Rain and storm for Cpt

[Gordon_R]

Millennials everywhere. A few drops of rain and "storm".

https://www.news24.com/SouthAfrica/...-falls-on-his-car-on-m3-in-cape-town-20190730

An elderly motorist was injured when a tree fell onto the M3 in Cape Town and hit his car on Tuesday morning, as gale force winds and inclement weather continued to hold the city in its grip.

The man, believed to be about 80 years old, suffered injuries to his head, City of Cape Town traffic services spokesperson Maxine Bezuidenhout confirmed.

The tree, which fell across the M3 southbound after Woolsack Drive, landed on top of the man's Toyota Corolla.

Both lanes were blocked and traffic was diverted, while the City's parks department cut up the tree.

Definitely not a storm /sarcasm

 

[satanboy]

A mere breeze.

 

[Gordon_R]

Anyone know what "DT Limit exceeded" means on the DWA site?
http://www.dwa.gov.za/hydrology/Unverified/UnverifiedDataFlowInfo.aspx

I never looked at the outflow from the Berg River Dam before! If you look at the actual graph, it is clear the parameter limit (datum height) is broken, 14m above the top of the dam wall seems unlikely! http://www.dwa.gov.za/hydrology/Unverified/DetailStageFlow.aspx?Station=G1H077FW&Type=Stage&Rain=N

The graph for Zonquasdrift looks fine, but obviously it is downstream from the dam, so the height cannot be compared to previous flow calibration figures: http://www.dwa.gov.za/hydrology/Unverified/DetailStageFlow.aspx?Station=G1H079FW&Type=Stage&Rain=N

Edit: The level of the Berg River Dam is increasing again, after being above 100% for several days: http://www.dwa.gov.za/hydrology/Unverified/DetailStageFlow.aspx?Station=G1R004FW&Type=Flow&Rain=N

 

[jones123]

I wonder why they didnt increase the berg river dam capacity when they had the chance ?

 

[Arzy]

I wonder why they didnt increase the berg river dam capacity when they had the chance ?

Couldn't agree on the "commissions"

 

[Gordon_R]

I wonder why they didnt increase the berg river dam capacity when they had the chance ?

There was limited scope for increasing the capacity of the Berg River dam, as it is already 68m high. This question was intensively studied in the decades before construction: https://en.wikipedia.org/wiki/Berg_River_Dam

Instead there is a tunnel and pipeline connecting the Berg River Dam to Theewaterskloof, so that excess inflow can be transferred at a rate of 300 Ml/day. This is all part of the system interconnecting the various dams: https://en.wikipedia.org/wiki/Western_Cape_Water_Supply_System

Edit: There are also environmental constraints, as discussed in this recent paper: https://www.news.uct.ac.za/article/-2019-07-30-managing-the-berg-river-dam-overflow

Last week (23 July 2019) the Berg River Dam reached full capacity for the first time in five years. Capetonians were relieved to see the first of its supply dams overflowing and releasing water into the Berg River.

Signs are encouraging that the major dams supplying Cape Town and the surrounding region will be 80% full by 1 November, which signals the start of the hydrological year, compared to 34% in 2017. However, the sight of overflowing dams raises a question often aired in the media, that “overflowing dams are a waste of water”.

Dam managers clearly understand the storage part, but they have to deal with a complex set of requirements, such as groundwater recharge, abstraction of water (legal or otherwise), maintenance of aquatic life and discharges to release the build-up of pollutants, in addition to supplying sufficient water for downstream users. There is also a disjunction between the information required to manage a storage dam, particularly during extreme conditions of droughts and floods, and the condition of the receiving river.

The record of decision that followed the environmental impact assessment stated that the dam must ensure sufficient flow to service the ecological reserve. This concept means that the dam had to be managed so that sufficient water is released to maintain important aquatic life, biodiversity and habitat integrity; support ecological goods and services; and ensure sufficient water for downstream users. All of this is a big ask for reservoir managers whose brief is to operate a storage system, particularly while they have limited feedback about the condition of ecological systems and water requirements in the Berg River, which stretches for over 300 km from the dam.

At the very least, the operating conditions for the Berg River Dam were progressive in the sense that it was required to release low flows and high flows that coincided with natural inflows and natural flood events.

Data on the ecological health of the Berg River is absent – perhaps still being processed by researchers. Instead, a proxy indicator will be used to illustrate the condition of the Berg River downstream from the dam. Studies of the Berg River upstream from the dam show that the stretch between Paarl and Wellington are permanently hypertrophic (very high in nutrients), resulting from failed or poorly functioning municipal sewerage systems and contaminated storm water, but mostly from runoff from informal settlements.

Releasing more water from the Berg River Dam helps to flush out the build up of nutrients in the Berg River, but is by no means an effective way of managing a deteriorating river system. Water-quality data taken near the small town of Hermon – the only sampling site downstream of Paarl and Wellington with some consistent data for the period 2010–2018 – shows how phosphorous, as an indicator of nutrient levels, varied during the wetter and drier period.

It seems that there is a long way to go before new dams are considered for storing excess water without understanding the effect on riverine ecological goods and services. The blame cannot reside entirely with the management of the Berg River Dam, considering the limited feedback that they receive.

 

[jones123]

There was limited scope for increasing the capacity of the Berg River dam, as it is already 68m high. This question was intensively studied in the decades before construction: https://en.wikipedia.org/wiki/Berg_River_Dam

Instead there is a tunnel and pipeline connecting the Berg River Dam to Theewaterskloof, so that excess inflow can be transferred at a rate of 300 Ml/day. This is all part of the system interconnecting the various dams: https://en.wikipedia.org/wiki/Western_Cape_Water_Supply_System

Edit: There are also environmental constraints, as discussed in this recent paper: https://www.news.uct.ac.za/article/-2019-07-30-managing-the-berg-river-dam-overflow

wow thanks for the informative answer

 

[Gordon_R]

wow thanks for the informative answer

I just found that link now, when I searched for an answer to your question!

The Berg River Dam only released the "legal minimum" of water during the period from 2015-2019. That outflow is a tiny fraction of the peak inflow of 180m^3/sec recorded last week, which was above the annual flood stage.

Effectively the Upper Berg River never flooded during that 4 year drought, which would have had an effect on the ecosystem, and was probably never foreseen by the original designers. Fortunately that dam is not the only source of runoff, and other nearby valleys would have provided significant flows further downstream during periods of heavy rain.

 

[Segg]

C'mon guys - looking at the satellite pic this storm doesn't look that bad

 

[Gordon_R]

C'mon guys - looking at the satellite pic this storm doesn't look that bad

The amount of rain has been quite low, but I predicted that long before the storm arrived. The satellite image doesn't show the wind, which was quite strong.

If you look at the synoptic chart, you get a different picture!

 

[MirageF1]

The amount of rain has been quite low, but I predicted that long before the storm arrived.

Err no.

 

[air]

Dammit, fair bit of rain we had in Gardens/Cape Town last night

Dwarsberg/Jonkershoek hit 800mm of rain last night for the month, with more coming through this morning - what an incredible month. YTD, we are nearly at the 2000mm mark, well ahead of any year in the past 6

 

[Icemanbrfc]

Dammit, fair bit of rain we had in Gardens/Cape Town last night

Dwarsberg/Jonkershoek hit 800mm of rain last night for the month, with more coming through this morning - what an incredible month. YTD, we are nearly at the 2000mm mark, well ahead of any year in the past 6

Water price increase lol

 

[Gordon_R]

Quite a welcome increase in dam levels in the last two days, up 2.5% to 74.6%! The Berg River Dam is already 100% full, so most of that increase was Theewaterskloof, which rose 3.1% to 65.2%. See: http://www.capetown.gov.za/Family and home/residential-utility-services/residential-water-and-sanitation-services/this-weeks-dam-levels

 

[Craig_]

At around 11h30 it pissed down properly. I was in a meeting then and it rained so hard that we could barely hear each other.

 

[satanboy]

At around 11h30 it pissed down properly. I was in a meeting then and it rained so hard that we could barely hear each other.

Switch your meetings from tents for bricks and mortar buildings.

 

[Craig_]

Switch your meetings from tents for bricks and mortar buildings.

Tin roof.

 

[satanboy]

Don't mind if I do.

 

[MirageF1]

...we could barely hear each other.

Probably for the best.... puh! meetings
Biggest reason I left corporate employment.

 

[Segg]

It's looking nice and green down there! Even a bit towards PE & EL, I wonder how their situation is doing...