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The Neusberg Weir, planned as far back as 1897 by the British Colonial Officers of the
time , was finally completed in 1993. The weir is 995m long with an average height of 5m
and was both designed and constructed by DWAF. The weir is located approximately 12km
upstream of Kakamas and forms a small reservoir in the Orange River with a storage of
almost 2 million m3.
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The weir diverts water into two canals, one on each bank of the Orange River which
supply water to the Kakamas Irrigation Scheme. The Kakamas Irrigation Scheme produces high
value table grapes for both local and international consumption - it is one of the most
valuable and productive irrigation schemes in South Africa. The irrigation scheme was
developed before the Neusberg weir had been commissioned and problems were experienced
creating sufficient flow in the main irrigation canals, particularly the canal on the
South Bank of the Orange River. Neusberg Weir was therefore developed to:
- alleviate supply problems previously experienced with the main irrigation
canals.
- to increase the capacities of the main supply canals from approximately 3
m3/s to 7.5 m3/s and 6.8 m3/s for the north bank and
south bank canals respectively. This in turn allowed the area under irrigation to increase
to the current level of almost 7000 ha.
- to create a flow measuring facility on the Orange River before the river
becomes an international boundary with Namibia.
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Neusberg Weir was constructed using Roller Compacted Concrete (RCC) and is made up of
three notches separated by four director walls. The director walls extend 10m upstream and
are designed to provide more accurate flow measurements. There are two notches for the low
to medium flows located on the left and right banks. The 330m long low notch on the left
bank is 250 mm lower than the 250m long notch on the right bank. The central notch is the
high flow notch and is 1600mm higher than the left bank notch. The notches are designed to
provide flows of reasonable accuracy over a wide flow range. The lowest notch on the left
bank will measure flows up to 140 m3/s before the right notch comes into
effect. The central notch only comes int effect at flows in excess of 1 870 m3/s
and the combined spillway is designed to provide reasonable estimates of high flood flows
up to 11 800 m3/s which represents the 1 in 50 year flood.
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A small fishway was included in the flow director wall at the left low flow notch to
provide access for fish moving upstream. This is the first time that the so-called
vertical slot concept has been used for a fishway in South Africa. It consists of a 2m
wide by 2.5m deep rectangular channel in which pre-cast concrete baffle walls were
provided at 3m intervals. By careful placing of the baffle walls, resting pools were
created for the fish moving upstream against the strong currents.
Full structural and design details of the Neusberg Weir can be obtained from DWAF.
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