APPLICATION: FLOOD FORECASTING MODEL FOR KLODZKO CATCHMENT (POLAND) - Modelling Uncertainty in Flood Forecasting Systems - page 83

Klodzko catchment is located on the river Nysa Klodzka. The river serves as a highland
tributary of the upper Odra River. The Klodzko catchment is a small mountain basin with
a very short lag time between rainfall and runoff (see Kundzewicz at al., 1999 and
Szamalek, 2000). The river Nysa Klodzka and its tributaries are shown in Figure 5.1.
The area was heavily inundated by the great flood, which took place in the region in
July 1997. The town of Klodzko (31,000 inhabitants) located on the river Nysa Klodzka
was virtually ruined by this flood with several casualties and the destruction of numerous
houses (Kundzewicz at al., 1999). Over 500 families in Klodzko lost virtually everything
they owned. Since then flood forecasting and warning has been one of the important
considerations for the people and authorities in the area.
The Klodzko model is a rainfall-runoff-routing type of model in which rainfall is a
major time series input. The objective of the application is to assess the uncertainty in
forecasted discharges due to the uncertainty in the forecasted precipitation. One
important characteristic of a quick-response basin like the Klodzko is that the future
situation of the flood depends heavily on the precipitation yet to occur. The nature of the
basin provides a justification for its selection for the application of the methodology.
5.1.1 Description of the model
The rainfall-runoff-routing type flood forecasting model was built with HEC-1 (USACE,
1998) and HEC-HMS (USACE, 2000 and 2001) produced by the Hydrologic
Engineering Centre of US Army Corps of Engineers. In particular, HEC-HMS (its
Calibration Module) was used for model calibration and HEC-1 was used for simulation.
HEC-1 is one of the most frequently used rainfall-runoff models in the United States
(Melching et al., 1991). This model is a semi-distributed conceptual model for catchment
modelling. The model simulates the precipitation-runoff and routing processes. A typical
HEC-1/HEC-HMS representation of catchment runoff processes is shown in Figure 5.2.
To represent the different components of the runoff processes, HEC-1 and HEC-HMS
use different models including:
1. Models that compute runoff volume.
2. Models of direct runoff (overland flow and interflow).
3. Models of base flow.
4. Models of channel flow (routing model).
The flood forecasting model presented here covers the basin up to the hydrological
station at Bardo (Fig. 5.1) on the Nysa Klodzka. The basin is subdivided into 9
subbasins. The subbasin areas range from 64 km 2 to 280 km 2 with a total area of 1744
km 2 . Some of the parameters of the model are estimated by calibration and some are
estimated from available data and engineering judgement. The calibration is performed
using the calibration module of HEC-HMS. In particular, the SCS Curve Number, time
of concentration, storage coefficient and Muskingum K are calibrated.