What does discharge in m³/s mean?

1 m³/s means that at a measurement cross-section, one cubic metre of water passes every second – that is 1,000 litres per second. In one minute that is 60,000 litres, in one day 86.4 million litres. A river at 100 m³/s therefore carries a hundred times as much.

This conversion makes the order of magnitude visible, but says nothing about a hazard. Width, depth, gradient, bank shape and protective structures all determine the effect of the same volume at a specific place.

A station usually measures water level continuously. Separate discharge measurements at different water levels allow the operator to establish the level–discharge relationship: the rating curve. This converts the ongoing level reading into discharge. The relationship needs checking because floods, sediment or engineering works can change the channel.

The published m³/s value is therefore a technically derived quantity, not a direct count of individual litres. Seepegel takes the values of the named operators unchanged and shows the station, measurement time and source.

Normally discharge grows as tributaries join. In between, however, there can be withdrawals, infiltration, reservoirs, power plants or the buffering effect of a lake. Two stations on the same river therefore need not show the same development at the same moment.

A flood wave takes time to travel downstream. Upstream the value may already be falling while further down it is still rising. For a reliable overview, several stations and the trend over time are more helpful than a ranking of the latest single value.

Compare a station first with its own past: with yesterday, the past weeks or a seasonal reference value. Comparing two different rivers directly only makes sense for the volume carried, not automatically for flood hazard, current or usability.