SR article

Waterdrainage

To lighten the load on the electrical pump and to add not only to financial sustainability of the resource centre, but also to sustainability in general, rainwater should be stored. This article elaborates on various options.

Water drainage

To make the Pavilions not only financially self-sustaining, but also environmentally self-sustaining, they have been designed to catch a sufficient amount of rainwater from the roof. Aiming to be able to supply the compound with washing and drinking water as well as water for the crop fields during the dry season in Okana, a storage system needs to be thought of. In this part of the report various options will be discussed. Firstly there will be expanded on how the rainwater will be used.  An example of a successful water project will be given. Then the various options will be discussed. followed by the aesthetic issue that comes with this particular water drainage. In conclusion the best option for this particular building and area will be decided.

Rainwater and water fitration

SRI has its own borehole where they can tap ground water from with an electrical pump. They use this water for showering, washing and most of the people on the compound also use it for drinking.  Crop fields that generate income for the organisation cover a big part of the compound. In periods of drought these crop fields need to be irrigated, to provide a stable income. The problem is that the water from the borehole is not suited for irrigation. This because the water has a high level of toxic ions and that kills the crops on the long haul. Now in the dry period there is no source of income from the fields. By collecting rainwater the fields could be irrigated without them getting poisoned. Because of the big roof surface of the pavilions, they could provide enough irrigation water to cover the dry period. (Rouwendal&Straehle, 2016)

An extra feature for a water drainage system is the possibility to ad a water filter, to make the water cleaner. There are a lot of filters, but for rainwater harvesting most commonly used is a slow sand filter.  It’s an easy, cheap and widely available way to filter water. The principle is very simple: you take any container and fill it firstly with a layer of gravel, then a layer of coarse sand en then a layer of fine sand. The water will come in from the top and travel trough the different layers to come out clean. (Slow Sand Filter, 2014) Adding a slow sand filter in the design, will give an opportunity to provide a higher quality of clean drinking water.

Thailand Water Jar and Tank Programme

Not only in Africa the importance of using rainwater has been noticed. In Asian countries they also cope with dry and rain seasons. Through the whole of south-east Asia collecting rainwater via the roof has gained popularity.  In Thailand even the government has noticed the importance of storing this water during the rain season for security when it is dry. A nice example of a successful water project is the Thailand Water Jar and Tank programme.  In 1980 several people created a manual for the construction of a water jar made out of cheap and readily available materials in the rural areas of Thailand. The design was based on an authentic Thai water jar, which made it fit the aesthetics of the area (image 1 (Luong, 2002)). The government funded training in building these water jars, which created employment. Making sure these jars could be sold at around 20 usd it was affordable for most households. “The programme was an unusual initiative involving a broad range of stakeholders, including households, communities, NGOs, universities and the private sector with support from the Government at local, provincial and national levels. The result of this “bottom-up” meeting “top-down” approach was a programme that was unprecedented in the way it facilitated the access of rural people to potable water supplies, especially in northeast Thailand.” (Luong, 2002) Even though in the case of the pavilions it is a much smaller scale, hopefully it will show the community that with a small budget it is possible to store rainwater and use it.

Thai Waterjar
Image 1- Thai water jar 

Options

 Looking at image 2  (Rouwendal & Straehle, 2016) during the rain season each pavilion will catch 10000 litres of excessive rainwater (Rouwendal & Straehle, 2016).  To be able to store this for usage during the dry season per pavilion a water storage device holding this amount should be placed.  With the available budget at this particular moment this is not possible yet. Therefore there has been decided to store 10000 litres of the rainfall. This is not enough to make the pavilions completely self-sustaining, but it will be a start. In a later stage more tanks can be added.  It has been chosen to place two 5000 litres tanks. One to supply the pavilions with drinking and washing water and one to supply the crop fields. Various options could be opted for. Next these will shortly be discussed.

 

Rainwater harvesting

 Image 2 - Rainwater collection through the year

Above ground plastic tank:

By far the cheapest option is an above ground plastic tank. These tanks are widely available in the Kisumu area. These so called POA tanks are available in various sizes. It is simple to install, so labour cost will be low. There are some issues with an above ground water tank that should be taking into account. Firstly there is the problem of evaporation by the sun. The tank needs to be completely sealed off to ensure no water will evaporate. Also in areas with temperatures like in Okana the water will heat up sufficiently, which will accelerate biological activity and therefore contamination of the water. Lastly above ground water tanks are exposed to various weather conditions and therefore will wear out faster (Technology, 2008).

Underground plastic tank:

To be able to cope with the problem of the evaporation and heating of the water in a above ground tank, there could be chosen for an underground tank instead. Since the water stays cool by the surrounding ground, there will be no evaporation. Underground tanks create a dark and cold environment which limits algae and microbial growth. The lifespan is very high, since it is not exposed to the weather and the tank can be reused if needed. The issue with building an underground tank is the excavation. Some safety measures should be taking into account while excavating a volume of such size, which will bring extra costs. Another problem is the type of tank. To be able to endure the expansion and contraction of the ground a simple POA tank cannot be used. Especially in periods were there will be no water in the tank at all, it will collapse under the force the ground has on the tank. Needed is a special designed reinforced tank which is not available in the Kisumu area. To get a tank like that here would cost a sufficient amount of money. Lastly an underground tank needs a pump to get to the water. A simple hand pump would suffice in this case. Later could even be opted for a solar pump (Technology, 2008).

Concrete tank:

A simple option is a concrete tank. This could be build above ground as well as below ground. Cement, sand and ballast including workers with the proper skills are available in the Okana area. The life span of a cement tank is very high. If chosen for reinforced concrete called ferrocement it can be up to 30 years. There is no limitations in size and since the concrete has an isolating function as well, evaporation and biological infestation is limited as well. Still there are some issues. It is a very expensive operation. Also, a the quantity of cement, ballast and sand needed is very big. In case of using ferrocement this could be brought back a bit, but still will be very high. Therefore transport cost and labour cost will be high. In case of an underground tank the excavation problem as discussed before will be a problem. Lastly it is not reusable or movable to a different place once it has been build (Desai)

Aesthetic

The architects main goal for the project was to design a integrated building that would be self- sustaining in its water and energy supply. This to make it more feasible to maintain the building with a small budget, but also to set an example for other architects that it is possible to do this. In the original design they integrated the water drainage system within the pavilions by putting a water tank under ground in the middle of every pavilion. Each pavilion has a square opening in the middle of the roof, where rainwater could directly transfer into the water tank. Water would be included into the experience of the building but the storage would be out of sight. This principle would be ideal in their concept, but when they arrived in Okana they found out that it could not fit into their budget. They would have needed a lot of extra concrete foundation to make it work. They decided that they would leave the water drainage until the building was finished and then make a new plan.

 If you look into the options presented above, one of the considerations should be the aesthetics. The architects made the building complex as a whole, with the different aspects flowing into one entity. The buildings are formed in square and triangular shapes and the water storage should be formed in the same type of shape or it should be out of sight. The gutters have already been made and they are around the pavilions, which will contribute to experiencing the water around the building.

Conclusion

Since an exact overview of costs is not possible for all options, a table was created rating various factors from 1 to 5 (table 1). 1 being  very feasible and 5 non feasible. Using this the compare the various options it is clear there is not one  perfect option for this particular case. After talking to a local expert on water storage a solution was opted. Using a technique of isolating a cheap POA tank with fine sand will make sure it can cope with contraction and expansion of the surrounding soil. It will be underground, therefore the aesthetic problem as well as the evaporation and infestation problem are taken care of. The sand, tank and labour are locally available.  As shown in table 2 the costs are low enough for it to be feasible for this particular project.

 

Cost Tank

Cost Labour

Evaporation risk

Infestation risk

Availability

Reusable

Lifespan

Aesthetic

Above ground Plastic tank

1

1

3

4

1

1

3

4

Underground plastic tank

5

3

1

1

5

1

1

1

Above ground cement tank

3

3

2

2

1

5

1

2

Underground cement tank

3

4

1

1

1

5

1

1

Above ground ferrocement tank

2

2

1

1

1

5

1

2

Underground ferrocement tank

2

3

1

1

1

5

1

2

                   

 Table 1 - factor overview

Final design

Image 3 - Final Design

Still there are some things that should be taking into account. As shown in image 3 it is quite a volume that needs to be excavated. Some safety measures should be taken into consideration. To ensure no collapse of the hole  it should be dug out at a 45 degree angle to at least halfway of the total depth. This means that afterwards this should also be filled up again. The soil removed to be able to place the tank will be enough, so extra costs won’t be made. But it does mean there needs to be enough room for this excavation to take place. As shown in image 4 the positioning of the tanks that has been chosen for right now will not interfere with this. But if this option is used for a possible third tank accompanying one of the future pavilions this should be taken into account.

 

Costs in shilling

Amount

Total

5000 litre poaa tank

32000

1

32000

Handpump

3000

1

3000

Unskilled worker 1 day

200

4

800

Skilled worker 1 day

350

2

700

Transport costs

1000

1

1000

Total costs one tank

 37500 ksh

 Table 2 - Cost overview

Position watertank

Image 4 - Positioning watertanks

 

Bibliography

Desai, J. A. (sd). Opgeroepen op januari 13, 2017, van www.jadferrocements.net: http://www.jadferrocements.net/water-storages-tanks.html

Luong, T. (2002, September). Harvesting the Rain. A Construction Manual for Cement Rainwater Jars and Tanks . Bangkok, Thailand: UNICEF East Asia and Pacific Regional Office.

Rouwendal, E., & Straehle, L. K. (2016). From Landscape to Roofscape. Delft: Delft University of Technology.

Technology, C. (2008). Opgeroepen op Januari 12, 2017, van www.conservationtechnology.com: http://www.conservationtechnology.com/rainwater_storage.html

 Slow Sand Filter. (2014). Retrieved from Centers of desease control and prevention: https://www.cdc.gov/safewater/sand-filtration.html