Threshold effects in catchment storm response and the occurrence and magnitude of flood events: implications for flood frequency

Abstract

Abstract. The aim of this paper is to illustrate the effects of selected catchment storage thresholds upon runoff behaviour, and specifically their impact upon flood frequency. The analysis is carried out with the use of a stochastic rainfall model, incorporating rainfall variability at intra-event, interevent and seasonal timescales, as well as infrequent summer tropical cyclones, coupled with deterministic rainfall-runoff models that incorporate runoff generation by both saturation excess and subsurface stormflow mechanisms. Changing runoff generation mechanisms (i.e. from subsurface flow to surface runoff) associated with a given threshold (i.e. saturation storage capacity) is shown to be manifested in the flood frequency curve as a break in slope. It is observed that the inclusion of infrequent summer storm events increases the temporal frequency occurrence and magnitude of surface runoff events, in this way contributing to steeper flood frequency curves, and an additional break in the slope of the flood frequency curve. The results of this study highlight the importance of thresholds on flood frequency, and provide insights into the complex interactions between rainfall variability and threshold nonlinearities in the rainfall-runoff process, which are shown to have a significant impact on the resulting flood frequency curves.

Rain event properties at the source of the Blue Nile River

“…Such applications include studies of runoff generation (e.g. Milly and Eagelson, 1987;Kusumastuti et al, 2007;Rientjes, 2005, 2010;Zhang et al, 2005;de Vos and Rientjes, 2008), soil erosion (e.g. Angel et al, 2005), interception losses (e.g.…”

“…For a synthetic watershed, Kusumastuti et al (2007) showed that variability within a rain event which is referred to as intra-event variability can largely affect quick runoff processes and consequently flood generation. Menabde and Sivapalan (2001) showed that runoff discharge is proportional to the watershed area for relatively small watersheds with a response time less than the mean duration of rain events.…”

Rain event properties and dimensionless rain event hyetographs at the source of the Blue Nile River

“…Such applications include studies of runoff generation (e.g. Kusumastuti et al, 2007;Milly and Eagelson, 1987), soil erosion (e.g. Angel et al, 2005), interception losses (e.g.…”

“…Wooliser and Osborn, 1985 Properties of single rain events often vary at scales much smaller than a watershed scale and event properties consequently affect runoff generation. For a synthetic watershed, Kusumastuti et al (2007) showed that variability within a rain event which is referred to as intra-event variability can largely affect quick runoff generation mechanisms and consequently affects flood generation. Robinson and Sivapalan (1997); Menabde and Sivapalan (2001) showed that the runoff discharge is proportional to the watershed area for relatively small watersheds with a response time less than the mean duration of rain events.…”

Influence of infiltration and soil storage capacity on the skewness of the annual maximum flood peaks in a theoretically derived distribution

“…McGrath et al, 2007). Kusumastuti et al (2007) focused on catchment storage and derived the flood frequency distributions by Monte Carlo simulations, using a non-linear conceptual rainfall-runoff model. Struthers and Sivapalan (2007) illustrate the impact of heterogeneity associated with threshold nonlinearities in the storage-discharge relationship associated with the rainfall-runoff process upon flood frequency behaviour.…”