Water Blogged

Githunguchu Catchment Tank

Posted by Steve Hall on January 27, 2020

We have been supporting projects with our implementing partner, Kenya Rainwater Association (KRA), since 2007. Through this partnership, we have implemented over 20 water, sanitation and hygiene education projects in Kenya. Here is their report on the project at Githunguchu Primary School:

A project management committee (PMC) comprised of representatives of the School Board (PTA), the Headmaster and KRA technical team was formed to undertake the following roles during the project implementation at Githunguchu Primary School:

– Coordinate the daily running of the project activities which included procurement of construction material and supervision of skilled and unskilled labor
– Community mobilization and sensitization on the project activities
– Security and storage of construction materials
– Participatory monitoring and evaluation (M&E)The project implementation commenced October 2019 and was completed in December 2019.

Construction of 75m3 rainwater storage tank: The masonry tank was constructed using dressed quarry stones (12″ x 9″ x 9″ and 12″ x 9″ x 6″), which were used for the tank walls. Each masonry layer of stone is reinforced with Y-10 twisted bars. After completion of the tank walls, plastering was done on the inner side using a 20mm thick mortar of 1:3, sand:cement ratio. A similar mortar mix ratio was used for the 20mm thick tank floor plaster.The dome-shaped reinforced concrete of the tank roof, including an 18” square manhole, was constructed. The formwork for dome-shape roof was made of timber (to hold concrete and reinforcement bars) and held by posts/poles from the inside. The water drawing points, which also serve as a hand-washing facility, were extended to about 6m from the tank with two taps to serve the pupils more effectively and reduce damage to the tank by pupils. The tank outlet was also fitted with a lockable manhole, which also provides the tank drain plug – used during periodic tank cleaning.

The following is an outline of the tank construction process in a chronological order:
1. Site clearance and foundation layout
2. Excavation of the foundation
3. Laying and blinding of hardcore
4. Construction of the concrete slab reinforced with heavy gauge weld mesh and Y12 and Y10 bars
5. Construction of tank wall, using a single masonry layer reinforced with barbed wire placed every 2 layers
6. Internal plastering of the wall and floor. Chicken wire was used to reinforce the internal wall
7. External plastering or keying of the masonry joints
8. Construction of the dome-shape ferrocement roof, which start with setting up the timber formwork, followed by laying of the reinforcement (using heavy gauge weld mesh, Y8 bars and chicken wire) and central pillar to hold the roof
9. Construction of water draw off points, including drain outlets
10. Installation of guttering system – including foul-flash device
11. Painting of the completed tank, signage for visibility and fencing around the tank

Installation of Guttering System: After construction of the tank, the guttering system was installed. This involved fitting the roofs with fascia boards made of 8″ x 1″ timber along the roof edge. The 2m long gutters (4″ x 4″ x 5″ (to allow 1” overhang to reduce overshooting of runoff from the roof)), were held by metallic hooks fixed on the fascia board. The gutters were laid in such a way to allow the flow/conveyance of water from the furthest end into the tank, through the foul-flash system. The foul-flash system is necessary to allow dirt water from the first rains (after a dry spell) to be diverted from the storage tank – a simple self-cleaning system – to improve the water quality.Thanks to the following for supporting this project!

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