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.
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