TABLE OF CONTENTS
ABSTRACT i
ACKNOWLEDGEMENTS ii
1 INTRODUCTION 1
2 STUDY ZONE PHYSICAL ASPECTS 2
2.1 Geology Elements 2
2.2 Climate elements 3
2.3 Soils and Vegetation 5
2.3.1 Types of soils 5
2.3.2 Vegetation 5
2.4 Zio Hydrological characteristics 5
2.4.1 Hydrographic network and catchments area 6
2.4.2 Zio Hydrological assessment 9
2.5 Zio valley morphology 10
2.5.1 Zio basin plates 10
2.5.2 Inshore bars zone 10
2.5.3 Zio river sediment terraces 10
2.5.4 Zio low alluvial plain: flooding zone 11
3 MECANISM OF RIVER SILTING UP 12
3.1 Types of basin erosion 12
3.1.1 Splash and waters extract 12
3.1.2 Stream 13
3.1.3 Rain erosion and river erosion 13
3.2 Zio river silting 13
4 HUMAN ACTIONS FACTORS OF ZIO RIVER SILTING UP AND BASIN
DEGRADATION 15
4.1 Deforestation 16
4.2 Pollution 16
4.3 Uncontrolled occupation and socio-economic activities
18
4.4 Impacts of human action 18
5 SOLUTION APPROACHES OF RIVER SILTING UP AND BASIN
DEGRADATION 19
5.1 Basin reforestation and fire management 20
5.2 Biodiversity protection 21
5.3 Fight against eutrophication 22
5.4 Bordering populations awareness 22
5.5 Anti-erosive measurements and soil erosion control 23
6 CONCLUSION AND RECOMMENDATIONS 24
REFERENCES 25
1 INTRODUCTION
Togo coastal sedimentary basin, of passive margin, is integral
part of West Africa sedimentary unit extending from Ghana to Nigeria; it is
presented as a plate dissected by a hydrographic network which belong Zio river
is the subject of this study. Located between 6°11' to 6°32' LN and
1°01' to 1°29' LE, study zone extends on 80 km from Kpédji to
Agbodrafo and roughly covers a surface of 400.000 ha. It is under the
subequatorial climate influency characterized by weakness precipitations. Also
it shelters savanna vegetation raised on ground with ferrallitic
predominance.
Like Mono and Haho, Zio river, main course water of
South-Togo, has a 178 km length, takes his source in Togo Mountain, drains the
plain terrazzo-gneissic upstream and coastal sedimentary basin downstream where
it carries out meanders before being thrown in lake (Lac-Togo) which
communicates with the Atlantic Ocean by an pass in Aného. Developing
forest extents and farm in past, the zone provides for bordering and urban
populations surround important natural resources: food products, wood, water,
and pastoral resources.
Face of the resident's demographic pressure and its
surroundings, the target area knows serious degradation problems, natural
resources and its environment which is means in erosion term by the silting and
river bed progressive drying due to the massive forest destroying. To solve
these environment problems and for a greater comfort of the bordering
populations and other recipients, it is important to arrange it suitably. This
project requires a good knowledge on the zone and preliminary studies, step
essential for any attempt to durable human development. It is accordingly that
we propose in this final paper as regards management environmental to
contribute our modest share.
Study zone profited from former studies on pedo-hydrology
(ORSTOM, 1967); geomorphology (GNONGBO, 1989); impact of the climate on the
river catchments area evolution (KLASSOU, 1989); hydro-geomorphology (AKIBODE,
2000). But in a specific way, all work studies truly did not develop river
silting up topic then make proposals fight measures.
To take up the challenge, study proceeds evaluation of the
area degradation and proposes standard models foresters and rivers measure
protection to stabilize, protect, restore these banks against silting up and to
fight effectively deforestation and erosion. Results of analysis and
interpretation of documentation, information collected and field work for
observations and checking allowed dividing plan of this document in four
chapters:
First entitled, Study Zone Physical Aspects which bring
information on, Geology Elements, Bioclimatic Environment and Basin
Hydro-geomorphologic Characteristics; second, Mechanism of Zio River Silting;
third, Human Factors of Zio River Silting and Basin Degradation and fourth,
Solution Approaches.
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