# Drainage donation

The discharge rate is the quotient of the discharge and the catchment area of a flowing water . The runoff donation enables a comparison of the general conditions of different catchment areas. Influencing factors include geological composition, vegetation and rainfall. It can come from the catchment area above or below ground.

The drainage donation is calculated according to: ${\ displaystyle q}$

${\ displaystyle q = {\ frac {Q} {A_ {E}}}}$

With

${\ displaystyle Q}$ = Outflow, in liters per second
${\ displaystyle {A_ {E}}}$ = Catchment area

The unit of measurement is l / (s · km²) (liters per second and square kilometer); in most specialist books it is written in the form l / s · km² or l / s km² .

If the catchment area of ​​the water body is affected by inflows or outflows, it is necessary to use the corresponding effective catchment area instead of the natural catchment area for the calculation of . ${\ displaystyle q}$

The mean discharge rate (Mq) indicates the average amount of discharge rate over many years. It makes statements about the amount of precipitation in the catchment area and about seepage. With the help of an assumed Mq for the estuary area - this will usually be below the Mq value for the last level - the mean discharge values ​​MNQ, MQ and MHQ from the last level of a river can be extrapolated to the estuary.

## Typical Mq values

Water type Typical
Mq values
in l / (s · km²)
Examples of waters Mq of the examples
in l / (s · km²)
Lowland rivers of moderate climates with catchment areas in the rain shadow of low mountain ranges << 5 Salza (rain shadow from the Harz and Thuringian basin rim)
Selz (rain shadow from the North Palatinate mountains and Hunsrück)
001.8
002, 0
Lowland rivers of temperate climates ≈ 5 Unstrut 005, 0
More water-rich lowland rivers of moderate climates ≈ 10 Lippe (tributaries from the windward side of the Egge and from the northern slope of the Rothaargebirge) 009.2
Central mountain rivers of moderate climates with catchment area on the lee side Ahr (leeward side of the Eifel) 009.6
Low mountain rivers of moderate climates on the windward side with a lot of precipitation ≈ 20 Sieg (windward side of the slope of the Rothaargebirge) 019th, 0
Rivers of high mountain ranges in moderate climates on the windward side > 30 Murg (windward of the Black Forest) 035, 0
High mountain rivers in temperate climates Aare (Alps) 033, 0
Large rivers in the wettest parts of the tropics >> 50 Río Caura (Venezuela) 062, 0
Karst rivers with a small, but significantly larger, underground catchment area Pader (61 km² above ground)
Krumme Steyr (21 km² above ground)
073 148, 0
, 0
Rivers with glacier-shaped catchment areas Vernagtbach (Ötztal Alps, 21 km²; proportion of glaciers in the catchment area: 72%) 103, 0

## Individual evidence

1. Drainage and drainage donation, Saxon Ministry of the Environment - PDF, 1.21 MB ( Memento from November 11, 2014 in the Internet Archive )
2. Gustavo Silva León: La cuenca del río Orinoco: visión hidrográfica y balance hídrico (Revista Geográfica Venezolana, Vol. 46 (1) 2005, pp. 75-108; PDF; 1.4 MB)