NDLI: Influence of groundwater on the degradation of irrigated soils in a semi-arid region, the inner delta of the Niger River, Mali

Content Provider	Springer Nature Link
Author	Valenza, A. Grillot, J. C. Dazy, J.
Copyright Year	2000
Abstract	The problem of soil degradation through alkalinization/salinization in an irrigated area with a semi-arid climate was examined in the inner delta of the Niger River, Mali, by the study of groundwater hydraulics and hydrochemistry in an area recharged by irrigation water. On the basis of data analysis on various scales, it is concluded that the current extent of the surface saline soils is due to a combination of three factors: (1) the existence of ancient saline soils (solonchaks) resulting from the creation of a broad sabkha west of the former course of the Niger River, now called the Fala of Molodo. These saline crusts were gradually deposited during the eastward tilting of the tectonic block that supports the Niger River; (2) the irrigation processes during the recent reflooding of the Fala of Molodo (river diversion in 1950). These used very poorly mineralized surface water but reintroduced into the alluvial groundwater system – generally of a low permeability (K=10–6 m s–1) – salts derived from the ancient solonchaks; and (3) the redeposition of the dissolved salts on the surface due to the intense evapotranspiration linked to the present Sahelian climate. In this context, only efficient artificial draining of subsurface alluvial groundwater can eliminate most of the highly mineralized flow and thus reduce the current saline deposits. En périmètres irrigués sous climat semi aride (delta intérieur du fleuve Niger, Mali), la dégradation des sols par alcalinisation/salinisation est abordée par l'analyse hydrodynamique et hydrogéochimique des eaux souterraines sous-jacentes. A partir d'informations recueillies à différentes échelles, nous proposons un mode de mise en place actuelle des salants en surface sur la base de trois concepts: (1) l'existence de salants anciens résultant de la création d'une vaste zone de sebkhra à l'Ouest du cours ancien du Niger (Fala de Molodo). Cette mise en place se serait faite progressivement au cours du basculement vers l'Est du bloc tectonique supportant le fleuve; (2) au cours de la remise en eau récente du Fala (1950), les processus d'irrigation à partir d'eau de surface très peu minéralisée, réintroduisent dans la nappe alluviale globalement peu perméable des sels provenant des mises en solution des salants anciens; (3) par phénomène d'évapotranspiration intense lié au climat actuel, ces sels se redéposent en surface. Dans un tel contexte, seul un drainage artificiel efficace des eaux souterraines de sub-surface (nappe alluviale) permettrait de soustraire le maximum de flux très minéralisé et, en conséquence, de limiter les dépôts salins actuels. En perimetros irigados bajo un clima arida (delta interior del rio Niger, Mali), la degradacion de los suelos (alcalinisacion/salinisacion) es analizada con respecto a las aguas subterraneas. A partir de recoleccion de dadas en hidrodinamica, geofisica y hidroquimica, proponemonos un modo de formacion actuale de los salinos segun tres episodios sucesivos: (1) salinos antiguos que se deducen de la formacion de una Sebkhra, situada al Oeste del curso antiguo del rio (Fala de Molodo). Esta zona resulta de un volteado a hacia el Este del bloque tectonico del rio Niger; (2) la alimentacion del Fala (desde1950) con aguas superficiales jovenes poco mineralizadas introduce, en la capa aluviale de pequena permeabilidad, salinidad por disolucion de los salinos antiguos; (3) a causa de la evaporacion mucho fuerte atada al clima arida, salinos jovenes se desponen sobre el suelo. Solo un drainaje artificial eficaz de la capa aluvial puede sustraer una parte grande del flujo muy mineralizado, y asi limitar la alcalinisacion/salinisacion de los suelos.
Starting Page	417
Ending Page	429
Page Count	13
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	8
Issue Number	4
e-ISSN	14350157
Language	English
Publisher	Springer-Verlag
Publisher Date	2002-10-01
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Hydrogeology Geology Waste Water Technology Water Pollution Control Water Management Aquatic Pollution
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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