SubSurface Dams - Sustainable Sanitation and Water Management ...

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3-4 Surveys carried out in this project3-4-1 Interpretation of satellite images and aero-photographsSatellite images and aero-photographs are useful means of examining the physical conditions(landform, geology, surface water, vegetation, etc.) of vast areas. They are particularlyvaluable in surveying flat relief areas without precise topographical maps like Africa.In this project, satellite images and aero-photographs were interpreted to identify appropriatesites for subsurface dams.(1) Landforms considered as appropriate sites for the subsurface damIn the interpretation of satellite images and aero-photographs, the following landforms wereconsidered:1) Landforms suggesting the potential presence of fossil valleys: These are landformswith excessively wide flood plains, whose line is similar to that of the current rivers(wadis, in many cases), compared with the discharge of current rivers (wadis).2) Ring-shaped landforms: These are landforms whose ridges range in a ring shapewith a gapped part due to denudation. These landforms are often observed in thearea of volcanic rock. Groundwater recharged with rainfall within these landformsconverges at the gapped part.3) Bottleneck-shaped landforms: These are landforms with a bottleneck part of thebasement rock, buried by unconsolidated sediment, possibly accompanied byunderflow water.(2) Procedure for interpretationFirst, false color photographs on a scale of 1/200,000 or 1/500,000 were made fromLANDSAT TM (Thematic Mapper) images covering the central or the northern part ofBurkina Faso. On the basis of the interpretation of these satellite images, 13 sites wereidentified as having potential geomorphological and geological structures appropriate for asubsurface dam.Next, preliminary exploration in a large area including these 13 sites was carried out. As aresult, 6 sites were selected, excluding sites with the following problems:- Estimation of the underground structure was difficult, or the scale of the undergroundstructure was too large for the model project.- Access from the capital, Ouagadougou, was too difficult.- Many other projects already existed.Detailed landform classification maps were then drawn from black and whiteaero-photographs on a scale of 1/20,000 or 1/50,000 that covered the selected 6 sites. As theresult of this process, 6 sites were narrowed down to 5.It is recommended that aero-photographs be used for the interpretation of limited areasbecause the resolution of the LANDSAT images is low and the geomorphological andgeological structures interpreted from them tend to be biased toward larger ones.(3) Results of the selection of possible sites21
The results of the selection of possible sites for a subsurface dam by the interpretation of thesatellite images and aero-photographs and preliminary exploration are summarized in Table3.1.Table 3.1: Results of the selection of possible sites for a subsurface dam by the interpretation ofsatellite images and aero-photograph and preliminary explorationRegions preselected from LANDSAT imagesName ofprovinceName ofvillageCheckedlandformResults of preliminaryexploration(Reason for rejection)Results of interpretationof aero-photographs(Reason for rejection)Oudalan Saouga Fossil valley Possible PossibleSeno North of Dori Fossil valley Impossible(The zone could not beidentified.)Seno Yakouta Fossil valley Impossible(The structural scaleSeno Gangaol Fossil valley -wadiwas too large.)PossibleNamentenga Nare Fossil valley Possible PossibleSanmatenga Kouloga Bottleneck Impossible(The unconsolidatedsediment layer might betoo thin.)Sanmatenga Louda Ring-shaped Possible PossibleSanmatenga Bassneile Ring-shaped Possible PossibleSanmatenga Tangapore Bottleneck Possible PossibleSanmatenga Balou Bottleneck Impossible(Poor access)Sanmatenga Santabe Bottleneck Impossible(Poor access)Bam Around Loga Ring-shaped Impossible(Many projects hadalready existed.)Yatenga North ofGongoureBottleneckYatenga North of Ban Special reason*Impossible(Poor access)Impossible(Poor access)--Impossible(The catchment areawas too small.)Note: It was requested by S.P.CONAGESE that the subsurface dam be constructed here because of thethreat of forest extinction.------22
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 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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