Silting of Togo inshore sedimentary basin rivers and protection measures: Case of Zio river

CIPSEM - Centre for International Postgraduate Studies in Environmental Management

30^th INTERNATIONAL POSTGRADUATE COURSE ON ENVIRONMENTAL MANAGEMENT FOR DEVELOPING AND EMERGING COUNTRIES

FINAL PAPER

TITLE:	SILTING OF TOGO INSHORE SEDIMENTARY BASIN RIVERS AND PROTECTION MEASURES: CASE OF ZIO RIVER
AUTHOR:	Mr. AKINTOLA S. NELSON AKIBODE
COUNTRY:	TOGO
SUPERVISOR:	Prof. K. H FEGER
DATE:	JULY 2007

ABSTRACT

The main courses water of Togo inshore sedimentary basin are in silting up and drying. This situation of environmental degradation which worry or concern for since long time the Ministry of Environment and Forestry Resources. Despite protection measures used today, rivers degradation is not stopping.

In this executive training entitled «30th UNEP/UNESCO/BMU International Postgraduate Course on Environmental Management for Developing and Emerging Countries» which take place in Dresden (Germany) of the 15 January to 15 July 2007, to improve ours knowledge and experiences in matter of basin and river protection against erosion, Zio river affected too by the silting up phenomenon does be the subject of the present study in final paper as topic: «Silting of Togo inshore sedimentary basin rivers and protection measures: case of Zio river».

Zio river, length of 178 km, takes his source in the Mounts of Togo, drains two main geology surfaces, gneiss granite upstream and down-stream inshore sedimentary basin where it is makes meanders before throwing in the «Lac-Togo» that communicates with Atlantic Ocean by a pass in Aného. In the inshore sedimentary basin, the river spreads on 80 km and his valley covered roughly 400 000 ha. Under the subequatorial climate characterized by weakness and irregularity rain, the course water after mountain forest crossing savanna vegetation on ferralitic soils.

Developing vast area of lumbering and agricultural in the past, Zio basin provides to the riverside residents and urban populations important natural resources notably earths, wood, fish, pastoral, hunt, medicinal plants, sediments, and water that constitutes for the first the basis of subsistence and wealth and for the second a supplies source within research of hands in woods energy and derivative.

Currently, facing a riverside resident pressure (population increasing), study area knows a serious deterioration problem of these natural resources and his environment. River basin degradation is expressed by the drop of yield agriculture income activities. In fact, silting up or embankment found his origin in the fore stry destroying and the soils erosion which bring in river bed the sand and other charges.

Present study gets out the basin environmental degradation assessment and proposes the standard models to protect and restore the river banks against the silting up or erosion. It is recommended about conducting a participating and lasting forest reforestation of the basin, the agro forestry promote, bush fires managing, biodiversity protect, river users awareness, and practicing the anti-erosive measures. New technical measures of environmental protection implemented will be braking or reducing erosion speed in the basin and improving as well the riverside resident's life conditions.

ACKNOWLEDGEMENTS

Since we were allowed with the Ministry of the Environment and Forestry Resource, precisely in Office of Water and Forestry, our major concerns is desertification phenomenon one of main causes of Togo rivers silting up.

In fact, profit-sharing environmental problems was born from the orientation of our university course which we buckled for obtaining the diploma of ?Maitrise-es-Lettres" geography physical option by define on the topic ?Contribution to the hydro-geomorphologic study of the Zio low valley ". It should be noted that ground work for memory drafting and our regular presence in the valley which more drew our attention on the river silting up.

With aim of look further into the problems and to draw attention of the ministries developing decision makers and other basin managers on his degradation, that for this professional advanced training course registered during ?International Training one Program Environmental Management for Developing and Emerging Countries", we are targeted again the same area study through the topic entitled ? Silting up of Togo Inshore Sedimentary Basin Rivers and Protection Measures: case of the Zio river".

The study proposes to give a report on the places, to examine the mechanism of river silting up in order to put forward concrete measures having to contribute to stabilize, protect the banks and to fight effectively against defore station and desertification.

At the time of having results of this study, I would like to express my very sincere recognition and my thanks for all institutions and people who worked materially and morally for the happy result of this final paper; for this purpose, my thanks go to:

- Institutions which granted this purse of training course and to organize this vocational training, I quote, United Nations for Environment Program (UNEP); United Nations for Science and Culture Organization (UNESCO); Germany Federal Ministry for the Environment, Natural Conservation, and Nuclear Safety; Centre for International Postgraduate Studies of Environmental Management (CIPSEM)- TUD in Dresden/Germany;

- Togo Government authorities in particular those of Ministry of Environment and Forestry Resource, which in the permanent concern human resources capacity reinforce does not spare any effort to maintain within this framework a profitable policy international co-operation;

- Dr. - Ing. Rolf Baur, Head or Course Director, for all its efforts authorized for the good walk of academic activities to the Center for International Postgraduate Studies of Environmental Management;

- My supervisor, Prof. K.H. Feger which over his lectures accepts to follow me in my final paper writing and gives me the best protection aptitudes as regarding erosion of sedimentary basin soils and rivers;

- All staffs of Secretariat Course (CIPSEM) and colleagues of promotion with I quickly familiarized itself during my German enjoy;

- My love Youlmane who supports me in my moods without I could not taken this step in my career; I share with you the paternity of this diploma sanctioning the end of this training;

- Nicodème and Mazarine, like the ploughman and these children of FABLE, I highly recommend you to work without respite because only the careful work is the man liberator.

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.

2 STUDY ZONE PHYSICAL ASPECTS

2.1 Geology Elements

The geographical framework crossed by the Zio river comprises two great geological formations, base terrazzo-gneissic of Precambrian upstream and coastal tertiary sedimentary basin (Fig. 1) downstream:

- Base terrazzo-gneissic, from Kpédji to Mission-Tové, on approximately 25 km, the river runs on a crystalline structure of hard stones constituted of, Micro-diorites quartzes; Compound gneisses to biotites; fine gneiss to biotites and leptynites; Rawboned gneisses to quartzes beds; Orthogenesis anatectic to biotites, amphiboles and garnet;

- Basin sedimentary, according to Coque (1977), is a structural unit morphology corresponding synergies of platforms covered by sediments following prolonged subsidence. In South-Togo, structure is characterized by the same slope and direction NNW-SSE, a vast plate sedimentary which layers constituted by three formations of ages located between Cretaceous and the Eocene laid in discordance on the Precambrian base (JOHNSON, 1987).

The sedimentary sequence, from bottom to the top, presents marine origin, «Continental Terminal» and quaternary formations:

· Marine formations, geology former work research proved the presence of the:

- Maastrichtien, resting in discordance on the base and constituted of sands at the base surmounted of sandy then after the black clay limestone;

- Paleocene, represented by lower sands and limestone of Togocyamus seefriedi of Tabligbo above which rest a glauconitic layer;

- Eocene, primarily made up in its half lower of clays laminated than Palygorskite (attapulgite) and in its higher part of limestone layers, argillaceous and phosphate layers.

· «Continental Terminal» and quaternary formations:

- Continental Terminal, qualified higher diacriticals series (JOHNSON, 1987), rests in discordance with an erosive base on the marine series and constitutes of diacriticals deposits, sands, clays and gravels. According to SLANSKY (1962), the Continental Terminal is developed very little with the Zio basin level;

- Holocene, constitute essential of the sedimentary material currently drained by the river. On 40 km, from Gatigblé to Dévégo, more and more silt, Zio runs in owns formations made of clays and sands then on 10 kilometers, erodes the marine origin formations described of internal inshore bar or ``yellow sands" (BLIVI, 1993).

These geological and sedimentary formations constitute the source of sediments transported by Zio river. Their supply is in connection with the hardness of the bed rock and the mechanical or physicochemical erosion effect.

Figure 1: Study area chart: localization and geology

2.2 Climate elements

- Temperature, Zio basin is characterized by high and constant temperatures with an annual average of 26°C. Low annual average amplitude thermal does not exceed 40°C. Table (1) has the monthly average temperatures of Mission-Tové and Lome-airport over 25 years period.

Table 1: Average monthly of the temperatures from 1980 to 2005

Months														Stations
J	F	M	A	M	J	J	A	S	O	N	D		Lomé-aéroport
27,1	27,8	28,1	28	26,8	25,5	25,4	25,5	26,1	27,8	27,1	27,2		Missio-Tové
27,4	28,6	28,6	28,1	26,8	26,3	25,5	25,6	25,6	26,6	27,5	28

Source: Météorologie Nationale - Lomé

Graphic interpretation (Fig. 2) of the data shows that the duration of the strong temperatures during year on the basin is long (8 months) and would intervene in the river functionally.

29 28 27 26 25 24 23

J F M A M J J A S O N D

Months

Lomé-aéroport Mission-Tové

Figure 2: Curves of the monthly average temperatures of the basin over 25 years

- Rain, the area has two rainy and dry seasons; annual average total is 1000 mm lower than high basin (1500 mm). Average monthly magazines recorded during 30 last years are constant (tab 2).

Table 2: Monthly averages of precipitations of 1975 to 2005

Month Stations	J	F	M	A	M	J	J	A	S	O	N		D	Lomé-aérot
15,17	26,35	88,43	120,1	151,83	182,56	93,25	44,18	117,24	128,2	66,94	20,15		Agoénynivé
16,52	30,25	60,25	91,64	140,51	216,29	81,19	24,55	40,47	92,34	33,23	11,95		Togblékopé
10,55	39,67	68,70	123,10	126,10	232,08	103,13	38,30	61,66	53,73	20,99	9,17		Mission-T
16,67	33,17	72,10	104,32	146,22	275,74	100,02	27,12	45,84	93,15	24,98	10,41

Source: Météorologie Nationale - Lomé

Rainfall graphs (Fig. 3) take a bimodal form with two peaks located in June and October for the 4 stations. They indicated that the dry seasons extend on 6 to 7 months and the quantities of recorded rains lowers upstream and downstream.

Lomé-aéroport Agoènyivé Togblékopé Mission Tové

300

P

R E C I P I

T A T I O N

S

250

200

150

100

50

0

J F M A M J J A S O N D

Months

Figure 3: Rainfall graphs of the monthly averages of the basin over 30 years

Other elements of the climate which also play a part in the basin function are the sunstroke, evaporation and humidity.

- Sunstroke, South-Togo area receives 4 months of too strong sun during the dry seasons (December to March) the minima are recorded during July, June and August (Fig. 4);

- Evaporation, directly related on the temperature and the sunstroke, his maximum is recorded during in dry seasons.

Table 3: Monthly averages of the sunstroke from 1980 to 2005

Months														Station
J	F	M	A	M	J	J	A	S	O	N	D		Lomé-
220,1	215,6	225,3	223,5	195,4	150,1	141,7	149,2	180,8	220,2	235,7	218,9		aéroport
85,25	75,15	81,75	74,60	66,23	51,50	49,60	56,40	55,10	65,35	67,80	78,65

Source: Météorologie Nationale - Lomé

90

80

70

60

50

40

Lomé- aéroport

85,25

F M A M J J A S O N D
M ois

30

20

10

0

Lomé-aéroport

Mois

250

200

150

100

50

0

Figure 4: Curves of evolution of the monthly averages of sunstroke and evaporation in the basin

- Relative Humidity, average reaches 80% mornings; Harmattan, cold wind from the North- East accentuates the moisture effect; the maximum going up to 90% during January and December.

Months of strong temperatures and sunstroke call a high evaporation, during which a great volume of water escapes from the soil exposing the basin very little vegetation covered to a hydrous deficit. The water level in dropping, the river deposits his load.

2.3 Soils and Vegetation

The zone covers three types of grounds on the Maritime Area soil chart (ORSTOM, 1967; Institute National des Soils, 1987); there are ferralitic soils, hydromorphic or not and the vertisoils. Their genesis would be closely related on topography, climate, and vegetation factors.

2.3.1 Types of soils

- Ferralitic soils, characterized by the prevalence of the iron oxidation actions and sand argillaceous texture; they are red and thick soils from 10 to 15 m; they are widest in the zone;

- Hydromorphic soils, located along the river in a discontinuous way, in the depressions and mouth; muddy clay texture to sand spreader, they are identified by the red beige color;

- Non-hydromorphic soils, little extended, they are made of a fine colluvium's from 30 to 70 cm thickness, found in edge of the plates, and presented in the form of micro-reliefs slightly corrugated;

- Vertisols, located in the depressions and the mouth, they are constituted of clays inflating very permeable with water.

According to the agriculture soils study carried out by the National Institute of the Soils (INS, 1987), these grounds are very permeable and eroded easily when they are without vegetation.

2.3.2 Vegetation

Study zone shows two vegetable formations, flood zones and non-flood zones vegetation:

- Flood zones vegetation, it is an herbaceous vegetable formation with some ligneous which the height does not exceed 10 m. Theses ligneous are Ceiba pentendra, Uapaca heudeti, Cola gigantea; the sand banks in the minor bed carry hygrophilous species like Cyperaceae, tufts of bushes made up of Mimosa pigra and Phyllantus reticulatus;

- Non-flood zones vegetation, extending in the plates and slopes; they are the formations: . Arborescent higher, 15 m in height populated of Adansonia digitata and Vitex doniana;

. Arborescent lower and shrubby, composed of Guinean savannas species with Vitellaria paradoxa and Terminalia glauxesens;

. Herbaceous, not exceed 2 m height and dominated by Andropogon gayanus and Panicum maximum.

These bioclimatic facts justify the savanna field extension in the sedimentary basin whose complex soil-vegetation is influenced by the climatic mode and Zio hydrological characteristics.

2.4 Zio Hydrological characteristics

Zio river, with its arms Edin in Togblé and Adougba in Tonoukouti, shows a small dense hydrographic network in the coastal sedimentary basin.

2.4.1 Hydrographic network and catchments area

- Hydrographic network, Zio river, inside type belongs to the hydrographic system of the South-Togo has North-South direction. The basin develops an alluvial plain in the shape of funnel which is spread out towards the mouth characteristic of the silting phenomenon. Depending of the sedimentary structure, Zio valley little boxing shows very weak unevenness of gradients which values ranging between 0, 5 and 2%;

- Zio catchments area, with these effluents, the river runs in a mixed area catchments crystalline structure separated upstream from the sedimentary basin by a change of incline altitudinal to the latitude in Mission-Tové. From the supply point of view water of the bed, Zio collects its water according to the diagram hereafter:

Evapotranspiration
(Vegetation)

River bed (talweg)

Groundwater

Rain

Stream

Infiltrations
Hydro-
network

Figure 5: Water supply of the Zio river

Figure 6: Zio catchment area and hydrographic network

- Rain mode, the data of table (4) show the rate/rhythm of evolution of annual average rainy in the area catchments of the South to North; the annual cycle of precipitations in the various stations appears irregular.

2500

2000

1500

1000

500

0

1 4 7 10 13 16 19

Assanhoun Mission Togblékopé

2500

2000

1500

1000

500

0

1 3 5 7 9 11 13 15 17 19
Anné e s

Adéta Kati Kpédji

Figure 7: Curves of evolution of annual average precipitations over 20 years

Over 20 years' period, it is notes that the catchments area records the strong and weak rains. This variation of the fallen quantities of water explains also the behavior of hydrological flows of Zio.

Table 4: Annual averages rain stations of the Zio catchments area (in mm)

	High valley				Low valley			Stations years
Adéta	Kati		Kpédji	Assanhoun	Mission-T	Togblékopé	1980
1415,1	1395,5		1323,4	1678,7	1079,4	1276,5	1981
1484,0	1462,8		1138,5	1905,4	1109,7	1237,0	1982
1979,7	2037,4		1570,2	1789,6	1450,6	1800,9	1983
1443,0	1450,6		1126,5	1125,4	0818,3	1175,2	1984
1359,3	1397,5		0730,8	1022,3	0800,0	1148,8	1985
1262,9	1367,4		0950,3	0949,2	0958,1	1190,2	1986
1027,4	1217,6		1031,8	1218,8	0907,9	1133,7	1987
1385,5	1418,9		1150,0	1040,1	1039,8	1201,0	1988
1577,0	1375,8		1146,6	1034,9	1081,6	1257,4	1989
1588,0	1531,0		1201,1	1103,2	0984,8	1293,2	1990
1273,6	1234,3		0971,7	0935,6	0646,8	0996,4	1991
1362,3	1048,1		0782,1	0650,1	0613,7	0978,3	1992
1451,1	1527,2		1149,1	0924,2	0798,5	1206,8	1993
1596,0	1689,0		1184,0	1205,7	1024,5	1341,3	1994
1701,2	1674,2		1351,7	1171,1	0945,4	1414,2	1995
1446,7	1463,1		0832,8	0903,3	0840,3	1089,5	1996
1118,3	1357,2		0863,6	1097,7	0830,1	1113,4	1997
1327,0	1440,6		0995,0	0762,0	0805,8	0963,9	1998
1346,3	1508,1		1126,5	1051,2	0856,9	1460,5	1999
1322,6	1596,9		1319,0	1192,1	0697,5	1319,7

Source: Météorologie Nationale - Lomé

- Zio hydrological mode, it is characterized by the succession high and low waters periods. The high waters correspond the rains seasons while low waters coincide with the dry seasons. It is rises from this water periodic distribution, the seasonal variations of the flow gives of the river a subequatorial functionally mode.

Analysis curves (fig.8) of interannual average monthly Zio flows with Kati, Kpédji and Togblé make it possible to identify and to know its hydrological characters: increase and low water level.

. Season of swell waters and floods, the period of high waters is approximately 5 months with two maximum. It goes from July to November; the first maximum is recorded towards the end of July where the height of water is important and causes the great rising; the flow overflows the average bed and occupies the major bed on several meters; it is the period of strong flows; the erosive action of water is accelerated. The second maximum is between September and October with relatively low heights of water;

. Season of low waters, it is spread out over 6 to 7 months, from December to May or June; the period of low waters is copied almost on that of the great dry season. The minor bed undergoes a low water level or a draining which is accentuated during February, January and March.

It comes out from these observations that the Zio hydrological mode is seasonal and characterized by one high waters period in July and low waters in January. There is thus a similarity between the climatic seasonal mode of the sector and the behavior of river hydrological flows. The basin is thus subjected to a subequatorial rainy mode with the rather irregular seasonal characteristics justifying the interannual variability flow.

- Interannual variability of Zio flow, flow values (tabl.5) of Zio over the period considered, show that the flow knows hydrologic variations which related to the rate/rhythm of rain; the high flows correspond to years of strong rains.

Table 5: Zio annual average flows on 21 years (in m³)

Stations years	Kati	Kpédji		Togblé	1980
4,48	7,26	9,26		1981
4,98	9,43	9,35		1982
8,11	24,10	18,88		1983
4,82	8,52	6,35		1984
4,49	3,47	5,83		1985
4,42	7,37	6,65		1986
3,12	4,49	5,68		1987
4,62	5,60	6,18		1988
4,31	6,58	7,96		1989
5,77	8,66	9,29		1990
3,88	3,82	3,26		1991
1,82	1,91	1,40		1992
4,96	4,35	4,92		1993
6,28	14,53	10,51		1994
6,19	15,36	10,55		1995
4,24	6,18	7,59		1996
4,52	3,20	4,56		1997
4,72	0,40	1,06		1998
4,80	10,66	12,69		1999
3,25	11,24	7,67		2000
3,20	11,36	7,75

Source: Service Hydrologie-Lomé

Curves analysis (fig.8 and 9) concludes that the Zio water reaction is closely related to the rain mode of the study zone.

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

15					Kati			15
10								10
								5
5								0
									3		5	7	9 1 1 13	1 5	1 7 19 21
0 1 3	5		7	91113151719									An née s
				Année s				Kati					Kpédji		Togblé

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

2.5 Zio valley morphology

Geomorphology sketch interpretation (fig. 11) carried out starting from the air photographs of the study area made it possible to recognize that the morphology of the Zio valley in the sedimentary basin which is delimited in the West by the plate of Agoènyivé, in the East by those of Kpogan and Tsévié and in the South by the offshore bars. These covered geomorphologic units little vegetation are the main sediments providers of course water.

2.5.1 Zio basin plates

- Agoènyivé plate, extending approximately on 45 km with average altitude 40 m, is lengthened with the sinuous edge, delimits right river bank;

- Kpogan and Tsévié plates, respectively average altitude 30 m and 90 m, they are laid out the first and are almost parallel to separated by the LAMA depression; they extend approximately on 50 km with slopes to the convexo-concave pace.

2.5.2 Inshore bars zone

Showing the sea sand cords internal and external primarily made up at constant sand; they are below laid out plates of soil bar and average height varying between 4 and 6 m (BLIVI, 1993). Zio drains the offshore bar interns on 14 km where it is carried out many meanders justifying river erosive dynamics and the flatness of the valley in the mouth.

2.5.3 Zio river sediment terraces

From the morphological point of view, the alluvial terraces is a system of projecting ledges or stages below deposited in slopes of valley by a river. The top of the projecting ledges is covered with sediments corresponding to the bottom of the river successive beds. The valleys generally show three kinds of levels at knowing, high, average and low terrace. Also, these terraces are differenced by their conservation degree, iron oxidation and hard sedimentary material which compose them.

While basing itself on these criteria of terraces recognizing, the study zone presents the gravel terraces in Assomé (GNONGBO, 1989) and those alluvia in Togblékopé (AKIBODE, 2000) located at about thirty kilometers at the South-east of the first. There is transition zone with approximately 3 km between these two alluvial formations where sedimentary material in extraction is a mixture of gravels, clays, and sands.

A transect from Agoènyivé plate to Togblékopé shows the space provision of the terraces with alluvia (fig.10); deposit of these terraces was done in a discontinuous way. This diagram is almost the same to Dévégo but with two alluvial terraces levels below the internal offshore bar.

Figure 10: Zio alluvia terraces space provision

2.5.4 Zio low alluvial plain: flooding zone

It is a plain of accumulation of surface corresponding to the low valley top fill; weak slopes, results from the contributions plio-quartenary made up of alluvia with clay and sand texture.

Slightly boxed, Zio valley presents unevenness from 1 to 2 m and slopes ranging between 0,2 to 2%. This topography shows that the low valley is old silting clogged by alluvia coming from the high basin following the deterioration of the crystalline rocks (GNONGBO, 1989). It is in these alluvia that easily flooded zones are extended arms and spreading out river bed.

- Major bed, it is the bed which the river can cover by current alluvia after flood; furrowed of old axes of drainage and supplied with colluviums, it extends on average on 1 km and receives water of exceptional, unforeseeable risings. To up horizontal topography, this bed is related to the minor by banks of average unevenness 3 m.

- Minor bed, in the shape of ?U`` or in cradle and broad 10 m on average, this bed presents a slightly tilted flat bottom in direction of the south. Current channel of Zio flows, its convexoconcave banks are cut in sandy and clay material. Concave sectors, of slopes precipice are indication of water strong erosive activity. At the end of the dry season, the minor bed apparently merges to the bed at low water which is encumbered many sand banks of dimensions variable and intercalated by ponds.

Figure 11: Recognizing geomorphology sketch of Zio valley in coastal sedimentary basin
(Akibodé, 2000)

3 MECANISM OF RIVER SILTING UP

River water and runoff constitutes the main agents of erosion and transport in the basin through the processes of splash and stream to work interfluves, slopes and plains. The human action also contributes to the environmental degradation in the basin.

3.1 Types of basin erosion

3.1.1 Splash and waters extract

- Splash, more widespread in the culture field where the grounds are entirely stripped; the rainy in dropping compress the movable superficial level;

- Water extract, of hydrous origin, it causes fragmentation by alternations of moistening and desiccation of the grounds. It affects the materials inflating such as clays which absorb a lot of water. Also infiltrated water accomplishes a transport of fine particles in-depth thus creating a vacuum under the horizontally packed ground; this subsides under the effect of its weight. Racking would be at the origin of the closed depressions and would have also generated the installation of the ponds.

3.1.2 Stream

- First stream, it starts at the beginning of the rain, transports the fine particles in particular the beforehand detached silts and erodes the ground of a few centimeters;

- Concentrated stream, it is started when the quantity of rainwater is important on the ground surface which sometimes sporadic flow. Water incises the ground vertically; on the slopes, the concentrated stream prints model of drains, the gullies. As indication, the measures taken in the concave sectors of the slopes starting from the meter ribbon and a plumb line of the incisions marks in two localities arise as follows:

Togblékopé Tonoukouti

Modelled

Dimension

Gullies

0,1 à 0,3m

Ravines

1m

Modelled	Gullies		Ravines	Dimension
0,1 à 0,3m	1,2m

It is noted that the ravines have abrupt banks and in the other hand present sometimes a broad bottom at the transverse profile in ?U" the gullies have a pace in «V». The presence of stiff banks proves that erosion is carried out in a vertical way. Incised slopes of ravines show an aspect of «bad-lands».

3.1.3 Rain erosion and river erosion

- Rain erosion, according to TRICART (1977), it is caused by torrential rains; the water drops while falling in quantity and at a high speed on the naked ground exert a pressure of potential origin which involves the detachment of the particles or group particles called disintegration;

- River erosion, it is summarized of river water mechanical action which drains its own alluvia and this at the time of the exceptional risings after the strong rains. These risings of ten days approximately cause the overflow of water which involves the sweeping of sediments and remains vegetable of the basin in direction of the Zio bed.

At the end of the risings, the sand banks settle along the maximum limit reached by high waters; the provision parallel of the sand banks with the alluvial plain indicates that the risings carried out a lateral cutting. These sand banks are taken again by surface waters after the rising period.

The major form of fluviatile erosion is the meander characterized by curves alternated more or less regularly; in the alluvial plain, Zio carries out about thirty meanders. Also, in this alluvial plain, there are two types of depression:

. Depression floods, which drain their water with the fall; stagnant water almost does not remain, however in certain depressions the humidity is maintained by the water flasks with a papered bottom of fine silts;

. Depressions of decantation, closed, from circular form, they receive water of raw which remains for a long time. Clays are elutriated, also there are remains organic (died sheets, tree trunks etc) at the bottom of these depressions.

3.2 Zio river silting

Zio valley evolution in coastal sedimentary basin finds well its explanation in river water dynamics, climatic and morphogenetic phases during geological eras. Thus, according to SLANSKY (1962) quoted by GNONGBO (1989), stranding or embankment of river bed would be due to a raising of the basic level subjacent with sedimentary basin which is carried out in liaison with the tropical Africa landscapes in the north of equator. This support glacis system establishment and staged terraces. The sedimentary material in valley would have undergone deep revising afterwards the climate modifications which have taken place with origin dense forest disappearance to the profit of savanna, a vegetable cover sparse.

Without to draw outside the thesis which SLANSKY supports, the present study wants to highlight deforestation and human activities as causes of river silting up in an short interval time, from independences period to nowadays or 50 years duration; reference period of the demographic boom and migrations arable lands investigations towards the wetlands in under area where the living conditions are favorable to the human settle. It is in this context that the river basins of sedimentary coastal of Togo knew a population increasing in record time.

The recorded demographic data of the river basins during the targeted period show indeed that the densities of populations knew an evolution out of arrow with the average of 150 inhabitants per km². Zio river basin, offering an environment ecologically favorable to the activities of forestry development, agricultural and artisan, shelters the strong densities exceeding 300 inhabitants /km² sometimes. From the 1980s, the bordering populations to solve the problem of insufficiency of grounds extend spaces to be cleared on the forest surfaces including the galleries up difficulty protected by the State.

Incomes of agricultural outputs becoming increasingly weak, the perverse effects of the economic crisis and the insufficiency of the intervention by means lack of the public authorities in basin management supported the abuse use of the forest resources main natural protective of the grounds against any erosion form.

The topographic sketches carried out (fig.12), starting from the cartographic and aerial photo data recorded in the 1 960s within the framework of geological work of basin prospecting by the NGI (National Geographical Institute - France) and adjusted in 1979 show the various levels of the river bed flow.

Although there are not other work of raised in the coastal sedimentary basin being able to
justify with exactitude the zio silting phenomenon, it is currently noted, that some of these

levels in the zones of thorough deforestation evolved or moved in trend of it embankment and that is in party due a large volume of colluviums sediments contribution. Measurements of unevenness of the thalweg (ADDRA, Topographer/ODEF) within the framework of this study showed compared to the data of 1979 a difference of coast varying from 0, 7 to 5 m (Fig. 12).

Figure 12: Zio basin topographic sketches indicating the silting up level

Thus, while taking as reference the river along the Classified Forest of Eto where the basin is covered with sufficient vegetation and galleries forests, banks are little degraded, slopes ranging between 0,50 and 2%, Zio is perennial flowing, average coast value is lower to 1 m indicating the silting up unimportant or marked very little in this zone.

Fields of farm and forest use where banks are almost not protected, slopes lower than 0,50%, water flow temporary or seasonal, coast of thalweg raising be from 2 to 3 m corresponding at a stage of advanced fill. Values from 4 to 5 m are those population area establish, wide market-gardening activities where the river bed merges almost with alluvial plain floor with absence of banks, final phase of course water silting up process.

4 HUMAN ACTIONS FACTORS OF ZIO RIVER SILTING UP AND BASIN DEGRADATION

According to the statistical data of the Maritime Regional Management of the Plan on the evolution and the pattern of the settlements these last years, only the plate of Tsévié is fairly populated with a density around 80 inhabitants/km²; other hand, the plates of Agoènyivé, Kpogan and the inshore bar concentrated high densities from 200 to 300 inhabitants/km² and thus know spaces problems.

Fringe zones of the Lome capital over populated extend in the Zio low valley which appears for the residents a favorable site to conclude their activities without much constraint (public taxes, authorities' orders...). The activities which prevail and concentrate a strong population are: agricultural activities, breeding, gravels extraction, taking away of sediments, fishing and drives out (bush fires), waste incineration and draining of latrine, wood exploitation, habitat construction and infrastructures (bridges, roads, agricultural hydro dams, electric posts, channels and sewers, automobile parks, drilling of prospecting, factories etc...).

These activities in their execution disturb the balance of the basin environment in several manners in particular by deforestation, pollution, uncontrolled occupation or tenure; their main common causes are:

- Demographic pressure, it is explained by, the strong populations migration in land use research, the keen wood demand source of energy not only for domestic use but also to satisfy the needs for the local industrial trooper activities (fish smoked, distillation of any nature etc..) and for the habitat construction;

- Incomes dropping, capacity purchase in falling, riverside residents, rural and urban populations surrounding think of balancing equation budgetary for hearths by receipts on the basin and the river natural resources.

4.1 Deforestation Main causes are:

- Burn on itinerant agriculture, ancestral technical which is crossing entirely or cutting a forest, and let dry the vegetation, then to put the fire of cleaning before the first rains. The piece is cultivated during two or three years, limiting of exhaustion of the reserves of the stripped ground what obliges the peasant to clear another. Thus, several hundreds hectares of basin natural vegetations disappear each year;

- Forests relics use, residents and large owners are identified main persons in charge. Bringing back easy profit exploitation always does not respect the forest legislation into force. It is done in the form of heat wood production, of saw log and charcoal. Also, it can be mentioned exploitation for medicinal use but this although concerning certain threatened species does not appear to have a dominating influence in the forest degradation;

- Gravel pits anarchic exploitation, the marketing of the gravel pits is today capital for the area economy. Open cast mining of the careers requires the systematic demolition of all vegetation which is there followed clearing of the ground covering. This is gradually transported in the river bed by surface waters.

4.2 Pollution

The basin is the subject of aggression multiples related to human intervention which either reinforces already evoked natural degradations, or new faces of pollution like developed eutrophication in Zio mouth and in Lake (Lac-Togo). In fact, pollution in general is due to the bush fires and the waste poured in the basin in particular the products hydrocarbons, toxic worn water, from industrial and domestic use:

- Hydrocarbons, several standards, their presence in the basin is due to the use of trucks and machines of any category for extraction, the collecting, the washing of gravels and sediments transport. Increasing man power of the machines, their maintenance involves the hydrocarbon discharge which is spread and sometimes infiltrate in the ground. The concentration of the high-carbon products is not without effects on the environment; they take part in situ destruction or disturb the reproduction of certain vegetable and animal species and could cause modifications on soil physical property;

- Domestic sewage water, the thorough and anarchic urbanization of Lome and its fringe or peripheral zones at ends, tourist, residential involved the worn water increase which for is most of the time drained or thrown in the basin without any specific treatment in order to preserve the basin environment;

- Industrial sewage toxic water, it does not know yet the specific impact of each type of industry (throwing metal, acid ions amino, lipids, carbides...) which uses the basin as dump. This water generates degradations which enter within the framework general of pollution by sewage water and overloads surface water or in suspension;

- Eutrophication, according to Ryding and Rast in «The Control of Eutrophication of Lakes and Reservoirs» (vol. 1, 1989, USA), it is an undesired over-fertilization of the water bodies with inorganic nutrients, manly phosphorus, ?P? as phosphate and nitrogen ?N? as nitrate and ammonium. Using sun light, air-born CO2 and these nutrients, if they are available in excess, phytoplankton (micro algae, cyan bacteria) or macrophytes (water hyacinth) can produce through photosynthesis enormous amounts of organic matter (biomass):

+P, +N, + light

6 CO2 + 6 H2O -* C6H12O6 + 6 O2

Phytoplankton biomass will sink down later into the lower dark layer where it cannot survive. Their dead are finally decomposed by heterotrophic bacteria in the water deep layers causing strong oxygen depletion through this biochemical process:

Darkness

C6H12O6 + 6 O2 -* 6 CO2 + 6 H2O

Main control strategies can be derived from the phytoplankton balance equation:

dX/dt = D . Xo + u . X - D . X - B . X - G . Z . X

import growth export sedimentation grazing

* Where/ X = lake phytoplankton biomass; Xo = inflowing water biomass; t = time; D = dilution (or flushing) rate ; u = phytoplankton growth rate; B = sedimentation rate ; G = zooplankton grazing rate; Z = zooplankton biomass. Rates are related with ecosystem variables in following way: D = Q/V or water residence time t = 1/D (Q = discharge, V = lake volume) ; Z = f (fishbiomass) ; u = f (light intensity, temperature, nutrients) ; G = f (temperature, biomass phytoplnkton) ; B = Vs/Zmix (Vs = phytoplankton sinking velocity, Zmix = water depth)

* When dX/dt is/

- Positive (+dX/dt), means that phytoplankton biomass increases if gains (import and growth)

- Negative (-dX/dt), means that phytoplankton biomass exceed losses (export, sedimentation and grazing)

4.3 Uncontrolled occupation and socio-economic activities

Zio basin concentrates dense populations which settle in the flood plain without any respect to D.G.U.H (Office of town and Habitat planning) recommendations. These later have for activities agriculture, breeding, fishing, hunt, trade, forestry exploitation, extraction and washing gravel. Agriculture is intensified with water reserve (hydro dam) for rice crop.

The basin is crossed by main road and railway axes (fig.13) which partly serve the Maritime Region and the country remainder; it is Inter- State road connecting the coastal zone to Burkina Faso, landlocked country. In Togblé, the passage on the river required the road bridge installation of large tonnages; it is same for the railroad which connects cement and clinker industries in Lome and Tabligbo. The secondary road network made up of tracks and paths emerge most of the time with the river.

Figure 13: Zio basin tenure (Akibodé, 2000) 4.4 Impacts of human action

According to estimates' of FAO and OIBT (International Organization of Tropical Wood) during 2000 to 2004, several million forest hectares disappear in developing countries and this in despite the world forest community mobilization. In West Africa, more than 2/3 of wooden surfaces disappeared these last decades. In this context that Zio basin forest destruction is registered.

The history recalls that it quasi totality of the basin was covered by an abundant forest, including gallery forest before the human occupation (GAYIBOR, 1988); just as of other work (ORSTOM, 1967), agree to recognize vegetable cover importance in pass and devastations operated by the man. Thus, basin forests degradation led to:

- Marked fall of the soil fertility, made uncultivated following, an accelerated migration of the fine particles (effects of deflocculating of clays and dispersion of colloids); none recycling of the organic matter; an induration's of the pedological profiles;

- River and effluents silting, due to the important deposits of alluvial loads continuation to the draining making intermittent the flow and difficult for economic activities depended to the river exploitation;

- Loss of biological diversity, floristic and fauna richness basin consequently its economic capital in long term as regards wood in all its forms, products of fishing and hunting;

- Progressive basin turning into a desert, justified with the increasingly noticed presence of certain woody species like Adansonia digitata commonly called «Baobab» characteristic of the zones strongly touched by the phenomenon;

- Extension of «badlands» reduced cultures surfaces, leading to the fall of the agricultural outputs and consequently incomes of the riverside residents.

Taking into consideration of precedes; it can admit that the vegetable cover is used of natural screen guard or against grounds erosion and Zio river silting up. The chart below indicates the various sites of the basin affected by degradation.

Figure 14: Indicators chart of Zio basin environmental degradation (Akibodé, 2000)

5 SOLUTION APPROACHES OF RIVER SILTING UP AND BASIN

DEGRADATION

Zio basin can be considered as a territorial entity, ecologically rich which would have known in the pass an environmental stability. But, nowadays, the situation of strongly increasing population it undergoes a considerable degradation of its natural resources such as forest formations. The major environmental problems in the basin are:

· Deforestation about culture, charcoal and wood production;

· Soil impoverishment by hydrous erosion and human factors;

· River banks instability (degradation);

· Zio River silting up and water resources lacking;

· Eutrophication;

· Air and hydrous pollution;

· Biological diversity in loss;

· Desertification (soil degradation ...).

Solution of these problems requires urgent measures of environmental protection and dispositions go from defense to respect basin dynamics function. In fact, the problem of management of the basin environment and natural resources arise in term of prevention and conservation: prevention of the damage which can inflict the combined effects of poverty and development efforts and rare resources conservation and fragile forest ecosystems.

This study proposes to make a global and integrated solution of the environmental problems. Thus, it considers a multitude effective solution experimented in the country or in the West Africa to fight in general against erosion and river silting. Process, regarding basin reforested by »Taungya system» with idea to promote agroforestry, and to manage effectively bush fires practice, to protect the biodiversity, to sensitize the bordering populations, to limit or control eutrophication, to practice inexpensive anti-erosive measurements and control soil erosion.

Agroforestry, an innovative farming approach includes the culture of the trees and shrubs providing, fruits, nuts, fibres, medicinal substances, heating and work wood. Experiences show that this mode improves peasant food, also other existing conditions. Tongya technical allows the peasants to associate crop and wood production.

5.1 Basin reforestation and fire management

Reforestation is replanting and maintaining the trees, keystone of fight against deforestation, desertification and soil impoverishment. Basin vegetable cover degradation appears like thorough that the idea of a systematic prohibition of any form of exploitation comes at to mind. Also, the regulation is the legal way to submit the wood owners to the principles of environmental and natural resources protection.

However, it will be more judicious to intensify the national policy of reforest instituted since 1977 (1 st June, Tree Day) in the basin. Rehabilitation of the old clearings is an alternative to be considered.

In a general way, efforts of reforestation are far from compensating the fires destruction often practiced by the peasant breeders to facilitate herbaceous carpet pushes back for the pasture. In addition to the suitable regulation for the practice of fire, restraint measures considered relate to the massive introduction of fodder species of substitution making allow herds to wait the first rains and the new vegetable.

For this forest settlement or natural vegetation restoration, several objectives can be associated through the wood production or firewood for other uses, such as agroforestry, timbering of the village tributary of the river regarding Taungya principles following the strategy proposed in Table 7 below:

Table 7: Agroforestry strategy to limit erosion effect in basin

Agroforestry practice	Category Species		Propagation Method	Uses
Live-fencing and basin boundaries	Chosen following soils taxation (vocation, study)	Exotic (E)	Cuttings Cutting/seed Seed, Suckers	Protection, Fibre Fruit, Timber/Poles Fuelwood & Windbreak Protection
		Indigenous (In)	Truncheons Truncheons/Seed Seed left to grow	Protection, Fruit, Firewood, Timber, Medicinal, Fodder, Seed, Shade Nutrients Alleviation Protection
Trees in Pasture Land
Vegetable Garden/Homesteads		E	Left to Grow/Planted Left to Grow	Shade, Fodder, Fertilizer, Fruit, Timber, Fuelwood
		In	Left to Grow/Planted	Timber, Shade, Seed
Trees in Cropland Conservation Structures
		E	Seed/Buds Seed, Sucker Seed/Graft Cutting	Fruit, Fuelwood, Poles Medicine
		In	Left to Grow Left to Grow/Planted	Fruit, Fuelwood, Poles Medicine, Timber Nuts, Sculpture
		E	Seed/Graft, Seed Planted	Fruit, Shade, Poles Timber, Fuelwood
		In	Left to Grow/Planted Left to Grow	Live fencing & Medicine, Poles Fuelwood, Fodder Carvings, Shade, Food, Fruit, Fertilizer

5.2 Biodiversity protection

Only by taking account of information received from the riverside residents, it is can think indeed that impoverishment in biological resources of the basin would be accelerated considerably with the population increase. Also, although specifically inventories do not prove the hypothesis, it estimates with the rhythm of current deforestation that several hundreds of floristic and fauna species are threatened of extinction or disappear.

Face to this situation, it is pressing to protect the basin zones being of ecological interest not only ethical but also economic. Aside, Wouto forest classified, the complex forest of Eto-Lili in rehabilitation, some forest gallery maintained and Bayémé Zoo restoration project in sight by Ministry of Environment and Forest Resources, it can create in the strongly degraded zones other forest reserves and integral surfaces protected with participative management like Togodo and Amakpapé forests classified respectively in the Mono and Haho basins and this by taking account soil vocation and bordering populations daily considerations.

5.3 Fight against eutrophication

According to Ryding and Rast, fighting key is the bio-filtration process which is efficient and consists in enhancing large filtrating zooplankton. Amount of zooplankton filtrating needs to balance respective phytoplankton production, which can be achieved by appropriate fish stock management. Daphnia sp. is organism recommended for phytoplankton removal by filtration.

Also, denitrification process through this balance equation: NO3^- -* NO2, is chemical reaction only takes place under anoxic conditions. Thus, the bacteria employ the NO3^- as source of oxygen. Many saprophytes carry out the process such as Micrococcus, Spirillum, Bacillus, Escherichia, and Pseudomonas ...

Two others strategies with their methods can be using to control and restrict eutrophication in Zio river and lake (Lac-Togo); they are: Ecological control variable and Technological measures outline (Table 8) below:

Eutrophication control
Ecological control variable		Technological/Ecotechnological measures
External nutrient-load from the drainage basin		* Control of point sources : sewage treatment, algal ponds, sewage diversion from the catchments area, water-saving technologies in industrial establishments, reduction of liquid manure losses in animal husbandry, low P-content in detergents ; * Control of diffuse sources : protective zones, proper application of fertilizers, soil stabilizing- technical in agriculture, afforestation, seepage trenches, pre-dams, P-elimination plant, reed belts, retention basins for storm water
Internal load from the sediment	Phosphorus	* Hypolimnion aeration * Injection of nitrate into the lake sediment
	Nutrient	* lake bottom sealing * sediment dredging
Export of nutrients by discharge		Deep water release (reservoirs)
Export of phosphorus into the sediment		Precipitation by means of Al- or Fe-minerals
Water residence time		Flushing with water low in nutrients
Phytoplankton sedimentation		* Subdivision of the water body by baffles * Introducing mineral substances
Zooplankton growth		Produce artificial feeding of zooplankton during the lack seasons
Zooplankton mortality		Reduction of zooplankton eating fish by high stocks of predacious fish (biomanipulation)

Source: Ryding and Rast in «The Control of Eutrophication of Lakes and Reservoirs»

(vol.1, 1989, USA)

5.4 Bordering populations awareness

According to the dictionary Larousse (1990), quoted by KLASSOU (thesis, 1996), «environment, is the unit, at a moment, physical agents, biological and the social factors likely to have a direct or indirect, immediate effect or in the long term, on the living organisms and the activities human». From this definition, it can admit that the Man takes a significant part in the environmental degradation, his space life.

Nowadays, environmental degradation is a serious concerns subject in many areas of the world; thus, many projects of development and institutions charged to protect the environment tried to solve the problem in margin of the populations, but the objectives appeared out of attack. The failure comes from the ascribable start to the fact that did not know to realize environment management contained also socio cultural dimensions.

It is thus convenient, for the sustainable development of the Zio basin, to involve directly all bordering populations; by sensitizing on the principles of participative local development, the awakening of the environmental stakes of site users. It acts, to some extent to include so much the aspect environment in all socio cultural activities; to develop relationship between culture and environment at all levels; to integrate the concept into lived daily of the populations so as to respond them face their own becoming.

5.5 Anti-erosive measurements and soil erosion control

There are several technical to protect basins slopes and courses water against the silting up. Those which can be adapted in Zio basin are stop shoulders, renewable organic matter stock; establish anti-erosive works, drainage, contour and terraces crop. Not very expensive, they were tested successfully in Ghana, Togo neighboring country, precisely in Volta valley:

- Stop shoulders, as their name indicates, they stop sediments transported by surface waters and are built either using plants perennial settings in hedge laid out perpendicular to the slopes either carried out starting from stone or deadwood. It can associate two manners to reinforce the fight. Also, benches settlement is effective to fight against erosion. Benches technical, is practiced to slow down erosion speed, with the intercalated cultures (tomato, corn, bean, groundnuts etc...); alleys of benches are used to cultivate the graminaceous consumable or not.

- Organic matter stock reconstitution, to rehabilitate a temporarily abandoned ground, it can carry out the mechanical clearing to make clean the culture field; the peasant can give again a structure supporting the ventilation of the ground by some animal and vegetable wastage (scum of sugar cane so much produces in the basin);

- Cultures in contours line and terraces, to intensify the protection of the slopes emphasized, it can practice the culture in contours, a culture established according to the level lines; balks of culture, obstacles to the surface waters cross the slope following his undulation. Terrace cultivation practiced to slow down speed of surface waters in staircases or levels;

- Work anti-erosive and drainage, it reinforces the device enumerated above and relates construction of the water channels which will substituted drains, gullies and ravines. Laid out slopes parallel, this latter will be used to evacuate surface waters towards the principal flow; grids will be posed at the ends of the channels so to avoid their filling up by clearing products.

In the low of the slopes, dams and stakes of stop are indicated to fight against hydrous
erosion; they resist the attacks of water and last a long time when they are out of concrete.

The latter block the sediments of erosion which can be taken to rehabilitate the slopes exposed by water or for other work.

About soil erosion and according to Meyer and Wischmeier (USA, 1980) quoted by Fenli (CIPSEM, 2007), soil erosion control in river basin can use Erosion Prediction Model which allow to, develop easily a reasonable estimate of soil loss, manage soil adjusted decisions, evaluate management impacts and assess resource inventory. This model uses Revised Universal Soil Loss Equation, Version 2 (RUSLE 2) which is:

A = EI x K x LS x C x P x SSF

Where:

A = Average annual soil loss in tons/acre/year; EI = Rainfall energy and intensity; K = Soil erodibility (Texture, Structure); LS = Slope length, grade, shape; C = Cover-management factor (Rotation, Tillage); SSF = Adjustable factor for Slope shape; P = Supporting practices (Terraces, Contours, Buffers)

Soil discharge quantity obtained per year will be an indicator to know if the basin area concern will submit with reforest or not.

6 CONCLUSION AND RECOMMENDATIONS

The project to fight against Zio river silting up and erosion in the basin requires a perfect knowledge of the zone and its state of degradation so to identify suitable measurements of fight. Those are concerned which made object of this study resulting from its work arrived at the conclusions and recommendations hereafter:

- From the geological and geomorphologic point of view, basin of Zio is cutting in a sedimentary material sandy and clay with low water holding capacity; which justifies the fast infiltration of the an important volume rainwater to be collected towards the principal flow;

- River silting up and erosion, in the basin are the major problems of degradation due to the combined effects of the factors natural and human of destruction of the environment;

- Zio river in the coastal sedimentary basin runs, in a channel of relatively weak unevenness whose value of the slopes does not exceed 2%; what facilitates the deposit of loads during the falls and low water levels contributing to the stranding of the river bed;

- Degradation of the basin forestry cover, has naked the grounds is the principal cause of erosion.

To protect Zio river banks and fight against erosion in the basin, the study recommends the participative and sustainable reforestation with the idea to promote the agroforestry and to manage the bush fires effectively, to protect the biodiversity, to limit eutrophication, to sensitize the bordering populations, to control soil erosion and put anti-erosive measurements into practice.

Although efforts are in hand on the various sectors level concerned with management studied zone to constitute a data base, there is a crucial lack reliable and recent data on sedimentary basin coast. This situation does not encourage initiative to undertake studies on the area. Thus, it pressing for the ministries concerned regarding question to create harmonized data base on the sedimentary basin coast and with need together for all territory with for coordinator the Ministry of Environment and Forestry Resources.

We are convinced if all these measurements taken into account and implementations, it obvious that very soon the environment of a favorable environment for the bordering populations will reappear in the basin.

To finish, we launch a call to all those which work for fundamental research in connection with river basins, in particular those of the coastal sedimentary basin of Togo, to take account of the well-elaborated intentions in the various work studies. It through this frank scientific collaboration, the spirit of interdisciplinary can really contribute to the human and sustainable development of our country.

REFERENCES

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AKIBODE, A. S. Nelson (2000): Contribution a l'Etude Hydro geomorphologique de la Basse vallée du Zio, Memo, Univ du Benin, Lome, 75 p

ANONYME (1981): Périmètre irrigué du Zio, étude socio-économique, Rapport SOTED, Direction du Plan, Lomé, 48 p.

BLIVI, A (1993): Géomorphologie et dynamique actuelle du littoral du Togo (Afrique de l'Ouest), Thèse de Doctorat, Bordeaux, 458 p.

CHURCH, H et MOSS, R. P (1980): West Africa, a study of the environment of man's use of it, Londres, 526 p

COLOMBANY, J (1968): Notice hydrologique sur le Bassin du Zio à Kpédji, ORSTOM, Lomé, 42 p.

COUDRAY, J et BOUGUERA, M. L (1994): Environnement en milieu tropical, ESTEM, Paris, 19 p.

GNONGBO, T. Y (1989): Contribution à l'étude géomorphologique de la basse vallée du Zio, Mém, Univ. Du Bénin, Lomé, 124 p.

GU-KONU, Y et al (1981): Atlas du Togo, J.A, Paris, 64 p.

HERVIEU, J (1968): Contribution à l'étude de l'alluvionnement en milieu tropical, Mém, ORSTOM, n0 24, Paris, 58 p.

IROKO, O. Yao (2006): Fondements pour l'Elaboration du Schéma Directeur de l'Aménagement Environnemental de la Région des Plateaux, Mém, InSTEC, La Havane/Cuba,

JOHNSON, K (1987): Le Bassin côtier à phosphates du Togo, Thèse, Univ. de Bourgogne- Dijon, 248 p.

KLASSOU, K. S (1989): Impact du climat sur l'évolution du régime hydrologique, le cas du Zio et du Haho, Mém, Univ du Bénin, Lomé, 120 p.

Martin, P. Wanielista (1990): Hydrology and Water Quantity Control, Univ. New York, USA MICHEL, P (1990): Géographie physique tropicale (Approche aux études du milieu), Karthala-ACCT, Paris, 351 p.

NORMAN, C (1982): Pluies de grains, pluies de mousson et environnement dans la zone maritime du Togo, Mém, Univ. du Bénin, Lomé, 122 p.

PECH, P et REGNAULD, H (1992): Géographie physique PUF, Paris, 315 p.

PIERRE, G (1974): Dictionnaire de la Géographie PUF, Paris, 346 p.

RYDING, S.O. and RAST, W. (1989): The Control of Eutrophication of Lakes and Reservoirs, MAB (UNESCO) Vol. 1, Paris, 314 p.

SLANSKY, M (1962): Contribution à l'étude géologique du bassin sédimentaire du Dahomey et du Togo, Mém du BRGM, n^o11, Paris, 270 p.

SOGBEDJI, M (1987): Etude de la pluviométrie au Togo Méridional, Rapport ORSTOM, Lomé, 24 p.

TIMO PUKKALA and KALLE EERIKAINEN (1998): Modelling the growth of tree plantation and agroforestry system in South and East Africa, The University of Joensuu, Falcuty of Forestry, Reaseach Notes 80, 1998, 256 p.

VIMARD, P (1979): Enquêtes démographiques sur la Région Maritime, ORSTOM, Lomé,

34 p.

CHARTS AND FLY PHOTOS DOCUMENTS USED

- Togo topographic charts/ 1/50 000 IGN, Paris, 1954, covering study zone:

1.	Kouété		Feuille NB-3 1 -XIX-2b	2.
Kati	Feuille NB-3 1 -XIII-4d		3.
Palimé	Feuille NB-3 1 -XIV-4b		4.
Lomé 3a	Feuille NB-31-XIV-3a		5.
Lomé 1c	Feuille NB-31-XIV-1c		6.
Lomé 1d	Feuille NB-31-XIV-1d		7.
Lomé 1b	Feuille NB-31-XIV-1b

- Fly photography/ 1/30 000, Maritime Region covering study zone:

1.	Vol. 77-TOG-31/300:	2475	- 2476	- 2477	- 2478	- 2479	- 2480
		2491	- 2492	- 2493	- 2494	- 2495	- 2496
2.	Vol. 78-TOG-31/300:	3368	- 3369	- 3370	- 3371	- 3372	- 3373
3.	Vol. 79-TOG-31/300:	3584	- 3385	- 3586	- 3587	- 3588	- 3589

TABLE OF FIGURES

1. Study area chart localization and geology

2. Curves of the monthly average temperatures of the basin over 25 years

3. Rainfall graphs of the monthly averages of the basin over 30 years

4. Curves of evolution of the monthly averages of sunstroke and evaporation in the basin

5. Water supply of the Zio river

6. Zio catchments area and hydrographic network

7. Curves of evolution of annual average precipitations over 20 years

8. Curves of annual medium flows of Zio over 21 years period

9. Curves of evolution of Zio flowing over 21 years

10. Zio alluvia terraces space provision

11. Recognizing Zio valley geomorphology sketch in coastal sedimentary basin (Akibodé, 2000)

12. Zio basin topographic sketches indicating the silting up level

13. Zio basin tenure (Akibodé, 2000)

14. Indicators chart of Zio basin environmental degradation (Akibodé, 2000)

Sources:

TOGO:

. Ministère de l'Environnement et des Ressources Forestières

. Départements de Géographie, de Géologie/Université de Lomé

. Direction de l'Urbanisme et du Cadastre

. Ministère de l'Agriculture, de l'Elevage et de la Pêche

. Ministère des Mines, Energie et Eau
. Riverains et autres usagers du basin

GERMANY:

. Technische Universität Dresden - Library/Dresden

. Institute of Soil Science and Site Ecology/TUD/Tharandt

. Ministry for the Environment, Nature Conservation and Nuclear Safety, Berlin . Centre for International Postgraduate Studies of Environmental Management (CIPSEM)/TUD

. Neunzehnhain Ecological Station: Training and research Center of Water Engineering Department of the Faculty of Forestry, Geo- and Hydrosciences TUD

. The International Academy for Nature Conservation, Isle of Vilm . German National Park

. Regional Commis sion/Council Integrated Rhine Programme, Freiburg

Others:

. Czech Republic: Institute of System Biology and Ecology, Academy of Sciences of the Czech Republic, Ceske Budejovice & Prague

. France: National School for Water and Environment Engineering, Strasbourg (Research Centre in Agricultural and Environmental Engineering)