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| ==Literature Review== | | ==References== |
| This is a review of the available literature pertinent to rainwater catchment/harvesting systems.
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| ===Overview & History of Rainwater Catchment===
| | [[Category:Engr305 Appropriate Technology]] |
| Rainwater catchment (rainwater harvesting) is an age-old technique of capturing precipitation and water run-off, and storing it for future usage. These man-made systems use gravity to collect rainwater, or run-off, which makes them inexpensive and easy to use. <ref name="Maczulak">Maczulak, Anne. Environmental Engineering: Designing a Sustainable Future. New York, Page 149.</ref> The water is channeled into a downspout and directed into a holding tank, which can be above or below ground. Various design methods are used to harvest rainwater - from primitive construction to elaborate systems - depending on factors such as budget, usage, climate and geographical location.
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| “The appropriate design and evaluation of a rainwater harvesting (RWH) system is necessary to improve system performance and the stability of the water supply. The main design parameters (DPs) of an RWH system are rainfall, catchment area, collection efficiency, tank volume and water demand and duration of water demand from the tank. Its operational parameters (OPs) include rainwater use efficiency (RUE), water saving efficiency (WSE) and cycle number (CN). The sensitivity analysis of a rooftop RWH system’s DPs to its OPs reveals that the ratio of tank volume to catchment area (V/A)”</blockquote> <ref>From the Journal of Environmental Management (Volume 93, Issue 1, Page 147)</ref>
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| The captured run-off supplies societies and individuals with a fresh water source and helps enable sustainable living. These catchment methods have been practiced for thousands of years, recoded as far back in time as ancient Rome, where courtyards were paved specifically for catchment, and residencies had individual cisterns to capture rainwater. <ref>"Rainwater Harvesting Policy Resources", information on Australian law, http://www.oaecwater.org/rainwater-resources.</ref>
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| Globally, many civilizations are shaping their cultures and becoming keener on ecological modernization, which favors rainwater catchment and other appropriate technologies. Some regions have mandated collection of rainwater, such as in Gold Coast, Australia, where the City Council declared that all new homes past 2007 must have rainwater catchment set-up for non-potable usage. <ref>Rainwater Harvesting, information on history of harvesting, http://www.tn.gov.in/dtp/rainwater.htm.</ref> Laws such as these assert that rainwater catchment is an important and necessary tool for many areas in the world.
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| Rainwater catchment is mostly used in areas that are arid or semi-arid, and that may not have a constant flow of run-off annually; areas that are dependent on a local, nearby stream or river; and when the catchment area, volume of storage and capital investment in the system is usually small-scale. <ref>Boers, Th., Rainwater Harvesting in Arid and Semi-arid Zones. Environmental Engineering: Designing a Sustainable Future. New York. Page 1.</ref>
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| ===CAPTURING===
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| There are different ways to capture rainwater, and the most common systems are: roof catchment, ground catchment and rock catchment.
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| This Appropedia page has focused efforts of research on roof catchment systems, which are the most common. There are three main parts to this system, a catchment surface, a gutter and a down spout, and a tank. <ref name=Gould>Gould, John. Rainwater Catchment Systems for Household Water Supply. Bangkok, Thailand, page 4.</ref>
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| <blockquote>
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| “Rainwater collection systems use gravity to do the work, making these systems easy to use and inexpensive. Rainwater collects into large cisterns, barrels or roof top tanks connected to a down spout that carries it to a holding tank on or under the ground."<ref name="Maczulak"/>
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| </blockquote>
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| ====Roof Materials====
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| Galvanized corrugated iron sheets, corrugated plastic or tiles and thatched roofs with the right type of palm (like coconut)are all good catchment surfaces. Roofs with asbestos or lead based paints should not be used. The roof type and material will affect the amount of water collected. The amount of rainwater available to collect for supply depends on the amount of rainfall and the area of the catchment and the runoff coefficient, which is usually considered to be 0.8 based off of factors such as leakage, evaporation, etc. <ref name=Gould/>
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| ====Area Calculation Methods====
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| These are methods used to calculate the amount of runoff/rainwater catchment supply available by area:<br>
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| =====Mean Annual Runoff Equation=====
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| The most common method is using this equation that demonstrates the amount of supply available: S = R x A x C
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| Where S = Rainwater Supply, R = Mean annual rainfall, A = roof area in sq meters and C = the runoff coefficient.
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| Look here for data on [http://water.weather.gov/precip/| precipitation] and [http://www.nws.noaa.gov/tg/siteloc.shtml| individual site data].
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| =====Graphical Method=====
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| The mean monthly rainfall times the roof area is used to calculate the mean monthly roof runoff. Graphing on a monthly basis can display how much water you have during the year to use. A line representing usage can be drawn on the graph to show the extra and the insufficiencies in your system and at what month of the year they will occur. In order to determine potential rainwater supply, reliable rain fall data are required, preferably for a period of at least 10 years.<ref> Schiller and Latham, (1982) </ref> Note, in mountainous regions considerable rainfall variations can occur over short distances.
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| =====Statistical and Computerized Methods=====
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| *PEquals.com is an efficient way to calculate the estimated runoff amount your roof may supply: www.pequals.com/rain
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| *Here is another way to calculate water [http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/rainwater-harvesting-online-calculator/| usage].
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| ===DIVERSION===
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| Once the rain or precipitation lands on the roof, it is diverted into the tank through the following means:
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| ====Gutters and Downspout====
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| These lead to the storage tank and incorporate a first flush into the catchment system. A small slope on the roof will help save on costs when it comes to buying materials for gutters. All gutters will divert water into the water holding tank and should have a constant gentle slope to ensure that the water reaches it’s destination and to aide in prevention of blockages. <ref name=Gould/> To collect all available water off the roof all down spouts will need to be directed to the first flush device then to the holding tank.
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| A general rule is that all gutters should have 1cm^2 of guttering for every m^2 of roof area <ref>Hasse, 1989</ref>, or they should have a cross-sectional area of about 200 cm2 to minimize overflow when downpour of rain is very heavy. <ref name=Gould/>
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| ====First Flush====
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| Also know as a foul flush mechanism.
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| This ensures that the waste entering the system that has accumulated on the rooftop between rains is diverted from entering the tank. The amount of water that is diverted from entering the storage tank depends on the size of the roof that is collecting the water. These first flush systems are often simply designed, even a downspout from the root that has a small hand operated diversion valve will suffice. <ref>Nagy, Erik. An Analysis of Three Slow-sand Rooftop Rainwater Catchment System Filters. Page 10</ref>
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| ====Filter====
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| An important thing to keep in mind when capturing rainwater is keeping as much waste and debris from entering the system's storage tank as possible. There are different filtration methods available, such as installing screens on each of the gutters or downspouts to keep large particulates out of the system.<ref>A Simple Rainwater Harvesting Design, http://www.harvesth2o.com/simple_system.shtml</ref>
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| ===STORAGE===
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| Once the water has been captured it is diverted into your holding facility. There are many important factors to consider when storing rainwater. The tank is usually going to be the most expensive part of the system. Here are some things to look for when choosing a tank:
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| *A solid secure cover to keep out children, animals, breeding insects, dirt, and sunshine.
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| *A manhole, sump, and drain for cleaning.
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| *An extraction system that does not contaminate the water; e.g. tap or pump.
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| *A soakaway to prevent split water from forming puddles near the tank.
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| Extras
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| *A maximum height of two meters to prevent high water pressure.
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| *A devise to indicate level of water in tank.
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| *Lock on the water tap.
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| *A second sub-surface overflow tank to provide water for livestock, etc...
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| ====Tank Size====
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| To determine the size of the tank in your system, you must determine the amount of water that will be utilized and the amount of water that you can catch. (You can use one of the methods of calculating amounts of water collection listed above.)
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| ====Tank Location====
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| The location of the tank should be below the level of the roof where the water is being collected and the gutter system to allow gravity to do the work of moving the water to the first flush device and storage tank. In a well designed system, gravity will move water along a continuous downward slope from the roof to the gutter and eventually into the tank. The location of the tank to where the water will eventually be used is also important. It is easier if the tank is located uphill from where the water is needed to provide adequate head pressure to distribute the water by way of gravity feeding. Otherwise a pump will be needed or manually hauling the water up hill or a distance far away will be needed for water distribution. Tank location can be on the surface or sub-surface or a combination of both. A tank that is below the surface will need a pump to retrieve the water back to the surface or a pipe that leads downhill and back out to the surface if this is also where the water is to be used.
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| ====Over Flow====
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| When the storage tank reaches its volume maximum or level of water that makes the structure unsafe to hold anymore water, an overflow pipe is needed. The use of an overflow pipe is to purposefully direct excess water out of the tank to a location of choosing other than creating puddles near the tank that could weaken the foundation of the tank, house, or structure. The surplus water could be diverted to another holding tank or to a livestock trough, etc.
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| The extra water could start to cause erosion if not dealt with and sitting puddles could start to attract breading mosquitoes around the tank.
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| ====Water Quality:====
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| Cleaning & Sediments:
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| “As soon as the rain hits the roof it is subject to contamination by pollutants that were deposited on the roof by wind, animals, insects, or by the leaching and dissolving of the material that the roof is made of. If you go outside and look around your house, you’ll get a good idea of what is deposited on your roof between rains. Leaves, dirt, fertilizers, chemicals that you put on your land, animal waste, nearby industrial discharge and just about everything else around you will be blown or dropped onto your roof in some form or another over time.”<ref>Roof and Gutters: Safe Materials, http://www.thecenterforrainwaterharvesting.org/2_roof_gutters2.htm</ref> It is a good idea to clean the sludge and sediment out of your tank at least once a year to prevent build up that can block your system. A valve that can be opened below the outtake tap at the bottom of the tank in order to flush out sediment and sludge will be useful in cleaning.
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| Taps on roof tanks should be at least 30 cm above the base of the tank as this allows debris entering the tank to settle on the bottom where, provided it remains undisturbed, it will not affect the quality of the water in the tank.
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| ====Foundation:====
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| The ground under the tank should be able to hold the weight of the tank when full of water. The area around the tank should have adequate drainage.
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| ===Material Maintenance:===
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| During the construction of the gutters, downpipe and tank, it is prudent to have local participation to ensure that the future construction and maintenance of the tanks is accomplished with locally developed skill and that the talent stays in the area . The incorporation of local building materials can allow ease of future building projects. Local material to industrial processed supplies are available for construction. For those made out of organic material, more time on maintenance and replacement will be required. The use of organic building material for the Gutter and Tank for primary use or as reinforcements must be used with caution because of termite, rot, bacterial, and fungal attacks to the system could occur. If using organic material it is encouraged that you treat and or seal it.
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| ====Tank:====
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| Materials for the tank can include: Cement Jars, Concrete Ring Tanks, Ferrocement Tanks, Brick and Block Tanks, Metal Tanks, and preformed Plastic tanks. Tanks should be cleaned annually to avoid build of debris that could affect water quality or block water transportation in the system. Annually cleaning would also help reduce pathogens and other vectors that have built up in the water tank. A tank designed for above ground use has a different design than a tank designed to be put in the ground. Most preformed plastic tanks will have operational standards to their specific design. Most plastic tank walls will start to weaken in constant operating temperatures of 100 degrees Fahrenheit (38 Degrees Celsius). Most plastic tanks can operate around and above freezing but the liquid inside when frozen will expand and could cause a failure of the tank walls if there is no extra room for the expanding substance. Most plastic tanks are not designed to contain pressure or a vacuum and must be constantly vented to atmospheric pressure or the walls of the tanks could fail. Plastic tanks will expand and contract with changes in temperature, so if using tie downs or fastening rings an account of this needs to be made.
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| ====Gutter and Downpipes:====
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| The system of gutters and downpipes should also be cleaned annually along with the tank to remove leaves, branches, and other debris that has accumulated over time. The removal of branches that overhang the roof and gutters will alleviate debris buildup and reduce bird and animal fecal matter introduced into the water system.
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| ===Usage:===
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| The types of usage for rain water can be either grey water usages or treated for potable water use.
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