Water Storage and Flow Control

Water storage in a river can serve several purposes:

• Controlling the river flow through controlled water release and thus mitigating droughts or floods;
• Providing a reserve of water that can be used for domestic water supply or irrigation;
• Establishing a certain water level for hydroelectric power generation;
• Providing or improving particular ecological areas;
• Providing a recreational area; and
• Ensuring a minimum water depth for navigation.

In the Kunene River basin, storage is mainly intended to serve the first three of these purposes, whilst at the same time changing ecological areas and providing recreation possibilities.

The purpose of river flow regulation is to mitigate problems associated with the variation of the flow, for example those associated with floods or droughts. Flow regulation provides more uniform flow conditions along the river course. A regulated flow in the Kunene would enable an optimal generation of electricity in the power stations at Matala and Ruacana and for future hydropower stations.

The average long term annual flow of the Kunene River at Ruacana is around 5 km³ (5 000 Mm³). The total annual rainfall varies across the basin from over 1 000 mm in the Upper Kunene to less than 100 mm in the lower reaches of the river with, 90 % of the rain occurring between November and April (see Climate in the Basin). From year to year the rainfall can vary from between 50 % to 200 % of long term averages and there are prolonged periods of drought.

The result is that the flow of the Kunene River varies widely from month to month and from year to year. This has serious consequences for users of the river.

At Ruacana, the weir provides only very limited storage and no flow regulation, low flows have a serious impact on electricity generation at the hydroelectric station there. Electric power generation is thus unpredictably variable from year to year, und indeed during any given year.

In the 1969 Third Water Use Agreement for the Kunene River foresaw the use of the Gove Dam in the Upper Kunene to provide a regulated flow of 80 m³/s at Ruacana. However the completion of the Gove dam coincided with the outbreak of war in Angola and the dam has never served to fully regulate the flow of the Kunene. In 2010 however work was underway to complete the Gove dam and ensure it fulfils its intended function.

The storage and controlled release of water in the Kunene River could provide a more useful contribution to flow regulation in the river and ensure a more uniform flow. With over 80 % of water storage on the Kunene River being behind the Gove dam, it has a key role to play in flow regulation. The other main storage areas along the river can be seen in the table and are described in Dams and Infrastructure.

Storage of Water from the Kunene River

Structure	Storage capacity
Gove dam	2 570 Mm³
Matala weir	60 Mm³
Calueque weir	475 Mm³ (design volume)
Ruacana diversion weir	20 Mm³
Olushandja Dam	42 Mm³
Total storage of Kunene River water	3 167 Mm³