Alluvions and Flooding of Waters in Uvira (DR Congo)

Volume 6, Issue 3, March – 2021 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
Alluvions and Flooding of Waters in Uvira

(Dr Congo)
MWENYEMALI BANAMWEZI Dieudonné1, KAHINDO NDJUNGU Joseph 1, FUNTA KYANDA Clément1,

TOMOMBWA KUMBUSA Patient1 and AMISI MANALA Christian2
1.
Hydrology department, Uvira hydrobiology Research Center, CRH-Uvira BP 73 Uvira, DR Congo.
2.
Department of Fisheries Socioeconomics, Uvira, Research Center CRH-Uvira BP 73 Uvira
Abstract:- The present work, carried out during the environment of populations living in periodically flooded
years 2000 to 2020 in rainy seasons, aims to describe the regions (Martin A et al. 2016).
impact of excessively abundant alluvium on the flooding
of rivers in Uvira. From direct observation of the facts The city of Uvira is facing the problem of flooding of
in the field, we have shown that the raising of the beds rivers, Lake Tanganyika and Nyangara lagoon. Flooding of
of the rivers and the obstruction of the outlets of the rivers in the city of Uvira is old and recurrent and has
water of the rivers by too abundant alluvium, are two already been investigated: (Mwenyemali B. et al. 2014;
factors. Which condition the flooding of rivers observed Mwenyemali et al 2020). This work focuses on the damage
in the city of Uvira for several years? caused by flooding and the human influence in this
damage.
We have proposed reforestation, anti-erosion
cultivation practices and systems, the prohibition of In addition, the formation of "debris flows", "flood-
untimely bush fires for farmers in all watersheds of alluvial" zones as well as the straying of watercourses and
watercourses in order to limit erosion based on intense the digging of ravines lead to the destruction of dwellings,
alluvial deposits that cause these river floods. drainage channels and roads of Uvira (Ilunga L.2006).
Keywords:- Alluvium, Floods, Watercourses, Uvira. Twenty-five Mitumba Massif rivers flow through the
city of Uvira. In certain rainy seasons, during torrential
I. INTRODUCTION crises, most of these rivers deposit excessively abundant
alluvium in their lower sections, the region of the piedmont
The submersion of land usually exposed by plains and those of the base level. Can this excessively
overflowing lakes or rivers is undoubtedly the major risk abundant alluvium explain the flooding of rivers in Uvira?
on all continents. The danger of human and economic loss The aim of this work is to describe and explain the impact
is accentuated by the construction of numerous installations of too much alluvium on the flooding of rivers in Uvira and
in flood-prone areas (Touchard L. 2003). to make concrete proposals on how to slow these
phenomena.
Rain and other factors cause flooding, the water of
which degrades the physical environment and the living
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ISSN No:-2456-2165
II. MATERIALS AND METHOD
a. Map of the study environment.
Fig.1 Rivers crossing the city of Uvira.
These streams (7 permanent and 18 temporary) from The data were collected in the lower reaches of the
Mitumba massifs cross the city of Uvira before emptying rivers, in their riparian zones, affected by "flooding-
into Lake Tanganyika or the marshes and lagoon located to alluvial" as well as in the regions of the middle and upper
the north of the lake. reaches of the watersheds. Data collection was carried out
during the period from 2000 to 2020 during the rainy
The city of Uvira, located at the extreme northeast of seasons, especially after floods, from December to May.
Lake Tanganyika, is bounded on the north by the Kawizi
river, on the south by the Sangeza river, on the west by the b. Direct observation of the facts in the field, through
Mitumba massifs and on the east by the Lake Tanganyika visits and excursions, is the general basic method.
and the Ruzizi river.
Observations focused on: the flooding phenomenon in
The city of Uvira comprises two geological and order to identify its direct causes and understand its
geomorphological groups: mechanisms, deposited alluvium, "flood-alluvial" zones,
 Mitumba mountains (2000 to 3000 m) to the west, the erosive phenomenon as well as the damage caused by
formed by Precambrian terrain: quartzites and mica flooding.
schists. There are also amphibolites, gneisses,
pegmatites as well as veins of white quartz. These rocks These observations were accompanied by:
form dipping layers of 40 ° to 90 ° (Weiss G. 1959).  Taking geographic coordinates, using a GPS (Global
 The plain (774 to 900) in the east, represented by the Positioning system) to locate the observed facts.
fluvio-lacustrine detrital formations of the Quaternary.  Measurements of block diameters, thickness and extent
of alluvial deposits, using a decameter and a metal lath;
The population of the city of Uvira is concentrated in collecting sand samples, using a shovel. This allowed us
this plain (3º17'03'S '; 3º26'27''S and 29º7'E; 29º12'E), to determine the morphometry and the granulometry of
crossed by the lower reaches of the rivers. The city is the alluvium.
crossed from north to south by the RN5.  Taking pictures of the observed facts, using a digital
camera, in order to compensate for direct observation.
 The hydrological survey, among residents and
eyewitnesses, to inquire about past floods.

ISSN No:-2456-2165
III. RESULTS These blocks and pebbles were deposited during a
flood in April 2020. This torrent is famous for its disaster
The results obtained are presented in figures (2, 3, 4, of February 2002, the results of which were heavy: more
5, 6 and 7). than 50 dead, and a lot of material damage (houses
destroyed, RN5 barred by big blocks for two weeks: no
a. Too abundant alluvium raises the bed, the rivers access to the lake port of Kalundu.
overflow and spread.
Fig. 2 Torrent Nyarumanga (03 ° 23'99''S; 29 ° 08'12''E. Fig.4. Rivière Kavimvira (3°32’47’’S; 29°15'89, 9’’E.
860m) 788m)
Torrent known for its recurrent flooding. Torrential Intense accumulation of sand and gravel, upstream
alluvium still made up of blocks, pebbles and clayey mud. and downstream of the bridge, during the flood of
This alluvium was deposited during the flood of 04/17/2020. Here, the human habitat and a small market are
23/04/2020, which had the effects: 8 houses buried by located upstream of the bridge on the left bank. Before the
alluvium and 10 destroyed houses. Spreading of alluvium flood, they were at a higher level than the minor bed. After
In May 2018, this torrent caused material and human losses raising the bed, they were flooded and flooded with
including 4 deaths, children from the same family who sediment. Subsequently, the market was completely buried
slept in their beds. and the habitat is at a much lower level in bed because of
sedimentation. Likewise, the bridge, which was 4.50m
above the water, is already at 2.40m. Spreading of
alluvium.
Fig. 3 Torrent Kamongola (03 ° 25'48''S, 29 ° 07'51''E.

796m) Fig.5 Rivière Mulongwe (03°20'18, 7’’S; 29°09'30''E.
787m).

ISSN No:-2456-2165
The river raised its bed by sandy-gravelly alluvium and the gullying of a citrus plantation located more towards
during the flood of 04/17/2020, and it is already above the the right bank downstream . Spreading alluvium.
level of the habitat. We observe the spreading of alluvium.
IV. DISCUSSION
b. Too abundant alluvium clogs fluvial or torrential
water flow nozzles, overflow and spreading. These alluviums are characterized by two size
classes: boulders and sands, varying from one stream to
another and within the same stream from one point to
another :
 Blocks: The accumulations of blocks, often associated
with pebbles, dominate in certain streams above (fig. 2
and 3) and others: Ruzozi, Sangeza, Nakagonjwa,…
These are quartzite blocks of decimetric size to metric:
the largest of 6.90m thick was observed in the
Mulongwe river, at the foot of the mountains where the
latter empties into the plain. These blocks reflect the
strong energies of the current of these rivers. The
quantity and size of the elements transported is a direct
result of the speed of the current. This depends on two
main factors: the slope of the land and the volume of
moving water (Laverdiere J.W. et al. 1959).
 Sands: Characterize other rivers, including fig. 4 and 5
and others: Kalimabenge, Kaala, Nyangwi,...
Sometimes gravelly sand is observed. Particle size
analysis shows that these are sands with various grains,
mainly coarse sand (500µ-1mm) with a large percentage
of medium sand (250µ-500µ) and very coarse sands
Fig.6 Torrent Kaala (03°12'45, 7’’S; 29°09'34, 4’’E.
(1mm-2mm).
806,7m).
This predominance of the sandy fraction in these
Torrent with recurrent floods. In April 2000 the
alluvium (sands, gravel, pebbles and boulders) blocked the rivers shows that mechanical disintegration outweighs
chemical decomposition in watersheds (Gryzbowski K.
nozzle, below the RN5, and forced the water to overflow
1984, Tricart J. 1968).
over the RN5. We observe the degradation of the RN5 and
the houses located downstream of the bridge.
This abundance of alluvium including boulders and
sands, associated with pebbles and gravel, can be explained
by the very active erosion observed in the watersheds of
these rivers. Indeed, it is very intense erosion, (Degree 4),
according to the classification system of fluvial and
torrential erosion developed by the US Forest Service
(Sheng TC, 1993).
This erosion is characterized by:
 landslides: we have counted more than 130, most of

which are located in the reception basins of these rivers:
45 in the Kavimvira watershed, 46 in Mulongwe, 1 in
Nyarumanga, 3 in Kabindula , 32 in Kalimabenge, 8 in
Kamongola, 3 in Ruzozi ...
 Intense gullying: many gullies, most of which are
temporarily drained.
 bank erosion in the beds of all rivers:

This erosion in these watersheds is under the
combined action of abundant rains (<1000 mm in the plain
and> 1200mm in the mountains), linked to climate change,
Fig.7 Torrent Rutemba (03°18'9, 1"S, 29°9'36, 4"E. 814m) steep slopes (of more than 50 °.) And characterized human
activities. by inadequate cultivation methods on steep
Torrent with recurrent floods. After obstruction of the slopes, deforestation, untimely fires for the farmer and
nozzle below the RN5, by alluvium in April 2000, the stockbreeder, pasture,…. The steepness of the slopes, the
water overflowed and resulted in the erosion of the RN5 weakness of the vegetation cause the rainwater to run off
and concentrate very quickly, gullying the sides of the

ISSN No:-2456-2165
slopes and causing a significant load of mud, pebbles and From all the above, it emerges that the too abundant
large boulders (Georges P.1974 , Taillefer et al. 1965). alluvium, the manifestation of which is the raising of the
beds and the obstruction of the outlets constitute a problem
It should be noted that, since 2005, only the based on flooding in the city of Uvira. We must therefore
Kakungwe torrent no longer experiences this problem of fight against this abundance of alluvium in order to smother
intense alluvial deposits. This situation is linked to the fact the floods caused by material damage and sometimes
that for several years its watershed has not been exposed to human losses.
agricultural activities as in the past.
Indeed, efforts to fight against floods have been
Indeed, the rivers, very laden with alluvium in rainy undertaken for a long time but in vain due to the intense
seasons, raise their beds and flow to a higher level than the alluvial deposits. These efforts have included dredging
surrounding regions: the water overflows and inundates the some streams and building dikes along others. This was the
regions occupied by human habitat (2, 3 , 4 and 5). This case with the dredging of the Kavimvira and Mulongwe
overflow of water is accompanied by the mobility of the rivers during 2008 and 2020. In addition, the dikes erected
bed and consequently the destruction of homes (Ilunga L. along the Nyarumanga torrents (in 1997 and 2016), by the
2006, Mwenyemali et al. 2020). Caritas of the Diocese of Uvira , Kaala (1919) were buried
This migration or wandering of the bed often results and destroyed by abundant alluvium.
in the displacement of the mouths of certain major rivers,
including Kalimabenge, Mulongwe and Kavimvira. V. CONCLUSION
On the other hand, the obstruction of the outlets The raising of the beds of the rivers and the
forces the water to flow over the road and move either in obstruction of the river flow nozzles are two determining
all possible directions or to wander the channel. Flooding factors which condition the flooding of these rivers and the
depends not only on the flow but also on the obstacles to consequent damage in the city of Uvira.
the flow (Touchart L. op.cit.). Thus, the alluvium clogs the
evacuation nozzles, overflows on the roads and will To deal with this problem of too abundant alluvium
partially bury the habitat located downstream up to the which conditions river floods in the city of Uvira, we have
height of the windows about 1.5m (Ilunga L. op.cit.). In proposed the following:
1988, alluvium from the Kalimabenge congested upstream  The reforestation of all the watersheds of the rivers
of the bridge and obstructed the underside of this bridge on crossing the city, especially in the reception basins
the RN5. After the water overflowed, this flood had caused where most landslides are located.
a great deal of material and human damage.  The sensitization of the population on anti-erosion
agricultural practices and systems as well as the
These floods linked to the obstruction of the fluvial prohibition of bush fires in the watersheds of rivers.
and torrential flow nozzles are observed in a recurrent  Widening of fluvial and torrential water outlets.
manner in most of the rivers of Uvira (fig. 5 and 6), Karigo,  The relocation of the riparian human population living
Kagenge, Kibondwe. in areas at high risk of river flooding.
These floods linked to the raising of the bed and the Geological, geomorphological, hydrological and
obstruction of the nozzles by alluvium have the effect of climatic studies of the watersheds of these rivers must be
flooding and spreading alluvium: it is "flooding-alluvial" carried out with a view to the protection, improvement and
which is accompanied by the destruction of the soil. rehabilitation of these basins located in mountainous areas.
dwellings.
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following observations made in certain neighborhoods in Tunisia: elements for reflection.
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granulometric analysis of the current sands of Uvira,
These sediments mobilized during floods Cahier du Ceruki, New series no 12.
accumulate especially in areas where the slope decreases as [3]. Georges P. 1974. Dictionary of Geography, PUF
well as in flared sectors (Fehri 2014) .These alluvial Boulevard Saint-Germain, Paris.
spreading phenomenon undoubtedly results in the [4]. Ilunga L. 2006. Study of major erosion sites in Uvira
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(Lamar, 2009). ). [5]. Lahmar L. 2009. Floods and their impact on the
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[7]. Martin A. et al. 2006, Flood in Benin: socio-
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Alluvions and Flooding of Waters in Uvira (DR Congo)

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Volume 6, Issue 3, March – 2021 International Journal of Innovative Science and Research Technology

Alluvions and Flooding of Waters in Uvira

MWENYEMALI BANAMWEZI Dieudonné1, KAHINDO NDJUNGU Joseph 1, FUNTA KYANDA Clément1,

IJISRT21MAR657 www.ijisrt.com 1328

a. Map of the study environment.

Fig.1 Rivers crossing the city of Uvira.

IJISRT21MAR657 www.ijisrt.com 1329

Fig. 3 Torrent Kamongola (03 ° 25'48''S, 29 ° 07'51''E.

IJISRT21MAR657 www.ijisrt.com 1330

 landslides: we have counted more than 130, most of

 bank erosion in the beds of all rivers:

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IJISRT21MAR657 www.ijisrt.com 1332

IJISRT21MAR657 www.ijisrt.com 1333

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