ENGGEN 115 Introduction to Design Faculty of Engineering University of Auckland Engineers Without Borders Conceptual Design Assignment Rainwater Collection and Storage System For the Supply of Drinking Water to Devikulam, Tamil Nadu, India 28 September 2011 CONTRIBUTORS M Fairley D Packwood P S Raymond T Zhang
Executive Summary The Devikulam community is a group of three small villages in India, with approximately 400 people across 90 households [2, 5]. As only one of three bores in the area can still be used to supply drinking water, residents are in dire need of a reliable and sustainable source of daily drinking water. Our solution is to construct several rainwater capture and storage systems in the area to meet this brief. It was decided the optimal solution was to build a series of smaller systems, each supplying and incorporating 5 houses. This creates reliability, as multiple systems reduces the chance of a system-wide failure, and also reduces the inconvenient high travel distance to a water source currently incident on residents [2]. Additionally, this removes the reliance on existing incomplete infrastructure, as households in the colony are not directly linked to the village supply, and rely on using a common tap to attain suitable drinking water [2]. The water collection system makes use of the existing roofs of the houses using each system. Bamboo halves, an easily replaced sustainable resource, are used to catch and channel rainwater into a gutter, which filters the rainwater to remove debris and flows downward sloping into a 10 000 L tank, thus requiring no pump. The tank can either be prefabricated from a polymer material, or constructed onsite from ferrocement. This solution has been projected, in context with average rainfall figures, to easily supply the community with continuous drinking water throughout the year, and even store plentiful water in times of drought, greatly easing the burden they currently live with every day. Background This project began with the goal of strengthening the reliability of water availability in Devikulum Village, Tamil Nadu, in India. The area containing about 400 people in 90 households [2, 5] is currently supplied with water for drinking, cooking and cleaning by three bores and three 30, 000 L water tanks [2]. The current system presents a range of issues that we sought to partially address through the design of a supplemental rainwater collection and storage system to supply the whole area with potentially all their drinking water requirements. The bore system has only one bore capable of supplying drinking water, with one other being described as saline and the other being out of operation [2]. This operational bore sourced its water from under the pond, an area also exposed to potential contamination from animal and human fecal matter that could mix with the water, especially in the Monsoon season [2, 3]. Water quality analysis has revealed very low bacterial levels of the current drinking water supply, but the danger of contamination is still present, and salt levels may rise making all the bores unsuitable for drinking water [2, 3]. There exists reliability issues with the current system, which requires repair and maintenance to desalinate water, remove leaks from pipes and other improvements, but it was also felt that due to the essential nature of drinking water, a rainwater ENGGEN 115 Conceptual Design Report 1
collection system that supplied drinking water to all villagers whilst they continued to source cleaning water from the bores would create a more robust water supply system [2, 3]. Furthermore, the area is divided into the Village, Thoppu and Colony, with houses in the Colony not having taps in each house to supply drinking water, only cleaning water, which required people to collect water from the tank in large buckets each morning and evening with the water being available only one hour each time, and susceptible to power failures of the pumps [2, 3]. Above all, with the provisioning of rainwater collection and storage we can provide the people with access to clean drinking water 24/7 directly from their houses. Project Objectives The objective has been to fulfil the requirements outlined in the Product Design Specifications, primarily collecting and storing rainwater for consumption within the community. This objective has been achieved by means of extended research, collecting relative data for modelling and evaluation of available technologies. The decision for the design solution was made using the following prioritised criteria: Performance: The potential for the solution to provide the volumes of water required for consumption with respect to the modelled rainfall data. Safety: Ensuring the safety of the structural components of the solution and the integrity of water quality. Environment: The feasibility of the solution being sustainable and have the absolute minimal environmental impact. Reliability: The ability of the solution giving a consistent performance with Longevity: minimal human input. The projection of how the solution will last before continued use is no longer a viable option. Maintenance: The combination of readily available resources and the technical knowledge required to service the solution during its operational life cycle. Cost: Minimising the costs involved with both purchasing the components, and to install the operational solution. Development Approach The consumption of drinking water was assumed to be constant every day of the year and calculated taking into account the villagers average exercise level, weight and temperature of their environment. The solution was designed with three main areas of functionality: Collection: The system of components associated with the collection of the rainwater relative to the modelled data. Collection itself was modelled by rain hitting a surface area and flowing down a slanted surface under gravity, with the total water able to be collected per month calculated by the equation: Rainfall (mm) * Surface Area (m^2) * Efficiency Coefficient = Volume Collected (L). Consideration was applied to the fact rainwater is exposed to pollutants and microorganisms when flowing over the roof. ENGGEN 115 Conceptual Design Report 2
Delivery: Storage: The system of components associated with the delivery from the collection system to the storage system, as well as from the storage system for consumption. Delivery was modelled by water flowing from a slanted surface into a gutter connected to a pipe leading to a water tank that filled up from the top. The system of storing the collected rainwater in a readily available state while maintaining its quality. The capacity of the water tank was calculated considering collection versus consumption figures and incorporating a safety factor to ensure the tank will store enough water during months of low rainfall. In order to streamline a viable solution for the entire region, several very specific assumptions and projections were required. These included that t the community comprised of 90 households, totalling 400 residents between them extrapolated from the 358 residents in 2008 [2, 5] (thus maximising the possible water requirements). It was assumed that each dwelling had a roof of dimensions 6m x 4m [2], that all roofs were suitable for construction of a collection system, and no houses were under a canopy. Based on research, each resident was projected to require 4L of water per day for drinking, a figure larger than that expected in practice to ensure requirements were met. In addition, an Efficiency of Collection (Run-Off) Coefficient of 0.8 will be used on all water collection figures, to allow for water lost through evaporation, leakage and general wastage [1]. Design Calculations The first logical move is to project the volume of water it possible to collect and/or store from the rooftops of the community, based on historical rainfall figures [4], and assuming a surface area of 24m 2 per roof [2]; Graph 1 Rainwater Projections* ENGGEN 115 Conceptual Design Report 3
*See Appendix 1.1 for Table of Figures pertaining to Graph 1 It was calculated that 1mm of rainfall falling on 1m 2 collects 1 L of water, which when adjusted for run-off and evaporation is assumed to be 0.8 L. From this exercise it was clear there was more than enough water for 8 months of the year, and that it was possible to collect enough rainwater to supply the drinking water for an entire year. However storage was required to meet rainfall consumption deficits lasting 4 months. The total deficit has been calculated to be approximately 2700L for this period in an average year. In addition, from our Product Design Specification, it has been identified that it would also be beneficial to store a 3 month water supply as a precautionary measure for unpredictable periods of drought. This totals approximately 144 000L. If the community is divided into 18 subsets of 5 households, each with their own system, this requires at least 8 000L of storage per system. Therefore, in order to provide certainty, a capacity larger than this must be provided. Note that all final collection figures have been adjusted for imperfections in capture with the Run-Off Coefficient. Recommended Design Following further research into our considered methods, and employing a Multi- Attribute Rating Technique to finalise the most suitable designs, the following solution to our Product Design Specifications has been recommended: Collection: Installation of a water catchment system on the roof of every residential building in the village; made of bamboo cut in half in the vertical direction and tied down and/or nailed strongly to the dwellings so the channel formed by the bamboo runs down the side of the roof towards a large similarly-bamboo gutter. The bamboo should be sourced locally, and be structurally solid and of a large diameter. Channels need to be tightly packed to create what is virtually a waterproof barrier, catching as much rain as possible. Gutter needs to slope downwards along the side towards the delivery intake, with the other end and sides encased to avoid overflowing. Delivery: Pipes connected to the bamboo guttering, running slightly downhill towards the nearest storage facility to promote water flow, avoiding stagnation and so a pump is not required. Plumbing should be made from white PVC (100mm standard diameter) or if possible sealed bamboo (on an individual basis), and at the point the system becomes closed a candle filter should be installed, requiring little maintenance but vastly improving water quality. Using a white material reflects heat energy, reducing the chance of fire, whilst clear material would promote bacterial growth [Sir Ray Avery, 2011]. A coupler to join the pipe to the gutter is also required. Storage: ENGGEN 115 Conceptual Design Report 4
Installation of one 10 000L storage tank per every 5 houses in the community, positioned as close as possible to each of the 5 houses it is supplying, to ensure the delivery system works. This creates ease of access, and certainty that the residents are not relying on one inefficient system. If financial constraints allow it, a tank made of a strong polymer should be purchased and transported to site, alternatively a tank can be constructed onsite from a ferrocement reinforced with bamboo [1]. A plastic tank would release phthalates, killing bacterium and increasing the storage life of the water [Sir Ray Avery, 2011]. Each tank requires intake from 5 houses, and the outtake tap must not have any horizontal features to avoid bacteria build up. To ensure delivery system into the tank is downward sloping, possibly build the tank into the ground. In addition, supply a set of educational manuals to instruct residents on how to maintain and most sustainably See Attached Computer Assisted Design Drawings Conclusions From the conceptual design process, it has been concluded that: - Modelling of the researched rainfall data shows that adequate water can be collected from this source - Collection of this resource by implementing the recommended solution in this report can be achieved within practical limitations of both existing infrastructure and further investment of resources - This solution provides significant flexibility of parameters both during the implementation, as well as over the course of the products lifetime References 1. WaterAid, England (Accessed 21/09/11) http://www.wateraid.org/documents/plugin_documents/rainwater_har vesting.pdf 2. Engineers Without Borders (Accessed 14-28/09/11) http://www.ewb.org.au/explore/initiatives/2011ewbchallenge http://www.ewb.org.au/housing http://www.ewb.org.au/watersupplyandsanitationsystems And all other resources provided / linked 3. Pitchandikulam Forest (Accessed 21/09/11) http://www.pitchandikulamforest.org/cms/content/view/23/31/ 4. World Weather Online (Accessed 21-25/09/11) http://www.worldweatheronline.com/weatheraverages/india/1017584/chennai/1023652/info.aspx 5. Unknown Organisation (Accessed 25/09/11) http://www.buzza.in/gramap2/devikulam_information.html 6. Sir Ray Avery, Personal Conversation with M Fairley, 26/09/11 ENGGEN 115 Conceptual Design Report 5
Appendices Appendix 1: Tables and Calculations 1.1 January 21 45360 36288 31 49600-13312 February 15 32400 25920 28 44800-18880 March 23 49680 39744 31 49600-9856 April 24 51840 41472 30 48000-6528 May 53 114480 91584 31 49600 41984 June 87 187920 150336 30 48000 102336 July 109 235440 188352 31 49600 138752 August 137 295920 236736 31 49600 187136 September 134 289440 231552 30 48000 183552 October 337 727920 582336 31 49600 532736 November 374 807840 646272 30 48000 598272 December 153 330480 264384 31 49600 214784 Total 1467 3168720 2534976 365 584000 1950976 Month Average Rainfall for Month (mm) Maximum Possible Volume Collected (L) Adjusted Maximum Possible Volume Collected (L) Days in Month Volume Consumed (drinking) (L) Surplus (L) Total Roof Area of Village = Average area per house * number of houses = 24m^2 * 90 = 2160 m^2 Village Drinking Water Consumption Per Day = Consumption per person * number of people in village = 4L/person * 400 persons = 1600L Rainfall, Collection and Consumption Projections ENGGEN 115 Conceptual Design Report 6
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D MODEL NAME TITLE EWB_ASSEMBLY 1 2 3 4 5 6 6120 D 2089.1 180 SCALE 19:1920 C 100 200 4000 4020.96 C 3000 100 1 B 100 6000 SCALE 19:1920 590 2200 B A 1780.72 146.62 6319.04 200 100 Centre Lines and Hidden Lines have been ommitted for clarity THIS DOCUMENT IS SUPPLIED IN CONFIDENCE. NO REPRODUCTION OF THIS DOCUMENT IN PART OR IN WHOLE OR THEREON OF THE ITEMS SHOWN MAY BE MADE WITHOUT THE COPYRIGHT OWNERS WRITTEN PERMISSION TITLE DRAWN BY CHECKED BY APPROVED BY SCALE 1:192 SHEET 1 OF2 A UNLESS OTHERWISE SPECIFIED ALL DIMENSIONS ARE IN MILLIMETERS. TOLERANCES ARE +/- 0.1MM +/- 1 DO NOT SCALE PROJECT MODEL NAME EWB_ASSEMBLY 1 2 3 4 5 6 ISSUE ASME STANDARD,MM
MODEL NAME TITLE EWB_ASSEMBLY 1 2 3 4 5 6 EWB Rainwater - Notable Components 150.07 150 3000 D 100 D SCALE 197.7 1:10 500 C 150 C 6120 4019.95 500 2089.1 B SCALE 19:960 150 180 B A 150 215 200 115 SCALE 6320 6340 19:960 Centre and Hidden Lines have been ommitted for clarity UNLESS OTHERWISE SPECIFIED ALL DIMENSIONS ARE IN MILLIMETERS. TOLERANCES ARE +/- 0.1MM +/- 1 DO NOT SCALE THIS DOCUMENT IS SUPPLIED IN CONFIDENCE. NO REPRODUCTION OF THIS DOCUMENT IN PART OR IN WHOLE OR THEREON OF THE ITEMS SHOWN MAY BE MADE WITHOUT THE COPYRIGHT OWNERS WRITTEN PERMISSION TITLE PROJECT DRAWN BY CHECKED BY APPROVED BY SCALE 1:192 SHEET EWB Rainwater - Notable Components Conceptual Design MODEL NAME EWB_ASSEMBLY 1 2 3 4 5 6 2 OF2 ISSUE A