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*One equation that demonstrates the amount of supply available:  S = R x A x C
*One equation that demonstrates the amount of supply available:  S = R x A x C
Where S = Rainwater Supply, R = Mean annual rainfall,  A = roof area in sq meters and C = the runoff coefficient.
Where S = Rainwater Supply, R = Mean annual rainfall,  A = roof area in sq meters and C = the runoff coefficient.
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<br><br>
*Graphical Method
<u>Graphical Method</u>
<br>
<br>
Obtaining Mean monthly roof runoff.  This is calculated from Mean monthly rainfall times roof area catchment.  Graphing on a monthly basis can display how much water you have during the year to use.  A line representing usage can be draw on the graph to show the extra and the insufficiency's in your system and at what month of the year they will occur. In order to determine potential rain water 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.
Obtaining Mean monthly roof runoff.  This is calculated from Mean monthly rainfall times roof area catchment.  Graphing on a monthly basis can display how much water you have during the year to use.  A line representing usage can be draw on the graph to show the extra and the insufficiency's in your system and at what month of the year they will occur. In order to determine potential rain water 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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<u>Statistical and Computerized Methods</u>
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<br>
*Statistical and Computerized Methods*
*PEquals.com is an efficient way to calculate the estimated runoff amount your roof may supply: www.pequals.com/rain
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*Another way to calculate water usage: http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/rainwater-harvesting-online-calculator/
**PEquals.com is an efficient way to calculate the estimated runoff amount your roof may supply: www.pequals.com/rain
**Another way to calculate water usage: http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/rainwater-harvesting-online-calculator/
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Revision as of 08:25, 13 February 2012

Template:305inprogress

Background

The Mattole Valley Community Center is looking to install a rainwater catchment system on site in Petrolia, California. The Mattole Board of Directors is interested in having a working rainwater catchment system to water a community garden and also to utilize the project for community outreach and education about the benefits of appropriate technology. This project is starting in January of 2012 and is projected to be finished by May 2012.

Problem statement

The objective of this project is to catch rainwater from the roof of the Mattole Valley Community Center in Petrolia. The water storage will help water and accommodate extra irrigation for a flower garden located on site. This project will be a demonstration for the local community and other organizations to learn about the benefits of rain water catchment, visually show the rain water catchment process, and along with the utilization of the instructions laid out on this Appropedia site other individuals will potentially be able to produce a system for their own usage.

Ideas for the future

Options to educate also include the creation of an instructional pamphlet or on site graphic image board that explains details on the project or how to make your own system.

Project Evaluation Criteria

The following Criteria will be used to assess the success of this project. These criteria were chosen based on the suggestions of the project coordinator as well as the diligent students who are working on the catchment system. The scale (1-10) represents the importance level of meeting the constraint of each listed criteria.


Literature Review

This is a review of the available literature pertinent to rainwater catchment/harvesting systems.

Overview & History of Rainwater Catchment

Rainwater catchment (rainwater harvesting) is an age-old technique of capturing precipitation and water run-off, and storing it for future usage. Various methods are used in rainwater catchment - from primitive construction to elaborate systems - depending on factors such as budget, usage, climate and geographical location. 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 and residencies had individual cisterns to capture rainwater. [1]
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. [2] Laws such as these prove rainwater catchment is an important and necessary tool for many areas in the world.
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 [3]

Capturing

There are different ways to capture rainwater, and the most common systems are: roof catchment, ground catchment and rock catchment.
The following efforts of research have been focused 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. [4] “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.” [5]
Roof Materials:
Galvanized corrugated iron sheets, corrugated plastic or tiles are all good catchment surfaces, as well as thatched roofs with the right type of palm (like coconut), and roofs with asbestos or lead based paints should not be used. [6]
The amount of rainwater available to collect for supply depends on the amount of rainfall, 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.. [6]
Here are a few methods to calculate the amount of runoff/rainwater catchment supply available:

  • One equation that demonstrates the amount of supply available: S = R x A x C

Where S = Rainwater Supply, R = Mean annual rainfall, A = roof area in sq meters and C = the runoff coefficient.

Graphical Method
Obtaining Mean monthly roof runoff. This is calculated from Mean monthly rainfall times roof area catchment. Graphing on a monthly basis can display how much water you have during the year to use. A line representing usage can be draw on the graph to show the extra and the insufficiency's in your system and at what month of the year they will occur. In order to determine potential rain water supply reliable rain fall data are required preferably for a period of at least 10 years.[7] Note, in mountainous regions considerable rainfall variations can occur over short distances.

Statistical and Computerized Methods


Diversion

Gutters:
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. [6]
A general rule is that all gutters should have 1cm^2 of guttering for every m^2 of roof area [8], or they should have a cross-sectional area of about 200 cm2 to minimize overflow when downpour of rain is very heavy. [6]


PVC and Downspout These lead to the storage tank and incorporate a first flush into the catchment system.

First Flush:
This ensures that the waste entering the system that has accumulated on the rooftop between rains diverted from entering the tank and are often simply designed, even a downspout from the root that has a small hand operated diversion valve will suffice. [9]

Filter:
An important thing to keep in mind when capturing rainwater keeping as much waste and debris from entering the system 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.[10]

Storage

Tank Size
To determine the size of the tank you will need, you must determine the amount of water that you need to utilize, and the amount of water that you can catch. (You can use one of the methods of calculating amounts of water collection listed above.)

Tank Location:
The location of the tank should be below the level of the roof where the water is being collected and 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 or manually hauling the water up hill or a far away distance will be needed for water distribution.

Cleaning & Sediments:
“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.”[11]

Over flow: 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.
The extra water could start to cause erosion if not dealt with and sitting puddle could start to attract breading mosquitoes around the tank.

Quality of water and usage:
Taps on roof tanks should be at least 30 cm above the base of the tank as this allows and 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. Ideally tanks should be cleaned annually if possible.

Platform/base:


References

Template:Reflist

Criteria Constraints Weight
(1-10)
Community Will be able to hook up to two inch fire hose from fire truck to supply extra water.
5
Maintainability Must be easy to clean the filter and remove debris, no more than 2 hours maintenance per month
6
Aesthetics Must be pleasing to the eye and look professional
7
Educational Aspect Must include an educational piece for community (something to explain or highlight the benefit or creation of a rainwater catchment system)
7
Safety & Placement Must not interfere with walking paths, stairwells, or people's heads!
8
Reproducability The structure could be reproduced by local builders
8
Usability Must sufficiently water the garden on site (with use of hose attachment)
9
Budget Must not exceed budget
9
Functionality Successfully captures and stores rainwater
10
  1. "Rainwater Harvesting Policy Resources", information on Australian law, http://www.oaecwater.org/rainwater-resources.
  2. Rainwater Harvesting, information on history of harvesting, http://www.tn.gov.in/dtp/rainwater.htm.
  3. Boers, Th., Rainwater Harvesting in Arid and Semi-arid Zones. Environmental Engineering: Designing a Sustainable Future. New York. Page 1.
  4. Gould, John. Rainwater Catchment Systems for Household Water Supply. Bangkok, Thailand, page 4.
  5. Maczulak, Anne. Environmental Engineering: Designing a Sustainable Future. New York, Page 149.
  6. 6.0 6.1 6.2 6.3 Cite error: Invalid <ref> tag; no text was provided for refs named gould
  7. Schiller and Latham, (1982)
  8. Hasse, 1989
  9. Nagy, Erik. An Analysis of Three Slow-sand Rooftop Rainwater Catchment System Filters. Page 10
  10. A Simple Rainwater Harvesting Design, http://www.harvesth2o.com/simple_system.shtml
  11. Roof and Gutters: Safe Materials, http://www.thecenterforrainwaterharvesting.org/2_roof_gutters2.htm
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