Geoscience Reference
In-Depth Information
The return periods for each of these flows was then determined from
the relationship:
1
T
=
F
(
q
)
,
(2)
1
−
where
T
is the return period of the flow.
2.3.
Flood routing
7
Both Channel and Reservoir routing were performed for all the years of
interest so as to determine Lake Albert's behavior either as a channel or
reservoir in attenuating flood peaks.
2.3.1.
Channel routing
In applying the technique of channel routing, the lake was assumed to be
a channel through which water was being conveyed. This is justifiable as
Lake Albert is oblong shaped, furthermore it is part of the western section
of the Great East African Rift Valley.
The change in storage (channel storage) ∆
S
, was therefore first com-
puted from the continuity equation given as
∆
S
∆
t
,
I
O
=
−
(3)
where
I
is the average of inflows of two consecutive periods (months)
O
the
average of outflows of two consecutive periods (months), and ∆
t
is the time
interval of one month. The storage volumes,
S
, were computed by summing
the increments of storage from an arbitrary datum.
Values of
S
were then plotted against corresponding values of inflow
and outflow.
It was assumed that the storage was a function of weighted inflow and
outflow as given by the Muskingham equation as below:
S
=
K
[
xI
+(1
−
x
)
O
]
,
(4)
where
S
,
O
and
I
are the corresponding values of storage, outflow, and
inflow, respectively.
K
is the storage time constant for the reach and
x
is
the dimensionless weighting factor between 0 and 0.5.
The values of
x
and
K
were obtained by trial and error
x
.Usingthe
values of the storage
S
already obtained for the different years, a graph of
S
against computed values of [
xI
+(1
x
)
O
] was plotted. Of the values of
x
assumed, the value that resulted in a graph conforming most closely to
−
