Effects of excess rainfall on the temporal variability of observed peak-discharge power laws

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA; Colorado Research Associates (CoRa)/Northwest Research Associates (NWRA), 3380 Mitchell Lane, Boulder, CO 80301, USA; Department of Civil and Environmental Engineering, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
Advances in Water Resources (Impact Factor: 2.41). 01/2005; DOI: 10.1016/j.advwatres.2005.03.014

ABSTRACT Few studies have been conducted to determine the empirical relationship between peak discharge and spatial scale within a single river basin. Only one study has determined this empirical relationship during single rainfall–runoff events. The study was conducted on the Goodwin Creek Experimental Watershed (GCEW) in Mississippi and shows that during single events peak discharge Q(A) and drainage area A are correlated as Q(A) = αAθ and that α and θ change between events. These observations are the first of their kind and to understand them from a physical standpoint we examined streamflow and rainfall data from 148 events in the basin.A time series of excess rainfall was estimated for each event in GCEW by assuming that a threshold infiltration rate partitions rainfall into infiltration and runoff. We evaluated this threshold iteratively using conservation of mass as a criterion and found that threshold values are consistent physically with independent measurements of near-surface soil moisture. We then estimated the excess rainfall duration for each event and placed events into groups of different durations. For many groups, data show that α is linearly related to excess rainfall depth and that the event-to-event variability in Q(A) is controlled mainly by variability in α through changes in . The exponent θ appears to be independent of for all groups, but mean values of θ tend to increase as the duration increases from group to group. This later result provides the first observational support for past theoretical results, all of which have been obtained under idealized conditions. Moreover, this result provides an avenue for predicting peak discharges at multiple spatial scales in the basin.

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    ABSTRACT: We propose an extended study of recent flood-triggering storms and resulting hydrological responses for catchments in the Pyrenean foothills up to the Aude region. For hydrometeorological sciences, it appears relevant to characterize flash floods and the storm that triggered them over various temporal and spatial scales. There are very few studies of extreme storm-caused floods in the literature covering the Mediterranean and highlighting, for example, the quickness and seasonality of this natural phenomenon. The present analysis is based on statistics that clarify the dependence between the spatial and temporal distributions of rainfall at catchment scale, catchment morphology and runoff response. Given the specific space and time scales of rainfall cell development, we show that the combined use of radar and a rain gauge network appears pertinent. Rainfall depth and intensity are found to be lower for catchments in the Pyrenean foothills than for the nearby Corbières or Montagne Noire regions. We highlight various hydrological behaviours and show that an increase in initial soil saturation tends to foster quicker catchment flood response times, of around 3 to 10 h. The hydrometeorological data set characterized in this paper constitutes a wealth of information to constrain a physics-based distributed model for regionalization purposes in the case of flash floods. Moreover, the use of diagnostic indices for rainfall distribution over catchment drainage networks highlights a unimodal trend in spatial temporal storm distributions for the entire flood dataset. Finally, it appears that floods in mountainous Pyrenean catchments are generally triggered by rainfall near the catchment outlet, where the topography is lower.
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    ABSTRACT: Several studies revealed that peak discharges (Q) observed in a nested drainage network following a runoff-generating rainfall event exhibit power law scaling with respect to drainage area (A) as Q(A) = αAθ. However, multiple aspects of how rainfall-runoff process controls the value of the intercept (α) and the scaling exponent (θ) are not fully understood. We use the rainfall-runoff model CUENCAS and apply it to three different river basins in Iowa to investigate how the interplay among rainfall intensity, duration, hillslope overland flow velocity, channel flow velocity, and the drainage network structure affects these parameters. We show that, for a given catchment: (1) rainfall duration and hillslope overland flow velocity play a dominant role in controlling θ, followed by channel flow velocity and rainfall intensity; (2) α is systematically controlled by the interplay among rainfall intensity, duration, hillslope overland flow velocity, and channel flow velocity, which highlights that it is the combined effect of these factors that controls the exact values of α and θ; and (3) a scale break occurs when runoff generated on hillslopes runs off into the drainage network very rapidly and the scale at which the break happens is determined by the interplay among rainfall duration, hillslope overland flow velocity, and channel flow velocity.
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    ABSTRACT: We have conducted extensive hydrologic simulation experiments in order to investigate how the flood scaling parameters in the power-law relationship Q(A)=αAθQ(A)=αAθ, between peak-discharges resulting from a single rainfall-runoff event Q(A)Q(A) and upstream area AA, change as a function of rainfall, runoff coefficient (CrCr) that we use as a proxy for catchment antecedent moisture state, hillslope overland flow velocity (vhvh), and channel flow velocity (vcvc), all of which are variable in space. We use a physically-based distributed numerical framework that is based on an accurate representation of the drainage network and apply it to the Cedar River basin (A=16,861km2A=16,861km2), which is located in Eastern Iowa, USA. Our work is motivated by seminal empirical studies that show that the flood scaling parameters αα and θθ change from event to event. Uncovering the underlying physical mechanism behind the event-to-event variability of αα and θθ in terms of catchment physical processes and rainfall properties would significantly improve our ability to predict peak-discharge in ungauged basins (PUB). The simulation results demonstrate how both αα and θθ are systematically controlled by the interplay among rainfall duration TT, spatially averaged rainfall intensity E[I]E[I], as well as E[Cr]E[Cr], E[vh]E[vh], and vcvc. Specifically, we found that the value of θθ generally decreases with increasing values of E[I]E[I], E[Cr]E[Cr], and E[vh]E[vh], whereas its value generally increases with increasing TT. Moreover, while αα is primarily controlled by E[I]E[I], it increases with increasing E[Cr]E[Cr] and E[vh]E[vh]. These results highlight the fact that the flood scaling parameters are able to be estimated from the aforementioned catchment rainfall and physical variables, which can be measured either directly or indirectly.
    Advances in Water Resources 01/2014; · 2.41 Impact Factor

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