Comparison of saturated areas mapping methods in the Jizera Mountains, Czech Republic

Understanding and modelling the processes of flood runoff generation is still a challenge in catchment hydrology. In particular, there are issues about how best to represent the effects of the antecedent state of saturation of a catchment on runoff formation and flood hydrographs. This paper reports on the experience of mapping saturated areas using measured water table by piezometers and more qualitative assessments of the state of the moisture at soil surface or immediately under it to provide information that can usefully condition model predictions. Vegetation patterns can also provide useful indicators of runoff source areas, but integrated over much longer periods of time. In this way, it might be more likely that models will get the right predictions for the right reasons

Flood frequency estimation by continuous simulation for a catchment treated as ungauged (with uncertainty).

A general methodology for flood frequency estimation based on continuous simulation is here applied to a gauged site in the Czech Republic treated as if it was ungauged. In this implementation, stochastic temperature and precipitation models are used to drive TOPMODEL to simulate stream discharges. The coupled model parameters are varied randomly across specified ranges using Monte Carlo simulation. The results from a sample of 48,600 simulations each of length 100 years using an hourly time step are conditioned on low return period regionalized flood frequency, snow water equivalent, and flow duration curve information. Performance measures for each predicted variable are combined using fuzzy inference and simulations considered as nonbehavioral are rejected. 10,000-year simulations are made with the remaining 2281 behavioral simulations to produce prediction limits for flood magnitudes and other response variables at different return periods. The results are checked against a historical series of annual maximum discharges available at the site for a period before it was destroyed by the construction of a dam. The results compare well and appear to give more realistic prediction bounds than statistical extrapolations based on the Wakeby distribution, particularly at longer return periods

Analysis of the time series of waste water quality at the inflow of the wastewater treatment plant and transfer functions

Time series of the daily total precipitation, daily wastewater discharges and daily concentrations and pollution loads of BOD5, COD, SS, N-NH4, Ntot and Ptot were analyzed at the inflow to the wastewater treatment plant (WWTP) for a larger city in 2004-2009 (WWTP is loaded by pollution from 435,000 equivalent inhabitants). The time series of the outflow from a WWTP was also available for 2007. The time series of daily total precipitation, daily wastewater discharges, concentrations and pollution loads at the inflow and outflow from the WWTP were standardized year by year to exclude a long-term trend, and periodic components with a period of 7 days and 365 days (and potentially also 186.5 days) were excluded from the standardized series. However, these two operations eliminated only a small part of the variance; there was a substantial reduction in the variance only for ammonium nitrogen and total nitrogen at the inflow and outflow from a WWTP. The relationship between the inflow into a WWTP and the outflow from a WWTP for the concentrations and pollution loads was described by simple transfer functions (SISO models) and more complicated transfer functions (MISO models). A simple transfer function (SISO model) was employed to describe the relationship between the daily total precipitation and the wastewater discharge

Flood frequency estimation by continuous simulation of subcatchment rainfalls and discharges with the aim of improving dam safety assessment in a large basin in the Czech Republic.

This paper applies a continuous simulation approach to the estimation of flood frequency for a dam site in a large catchment (1186 km2) in the Czech Republic. The models used allow for the simulation of both high intensity and low intensity rainfall events, and snowmelt events, over subcatchments in contributing to the flood frequency distribution. The methodology is implemented within a Generalised Likelihood Uncertainty Estimation framework that allows for uncertainty in the model parameters and for the realisation effect in reproducing the apparent statistics of potential flood events represented by the short series of observations. A fuzzy rules method is used to evaluate each model run, based on the available observations of peak discharges, flow duration curves and snow water equivalents. This yields a combined likelihood measure that is used to weight the flood predictions for each behavioural parameter set. The cumulative distribution for flood peaks for any chosen probability of exceedence over all behavioural models can then be estimated. This can be used to assess the risk of a potential flood peak (or duration or volume) within a risk based dam safety assessment

Flood frequency prediction for data limited catchments in the Czech Republic using a stochastic rainfall model and TOPMODEL.

A continuing problem in hydrology is the estimation of peak discharges for design purposes on catchments with only limited available data. A promising and elegant approach to this problem is the derived flood frequency curve pioneered by Eagleson (1972, WaterResour. Res., 8(4): 878–898). A number of studies using this approach have been published over the last 20 years but only a few have compared the predicted curves with observations. One exception used a simple stochastic rainfall model to drive a version of TOPMODEL (Beven, 1987, Earth Surf Processes Lardforms, 12: 69–82). The present study describes a new version of the stochastic rainfall simulator previously used with TOPMODEL and its application on three small catchments (1.87, 4.75 and 25.81 km2) in the Jizera Mountains in the Czech Republic. The rainfall model differentiates between high and low intensity events. The resulting rainfall statistics were checked by comparisons with measured data. The flood frequency curves predicted by the combined model were constrained by the regional estimates or a measured series for short return periods and used to predict longer return period flood magnitudes. Only one TOPMODEL parameter has to be adjusted—an effective average transmissivity. For the two smaller catchments also a rainfall parameter has to be adjusted depending on the size of the catchment. It is shown that the random sequence of rainstorms can have a significant effect on the predicted 100 year return period event, even for 1000 year simulations and without allowing for uncertainty in the rainfall model parameters

Testing the distributed water table predictions of TOPMODEL (allowing for uncertainty in model calibration): the death of TOPMODEL?

The distributed predictions of the original version of TOPMODEL are here compared with distributed observations of water table levels in the Uhlirska catchment in the Jizera Mountains, Czech Republic. The calibration of the model has been carried out within the GLUE framework, which allows the estimation of uncertainties in predicting the distributed patterns of the water table at different times. Many of the water table levels are predicted within the limits of uncertainty, but it is shown that the predictions could be improved by the calculation of a local effective transmissivity value (or local upslope contributing areas) at each observation site. These effective transmissivities show a similar relationship to the topographic index as found in a previous study of a small catchment in Norway. Some of the anomalies can be explained by deficiencies in the topographic analysis but this may also be an indication of possible structural deficiencies in the model. Interpretation is, however, difficult, and it remains to be seen whether these anomalies might be avoided in more dynamic distributed models

Comparison of saturated areas mapping methods in the Jizera Mountains, Czech Republic

Understanding and modelling the processes of flood runoff generation is still a challenge in catchment hydrology. In particular, there are issues about how best to represent the effects of the antecedent state of saturation of a catchment on runoff formation and flood hydrographs. This paper reports on the experience of mapping saturated areas using measured water table by piezometers and more qualitative assessments of the state of the moisture at soil surface or immediately under it to provide information that can usefully condition model predictions. Vegetation patterns can also provide useful indicators of runoff source areas, but integrated over much longer periods of time. In this way, it might be more likely that models will get the right predictions for the right reasons

A limits of acceptability approach to model evaluation and uncertainty estimation in flood frequency estimation by continuous simulation : Skalka catchment, Czech Republic.

In this study continuous simulation flood frequency predictions on the Skalka catchment in the Czech Republic (672 km2, range of altitudes from 460 to 1041 m above sea level), are compared against summary information of rainfall characteristics, the flow duration curve, and the frequency characteristics of flood discharges and snow water equivalent using the generalized likelihood uncertainty estimation limits of acceptability approach outlined by Beven (2006). Limits of acceptability have been defined, prior to running the Monte Carlo model realizations for subcatchment rainfalls, discharges (using rating data) at 5 sites within the catchment, and snow water equivalent in 13 snow zones, 4 of which have observed data. Flood frequency and flow duration data at the outlet of the whole catchment are not used in the evaluation but are used to test the predictions. In order to get sufficient behavioral models to assess adequately the prediction uncertainty it was necessary to refine the model structure, sample the model space more densely, and, in the end, relax the limits of acceptability to allow for a strong realization effect in predicted flood frequencies. We use a procedure of scoring deviations relative to the limits of acceptability to identify the minimum extension of the limits across all criteria to obtain a sample of 4192 parameter sets that were accepted as potentially useful in prediction. Results show that individual model realizations, with the same parameter values, of similar length to the observations can vary significantly in acceptability. Long-term simulations of 10,000 years for retained models were used to obtain uncertain estimates of the 1000 year peak and associated flood hydrographs required for the assessment of dam safety at the catchment outlet