SubSurface Dams - Sustainable Sanitation and Water Management ...

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A large amount of waterevaporates from the water surface.Parasites andgerms appear.Dam is constructedto store water on theground surface.Buildings, cultivated land, forests,etc. are submerged.Disadvantages of surface damLittle water evaporatesfrom the groundwatersurface.Buildings, cultivated land, forests,etc. are preservedDam is constructed to store water under the ground.Principle of a subsurface dam and its advantagesReserved water isof high quality.Fig. 2.1: Principle of a subsurface dam11
2-2 Advantages of a subsurface damCompared with a surface dam, a subsurface dam has the following advantages:(1) A water storage system without land submergenceA subsurface dam does not submerge land area in contrast with a surface dam because itstores water under ground. Therefore, it does not seriously damage the environment, nordoes it cause social problems such as the forced migration of the local people.(2) Prevention of evaporation of reserved waterA subsurface dam does not lose reserved water by evaporation because water is stored underground and there is very little evaporation, in contrast with a surface dam that often loses asignificant amount of reserved water due to evaporation in the dry season in arid or semi-aridareas.(3) Clean, safe waterReserved water using a subsurface dam is of fairly good quality because it is stored underground, and it can be used like ordinary well water, in contrast with reserved water using asurface dam that tends to proliferate parasites, anopheles that transmit malaria, and germs, andrequires purification for domestic use.(4) A stable, secure damIn general, a subsurface dam is more stable than a surface dam from the viewpoint ofdynamics because it is buried under ground, and thus does not need maintenance. Even if itbreaks, there is no damage to the downstream area because the breakage occurs under ground.(5) Utilization of renewable resourcesShallow groundwater consumed via a subsurface dam system is renewable because it isrecharged with rainfall. Therefore, a subsurface dam does not exhaust water resources.2-3 Disadvantages of a subsurface damHowever, it is necessary to note that a subsurface dam also has the following disadvantages:(1) Difficulties in site selectionContrary to a surface dam whose site conditions can be examined by visual inspection,surveys for site selection and calculating the water storage capacity of a subsurface dam relyon estimates of underground geological structures.(2) Low effectiveness of water storageIn case of a subsurface dam, water is stored in the pores of geological strata. Therefore, thevolume of reserved water is determined by the volume of those pores (effective porosity), andreaches only 10 to 30% of the volume of the reservoir layer.(3) Interception of downstream groundwater flowA subsurface dam may prevent downstream groundwater flow, and exhausts groundwater inthe downstream area. However, groundwater in the downstream area is not alwaysrecharged only with groundwater from the dam site area. It is also possible to design a damwith a structure that allows some of the reserved water to drain. Therefore, this problem canbe avoided by appropriate site selection that considers the mechanism of groundwater flow, or12
Page 2 and 3: Photo: Construction of the subsurfa
Page 4 and 5: Subsurface DamSmall-Scale Surface D
Page 6 and 7: ContentsIntroduction1. General desc
Page 8 and 9: 1. General description of the Model
Page 10 and 11: Department of the Environmentand Fr
Page 12 and 13: According to the results of an anal
Page 16 and 17: y adopting an appropriate dam struc
Page 18 and 19: 2-5 "Fossil valley", a suitable sit
Page 20 and 21: temperature of 30 to 34 degrees and
Page 22 and 23: 3-3 Distribution of fossil valleys
Page 24 and 25: 3-4 Surveys carried out in this pro
Page 26 and 27: Satellite image of the area around
Page 28 and 29: 3-4-2 Field explorationAt the 5 sit
Page 30 and 31: 3-4-3 Geophysical surveyAt the 5 si
Page 32 and 33: Groundwater level assumed from the
Page 34 and 35: 3-5 Detailed field surveys (test dr
Page 36 and 37: Groundwater level isalmost the same
Page 38 and 39: The village is on a peneplain with
Page 40 and 41: In this project at Nare, the "earth
Page 42 and 43: DownstreamFilled back soil3mCoarseg
Page 44 and 45: All the results of the quality test
Page 46 and 47: Photo 4.3: Construction of the subs
Page 48 and 49: 4) Basal stratum of the fossil vall
Page 50 and 51: 6. Observation of the water storage
Page 52 and 53: Table 6.1: Features of the faciliti
Page 54 and 55: PerchedwaterImpermeablelayer“Main
Page 56 and 57: Table 6.3: Annual rainfall in the K
Page 58 and 59: 3) The reserved water level during
Page 60 and 61: Ground surface level: 275.73mGround
Page 62 and 63: 6-4 Analysis of seasonal fluctuatio
Page 64 and 65:
SandysiltSiltSand(white)Sand(moist)
Page 66 and 67:
(1) Relation between the rainfall w
Page 68 and 69:
4) Subsequently, the cycle in which
Page 70 and 71:
7. Other studiesIn addition to the
Page 72 and 73:
these facilities:- 3 mill stations,
Page 74 and 75:
Photo 7.3: Water-supply station for
Page 76 and 77:
8. Recommendations for future subsu
Page 78 and 79:
advisable to arrange rainfall stati
Page 80:
AcknowledgementsThe Model Project t
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