River Basin Management III 455 Flood model of city of beer: Plzen City – Czech Republic M. Svobodová & J. Spatka DHI Hydroinform, Czech Republic Abstract Plzen City, know also as the City of the world famous beer Pilsner Urquel, was heavily flooded during the catastrophic flood in August 2002. This accident was a major driving force to create mathematical models of the rivers of Plzen City. In general, a hydraulic mathematical model of a city is not an exception in the Czech Republic. However, the mathematical model of Plzen City, thanks to an extremely complicated river systems is a very special hydraulic case. The presented model covers the hydrological and hydraulic conditions of five river bodies and four junctions and their mutual interrelations, which were found as significant. The most interesting part of the Plzen model was a special calibration procedure applied on mathematical models and the simulation of a number of different scenario combinations. A global 1D+ mathematical model was created, covering more than 60 km of river network and a wide area of flood plain using MIKE 11 software. The central part of Plzen City was schematized into a 2D curvilinear mathematical model using MIKE 21C SW. The main official outputs of this project were: • flood maps • maps of depths, water levels and velocities • longitudinal and cross-sectional profiles with an indication of water levels • evaluated proposal of the flood protection plan of Plzen City • HTML documentation The case of Plzen City is also special thanks to its location downstream of the reservoir Hracholusky on the Mze River, which creates a hypothetical risk for Plzen City. That is why the simulation of the Hracholusky dam break was carried out. Last but not least, an important feature of this project was a special way of creating the project documentation in HTML format. The documentation allows not only the viewing and reading of all documents and drawings, but also the preparation of user specific composition of final results and the ability to print them directly to a predefined scale, having installed only Internet Explorer. The finished model is nowadays frequently used for flood protection evaluation and the authorization of flood plain activities. Keywords: flood mapping, mathematical modelling, water management, 1D and 2D modes, dam-break, flood protection measures, HTML documentation. WIT Transactions on Ecology and the Environment, Vol 83, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) 456 River Basin Management III 1 Introduction In August 2002 a major part of the Czech Republic was affected by a catastrophic flood. Amongst the most heavily affected urban areas also was the town of Plzen and its surroundings and other suburban parts. The city of Plzen has over 200,000 inhabitants and its world-famous name is based on the brewery production of the world finest brand of beer “Pilsner Urquel.” Just after the catastrophic flood, i.e. during the period of 2003 and 2004, the flood model of the city of Plzen was designed. This model was drawn by DHI Hydroinform acting as a supplier and the customers Vltava River Basin Authority and the municipality of Plzen. Flood models of cities are applied to many locations in the Czech Republic, and DHI Hydroinform produced the vast majority of them. Most flood models of cities in the Czech Republic are used for description and evaluation of historical or potential flood situations in cities, where only one river usually flows through (for example cities like Pardubice, Decin and Usti nad Labem on the Labe river, Turnov or Mlada Boleslav on the Jizera river, Ostrava city on the Odra river and so on) or eventually in cities placed on junction of two rivers (for example the capital of Prague on the Vltava and the Berounka rivers or Ceske Budejovice on the Vltava and the Malse rivers). The flood model of Plzen city is rather special among the others due to very a complicated and atypical situation. Six rivers, which consecutive confluence each other with only one river named Berounka as an outlet from Plzen territory, run in the area of Plzen city. With this respect it is to say that flood model of Plzen city is, among other city flood models, the most complicated mathematical model in the Czech Republic. 2 Area of interest The study area of interest is determined by the river network of six rivers, which are to be found in the area of Plzen agglomeration. Namely we will speak about these rivers the Mze, the Radbuza, the Uhlava, the Uslava, the Berounka and the Vejprnicky creak. • In the frame of this project the below indicated river branches were taken into account: • The Mze river from Hracholusky reservoir to its junction with the Berounka river – 21,9 km • The Radbuza river from Ceske Udoli reservoir to its junction with the Berounka river – 6,9 km • The Uhlava river from profile Stenovice to junction with the Radbuza river – 14,2 km • The Uslava river from profile in Koterov village to junction with the Berounka river – 10,2 km • The Berounka from confluence of the Mze and the Radbuza rivers to weir in Bukovec – 9,7 km • The Vejprnicky creak from profile in Slovanske valley to junction with the Mze river – 2,9 km WIT Transactions on Ecology and the Environment, Vol 83, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) River Basin Management III 457 Figure 1: Map of the interest area with indicated rivers being solved. 3 Project aims Main topics of this study cover namely following activities and targets: • set-up of one-dimensional mathematical model (1D+) of selected rivers and flood plains and its calibration • set-up of detailed two-dimensional mathematical models (2D) for selected locations of higher interest and their calibration o drinking water treatment plant Homolka o waste water treatment plant o area of Koterov village o area of Roudna village o technical park of transport concern of Plzen city in Jatecni street o area around streets Malostranska – Ricni o historical centre and confluence of the Radbuza and the Mze rives • update or new generation of flood lines for discharges Q1, Q5, Q20, Q50, Q100, • identification of active zones of inundation areas for discharge Q100, • conception design of flood protection measures and evaluation of their effects on flow condition under flood situation (using mathematical models) • definition of flood risk area under specific flood conditions caused by dam-break of Hracholusky reservoir WIT Transactions on Ecology and the Environment, Vol 83, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) 458 River Basin Management III • creation of intuitive HTML project documentation comprising all the information about input data, different project phases results and all final project outputs in the form of final report, photo documentation, resulting flood lines and flood maps etc., with possibilities not only to view, but also to print technical maps in the selected scale, all from the single “operative” CD. Figure 2: Example of output - flood map for Q100 and identification of active zones. 4 Mathematical models Hydrological investigation of the area, where more than one river is placed, is quite specific. Rivers are affected by each other and it is not possible to solve them separately. Therefore each node of two and more rivers has to be solved with respect to complications and non-standard situations, which occur on rivers junction and its close surroundings. Mathematical models in the Plzen area solve six different rivers at once. Four junctions of above mentioned rivers were included into model setup in this project. Such complicated conditions of Plzen area are to be seen, above all, in more complicated process of model calibration, when giving definitions of boundary conditions and during post-processing of model results. Another factor, which plays its important role and which has to be considered, is the flood from August 2002, and consequential anthropogenic activities. Renovation work or prevention activities on flood protection measures and other WIT Transactions on Ecology and the Environment, Vol 83, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) River Basin Management III 459 activities in flooded areas were, as a result, executed just after the flood. It led to the use of different alternatives of mathematical models used for calibration and for scenario simulations. Mathematical models were calibrated under real topographic conditions during flood 8/2002, but to calculate valid flood lines the most actual topographical data were used in the model setup (actual river cross section shapes and actual relief of flood plain as well). To model such a complicated area, selection of proper mathematical tools played a key role. Finally the mathematical modeling package MIKE 11 was used for 1D modeling and MIKE 21C respectively for 2D modeling. Both packages were developed by Danish Hydraulic Institute (DHI) production. The list of different mathematical models developed under this project can be divided between global 1D+ models of area of interest and detailed 2D models, solving in great detail water flow conditions in seven key areas of Plzen agglomeration. Figure 3: Horizontal plan of global 1D mathematical model. 4.1 Global 1D model MIKE 11 Mathematical model MIKE 11 was created to cover the entire area of interest. The global mathematical model was designed with respect to the complicated river network and extent of flood plain in project area. This model provides full dynamic simulations on complex branched and looped computational network. WIT Transactions on Ecology and the Environment, Vol 83, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) 460 River Basin Management III 1D mathematical model was primarily used for definition of flood zones and calculation of water level distribution across the area of interest where no detailed 2D mathematical models were available.