the costs and benefits of water buffering

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Costs and benefitsThe costs reported here are extracted from the report “water harvesting potential for Africa, anassessment of costs and impacts”, by N. Goltzback et al (2011). The report describes various soilmoisture enhancements techniques. Some of the techniques are low-cost, as is outlined below.Because the water retained is not available freely, but is available for the crops, the costs areexpressed in ha instead of per m 3 .Low-cost material that can be used for mulching are agricultural residues, cut weeds and straws.The costs including labour and operation costs for mulching are USD 40 - USD 120/ha. Compostingassociated with planting pits may be as cheap as USD 8/ha, with the cost covering the digging,fertilization of manure and composting. Tillage (zero, chemical, or reduced) and adapted ploughingcosts are in the order of USD 40 - USD 120/ha. Loss of area to grow crops is also a cost that ismentioned in many publications, and should be included.For bunds, the price depends on the available earth or stone material and on the price of labour.Construction costs USD 8- USD 350/ha and maintenance USD 10 - USD 35/ha or 10 to 20 days/ha.Terraces are more expensive at USD 275 - USD 1840/ha. Labour is the main component of this cost.Maintenance of the terraces costs about USD 45 -USD 365/ha/year.The benefits include increased crop yield and support to a wider range of crops, saving, as well asthe protection of fertile soil on the land that leads to reduced fertilizer costs.Financing mechanismsThese measures are typically taken at community-level. The measures could be implemented andfinanced through, for example, users’ associations, community groups or farmers’ associations.There will be sufficient appetite for these measures to be financed and implemented, if there aresufficient financial returns in terms of increased agricultural production. In that case, the financingcould take place through tariffs or levying fees with (pre)financing through (communal) loans orfunds from the government budget. Due to the proven benefits of plastic mulch, subsidy programs(upto 50% of the cost) are in place in many countries topromote its use, especially in the Asiancontinent.ImplementationSoil moisture conservation practice can be applied independently, or in combination with othertechniques. For example, within the category of soil moisture storage, spate irrigation can becombined with contour bunds or terraces hence the spate water remains longer in the fields andcan infiltrate. Soil moisture conservation methods can also be successfully combined with methodsof other water retention categories. Irrigation water storage can be optimized when combined withsoil water retention methods. For example, less irrigation water will be lost when the soil’s waterholding capacity is improved, or when mulching is applied. Terraces may make efficient irrigationpossible at locations that were previously to steep. For efficient agricultural practice, soil moistureoptimization techniques often form a relatively cost effective basis.17
2.3.3 Storing in closed tanks and cisternsTechnologiesThe classic example of this category of 3R technology is the collection of rainfall from roofs and itsstorage in a tank. Alternatively runoff water can be harvested from prepared surfaces (includingstorm water runoff in urban areas, roads) and stored in underground reservoirs and cisterns.A rainwater harvesting system usually consists of three basic elements: the catchment system,the conveyance system, and the storage system. Catchment systems can vary from the rooftop ofa domestic household to a large ground surface catchment area that recharges an impoundingreservoir. The most widely used storage devices are tanks (or cisterns), with sizes typically rangingfrom 5-10 m 3 when used for drinking water purposes or 300 m 3 for supplementary irrigation. Smalltanks are made of polyethylene, ferro-cement, corrugated steel, plastered brick, concrete. Theiruse is typically complementary: water from the tanks may be used when collecting water fromelsewhere is not an option. Larger tanks may consist of excavated faults or natural depressions.The classification of rainwater harvesting systems depends on factors like the size and nature of thecatchment areas and whether the systems are in urban or rural settings.The appropriate storage capacity of a rainwater harvesting system is related to the amount anddistribution of rainfall. For example, in a region with abundant, steady rainfall all-year round,a small tank sufficient to hold a few days of rainwater will be enough to meet the demandsfor most of the year. On the other hand, drought-prone regions will need a significantly largercatchment area and storage tank to meet the water demand. Calculations take into account designparameters, based on a series of monthly rainfall data and sometimes supported by simple modelsfor the dimensions of a system.A point of attention in small tanks systems is the quality of the water. Common measures areavoiding the first foul flush to enter the tank, installing filters and screens, and regular cleaning.Figure 9 a,b,c. Closed storage options (Photos: Acacia Water and MetaMeta).Where to apply?Rainwater harvesting and tank storage can be applied where small catchment areas – includingroofs - are available and the rainfall patterns are such that the cost of storage remains withinacceptable limits. Such systems are generally expensive. They should be employed in areas where(IFAD, 2012):18
Page 2 and 3: Profit from StorageThe costs and be
Page 5 and 6: EndorsementI wholeheartedly endorse
Page 7: 5 Cases 385.1 Sand storage dams, Ki
Page 10 and 11: Box 1: Examples of economic cost of
Page 12 and 13: esilience and impact multiply when
Page 14 and 15: over time reduces their capacity. I
Page 16 and 17: can help bridge even an unusually d
Page 18 and 19: 2.3 The practice of water buffer ma
Page 20 and 21: Many different types and technologi
Page 22 and 23: ImplementationSmall MAR systems are
Page 26 and 27: ••Annual rainfall 3 is between
Page 28 and 29: levels. In other cases, the install
Page 30 and 31: Financing mechanismsThe choice of f
Page 32 and 33: Table 4. 3R solutions: use and scal
Page 34 and 35: Box 8: Self financed recharge movem
Page 36 and 37: 4 Calculating the costs andbenefits
Page 38 and 39: Box 10: Life-cycle costs of rainwat
Page 40 and 41: of a large number of roof top water
Page 42 and 43: improved integrated landscapes are
Page 44 and 45: It is important to mention that wat
Page 46 and 47: Table 5. Overview of cases in this
Page 48 and 49: Figure 16. Riverbed during the dry
Page 50 and 51: in siting and construction of sand
Page 52 and 53: Pasak Ngam is located in a part of
Page 54 and 55: Continuation and maintenance of the
Page 57 and 58: 5.3 Improved karezesQila Iskan Khan
Page 59 and 60: Figure 22. a) Villagers taking rest
Page 61 and 62: 5.4 Water augmentationthrough manag
Page 63 and 64: Table 9. Costs of water (2011)Exist
Page 65 and 66: 5.5 Creating fresh waterbubbles in
Page 67 and 68: Figure 29. a) Well construction; b)
Page 69: ••Injection of pond water can c
Page 72 and 73: ••The depression is fed by a la
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To avoid contamination by animals t
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drains, that normally discharge the
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Financing mechanismsAt the moment,
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from the streams, and keep water fr
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Table 14. Climate change impacts an
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Water-spreading weirs are usually b
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possibilities and prerequisites for
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Table 16. World mulch film market,
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efore or after the mulch is placed
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5.11 Soil and water conservationat
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There has been some additional supp
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ReferencesBerhane, G. et al. (2011)
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perpendicular to the direction of t
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Financing mechanismsThe contributio
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5.13 Buffering highland andspring w
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for about 15 years and a cheaper va
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5. 14 Rooftop harvesting andmultipl
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Wastewater from the kitchen, collec
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enter into an agreement with a micr
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Annex IClassification overviewof 3R
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Annex IIThe 2 Step wiseapproach tow
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Annex III Snapshot comparison ofthe
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Annex IVSelect impacts of Kenya’s
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