3Rd European Conference on Flood Risk Management

FLOODrisk 2016

3rd European Conference on Flood Risk Management

Innovation, Implementation, Integration

18 – 20 October 2016 - Lyon, France

Ref.author:

Georg Johann– Emschergenossenschaft

Kronprinzenstr. 24, 45128 Essen, Germany

Co-authors:

Alexander Hartung– Emschergenossenschaft

Kronprinzenstr. 24, 45128 Essen, Germany

Keywords:

flood forecasting, river gauging stations, precipitationmeasurement,hydrological and hydraulicmodelling

Title:

How to manage flood forecastingin a catchment with high flood risk - experiences from the Emscher

Abstract:

The Emscher,with an average discharge of 15 m³/s, isone of the smallest tributary of the river Rhine.Nevertheless it is one of the most remarkable. The Emscher area is a basin of 865 km² , which includes nearly 2.3 million inhabitants. According to the average of 2.700 inhabitants per km² nearly 60 % of the basin’s surface is sealed. 100 years of coal mining shaped the basin significantly. Up to now, most of the Emscher and it’s tributaries are an open sewer system.

Due to that open channel system, theEmscherriver shows a very quick reaction on precipitation. One can often observe a rapid rising of the waterlevel that achieves ratios about 10 cm in 5 minutes or 1,5m per hour.What does that mean for our flood forecasting?

We have to record our data of the river gauges in an adequate time interval, that is usually 1 min. We have to importthis recorded data from the gauges in our timeseriesdatabase every 5 minutes, including an elementary automatic control of the raw data. The flood forecasting models perform continuous calculations every half an hour. In several other time intervals we’re getting our precipitation data, the radar data and the available numerical weather forecast from the German Weather Service. All this serves as input data for multiple model runs. The hydrological models have an optimized grid size and include an adequate number of calculation elements so that the runtime of the model fits the given time interval of 30 minutes.

All in all we’re offering an hydrological forecasting service for the operational branch of our organization so that they can handle the occurring problems. The hydrologic forecast, describing the expected scenario, serves our management branch as a decision support tool.

If we’re expecting a serious weather condition there is an hydrologist on duty, who cares about the incoming data and the modelling results. It’s his task to interpret the hydrological situation and to select the most likely scenario. If necessary we’re performing this duty in a shift work system, so that we can offer a 24 hours service as long as needed.

Here the approach for the flood forecasting management for the Emscher with very rapid flood waves and an extremely high flood risk will be discussed.