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The Design and Construction of Neckartal Dam

Author: Edwin Lillie, Gawie Steyn
Conference: AFRICA 2017
Date: March 14-16, 2017

INTRODUCTION
Neckartal Dam is located on the Fish River, a tributary of the Orange River. The project will supply bulk water to a new irrigation scheme located 40km south-west of Keetmanshoop in Namibia. Keetmanshoop has a desert climate. The daytime temperature often rises well above 30°C during the summer and the mean annual precipitation is less than 150mm.


The construction of Neckartal Dam started in September 2014. The Employer is the Namibian Ministry of  Agriculture, Water and Forestry. The Contractor is Salini Impregilo S.p.A and the engineering design and site supervision is being undertaken by Knight Piesold Consulting (Pty) Ltd. Neckartal Dam is the largest dam currently under construction in Southern Africa. Neckartal dam will be 78.5m high, with a crest length of 518m and a gross storage capacity of 857 million m³. The main dam wall contains over 900 000m3 of RCC. The dam outlet releases water through two Francis turbines to an abstraction weir and pumping station located 13km downstream.  Neckartal Dam will be the largest dam in Namibia and the eight largest dam in Southern Africa by storage volume. It is a very important development project for the Namibian government and is aimed at stimulating economic growth in the Southern Region of Namibia. This paper describes some of the challenges faced during the design and construction.


Necartal dam has to accommodate very large floods, both during construction and operation. The PMF is over 20 000 m3/s. The diversion during construction has been undertaken in three phases, which included phasing for the dry season and wet season floods to provide an economic solution. The spillway was modelled tested and an optimum solution developed for the curved spillway.

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