2.4.2 Zio Hydrological assessment
Zio takes its source in the dorsal of Atakora whose extension
in latitude prolongs in soudanian zone which records 1500 mm per year,
characteristic of Guinean wet climate. This dorsal thanks to the impermeability
of its substratum schist quartzitic, the river maintains a area flow to 30
m3/s in periods of high waters. Other hand, in the more permeable
sedimentary basin where average rainy is 1000 mm in seasons of strong rains,
the flow is lower than 10 m3/s.
The years of low water level record severe about 1.4
m3/s or sometimes null flows when the year is very dry. This deficit
includes all water losses due to evaporation, evapotranspiration, and
infiltration. The report, ratio flow of flood/minimum flow and the flow
coefficients which are indicators of checking evolution and importance of past
water remain in together weak for the Zio river because clays abundance and
very permeable alluvia. Direct consequence of flow deficit is the small
quantity of the past water blades; table (6) presents the coefficients of Zio
flow over 20 years period.
Total rain amounts explain well the interannual variations of
the flow coefficients. It is thus advisable to specify that the distribution of
rains during year intervenes in the determination of the hydrological mode of
the river whose impacts appear through erosion.
Table 6: Calculated values of the Zio flow coefficients
Flow Coefficients (%)
|
years
|
Kati
|
Kpédji
|
Togblé
|
1980
|
11,1
|
9,2
|
8,8
|
1981
|
11,6
|
11,9
|
9,1
|
1982
|
14,3
|
20,8
|
12,7
|
1983
|
11,5
|
10,9
|
6,6
|
1984
|
11,1
|
4,7
|
6,1
|
1985
|
11,2
|
9,5
|
6,8
|
1986
|
8,9
|
6
|
6
|
1987
|
11,3
|
7,2
|
9,2
|
1988
|
10,8
|
7,9
|
7,7
|
1989
|
13
|
10,1
|
8,8
|
1990
|
10,9
|
5,7
|
4
|
1991
|
6,0
|
2,7
|
2
|
1992
|
11,2
|
5,3
|
5
|
1993
|
12,9
|
16,2
|
9,5
|
1994
|
12,8
|
16,3
|
8,5
|
1995
|
10
|
8,4
|
8,5
|
1996
|
10,4
|
4,4
|
5
|
1997
|
11,7
|
0,6
|
1,3
|
1998
|
10,8
|
12,6
|
10,5
|
1999
|
11,1
|
13,1
|
7
|
|
Source: Service Hydrologie-Lomé
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15
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Kati
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15
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10
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10
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5
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5
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0
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3
|
5
|
7
|
9 1 1 13
|
1 5
|
1 7 19 21
|
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0
1 3
|
5
|
7
|
91113151719
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An née s
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Année s
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Kati
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Kpédji
|
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Togblé
|
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Figure 8:Curves of annual medium flows Figure 9:Curves of
evolution of the flow
Zio river over one 20 years period of Zio over 21 years
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