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Kalman Filtering in Flood Early Warning Systems

Flood Early Warning Systems (FEWS) are used for predicting water levels and discharges at specific locations along a river network. Based on these predictions the authorities involved may decide to implement flood mitigation measures or to evacuate people and livestock. Hence it is important that accurate predictions for as long as possible a time-horizon are made. In the past several Flood Early Warning Systems (FEWS) were developed by Delft Hydraulics. Examples are the Nile FEWS in Sudan and the Indus FEWS in Pakistan.

The computational backbone of a FEWS usually comprises an ensemble of mathematical models, viz. a rainfall-runoff model (if applicable including snowmelt), reservoir routing models and a hydrodynamic (i.c. SOBEK) river flow routing model. In order to make flood forecasts it is essential that the computed hydraulic/hydrologic conditions meet the actual hydraulic/hydrologic observations. In order to achieve this a FEWS is regularly updated using available measurements. In the hydrodynamic (SOBEK) part of FEWS, Delft Hydraulics applies Kalman Filtering (KF), a data assimilation technique in which the optimal actual hydraulic condition of the hydrodynamic (SOBEK) model is established by statistically weighing computed and observed water levels and discharges.

Figure 1: The Flood Forecasting Model of the Orlice (tributary of river Elbe) FEWS in the North-eastern part of the Czech Republic.

Figure 2: The Orlice FEWS in the North-eastern part of the Czech Republic

Figure 3: The Kalman Filtering algorithm as applied to the Orlice (tributary of river Elbe) is seen to lead to adequate predictions

Linking PCRaster and ArcView

Delft Hydraulics assigned Carthago Consultancy to create a link between the software packages PCRaster and ArcView. The link will be part of the DELFT-FEWS system. This GIS-based system will hold several hydrological and flood forecasting models. The GIS combines the strength of the two geographical information systems: ArcView and PCRaster.

Time sequence of appearance heather (time steps 1, 5 and 10). Calculations are made using PCRaster. Presentation of the results is done in ArcView.

ArcView is a widely used desktop GIS with an easy to use interface. PCRaster on the other hand has powerful options for modelling complex processes including time sequences. The link gives the possibility to read and write ArcViewGrid files in PCRaster. The hydrological models for the DELFT-FEWS system will be written as PCRaster scripts and can now be run directly from ArcView. The results can be viewed in ArcView. The models to be included in DELFT-FEWS will be among others Sacramento (SAMO), HBV, XINANJIANG and LISFLOOD. Other models already written for PCRaster can also be used.

Delft-WISE: component based software development

Delft Hydraulics' software can be integrated in customer information systems. Delft-WISE was initiated, to attain full integrity of software products into an integrated software 'suite' for water systems. A component based development approach was adopted for improved interaction between software components including data exchange.

A team of IT-specialists has designed a component-architecture which builds on the latest developments on standardisation in the water and geographic information sector (e.g. OpenGIS, Adventus, AQUEST-Standard Framework Water, Open Modelling Systems). The architecture is open to other software developers and software products. It is foreseen that various software products of Delft Hydraulics will migrate to this component-architecture, sharing a common set of software components.

During the design, major attention has been paid to defining an appropriate level of abstraction for component identification and for the development of stable interfaces. Based on an analysis of the customer activities, their working procedures, and resulting data flows (see figure), a common set of components has been identified, e.g. a broker and publisher to enable controlled interaction, a data server and IO-library for data handling (management, storage and retrieval), simulators and various tools for workflow support, data processing and analysis, as well as for data editing and presentation. In addition to (de-facto) industrial data standards (e.g. OpenGIS), a common set of data structures has been specified based on the knowledge domain of the specific water system simulation (0D, 1D, 2D and 3D). Whenever possible, data semantics will be based on the Adventus data dictionary.

A generic DSS for flood management and landscape planning

The integrated approach to river and flood plain management is well established in the Netherlands. Due to a high population density and considerable economic activity, policy makers realise the importance of a multi-criteria evaluation of impacts and an integral weighing of interests. As interests are often conflicting, alternative strategies for river and flood plain management are being developed providing policy makers with realistic options to choose from. The assessment of impacts requires a rigorous and quantitative analysis of different processes in the river and flood plains. To promote an integrated and multi-disciplinary approach to the design and evaluation of plans for river and flood plain management, a generic decision support system (DSS) was developed. Flexibility has been the main focus in its development: the DSS should support policy analysis as well as provide a structure for the design of measures. The DSS has been developed within the framework of the LWI-research programme by a consortium of water management authorities including Rijkswaterstaat, research institutes and consulting companies. The development of the DSS was co-ordinated by Delft Hydraulics.

To cover the diversity of user needs, the DSS includes three different modes. The initiative mode of the DSS offers the user two means to give focus and direction to the planning of river and flood plain management: a Documentary Information System and an Expert System. The policy mode supports the evaluation of alternative strategies for river and flood plain management on a wide range of impacts including safety against flooding, environmental quality, navigation and costs. The ecological model LEDESS-1D and the hydrodynamic model SOBEK play a key-role in impact assessment. The design mode supports the design and elaboration of detailed plans for flood plain management. These plans are designed using an application of ArcView. Two dimensional models for water flow and ecology are used for the evaluation of the designs. LEDESS-2D determines the impacts on terrestrial and aquatic ecology, whereas WAQUA is used to evaluate impacts on currents and water levels.