The Barrage - how Rand Water determines the flows.

**GGY** · 05-01-07

I got this via e-mail from Kookie Langwenya who works for Rand Water.
This came from Carl Kleynhans who is responsible for the Barrage.

If you want to be added to the Barrage Flow mailing list - end her an email on:
Klangwen@randwater.co.za

The Barrage reservoir is controlled between 7.30m and 7.55m. Rain at Barrage, Vereeniging and Zuikerbosh will influence the river level quickly but usually with a short inflow characteristic. In order to lift the reservoir by 0.01m an inflow of 1,7 cumecs is required.
Rain in the Heidelberg/Springs area will flow to the Barrage via the Zuikerbosh River and takes +/_ 3 days.
Rain at Zwartkopjes (Brackenhurst) will effect levels within 1 day whilst rain south of Johannesburg takes +/_ 2 days.
In theory if 25mm of rain falls in the whole Barrage catchment, the inflow into the barrage would increase by 56 cumecs. but in practice it is found that it takes three or more wet days before the inflow increases to 60 cumecs.

It is best not to make an allowance in advance for rain when operating under normal conditions but rather to control on fact only i.e. once the level rises due to inflow of rain.
Under normal conditions the outlet at the barrage is determined by the outlet from the Vaal Dam. Currently the Vaal dam is releasing 10cumecs and the barrage 25 cumecs (Today 05/01/2007)

If the Barrage level is at 7.3m and there is 25mm rain in the barrage catchment, the Barrage will be overflowing within 24 hrs if adjustments to the gates are not made in advance. We had 66mm of rain in one day during December which multiply this effect, especially because we had other wet days before that day.
We control the Barrage at a lower level, between 7.3m and 7.4m, during the raining season in order to buffer the effect of rain. In that way you can control the outflow and it is not required to suddenly release high amounts of water that can cause damage to the downstream area.

For more information feel free to contact me.
Thanks,
Carl Kleynhans
District Superintendent
Barrage/Saolburg
082 389 2269

GGY's notes - it is always good to check the Vaal DAM outflows - it was at 10 cumecs during the high flows period at the end of December.

**Wade** · 05-01-07

Thanks for that info GGY. I think i will

**Gael** · 05-01-07

Thanks for the post Gary, I found it very informative.

So if I understand it correctly, the high flows over December was due to flows from the Suikerbosrand river and others like storm water as the outflow from the Vaal dam was only 10cms

**MaXiMuM** · 05-01-07

Thanks Gary, great info...

**Andre s** · 04-06-11

Interesting bit of info that Gary posted in Jan 2007

**poppernel** · 04-06-11

Originally Posted by Andre s

Interesting bit of info that Gary posted in Jan 2007

AND PAST APRIL SOME TIME BACK,you guys should be

**Andre s** · 07-06-11

Originally Posted by GGY

The Barrage reservoir is controlled between 7.30m and 7.55m. Rain at Barrage, Vereeniging and Zuikerbosh will influence the river level quickly but usually with a short inflow characteristic. In order to lift the reservoir by 0.01m an inflow of 1,7 cumecs is required.
Rain in the Heidelberg/Springs area will flow to the Barrage via the Zuikerbosh River and takes +/_ 3 days.
Rain at Zwartkopjes (Brackenhurst) will effect levels within 1 day whilst rain south of Johannesburg takes +/_ 2 days.
In theory if 25mm of rain falls in the whole Barrage catchment, the inflow into the barrage would increase by 56 cumecs. but in practice it is found that it takes three or more wet days before the inflow increases to 60 cumecs.

It is best not to make an allowance in advance for rain when operating under normal conditions but rather to control on fact only i.e. once the level rises due to inflow of rain.
Under normal conditions the outlet at the barrage is determined by the outlet from the Vaal Dam. Currently the Vaal dam is releasing 10cumecs and the barrage 25 cumecs (Today 05/01/2007)

If the Barrage level is at 7.3m and there is 25mm rain in the barrage catchment, the Barrage will be overflowing within 24 hrs if adjustments to the gates are not made in advance. We had 66mm of rain in one day during December which multiply this effect, especially because we had other wet days before that day.
We control the Barrage at a lower level, between 7.3m and 7.4m, during the raining season in order to buffer the effect of rain. In that way you can control the outflow and it is not required to suddenly release high amounts of water that can cause damage to the downstream area.

GGY's notes - it is always good to check the Vaal DAM outflows - it was at 10 cumecs during the high flows period at the end of December.
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So i noticed last week after the big release the level of the barrage was down to 6.91, 0.44 less than their minimum level. After dropping the flow to 8 cms for about a week. Yesterday the level was on 7.61, 0.06 higher than their max level. i am not sure what they have increased the barrage to now but Goose bay is currently on 38 cms and there is rain expected for the next 3 days............ i am in the process of buying a new 7 weight, but i might go buy golf clubs instead.