CHANGE IN THE HYDROLOGICAL REGIME OF THE MACTA BASIN IN THE NORTHWEST OF ALGERIA

Mohamed MEDDI, Amel Talia

Résumé


Abstract:
The precipitations determine the variability or, better, the irregular Inter seasonal and inter
annual surface runoff. The study of the flow and the rainfall series from 1941 to 2001 is used
to evaluate the sensitivity of oueds to climate change.
In order to better assess the impact of climatic factors on the hydrological regime, the Macta
basin which is situated in the North-West of Algeria. Which covers an area of 14380 km2 has
been selected. The inter-annual hydroclimatological changes are characterized from the
annual average flows of the various stations of the two basins components of the Macta. The
method adopted is that of difference between the annual average flows and the Inter-annual
average flow. Eight class of the flow whose boundaries correspond to the level of humidity
based on the degree of the difference between the annual mean flow and the annual average
flow were established. There is a major difference between the two hydrological regimes of
the West part (oued Mekerra) and the East part (Oues El Hammam). It is mainly due to the
mountain crest relaying South-West to the North-East with a maximum of 1400 m locally. In
the south, the limits of the basin constitute a real natural climatic threshold separating two
opposing rainfall regime. Through the comparison of specific discharge, we distinguish that
the average flows of Oued Mekkerra varies between 1.74 and 11 m 3 /s, while those of the
Wadi El Hammam are between 27.5 and 44, 3 m3 /s. The potential is estimated at more than
260 Hm3. In a perennial scale, changes in hydrological regimes reveal a generalized trend of
irregularities. The climatic irregularities were investigated through the annual variations of the
climate mean coefficient and its moving average calculated over 3 years. The results for the
period 1949-2001, are similar to changes in average annual discharge measured at the
downstream of the basin. Variations of this coefficient show that during the period between
1949 and 1963, the Macta basin has known a very important deficit episode followed by a
surplus period not more than 3 consecutive years. During those two periods, there is also a
year with exceptional rainfall:1950-1951 with a surplus of 170%. From 1972 to1973, a very
dry period of more than 19 years was installed in the basin with deficits ranging from 10% to
80%. The study of the impact of climate change on water resources in the planning and conduct of
the management of water resources in the studied basin and adjacent watersheds is a very
important tool for policy makers.

Mots-clés


Hydrological regime; climate Coefficient; Macta ; Algeria.

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