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Austrian hydropower: Extreme precipitation and flooding in week 32 (updated)

Eylert Ellefsen
Archived blog post. This blog post has been transferred from our previous blogging platform. Links and images may not work as intended.

During Sunday, 2 August and Tuesday 4 August there was an extreme precipitation incident across Austria, and partly Switzerland and Italy too.

Both the hydro reservoir areas in Tirol/Voralpberg and the river areas flowing to Donau were hit hard. The flowrate in Donau, around Vienna, increased from about 1200 m3/s from Sunday up to 6500 m3/s by midday on Wednesday 5 August. The flooding situation is currently retreating, but slower than the rising curve for the first days.

Energy Quantified has studied the hydropower situation during this extreme incident and amongst several factors focused on spilt water and spilt energy.

Precipitation

We have collected some information about precipitation on several key locations in the Austrian hydropower system from Sunday to Tuesday:

Sum precipitation on Sunday, Monday and Tuesday, 2-4 August at key locations for the Austrian hydropower system.

Calculated into energy terms, our model show about 2,2 TWh precipitation for these three days (700% of normal, 1.9 TWh above the normal).

The number of 2.2 TWh must be interpreted as a gross number, as the flooding will lead to a lot of water flow beyond the capacity of the hydropower plant, the so-called spillage of water. Thus we have studied the river plant production curves and our energy inflow data to get an impression of the spillage, and then modified our model data for this specific incident.

Inflow and run-river production

The chart below shows the hourly run-of-river production across Austria from Thursday 28 July until Wednesday 5 August. The output rose by about 2000 MW after the weekend and came close to the maximum capacity of 5700 MW. Probably a lot of plants had to reduce their production due to the high flow rates as we usually see in such flooding incidents.

As earlier mentioned the Donau flowrate at Vienna rose from 1200 until 6500 m3/s (hourly max), and a daily average increase of about 5300/1200 = 440%.

In the chart below, we show the modelled inflow curve (gross), which has increased by a factor 300/125 = 240 %, well below the Donau increase of 440%. Statistically, max inflow (net) has been about 215 GWh/day. Thus we modified our inflow calculation as seen in the chart.

Meaning that for week 32, we estimate about 240 GWh (15%) spilt inflow energy in Austria, and we will not see the run-of-river production increase to above 5000 MW.

Our latest reported reservoir filling number for end week 32 is currently 90.3%, up 18.8% from week 31. This number does not take into account an estimated water spillage of 240 GWh. The modified reservoir level is about 5% lower – at an 85.0 % filling rate. That is still a substantial increase of 13% from week 31.

Final words

The hydropower situation in Austria is now at a very high resource level. Production from the reservoirs will most likely have to be increased in the coming weeks to avoid further flooding and uncontrolled production levels. We assume that the run-of-river situation will normalize in a week or two. So far, we haven't seen any effect on the spot market as the German renewables are the main price drivers. However, the strong Austrian hydropower will contribute to slightly lower domestic spot prices.

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