SubSurface Dams - Sustainable Sanitation and Water Management ...

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3) The reserved water level during the rainy season of 2000 was very low comparedwith that of the previous years, and the lowest level between the end of the dry seasonand the beginning of the rainy season fell in 2001. This can be attributed to theexceptional drought in 2000 around Nare Village. The reserved water level was alsolow during the rainy season of 2001. It may reflect the fact that the annual rainfall in theupstream area of the Kolongo River basin was lower in 2001 than in 2000 (see Table 6.3).The reserved water level is thus closely related to rainfall within the drainage basin of theriver.Altogether, the reserved water level is rising year by year in spite of the obvious seasonalfluctuation and a fall in the exceptional drought year.Figure 6.5 shows the interannual fluctuation in the groundwater level observed in the wellNP-1 located 5 km upstream of the subsurface dam, which followed a similar pattern of risingwith seasonal fluctuation. This interannual rising trend of the groundwater level was alsoobserved in the other wells located upstream of the dam. It was thus concluded that thereserved water level of the subsurface dam is consequently rising with the upstreamexpansion of the reservoir area. The reservoir area was estimated to reach 5 to 6 kmupstream of the subsurface dam in 2002.55
RiverTopsoilFossil valleysedimentGroundwater level(2 October 1998)Groundwater level at the beginning ofOctober 1997 (B-2-7)Bottom of fossilvalley (surfaceof basementrock)Basement rockA: Groundwater level upstream and downstream of subsurface dam (2 October 1998)RiverTopsoilFossil valleysedimentDrop inwater leveldue topumpingGroundwater level(from 19 to 24th of February 1999)About5mBottom of fossil valley(surface of basement rock)BasementrockGroundwater level at the end ofFebruary 1997 (B-2-7)(m)B: Groundwater level upstream and downstream of subsurface dam (from 19 to 24 February 1999)Fig. 6.3: Change in reserved groundwater storage state56
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 14 and 15: A large amount of waterevaporates f
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 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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