Exceedance probability of selected low characteristic flows in mountain catchments

key words: 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

Summary:

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).

Citation:

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))