Port Loko Schools - Clarifications requested on the following issues:
This proposal lacks many details that need to be included before any reasonable assessment can be made of its value. As it stands, it does not explain the current source of drinking water (whatever condition it is in), but only say that “All schools lack safe dri...
Port Loko Schools - Clarifications requested on the following issues:
This proposal lacks many details that need to be included before any reasonable assessment can be made of its value. As it stands, it does not explain the current source of drinking water (whatever condition it is in), but only say that “All schools lack safe drinking water and are situated in rural communities, and wells in the near vicinity of the schools are not working or have impure water quality.†They must be consuming water from somewhere. In particular, they need to address the following issues:
Existing Situation - Currently the school apparently has no water. So what do they drink during the day? Bottled water? Dirty well water?
Population to be Served – The number of people getting “safe drinking water†is 2,500. Number of school children getting water is 1070. So is the total number of persons served 2,500 or 3,570?
Water Consumption – Domestic water users are typically allocated allocated at least 30 liters per capita per day (LPCD) according to WHO, UNICEF and other major donors working in the rural water sector. If you assume that 2,500 people will get that amount, you'll need 75 m3 per day. That's a lot of water to get from a rainwater catchment from a school roof. For the 1,070 school kids, you say that they are only getting drinking water, so I assume you mean about two or three liters per day, a total daily demand of about 2,140 – 3,210 liters. But what about the water they need to wash their hands after defecating, and for flushing the latrines? Or aren't there any latrines, or perhaps only VIPs? If not, you should consider building some school latrines, as this will likely have a major positive impact upon their health.
System Design:
Basic layout – You apparently want to collect water from the school roof, then pipe it to storage tanks that will be built, then install India Mk-3 handpumps to pump water (presumably) just to the surface so people can take it home in jerry cans.
Storage Tanks - The basic design includes three underground water storage tanks, each with a capacity of 100,000 liters (mentioned in the Q&A section, not in the original proposal). I don't see any information about what they are to be made of (steel tanks – too expensive, brick lined tank – more likely and cheap, ferrocement – even better, and not too expensive).
Rainwater Collection – The proposal does not say whether they intend to use a roof collectors (presumably the school roof) or a ground collector (see below). A ground collector is sometimes cheaper and easier to work with, but you probably propose to use the school roof. However, there does not appear to be any information about the size or composition of that roof, so I cannot assess whether or not it will be able to meet your likely water demand. However, I made a quick assessment of about how big the roof would have to be to meet your water demand (see below). You should find somebody who knows more about the local weather to develop a more accurate assessment of the required area of the rainwater collector before you build this system. Also, as someone else mentioned, there was no mention in your proposal about piping from the collector (roof) to the ground storage tanks, nor the cost of that piping.
Surface Catchments: Rainwater harvesting using ground or land surface catchment areas is less complex way of collecting rainwater. It involves improving runoff capacity of the land surface through various techniques including collection of runoff with drain pipes and storage of collected water. From the Introduction to Rainwater Harvesting (see website: http://www.gdrc.org/uem/water/rainwater/introduction.html), compared to rooftop catchment techniques, ground catchment techniques provide more opportunity for collecting water from a larger surface area. By retaining the flows (including flood flows) of small creeks and streams in small storage reservoirs (on surface or underground) created by low cost (e.g., earthen) dams, this technology can meet water demands during dry periods. There is a possibility of high rates of water loss due to infiltration into the ground, and, because of the often marginal quality of the water collected, this technique is mainly suitable for storing water for agricultural purposes. Various techniques available for increasing the runoff within ground catchment areas involve: i) clearing or altering vegetation cover, ii) increasing the land slope with artificial ground cover, and iii) reducing soil permeability by the soil compaction and application of chemicals.
Collection Area – Have you actually made any calculations about how much water you are likely to get from the school roof collector, based on local rainfall data? I made two rough estimates that you might want to consider. One way to look at it is through annual rainfall (although of course, it varies considerably over the year). Weather data (from 1951-1980) for Freetown shows that it gets 312 cm per year. On an average basis, that's 0.85 cm/day. If you needed 75 cubic meters per day, you would need about 8,774 meters square. That's a roof more than 90 x 90 meters. I doubt that the school roof is that big, but I don't know. A perhaps better way of looking at it is to look at the “average stormâ€Â, which according to the weather data drops 2.5 cm per storm. For a 75 m3/day demand, the roof collection area would “only†have to 55 m square. So how big is the roof?
Cost – Although there was a general cost breakdown in the proposal, there was not much detail. Three tanks cost $32,142, which is $10,714 apiece. It doesn't say what the materials are, or the type of construction.
Therefore, it seems that some additional information needs to be included before any decision can be made about the suitability of this proposed system.
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