## Exceedance probability of selected low characteristic flows in mountain catchments

### Słowa kluczowe: characteristic flows, flow duration curve, threshold value, SNQ, average annual minimum flow, WNQ, maximum annual minimum flow, NSQ, minimum annual mean flow, SSQ, average annual mean flow, Upper Vistula river

### Streszczenie:

In Polish hydrology and water management the term characteristic flow exists denoting a specific value of flow at the given cross-section of a river calculated as the long-term minimum, mean, median or maximum calculated using the annual minimum, mean, median or maximum flow taken for each year from a series of (usually) daily flows. Some of these characteristic flows are used to define the low-flow (o drought) periods while the another criterion: a percentage flow Qp taken from the long-term flow duration curve is also widely used.

In the paper the study on the frequency structure the empirical exceedance probability of a given characteristic flow made for some low and average characteristic flows (SNQ, WNQ, NSQ and SSQ) is presented. The results show that the exceedance probability of a given characteristic flow is variable, and the amount of this variability may be large, as is the case of WNQ and NSQ. So assigning a characteristic flow to a single FDC quantile value Qp (as can be find in the literature) cannot be justified.

Correlation analysis made for the pairs ( , characteristic flow), ( , catchment area) and ( , gauging station elevation) revealed some significant correlations. Only for SNQ is not correlated at all; correlation for other characteristic flows is statistically significant for at least one of the cases. The highest correlations (greater than 0.4 in absolute values) were found for the pairs ( , gauging station elevation) for NSQ and, for SSQ, ( , SSQ) and ( , catchment area).

### Cytowanie:

Węglarczyk
S.
2014, vol. 11. Exceedance probability of selected low characteristic flows in mountain catchments. Infrastruktura i Ekologia Terenów Wiejskich. Nr 2014, vol. 11/ IV (3 (Dec 2014))