Geography Reference
In-Depth Information
formations (South Massamassa village) and Mouran village. In the North part
of the study area only few sectors present very good potential are found at
Kossanto and south of Makana village (south of Sabodala village). Very good
and good groundwater potential zones are associated with intensive fracture
system that provokes a high secondary permeability. Good potential zones
occupy 18% of the study area and surround zones characterized by very good
potential. Most of these zones is localized in south of the 850mm isohyet,
however, some relics with good potential are noted in some sectors in the
Northern part of the isohyet 850mm. The NDVI results, calculated from
Landsat images April, 2010 (end of the dry season) (Fig.10), show that the
very good and the good potential zones are well correlated with zones which
show high vegetal activities. Very low potential zones and low potential zones
correspond to zones where, vegetal activity is very low as noted in major part
of granites (Sandikounda Soukouta and Saraya) and the northern part of the
sector above the isohyet 850mm (Fig.10). However, this good correlation
between the high intensity of vegetal activity and very good and good potential
zone does not exist in the northern part of the study area in vicinity of Soreto
village and this, could be related to xerophytic nature of vegetal communities
which are adapted on drought conditions and can maintain their activities at a
high level with a low soil moisture. This indicates that at this advanced period
of dry season, vegetal activity is essentially supported by groundwater
resources.
So, the NDVI can be a good indicator of groundwater presence but, its use
must require some caution because of deforestation and recurrence of fires
bush in the area during advanced dry season. These phenomena can mask the
intensity of vegetal activity in zones characterized by a low plants density.
Also we must take into account the depth of water table. Low vegetal activity
can be found in zones where, depth of water table exceeds 20m even though,
the results of GIS indicate sometimes a very good aquifer potential in these
zones, that is the case of the southern part of Mouran village. Borehole
productivities are also taking into account and show that, high borehole
productivities (about 11.5 to 30 m
3
/H) are observed in zone presenting high
groundwater potential resulting from GIS processing and very low well
productivities are shown in the north part of the study area corresponding to
the low and very low groundwater potential with productivities ranging from
0.6 to 2.5 m
3
/H. The results proved that, the north part of the study area