MIKE FLOOD Hydrological and Hydraulic Investigation in Slovenia Matija Bogdan Marinček Consulting, designing, agency and research Matija Bogdan Marinček s.p., Teharska cesta 13, SI-3000 Celje, Slovenia , emails: matija.marincek@siol.net Keywords spatial planning, flood risk management plan, river Reka, Karst, regional natural park, World Heritage Škocjanske Caves, NATURA 2000, hydrology, flood evaluation, MIKE FLOOD Abstract EU Directive(2007/60/EC) “ Flood management and evaluation” established and actualized a part of EU Water Framework Directive (2000/60/EC) and charged local Communities, the subjects of spatial planning in our country with relative heavy duties. The obligatory groundwork of spatial plane is also the drawing up of flood risk management plan. Relative sensitive aspect of this groundwork requires relative sophisticated hydrology and hydraulic approach. MIKE of DHI software is very useful tools, such as MIKE FLOOD program package. According to the financial possibilities of communities, the approach of preparing of plans is often particular, not even for the whole community, but the influence of such intervention on space is much larger. Similar case is described above. The community Ilirska Bistrica is preparing the spatial plan for a new tradesman’s area, which lies on the right embankment of the river Reka. Several problems had to be taken in account. At first, how to prepare reliable boundary conditions, not at last topography also, because of lack of data. At second, how to protect tradesman’s area, which is often flooded, but not to deteriorate other settlements areas and infrastructure. Not at last, how to take in account limitations of ecological protection regulations. The actual tradesman’s area lies directly to Regional Škocjanski Park, which protected the World Heritage Škocjanske Caves. The area on the left embankment of the river Reka and downstream wetland is covered by the Natura 2000. MIKE FLOOD was successful used for flood risk study and flood risk management plan. INTRODUCTION In Slovenia Country the Local Communities are the primary holders for spatial planning, except the state important interventions on space. EU Directive (2007/60/EC) “ Flood management and evaluation” established and actualized a part of EU Water Framework Directive (2000/60/EC), which implements flood water investigations and flood water protection planes as obligatory groundwork of the spatial planes. Our natural regulation accept the directive at whole. So two problems are: how to resolve the implementation the directive orders in the actual planes an second, how to make this procedures for future planning faster. The time of realisation of investments is very important for investors, of course.

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The first problem, because of poor budget of local communities, leads to make the spatial plans for particular, the most actual investment purposes, but not for the whole community areas. This trend is opposite the behaviour of flood phenomena. Influenced flood planes areas are often very much larger than actual investment areas. This approach is extensive and at last also more expensive. To speed the procedures of making the spatial planes and consequently the flood risk management plan is better to make them for the whole community area at once. But it need communities to collect more money at once. The most suitable approach will be the preparation of the flood risk planes for the whole possible flooded areas in the river catchments at once. This need collaboration of several communities at the same time. But in our country there are not established political or economy associations, which could support this approach. How looks likes the circumstances, mentioned in the first problem before, will be describe in the followed case. The subject is preparation of the flood risk management plan for a new tradesman’s area in the Community Ilirska Bistrica in Slovenia. The Community Ilirska Bistrica spreads in the area of 480 km2 . It lies on the south part of the Republic of Slovenia (see figure P039-1) at the border with Republic of Croatia.

figure PO39-1: Location of Ilirska Bistrica Comunity AREA OF THE SPATIAL PLANING The spatial plan zone for a new tradesman’s area lies on the south part of the town Ilirska Bistrica, the administrative center of the community (see figure

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P039-2). The zone is relatively often flooded. The last flood was happened in February 2009.

figure PO39-2: Location of actual spatial plane zone Several rivers occupy and have influence on the spatial plane area: the main river Reka, important tributary Molja, specific tributary Pila with its tributary Kozlek. At the east side of the spatial plane zone the main road goes. At the west side the spatial plan zone is bordered by railways. The left embankments of the Reka River opposite the spatial planning area and the confluence region downstream of the rivers Reka, Molja, Pila and Bistrica are protected by NATURA 2000 declared by Council Directive 79/409/EEC on the Conservation of Wild Birds - "The Bird Directive"). Beside this the whole track of the Reka River is protected as natural heritage. Several kilometres downstream its stream runs through World Heritage Škocjanske Caves. THE REKA RIVER AND ITS CATCHMENTS CHARACTERISTICS THE REKA RIVER STREAM The river Reka is not an ordinary river. The source of the river Reka is on the Gorski Kotar Mountains, the first barrier for the often weather fronts from the

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west and south. After about 8 km the upper stream passes to the middle stream. The bed slope becomes less steep, and the valley spreads(see figure P039-3).

figure PO39-3: The valley upstream Ilirska Bistrica After 22 km its stream passes the town Ilirska Bistrica and confluents with important tributary Molja River. The valley here is flat, the riverbeds of river Reka and tributaries make twist through many meanders. The river embankments are much overgrown by trees and bushes (see figure P039-4).

figure PO39-4: The valley downstream the spatial plane zone in Ilirska Bistrica, embankments of the river are overgrown, the land is often wetted This area is protected by NATURS 2000, as mentioned before. It is the bird reservation. Nearly 54 km downstream the river source the river Reka sinks in the Škocjanske Caves (see figure P039-5). After 33 km underground stream through the Karst it appears at Štivan near Trieste in Italy as Timav River. Than pours out into Adriatic Sea. The river Reka is not an ordinary river.

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figure PO39-5: The Škocjanske Caves, The Reka River underground stream; (source Wikipedija) THE REKA RIVER CATCHMENTS The catchment area of the Reka River has two different parts (see figure P039-6):

a) The part where orographic border define the catchment area of surface runoff of precipitation and the high water waves depend on surface characteristics,

and

b) The part of Karst area. There real border of the catchment couldn't be defined, it could only be estimated. It could be much larger than orographic catchment or could be very small, when water flows through underground ways to neighbouring catchments. The high wave peeks are normally lower (influence of underground reservoirs) and elongated.

The river Reka at the upper section and left tributaries collect water from orographic catchment area, that means from the part a). Fortunately at the middle stream of the river Molja two dams, Klivnik and Mola were constructed in past. The regulating regime of the dams offers collection of whole runoff of 1% probability and more frequent precipitation in the artificial reservoirs. So not more than half of the tributary Molja catchment runoff reaches the river Reka.

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For our study, the influenced catchment area from the part a) is 75 km2.

figure PO39-6: Two different parts of the River Reka catchment; tributeries, dams on the river Molja, important water gauging stations for the study The right tributaries come from the Karst region that means from the part b) of catchment area. Their behaviour is much different. The orographic area of this part is about 56 km2. TIME SERIES FOR BOUNDARY CONDITIONS PREPARATION Mathematical model MIKE FLOOD as dynamical model for upper boundary conditions needs data defined in time. In our case we used MIKE 11 for importing the boundary conditions in the computational area. Normal is, that hourly data are available. If not, preparing the data is more difficult. As you can see on the figure Po39-6 the location of the water gauging stations Trpčane and Trnovo could be appropriate. But the station Trpčane has no device for hourly data measuring, only daily peaks of runoff are read from the measured batten. So, the time distribution, that means the shapes of high water waves are unknown. The only way is to use some method for transformation of precipitation in the surface runoff and calculate the runoff hydrographs. But this way is not proper for the Karst region. In the surroundings of our model area there are several stations for measuring precipitation, but most of them annotate just cumulative 24 hours precipitation. Only one of stations has device for hourly data annotation. Using the correlation method is necessary. Another problem we found is, that the measuring periods

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of the stations differ. This had to be taken in account when probability analyses of the data were computed. As is mentioned before, the precipitation/runoff methods are not of need for the Karst regions. There the actual measurement runoff of the rivers we need. The river Bistrica collect precipitations from the Karst region and water gauging station is located upstream confluence with river Reka. The shape of its hydrograps, are used for river Pila and other right tributaries from the Karst region. TOPODRAPHIC DATA The bed of the rivers, we need for the row data of MIKE 11, was measured in situ. The computational area consists river beds of about 3000 m, describes with 47 row data. For MIKE 21 the digital model land data with square cells 10x10 was used for bathymetry definition. BUILD UP THE MODEL MIKE FLOOD MIKE 11 and MIKE 21 were built up and tested separately. Than MIKE 11 and MIKE21 Flow model were linked with lateral links for each side separately. Because of non uniform beds and embankments levels the time step had to be very short. Several bridges also controlled the river discharge. The computational area is seen on the figure PO39-7.

figure PO39-7: The computational area of the model MIKE FLOOD

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CALIBRATION AND VERIFICATION OF THE MODEL MIKE FLOOD The model was calibrated running the last flood accident, with the peak of high wave happened on 3 February 2009. After the event the highest flood levels were marked at some locations on the flooded area from the river authority. For the Reka River composed hydrograph was used, summarised by followed hydrographs:

i. The constructed hydrograph using the data of peak measured at water gauging station Trepčane, but with the shape of hourly measured hydrograph at downstream water gauging station Trnovo

ii. Unit hydrographs of the left tributaries. The shape of hydrograph was

compared with the shape of hydrograph at water gauging station Trnovo.

iii. Hydrographs with the shape of measured hydrograph at water gauging station Iilirska Bistrica on the river Bistrica, reduced by ratio of orographically defined area of the catchments of the right tributaries from the Karst region.

For river Pila (and its tributary Kozlek) upper boundary condition is constructed at the same way as for right tributaries. Used boundary conditions, when calibrating the model are shown on the figure PO39_8.

figure PO39-8: The upstream boundary conditions used in the calibration procedure of the model

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The computed outflow hydrograph of the model was than compared with the measured hydrograph at water gauging station Trnovo down streams and with in situ marked the highest flood levels. Beside this we had to estimate the probability of the event on 2 February 2009. It was found that probability of this event is about 10 to 4 %. On the same way we estimated and formed high water waves of 1% and consequently for 0.2% probability. RUNNING THE MODEL FOR 1%, 10% AND 0.2% RIVER DISCHARGE For preparing the carts for the flood risk management plan as the groundwork of spatial plane we had to investigate the situations when 1%, 10% and 0.2% river discharge could happen. First we simulated on the model taking in account temporary space situation. The result shows (see figure PO39-9) that the area of spatial planning is threatened by 1% probability. Our state regulation demand that such areas have to be protected from 1% probability floods.

figure PO39-9: The flooded area caused by 1% probability river discharge

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So we had to find solutions for mitigate the flood water treat. Because of ecological restrictions, the solutions like river arrangements were not feasible. Only local protection principles are suitable. One possibility was to up level the whole spatial plane area and other to protect the area by dykes. The first approach is more secure, if harder flood happen than 1% probability and if ground is not enough bearing. The second arrangement needs less material, but is more hazard. THE FLOOD RISK MAPS The flood risk management plan as obligatory groundwork have to contain the flood risk maps. For preparing the maps, these results of the hydraulic investigation are necessary:

• flood water extensions of 1%, 10% and 0.2% river discharge • flood water depths of 1% discharge (see figure PO39-9) • flood water speed of 1% discharge • products of flood water depths and flood water speed of 1% discharge

The flood risk map for the case, that actual spatial planning area is protected from the 1% flood probability, is shown in the figure PO39-10.

figure PO39-10: The flood risk map

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CONCLUSIONS The goal of European Water Frame Directive is Environment protection. Specially important is to take in account their obligations, when preparing the Spatial planes. The Flood Risk Management Plan is obligatory Groundwork. In the regions where different interest and intentions could make conflict situations, comprehensive tools like MIKE FLOOD program package are only convenient for investigation of flood risks. More economic is to prepare the Flood Risk Management Planes for the whole possible flooded areas in the river catchment at once. But, often this is not the case, unfortunately. The described case in this paper shows, that particular approach causes not less problems than entirely treat of the river catchment. REFERENCES Marko Kolbezen, Površinski vodotoki in vodna bilanca Slovenije (Surface Streams and Water balance of Slovenia), Ministrstvo za okolje in prostor, Hidrometeorološki zavod Republike Slovenije, (1998). Vodna bilanca Slovenije 1971-2000 (Water Balance of Slovenia 1971-2000), Ministrstvo za okolje in prostor, Agencija Republike Slovenije za okolje, (2008). Povratne dobe za ekstremne padavine po Gumbelovi metodi (Return Periods for Extreme Precipitation, Gumbel Method), Ministrstvo za okolje in prostor, Agencija Republike Slovenije za okolje, (2008). Hidrološki letopisi Slovenije (The Hydrological Annals of Slovenia) MIKE BY DHI, MIKE ZERO, Documentations (2009) Matija Bogdan Marinček, Hidrološko hidravlična študija s predlogi ukrepov za obrtno cono O1-2 v Ilirski Bistrici, Consulting, Designing, Agency and Research, Matija Bogdan Marinček s.p., Teharska cesta 13, EU3000 Celje (2009).