Geography Reference
In-Depth Information
Table 1. Classification of influencing factors on groundwater storage
Class
Weighted parameters
Very Good
9
Good
7
Moderate
5
Low
3
Very low
1
Rainfall 30%
2,7
1250-1150mm
2,1
1150-950mm
1,5
950-850mm
0,9
850-
750mm
0,3
750-650mm
Lineaments 25%
Lenght Km/Km²
2,25
38-48
1,75
28-38
1,25
19-28
0,75
9,5-19
0,25
0-9,5
Geology 20%
1,8
Gabbros
1,4
Volcano-clastic
1
Schiste
0,6
Granite
0,2
Basalte
Slope 15%
1,35
0-1%
1,05
1-2%
0,75
2-3%
0,45
3-5%
0,15
5-35%
Drainage 10%
Lenght Km/Km²
0,9
0-1
0,7
1-1,8
0,5
1,8-2,7
0,3
2,7-3,6
0,1
3,6-4,5
It is the most important parameter in groundwater recharge. In the area,
rainfall is concentrated mainly in rainy season which starts at the end of April
and continues until the end of October in the south part of the study area. By
cons in the northern part, rains start later in late June and usually stop at the
beginning of October. Maximum precipitation is recorded in August in the two
climatic provinces. The sector is characterized by a rainfall gradient change
from south to north (Mall. 2009). This is shown by a spatial distribution of
isohyets that increase from north to south with the 1250 mm isohyet observed
in south of Kédougou and 650 mm isohyet in the north part of the area. This
contrast between climatic provinces reflects a difference in the structure of
vegetal communities. The southern part is the domain of forest with a high
density of vegetation sometimes associated with gallery forests that follow the
meandering of rivers. Nevertheless, going towards the north part of the study
area, the forest gives way to savannah dominated by thorny vegetation well
adapted to drought conditions.
II.2. Geology
Type of geological formation is an important factor in the development of
water reserve in crystalline basement. Their petrography determines the type
of weathering profile that develops on it. Thus, the thickness of the regolith is
much higher on basic rocks than granites and schists as it develops more clay
on basic rocks than on granites. However, the granites are much more resistant
to weathering and mechanical disintegration than other rock types. So granites
could become good aquifer if they are affected by faulting. By cons become
