DETERMINATION OF THE REMAINING STORAGE IN THE ZARIA IMPOUNDING RESERVOIR USING BATHYMETRIC METHODS.
DETERMINATION OF THE REMAINING STORAGE IN THE ZARIA IMPOUNDING RESERVOIR USING BATHYMETRIC METHODS.
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Date
2012-11
Authors
KUDAMNYA, Ebenezer Agayina
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Abstract
Zaria impounding reservoir for now remains the only source of piped borne water supply to
Zaria and its environs since its impoundment in 1974 to date. However, its useful life is
constantly been threatened by continuous siltation with sediments originating from within its
drainage basin – the Galma drainage basin.
Owing to the great importance of the reservoir in the supply of potable water to Zaria and
environs, an attempt was made to determine the remaining storage. Two methods employed
are direct field method and indirect method using remotely sensed data. The direct field
method was carried out using a boat, measuring tape, satellite navigator (GPS) and a heavy
object to measure depth and edge of the open water table at the time the spillway is
overflowing. While the indirect method employed the use of ETM+ landsat images using
softwares; ILWIS 3.7 to geo-reference and process the satellite images, and GLOBAL
MAPPER 11 to determine the reservoir’s surface area and also generate the digital elevation
models (DEM) of the study area.
The storage volume determined from the indirect method for 1990, 2000 and 2010 were on the
high side. However, processed ETM+ landsat images for the respective years show a decrease
in surface area of the of the Zaria Impounding Reservoir with time as expected, owing to its
siltation. Results obtained from the direct field measurement shows that at present in year
2010, average weighted depth is 2.82 m. Also, the remaining storage capacity was estimated at
21,129,242 m3, corresponding to about 46% of the original volume. Therefore, the rate of
siltation between years 1974 to 2010 was calculated to be 685,299 m3/year. This corresponds
to an annual loss to bed load siltation of about 1.5% per year. Results from the study further
show that only the active storage is left remaining. The dead storage had completely been
silted up about 23 years after the impoundment or 13 years ago. Active storage volume has
been reduced by about 8,670,758 m3 by the year 2010. Erosion within the entire drainage
basin, which consists of the volume of dissolved sediment, suspended sediment and deposited
bottom bed load, was summed to an amount of 1,039,118 m3/year. Therefore rate of erosion
within the reservoir’s drainage basin occurs at an average depth of 0.0003 m/year or 0.3
mm/year.
By year 2041 the reservoir will be completely silted up, if necessary measures are not taken. If
no action is taken, water rationing in Zaria, caused by progressive siltation of the Zaria
impounding reservoir, will start in the dry season of year 2031. Gradually, it will develop to no
water in dry season starting from year 2033, and to a complete siltation of the reservoir in year
2042. Siltation of the reservoir can be reduced by taking measures such as afforestation and
other forms of environmental upgrading within its entire drainage basin. Also, plans to dredge
the reservoir should be put in place.
Description
A THESIS SUBMITTED TO THE
POSTGRADUATE SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD
OF A MASTERS OF SCIENCE DEGREE (M. Sc.) IN GEOLOGY
DEPARTMENT OF GEOLOGY
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
NOVEMBER, 2012
Keywords
DETERMINATION,, REMAINING,, STORAGE,, ZARIA,, IMPOUNDING,, RESERVOIR,, USING,, BATHYMETRIC,, METHODS.