Q&A of webinar - RWH and food security cases from Burkina Faso and Honduras

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RWH and

food security

cases from

Burkina Faso

and Honduras

Please find below the answers from IDE Burkina Faso to the questions posed during the webinar of the 23rd of September (in English only):

  • Does this breed mosquitoes since it is open to the environment?
We ask the villagers to add 5ml of cooking oil to any open water. It kills the mosquitos via suffocation. They breathe through their tails.
  • Why we were making experiments in Burkina Faso? When there are established process for rainwater harvesting?
We tried to develop a low cost technology for rainwater harvesting. We had only heard about expensive technologies based on ferrocement.
  • Is this water tank feasible for mountainous areas? How durable its structure is to cope heavy rains and slopes.
It should be feasible in mountainous areas digging more in the ground for stabilizing more the structure. For example in the case of a 2 meter structure it could be 1 meter inside and 1 meter outside the ground (half buried structure). The user would collect water at the bottom of the slope thanks to gravity flow. Thus mountainous areas including slopes would be an advantage for stabilizing more the structure as it offers opportunities for gravity flow from for example a half buried technology.
  • What would be the surface area for the roofing required to fill this tanks and based on average rainfall for your areas of work, how many days will the tanks take to fill? trying to see a cost benefit analysis.
In Ouagadougou, there is an average rainfall of 700 mm/year. The surface area for the roofing required should be at minimum 32 m2. 32*0,7= 17,9 m3. In that case the tank would take all the rainy season (3 months) to fill. Regarding the cost benefit analysis, we estimated that the water need of 50 m2 of gardening crops irrigated with drip systems is around 200 l/day. In the case of a variety that has a cycle of 3 months (90 days), we have a total water need of 0,2*90= 18 m3. Then the crops could be sold on the local market for providing income or feed the household.
  • You said that the tanks only had 9 m3 and they are 18 m3. Did you calculate, using local precipitation values, the roof area required to fill the tank?
See above
  • What was the motivation for the tank design with the metal roofing as opposed to something like ferro-cement? Was it solely cost?
We used metal roofing and an impervious plastic canvas because it was cheaper than ferro-cement. Our aim is to propose low cost technologies.
  • Is low cost designs the prime criterion for designing rain water harvesting systems?
For an agricultural use we try to reduce the cost at the maximum. However for providing drinking water the prime criterion is water quality. It would be preferable to have an air tight structure and/or a post water purification system (UV...)
  • Where is the bag produced, in India or locally in Honduras?
The blue bag is a plastic canvas produced in Asia and easy to find on the Burkinabe market.
  • How we can reduce evaporation rate while harvesting rainwater water. As I am from a arid zone area where temperature is very hot?
There is a solution using sand dams where you store the water protected from the heat and evaporation: http://upgro.org/tag/sand-dams/, http://www.rain4food.net/kenya/, http://www.akvopedia.org/wiki/Sand_dam and http://www.ircwash.org/resources/final-project-report-water-harvesting-multiple-use-ethiopia-mustrain. We can reduce evaporation using an air tight bag that would be a plastic canvas without opening in the upper part of the structure. If there is no air tight bag, a shed above the structure would also reduce the evaporation.

- R

Dear R,

As someone who doesn't, for technology reasons, participate in webinars, your reply to the questions was very helpful.

RWH for kitchen gardens (you cite a 50 m2 garden) was a hot issue in inland S Africa, which also has an annual rainfall around 700mm. However the storage structures used there were too expensive to be adopted without lots of government subsidy and the drip strategy wasn't followed. 4mm a day for drip irrigation is an (economically) attractive figure and it may go even lower during germination or during periods of 'rescue' irrigation following interruptions early in the wet season. However using RWH to supplement a weak wet season is more difficult to manage than getting a second small crop (in the dry season) which I suppose is your main focus. Your 90 day 'crop cycle' sounds like a grain, but I guess a small (1/20 ha) plot is more likely to be used for vegetables.

To cover or not to cover (the tank)? Covers are expensive and slightly tricky. In NE Brazil and also I think in Somalia, the use of fairly deep and linear tank pits significantly reduces evaporation without having a cover - especially in seasons where the sun isn't straight overhead and where some shading or wind-screening is feasible. With a membrane lining (e.g. tarpaulin), all the water's pressure can be transferred to the earth walls of the pit. However the lining might float up if the water table rises ahead of the tank filling. Pits, where feasible can also accept partially filtered ground runoff. They might however present a drowning hazard to small children and unless on a steep slope will need a rope-and-bucket or other means of extracting the water (your experience?)

Treating the surface with thin oil (to suffocate mosquito larvae) is cheaper than having a light-sealed cover. Does oil also inhibit growth of algae or spirogyra (weed) or does it feed them?


- T

Please find below also the answers from IDE Honduras to the questions posed during the webinar of the 23rd of September (in English only):

  • Is there any other rainwater harvesting, for example by private people themselves? And what are government attitudes?
Yes. Many programs have promoted rainwater harvesting through roofs into traditional plastic tanks. This has been awarded to farmer through grants and there have not been many intents to build cheaper reservoirs and making these available through local supply chains. iDE has a history of creating supply chains for base of the pyramid and in the case of RWH, we will train local capacity to build metallic tanks as the ones built in Burkina Faso and recently in Honduras. Also we are training (boyeros) people to handle the oxen in order to build the reservoirs on different types of terrain, taking advantage of the surroundings. The metal scraper is an adaptation to the wood scraper built originally by our partners in Philippines and now our local Technical Staff is working closely with local metal shops to produce our own designed (improved) metal scooper. These workshops have been setup to manufacture appropriate technology with the support of RELATA (Latin American Network for Animal Traction). The Government of Honduras has signed an agreement with IFAD and we are hopeful that iDE and Rain Foundation partnership will soon be able to implement many solutions for Rainwater Harvesting in the 5 driest departments within the zone of influence. iDE has signed and agreement with EmprendeSur and we expect to go to scale at the beginning of 2015.
  • If we lose the soil then we can allow for erosion?
This does not cause erosion since it is only the soil from which is taken to the edges around the reservoir. This is done to prevent erosion. Added to this we also use live barriers (Chrysopogon zizanioides, and also forage crop, Arachis pintoi).
  • Dry compaction is mostly not advised?
Correct, we make sure to wet the soil before compacting.
  • What measures are taken to stop evaporation?
We have not taken any measures to stop evaporation. We have recently built the first reservoir in July 2014 and the first rains started only until September. We have not experienced evaporation during the rainy season. As matter of fact, we have had too much rain, forcing us to improve drainage and consider increasing pond size for the future. The largest pond built by us in Honduras has a capacity of 540 m3 and it already experienced too much rain and we has surpassed capacity of reservoir. We have taken corrective actions.
  • How seepage rate could be reduced?
One way is a good compaction with clayish soil. If soil is sandy, it will require to transport clay from other site or to use plastic lining. Does not have to be too thick. Plastic can go around $0.25 for 1m2 (175 microns)
  • Is labour cost included?
It includes time of the oxen operator and the oxen. Any additional labor is not included. iDE technicians time in the field not included.
  • Did you try a cost/benefit analysis?
Not yet, we are trying to consolidate model by making it less expensive as possible and more efficient. We are also defining water requirement for x area of crops. This will be part of a larger study.

- R