Adesina, G.O.

Daddy, F.

Olokor, J.O.

English

Aquatic Commons

WATER HYACINTH COVER HYDROLOGICAL PATTERN
OF KANJT LAKE
J.O. OLOKOR, F. DADDY and G.O.ADESINA
National Institute for Freshwater Fisheries Research (NIFFI),
PMB 6006, New Bussa, Niger State, Nigeria
ABSTRACT
Bi-arinual circum-navigation of Kainji Lake between 1996 and 1999 to
determine the level of cover of water hyacinth show that the weeds are more
abundant in the high water periods than in the low water times. The surveys
were undertaken in August (period of low water) and December/January (period
of high water). Results from eight surveys show that all the high water periods
had the greatest spatial cover totaling 664.86Km2 or 56.18% compared to low
water coverage of 101 .74Km2or 8.6%. The reason for this can be attributed to
the annual hydrological cycle of the lake which cause the weeds to be pushed far
inland at high water and leaves them stranded at shore where they wither as the
floods recedes. Over the years the population of water hyacinth at high water
dropped from 16% in 1994 to 10.36% in 1999 and from 1.9% at low water to
0.74%. Communal removal, the impact of weevils that feed only-on the plant
and the establishment o the boon' across the lake are all factors that have
contributed to this declining trend.
INTRODUTION
Kainji lake which is located between
latitude 9°50' and 10o55'N and between
longitude 4032! and 4°45'E has a surface
area of about 1250Km2, a maximum depth
of 54.9m arid extends for 136.8Km
upstream beyond Yelwa. It is 24.1 Km at
the widest part (Niger Dam Authority,
1972) .The Kainji dam itself is 'ocated
1030Km from the Atlantic Ocean in the
south. The dam wall is 8.3 Km long rind
65.5m high (Imevbore, 1971).
The lake is home to wide variety of
aquatic plants and animals. The lake was
free of water hyacinth (Eichhornia
crasszpes) until 1989, it came with the
floods from the neighboring Niger
Republic. Since then the weed has
multiplied and spread across the lake
causing serious obstruction to
transportation and fishing activities. Ayeni
et al (1994) found out that water hyacinth
alone accounted for 16% of the total area
of the Lake. in the pre-water hyacinth
122
times, all the vascular plants on the Lake
accounted for only 0.5% (Tmevbore, 1971)
whiJe Chachu (1977), attributed the entire
cover to be 8.9%.
To continue monitoring the spread of
water hyacinth on the lake with the aim of
proffering management strategies for its
control, vigorous field surveys were
embarked upon twice a year, at high-water
and low water from 1994 to date. This
paper presents the findings of the field
surveys and discusses the annual cyclical
pattern of the hydroJor of Kainji Lake
and how it regulates the annual spread of
water hyacinth across the entire lake
MATERIAL AN]) METHODS
Circuin-navigation of the lake was
done twice a year: n August; period of
low water and in December / January;
period of high water. Two 45 horse Power
engines were used to power a fibre glass
Almarine boat. At a speed of 20Km/br, a
survey team comprising weed scientist,
range ecologist, geographer and
technologists circum-.navigated the entire
shores of the lake thaking stoppages where
necessary to collect data. Each trip took an
average of seven days. Other parts of the
lake were also checked for presence or
absence of the weed.
Geo-referencing of the Lake
Using the natural co—ordinates of the
take, the entire lake surface was divided
into about 1250 cells or grids coinciding
with the actual lake area. These grids were
printed on a hard copy map from a
123
digitized computer map. All the cells were
numbered 1-1250 representing 1Km2
ground. Data on the level of occurrence of
water hyacinth as collected on the field
were entered against the relevant cell.
Obtaining Water Hyacinth Cover
For Grids
To locate the position of a given cell
on ground, geo-position system (UPS)
(Magellan 12 BlazerR or GerrnainR UPS)
linked to orbiting satellites was used as
guide, which are capable of linking up to
12 satellites. The UPS tells the position on
ground where data is to be collected
corresponding to a known cell on paper.
Data are taken only on grids with water
hyacinth. Since a grid may have many
mats of water hyacinths, an average
measurement of the largest and smallest
mat (not less than im across) is taken and
multiplied by the total number of mats
(larger than 1 m across) in the cell to form
the value to be entered for the cell.
Measurements were done with a 30m-
fibre tape.
Calcuiating Water Hyacinth Cover
A data base using Micro-soft ExceJ'
was set up for the collected data . All the
numbered cells were assigned collected
data, which sum up to the total cover for
the lake. The lake was partitiooed into six
strata, corresponding to different co
ordinates. When this database is linked to
Geographical Information Systems (GIS)
package, a spatial spread of the cover of
water hyacinth across the lake is obtained.
GIS packages used during the course of
this study include Resource Information
Systems —5, developed at HTA Ibadan,
Mapmaker, developed in Europe and
Arc View.
RESULTS AND DISCUSSION
Table 1 shows the total cover of water
hyacinth in Km2 between 1994 and 1999
in all strata of Kainji Lake. Table 2 shows
the same information in Table I in
percentages. The table shows that by
August 1996 total coverage of water
hyacinth on the lake was 23.75 Km2 or
1.9%, December of the same year had
165 Km2 or 13.20%. In 1997 January the
cover stood at 199Km2 or 15.92% and
25Km2 or 2.00% in August. In March
1999, the cover of water hyacinth was
129.11Km2 or 10.36% and 10.49 Km2
0.74% in August.
Table I further shows that Strata 3
(NW) of the lake had the highest
concentration of the water hyacinth all the
year put together with 329.69Km2. Strata
3(NE) had 357.88 Krn. Strata 2(CW) had
179.50Km2, Strata 2 (CE) 130.50 Km2,
Strata 1 (SW) 59.375 Km2 and Strata 1
(SE) had 47.375 Km2. Figure 1 shows a
water hyacinth cover map of the lake in
1999 and the various strata of the lake.
Figure 2 is a line graph showing the
distributions of % cover of water hyacinth
of the lake at high and low water during
the study period. The tables show that at
low water peroids the level of occurrence
of water hyacinth is lower than during
high water levels.
Field observations show that the
perculiar hydrological behavior of the lake
is responsible for this cyclical high and
low water density. At high water, the in-
coming floods move the floating weeds far
into the adjourning shorelines. As the
water begins to recede, the floating weed
is left stranded at the shorelinQs. By
August when the water has reached the
lowest level, over 90% of the weed, which
came in with the flood, would have been
left on the shores. On the shores the weed
eventually dry up. The extent of
drawdown between the high and low
water can be very wide apart. At Shagunu
for instance, a shoreline draw down of 300
meters has been recorded between high
water and low water mark. In other low
lanU areas like Warra, over 3.5Km has
been recorded. At the periods when the
weed is left stranded at the shores many
communities gather and burn the weeds.
Many reasons for th high
proliferation of the weed at the northern
section of the lake compared to the other
parts as shown in the tables arrd figure 1
can be given. The first being that this
section serves as the entrance of the weed
into the lake such that the area is quickly
saturated with the weed compared to other
parts. Secondly, as the weed migrate into
the lake through the northern section the
numerous islands and grasses trap the
weed. A third reason is that the
124
Ta
b'
e 
1.
To
ta
l C
ov
er
ag
e 
of
 W
at
er
 H
ya
ci
nt
h 
(in
 K
m2
) B
etw
ee
n 1
99
4 a
nd
 19
99
 in
 al
l S
tra
ta
 o
f K
ai
nji
 La
ke
19
94
A
ug
us
t
19
96
D
ec
em
be
r
19
96
Ja
nu
ar
y
19
97
A
ug
us
t
19
97
D
ec
em
be
r
19
97
Ja
nu
ar
y
19
98
A
ug
us
t
19
98
M
ar
ch
19
99
A
ug
us
t
19
99
To
ta
l
Co
ve
r
(km
)
St
ra
tu
rn
3(N
W
)
51
.2
5
10
.0
0
55
.0
0
51
.1
3
15
.8
8
47
.7
5
41
.6
3
12
.7
5
40
.2
3
3.
88
32
94
9
St
ra
tu
m
 3
 (N
E)
63
.7
5
13
.7
5
48
.7
5
50
.1
3
9.
13
67
.1
3
51
.5
0
13
.2
5
37
.6
2
2.
88
35
7.
88
St
ra
tu
m
2(C
W
)
27
.5
0
0.
00
15
.0
0
39
.2
5
0.
00
40
.1
3
46
.3
8
11
,2
5
18
.8
8
1.
23
17
9.
50
St
ra
tu
m
 2
 (C
E)
37
.5
0
0.
00
22
.5
0
27
.6
3
0.
00
20
.0
0
19
.0
0
3.
88
3.
13
1.
00
13
0.
50
St
ra
tu
m
 I 
(S
W
)
16
.2
5
0.
00
12
.5
0
13
.6
3
0.
00
10
.0
0
6.
75
0.
25
11
.7
5
0.
25
59
.3
75
St
ra
tu
m
 I 
(S
E)
3.
75
0.
00
11
.2
5
17
.2
5
0.
00
8.
00
6.
00
1.
13
17
.5
0
1.
25
47
.3
75
To
ta
lC
ov
er
ag
e
20
0.
00
23
.7
5
16
5.
00
19
9.
00
25
.0
0
19
3.
00
17
1.
25
42
.5
0
12
9.
11
10
.4
9
10
19
.5
0
Ta
bl
e 
2.
 O
cc
ur
re
nc
e 
(%
) o
f W
at
er
 H
ya
ci
nt
h 
Be
tw
ee
n 
19
94
a
n
d
19
99
 in
 al
l S
tra
ta
 o
f K
ai
nji
 La
ke
Ja
nu
ar
y
A
ug
us
t
D
ec
em
be
r
Ja
nu
ar
y
A
ug
us
t
D
ec
em
be
r
Ja
nu
ar
y
A
ug
us
t
M
ar
ch
A
ug
us
t
19
94
19
96
19
96
19
97
19
97
19
97
19
98
19
98
19
99
19
99
St
ra
tu
m
 3
 (N
W
)
4.
10
0.
80
4.
40
4.
09
1.
27
3.
82
3.
33
1.
02
3.
25
0.
31
St
ra
tu
m
 3
 (N
E)
5.
10
1.
10
3.
90
4.
01
0.
73
5.
37
4.
12
1.
06
3.
01
0.
23
St
ra
tu
m
 2
 (C
W
)
2.
20
0.
00
1.
20
3.
14
0.
00
3.
21
3.
71
0.
90
1.
51
0.
09
St
ra
tu
m
 2
 (C
E)
3.
00
0.
00
1.
80
2.
21
0.
00
1.
60
1.
52
0.
31
0.
25
0.
08
St
ra
tu
m
 I 
(S
W
)
1.
30
0.
00
1.
00
1.
09
0.
00
0.
80
0.
54
0.
02
0.
94
0.
02
St
ra
tu
m
 1
 (S
E)
0.
30
0.
00
0.
90
1.
38
0.
00
0.
64
0.
48
0.
09
1.
40
0.
01
To
ta
l %
O
cc
ur
re
nc
e
16
.0
0
1.
90
13
.2
0
15
.9
2
2.
00
15
.4
4
13
.7
0
3.
40
10
.3
6
0.
74
Stratum 2
Stratum 1
[ — —] Strata boundaries
Water Hyacinth
Stratum 3NW 3.25/,
Fig. 1 Occurrence of water hyacinth on Kainji Lake in February, 1999.
icris5 Dr. S.S. Jagtap iLa
126
Stratum 2NE
0 akm
0.2 4
SE1.4
At NJ I
DAMS
Fi
g.
 2
. T
re
nd
s 
of
 H
ig
h
a
n
d 
Lo
w 
W
at
er
 P
er
ce
nt
ag
e
O
cc
ur
re
nc
e 
of
 W
at
er
H
ya
cin
th
 o
n 
La
ke
 K
ai
nji
be
tw
ee
n
19
94
 a
nd
 1
99
9.
18
4
16
_I
14 12 1O
0
8 6 0
Ja
n-
94
Pw
g-
96
D
ec
-9
6
Ja
n-
97 M
on
th
s 
an
d 
Ye
ar
s 
of
 S
ur
ve
y
Au
g-
-9
7
D
ec
-9
7
Ja
n-
98
Au
g-
98
Fe
b-
99
Au
g-
99
down stream parts of the lake have larger
water expanse thus causing stronger
waves generated by the strong impact of
prevailing winds whose impact cause the
weeds to be dislodged and broken into
tiny bits.
The variation of water hyacinth cover
over the years can also be attributed to
patterns of flood and rainfall. The level of
in-coming flood has been observed to be a
factor that determines the load of water
hyacinth to be brought into the lake.
Rainfall directly influences flood levels. In
recent years rainfall has been increasing
across the West Africa sub-region thereby
leading to unprecedented floods reaching
the lake. At Kainji the highest rainfall in
thirty years was recorded in 1999. Olokor,
(1999) has indicated that the years of
heavy rainfalls will record lower coverage
of water hyacinth compared to those of
lesser rainfall because of the stronger
impacts of floods on the weeds at such
times. Thus the veiy low watet hyacinth
coverage for August, 1999 was due in part
to the heavy rainfalls and floods, which
swept the weeds far inland. However, th
report indicated that as rains decline due
to the impact of the 10-year drought cycle
that affect the lake at the beginning of
every decade, population of the weeds will
increase between 2000-2003 and there
after drop sharply. Conununity
mobilisation and other control measures
are however necessary to put the weeds at
minimal level.
CONCLUSION
For more than half a decade, NIFFR
research team has been monitoring and
studying the spatial cover of water
hyacinth on Lake Kainji. Because of the
obnoxious characteristics of the weed, it
was worthwhile exercise to ascertain the
risk level of the lake being colonized by
the weed. This study has found that the
peculiar hydrological pattern of the lake
which at high-water moves the floating
weed to high ground and leaves them
stranded to die out, is a strong factor that
controls the ability of the weed to colonise
the Lake. With the combined impact of
other control measures, the Kaniji Lake is
likely not to be colonised by the weed.
It is hoped that with the establishment
of the floating boom, the total area
covered by the weed in years to come will
be less than the present. Olokor (1995), in
analyzing the cycles of the flood and
drought forecasted the year 2000/2003 to
be dry (although it may not be as dry as
the years 1970/1973). Subsequently, at
this time, the hydrological pattern of the
lake will be less enhanced, creating a more
riverine condition, with less waves and
tidal movement which annually move the
weed on-shore leading to a rise in the
population and concentration of the weed.
Increased effort at communal removal will
help mitigate the impact.
128
REFERENCE:
Akinyemiju, O.A (1995). An Inventorial Tour
of Lake Kainji. A report submitted to
National fnsfltute for Freshwater Fisheries
Research Institute, New Bussa. 3Opp.
Ayeni, J.S.O., F. Daddy, M. Mdaibli and
E.A. Obot (1994), Control and utilization
of aquatic weeds: Water hyacinth and
Niger grass on Lake Kainji. NJFFR
Annual Report. ISSN 0331-9296. Pp 20
24
Chachu, R.E.O. (1977). The Vascular Flora
0 Kainji Lake. Proceedings of the
International Conference on Kainji Lake
and River Development in Africa. Vol. 2
Kainj i Lake Research Institute Nigeria.
lmevbore, A.M.A.(1 971). Floating Vegetation
of Lake Kainji. Nature 230.599-60
Kusemiju, K (1994). Control of Water
Hyacinth on the River Niger. Report
submitted to National Institute for
Freshwater Fisheries Research. New
Bussa.23pp.
129
Obot, E.A (1984). Studies in the productivity of
Echinochloa stagnina (Retz) P. Beauty in
the Kainji Lake Basin of Northern Nigeria.
Ph.D thesis, University of Ife, Nigeria.
Olokor, J.O (1995). Climate of the Kainji Lake
Basin. 1925-1 993.Consultancy report for the
Nigerian- German Kariiji Lake Fisheries
Promotion Project. New Bussa.
Olokor, J.O., F. Daddy. Adesina G.O. and
H.A. Adeniji (1996). Mapping Water
Hyacinth Coverage of Kainji Lake
(Progress Report on Control of water
Hyacinth). National Institute for
Freshwater Fisheries Research, New
Bussa. 1996 Annual Report. ISSN 0331-
9296.
Olokor, J.O (1999). Status of Water Hyacinth
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1994-1999. Consultancy report for the
Nigerian-German Kanij i Lake Fisheries
Promotion Project, New Bussa.
W.B. (1990). World Bank Report (1990)



Water hyacinth cover and hydrological pattern of Kainji Lake

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Water hyacinth cover and hydrological pattern of Kainji Lake

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