks should be equipped with screened ventilation and sealed lids to avoid rainwater contamination. They also should be carefully sited to prevent stored rainwater from reaching temperatures favourable for Legionella to multiply. Note that rainwater can be safely stored 10-20 days without the treatment (Health Facilities Scotland, 2015).
Table 1. Types of materials used in storage tanks (UH Water, 2016)
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- Distribution System, made of pumps, pipes and controls that have the purpose of delivering the water to the appliance outlets. Depending on the need of the user, the RWH system could be equipped with more than one pump or even none in some cases (Medina, 2016).
When rainwater harvesting covers only a part of total water needs, as in this report case, water back-ups from the public water supply will be needed. It is vital to equip rainwater harvesting system with a backflow prevention device, which block rainwater from entering to the public water supply. Additionally, the pipes must be appropriately marked to avoid any criss-cross contamination. Air gaps are also very important as they prevent stormwater backflow to enter the storage tank. They protect stored rainwater quality, facilitate overflows detecting and stop insects from entering the storage tank (Health Facilities Scotland, 2015).
2.3. Rainwater harvesting systems
Rainwater harvesting systems can be divided into two categories, Gravity Feed Systems and Pump Feed Systems.
2.3.1 Gravity Feed Systems
- Gravity Only System is rare but possible to have. It works only using the force of gravity since both tanks, header tank and storage tank, are located above all appliance outlets. Despite being a tempting option because this system doesn’t use energy to run it does have some issues. The height of the components is crucial because it creates a high structural load on the building. It is also susceptible to fluctuations in the stored water temperature creating water quality issues (Rainwater harvesting methods, 2019; Water Treatment Services, 2020). Figure 3 graphically presents the system.
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Figure 3. Gravity Feed System (Freeflush, 2020)
- Indirect Gravity System (Header Tank)
Rainwater is stored in a tank either under or above the ground and pumped to a header tank located above the water appliance outlets. In case of pump failure water will still be supplied by the mains water top-up. The pump, located in the storage tank, only works when needed to fill the header tank and from there the rainwater is supplied by gravity, this RWH system is the most energy efficient of the systems equipped with pump, making it a preferable choice (Rainwater harvesting methods, 2019; Water Treatment Services, 2020). Figure 4 below presents the system graphically.
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Figure 4. Indirect Gravity System – Header Tank (Total Water Systems, 2020)
2.3.2 Pump Feed Systems
- Indirect Pumped System is similar to the above one, but not relying on gravity to feed the water appliance outlets. A booster pump provides pressurised water, making it possible for the header tank to be installed at any level of the building. Mains water supply is connected to the header tank. The fact that it is equipped with two pumps increases the energy consumption of this system (Rainwater harvesting methods, 2019; Water Treatment Services, 2020). In Figure 5 system diagram is presented.
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Figure 5. Indirect Pumped Rainwater Harvesting System (Total Water Systems, 2020)
- Direct Pumped System (Submersible)
This system doesn't use a header tank. Pressurised water is supplied by the pump on the storage tank, located above- or underground, directly to the appliances' outlets. This system is the most popular because of the simple installation and simplicity of the controls but not the most energy efficient system. Note that the pump located in the storage tank will run every time water is required in the outlets and if the pump fails no water will be supplied. Mains water supply is connected to the storage tank (Rainwater harvesting methods, 2019; Water Treatment Services, 2020). Figure 6 presents the system graphically.
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Figure 6. Direct Pumped System - Submersible Pump (Total Water Systems, 2020)
- Direct Pumped System (Suction) is a pressurised system similar to the system above, the main difference is that the pump is located outside the storage tank and sucks the water from the storage tank to the point of use under pressure. Mains water supply is connected to the pump in order to supply water in case the storage tank runs dry. Like the system above if the pump fails no water will be supplied. Take into account that this system also doesn't use a header tank, making it a viable option in cases where it is impossible or impractical to place a header tank in the building but the pump will run every time water is required at the outlets. (Rainwater harvesting methods, 2019; Water Treatment Services, 2020). Figure 7 presents the system graphically.
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Figure 7. Direct Pumped Suction System (Total Water Systems, 2020)
2.4. Rainwater harvesting system to be considered for Glasgow Avenues Project area
During this research Indirect Gravity Feed Rainwater Harvesting System (Header Tank) was chosen as the best possible solution for water supply within Glasgow Avenues Project area. The system will be used with partial frequency to cover only a part of water demand. Glasgow’s rooftops will be used as the catchment surface. Daily non-potable water demand will be pumped from the underground tank to the header tank located high in the building. From there water will be delivered to the outlets within the households by gravity. Energy use will be minimised as this solution optimises pump operation. Pump runs at a full flow only when the header tank requires refill (Abel S. Vieira et al., 2014). In the event of pump failure water will be supplied by the mains water top-up directly to the header tank. A disadvantage of this solution might be low water pressure, although the booster pump installation at the header tank can tackle this issue.
2.5. Summary
Existing rainwater harvesting technologies offer a wide range of systems to be used. All of them rely on collecting the rainwater from the catchment area and diverting them to the rainwater storage tank, which is located either above or below the ground. Water conveyance goes through the use of pipes, down pipes or gutters. Rainwater harvesting presents various benefits for people and the environment. By the use of filtration, it removes pollutants from the rainwater, which would otherwise reach surface water, soil and eventually ground water. They also alleviate flooding risk by the prorogation of the excessive runoff and release tension on the sewer system. Another benefit is a non-potable water resource ready to be used straight after the collection, without the need for water treatment. That results in potable water savings, which are usually provided by the public water supply requiring enormous amounts of energy. Rainwater harvesting systems can be installed on a big and small (domestic) scale, from different catchments, from the ground and rooftop level, for various uses and with use of different technologies.
Subsequent chapters of this paper will present methodology used to reach measurable results in terms of an answer to the research question.
3 Methodology
In terms of answering the question of this study, mixed methods of research will be used. Mixed methods are described as research, where elements of qualitative and quantitative techniques are combined to offer a broad and in depth understanding of the subject (Schoonenboom, 2017). Such a combination of research components expands and reinforces the study making it broader and more sophisticated. A study in which mixed research methods are used is of heightened knowledge and validity. Quantitative research involves an investigation of the subject by collecting quantifiable data and based on them producing statistical analysis (Yin, 2018). Quantitative research collects information about the investigated topic and depicts results in numerical form. After careful analysis of provided numbers conclusions and predictions can be made (Johnson et al., 2007). On the other hand, data collected and analysed in qualitative research is of no quantifiable character. It does not provide definitive answers like quantitative analysis, but it allows to make judgements about a problem or it may lay the foundation for future research in the same area (DePoy et al., 2016).
In order to answer the study question, potable water savings have to be determined and based on them the carbon footprint can be then estimated. To do so, daily rainfall from 2010 and 2011 will be investigated. This period of two years was chosen due to its extremely varying rainfall figures, especially when compared to other years from that decade. Additionally, all ten years between 2010 and 2019 will be examined for monthly rainfall, rainwater harvesting yield, potable water savings and carbon footprint. Available catchment will be determined. In this case total rooftop surface available for rainwater harvesting needs to be surveyed. For more accurate calculations, two roof types are distinguished and appropriate runoff factors applied. Once these calculations are completed, rainwater yield will be compared with water end-uses to determine whether rainwater can be used to cover water demands within the study area, and if there is enough rainwater to store for future use protection.
The study will consider domestic water end-uses within residential properties for which the total water consumption per person will be determined. Existing techniques of rainwater harvesting will be investigated to determine the optimum solution for the study area.
The quantitative research part of this study will mainly rely on analysing previously gathered statistical data. Data about daily rainfall, water consumption and water end-uses in Glasgow will be obtained from Scottish Water and SEPA. While total rooftop surface from the use of Google Earth survey. After the data is analysed total potential potable water savings will be determined, and carbon footprint savings established.
In the qualitative research literature about rainwater harvesting will be reviewed and data specific for Glasgow used in the Glasgow Avenues case study. Background information explaining the concept of rainwater harvesting, what is its importance, its advantages and disadvantages along with possible solutions, will be provided in the theoretical study of the existing literature.
3.1 Theoretical study
In order to answer the study question theoretical research is needed to provide a better understanding of the discussed topic and facilitate the process of coming to conclusions. Hence, preliminary background, in the form of an Introduction Chapter was produced to familiarise the reader with the topic of this study. The introductory part outlines a general overview of the project’s idea and its value within that field. This section links the study’s proposal with the way it can be accomplished (DePoy et al., 2016). The general concept of rainwater harvesting was presented to the reader with special consideration of the benefits of using rooftop surfaces in providing non-potable water resources. A brief explanation on how the study will be done and its relevance was also stated.
In the next part of the study, in Chapter 2 literature related to the topic was reviewed and synthesized. Existing scientific works from reviewed sources, have been assessed, to ensure the reliability of presented information. Literature research aims to explain in detail what was already done within the topic, define possible gaps within research, potential for research and to organize the information for further study works (). Existing rainwater harvesting systems and technologies were examined in depth and explained to the reader for a better understanding of the solution chosen as the best possible for the study area. Possible benefits and drawbacks were also considered.
Various technologies were investigated to draw up benefits and limitations arising from specific systems. Based on insightful analysis the best potential solution is identified to be used for rainwater harvesting within the study area.
3.2 Glasgow Avenues Project as a Case Study
The case study is a popular method of research that focuses on single case analysis. Its great popularity comes from possibilities for comprehensive investigation over a given topic. Profound study over a topic from different angles helps in the identification of potential opportunities and issues (Crowe et al., 2011). To do so qualitative and quantitative research methods and a variety of data collection methods (surveys, interviews, or observation) are used (Yin, 2018). Extensive analysis of existing documentation ensures that the topic is explored through many different points of view. That makes future actions, ideas or decisions easier to make.
The question of this research study is “Can rainwater harvesting within Glasgow Avenues Project area lead to potable water savings and carbon footprint reduction? Rainwater harvesting as a non-potable water resource”. To answer such a question Glasgow Avenues Project area located in the centre of Glasgow City is used as a case study. Using existing data was justified because the research question was specific for Glasgow and Scotland and involved retrospective data figures. Rooftops of the buildings directly adjacent to the Avenues were considered in the Google Earth survey. Rainfall data was obtained from the Scottish Environmental Protection Agency (SEPA) through website research and by email contact. To monitor rainfall in Scotland SEPA uses rain gauges that report on an hourly basis. The closest gauge, located around 2,7 km south-east from the furthest point of Glasgow Avenues Project (Duke Street-Belgrove Street) sits within Dalmarnock Sewage Treatment Works (STW) and its location relative to Glasgow City centre is shown in Figure 8.
Editorial Note: Figure 8 was removed due to copyright issues.
Abbildung in dieser Leseprobe nicht enthalten
Figure 8. Dalmarnock STW rain gauge in relation to Glasgow City Centre (Google Maps, 2020)
Rainfall data and surveyed rooftop surface were used to calculate potential rainwater collection in the study area within short and long-term timescale. To make estimates more accurate runoff coefficient was also applied in the calculations. Water consumption and end-uses were used to establish the feasibility of rainwater harvesting to satisfy non-potable water demand. The number of Glasgow Avenues Project area residents was estimated with the use of data from statistic.gov.scot and Google Earth survey, and accounts for 12 388 people. According to Scottish Government statistic website, Glasgow City Centre is divided into sectors with the number of residents given as detailed in Table 2.
Table 2. Glasgow City Centre population divided by sectors (Scottish Government, 2018)
Abbildung in dieser Leseprobe nicht enthalten
All sectors overlapping with the Glasgow Avenues study area were considered in calculations and are marked in Figure 9. Google Earth was used to determine the surface area of all sectors by use of polygons and was 2,95km². Total sectors surface was divided by the total number of residents living within all of these sectors (17866 residents). This way number of people living on square kilometre was determined (6056ppl/km²). Then it was compared with data known about the study area, which is its surface. By the use of simple maths rule of three, the number of residents living within the research area was estimated and is presented in Table 3 in section 4.1 of this paper (Resourceaholic, 2020).
Glasgow Avenues Project is a part of Glasgow City Region City Deal fund, known as Enabling Infrastructure Investment in Public Realm (EIIPR) (GCC, 2016). The City Council invested £115 million to upgrade several city centre streets to “avenue” status. It is the UK's biggest active streetscape enhancement project (Glasgow Life, 2019), which aims to make links between key gateways, promote sustainable transportation, improve street design to make it more visually attractive, greener and sustainable (GCC, 2013). Continuous pedestrian and cycle lines are designed to consider the needs of people with visual or/and mobile impairments (GCC, 2018). The more “people-friendly” and accessible city centre will bring more people in, which can help in terms of achieving city centre economic growth. Construction works started in 2018 with the transformation of Sauchiehall Street into Sauchiehall Avenue, as a pilot project (GCC, 2018) and were completed in 2019 (GCC, 2020). Figure 10 shows Sauchiehall Street before works began and visualisation after works are finished. Remaining Avenues are to be completed in phases before 2027 (GCC, 2020).
Avenues Project prioritises cyclists, pedestrians and other vulnerable road users over the cars to discourage vehicular traffic, create safer, cleaner and vibrant public space which will attract tourists and investors (Urban Realm, 2019). A detailed list of streets included in the Avenues Project can be seen in Table 3 in section 4.1 of this paper, while Phasing Map is presented in Figure 11 below.
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Figure 11. Glasgow Avenues Project area -phasing map (Glasgow City Council, 2020)
3.3 Computer programs
To facilitate the whole research process computer programmes will be utilised. At first available rooftop surface for rainwater harvesting needs to be determined and to do so Google Earth will be used to carry out the survey. Data gathered from the rooftop survey will be prepared in the form of tables and graphs with the use of Microsoft Excel program. Daily rainfall data, population, total daily water end-uses, carbon footprint, energy use and rainwater harvesting potential will all be presented in the form of tables and graphs based on them. Excel analysis will then be used to make potable water savings calculations and to estimate potential carbon footprint reductions.
[...]
- Quote paper
- Anna Treder (Author), 2020, Can rainwater harvesting within Glasgow Avenues Project area lead to potable water savings and carbon footprint reduction?, Munich, GRIN Verlag, https://www.grin.com/document/968778
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