DPA South Africa: Water Supply Scheme for a Dessert Town




		DELPORT DU PREEZ AND ASSOCIATES

CONSULTING ENGINEERS AND PROJECT MANAGERS

DOROP SOUTH WATER SCHEME

Index: Introduction, Scope of the works, Project costs


	INTRODUCTION

As a town situated in the Namib desert, Walvis Bay is totally reliant on the underground water resources for it's existence. Until 1990 the bulk of the town's water was obtained from the Rooibank aquafer in the Kuiseb river. The long drought inland led to a serious depletion of this resource, close to the point of collapse.

A study by the Department of Water Affairs and Forestry in South Africa indicated the existence of an untapped aquafer in the Kuiseb Delta that could be developed to provide a shortterm solution to the water supply problem. At the same time a study to look into the development of a desalination plant was commissioned.

In 1989 the total annual water consumption of Walvis Bay was 3.78 million cubic metres. This increased to 3.85 million in 1990 and to 3.94 in 1992.

The existing water supply scheme at that stage obtained water from the A and B aquafers at Rooibank. The pumping capacity from A area was 3.26 million cubic metres per annum. In 1992 approximately 2,2 million cubic metres had been extracted. Research however indicated that the long term yield was only 1.78 million cubic metres per annum. The sustainable yield from the B area was 0.8 million cubic metres per annum. The shortfall had to be imported from the Swartbank aquafer that supplied water to Swakopmundt and Rossing.

Approval was obtained from the Nature Conservation Authorities to develop the Dorop South Aquafer as a water augmentation scheme, subject to strict monitoring of the environment to ensure long term survival of the ecologically sensitive dune forests. Geohidrological studies indicated that approximately 5 million cubic metres could safely be extracted over a 5-year period.

Index

SCOPE OF THE WORKS

The new water scheme employed a network of 12 production bore holes and 8 monitoring bore holes. The production bore holes were equipped with electrically driven submersible pumps feeding water to the collecting reservoir at the B area via a network of underground uPVC pipes, ranging in size from 110 to 250 mm diameter and a total length of 4670 m. The main delivery line is 350 NB class 9 uPVC with a total length of 3270 m.

The electrical network consists of a 4780 main XPLE 11 kV feeder from B-area pumping station to two control stations, each operating 6 pumps. 400 V supply is provided through a 200 kVA Dyn transformer. Individual pumps are radially supplied with power via a network of underground PVC/SWA/PVC cables.

The two pump stations are remotely controlled from the control centre at Rooibank using a radio borne telecontrol system (ABB Indactic 15/RTU 200).

Index

PROJECT COSTS

The project budget on 1 May 1991 was R 5 405 633.


	The final project costs at the end of January 1993 was R 4 377 585:


	Drilling and bore holes

	Civil works

	Testing of bore holes

	Pumping equipment

	Pipelines

	Electrical services

	Monitoring and control

	Engineering fees


		R 1 000 000

	R 273 671

	R 43 815

	R 168 482

	R 960 558

	R 927 685

	R 893 374

	R 110 000

The Municipality of Walvis Bay contributed an amount of R 3 267 585 towards the cost of the project. The balance of the funds was provided by the Department of Water Affairs.

Index

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Page prepared by: P. du Preez.


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