The runoff regime is the mean seasonal runoff of a body of water , influenced by factors such as climate or relief . Waters can thus be assigned to certain discharge regimes (the best-known classification comes from Pardé ).
Drainage regimes are divided into simple and complex regimes.
Simple regimes only have one maximum runoff during the year, caused by rain or meltwater. There are relatively high fluctuations in discharge between high and low water.
The simple regime can be divided into several categories by the way the drain is fed:
- Glaciar regime: The glacial regime is created when a catchment area is covered by snow or glaciers all year round (at least 15–20%). The high water generated by the melting of the glaciers falls in the warm season and low water in the cold season (e.g. Rhone ).
- Oceanic rain regime: The highest runoff occurs in the winter months, the lowest in late summer or autumn (after the growing season ). The runoff curve is determined by the relationship between the precipitation and evaporation path (e.g. Seine near Paris ).
- Tropical rain regime: The tropical rain regime is determined by the change between rainy seasons and dry seasons . The maximum discharge is usually reached a few months after the highest point of the sun.
- Nivales regime: The nivale regime caused by the melting snow. It can be further divided into
- Complex regimes of the first degree
In the case of complex discharge regimes, the discharge curve has two to three peaks. Depending on whether precipitation in the form of rain or snowmelt predominates in the formation of the maximum discharge, a distinction is made between snow-rain regimes or rain-snow regimes.
Flow fluctuations are smaller in the complex regimes than in the simple regimes. This is because, in complex regimes, the different types of feed produce two or even three floods per year.
Pardé named the following complex first-degree regimes:
- nival regime snow transition type (e.g. Drac near Sautet)
- Snow-rain type (e.g. Emme near Emmenmatt)
- Rain-snow regime with a flood
- Rain regime with two floods (equatorial latitudes)
- Regimes with more than two maxima (e.g. in northern Japan )
- Complex regimes of the second degree
A complex regime of the second degree is the case with rivers that are fed by rain alone and flow through different climatic zones , or with rivers that flow through different regime areas on their course and are thus fed differently. The Rhine is an example of this. Its hydrograph first assigns it to the nival regime of the mountainous region, at Mainz it then shows itself as a nivo-pluvial (snow-rain-fed) and at Cologne finally as a pluvio-nivaler (rain-snow-fed) complex type.
- Manfred Hendl, Herbert Liedtke (ed.): Textbook of general physical geography. 3rd, revised and expanded edition. Perthes, Gotha 1997, ISBN 3-623-00839-7 (on the subject: pp. 470–475)