FLOOD MODELLING STUDY FOR THE CITY OF SKOPJE APRIL, 2016 Проектен контекст 09 This study has been prepared in the frame- work of the IКT Urban Resistance project, which is implemented with financial and technical support by the Development Program of United Nations TABLE OF CONTENT 08 PROJECT BACKGROUND 48 DIRECT ECONOMIC IMPACT ASSESSMENT Introduction Study objective Methodology 54 ECONOMIC VALUATION OF POTENTIAL FLOOD RISK MITIGATION MEASURES 10 EXECITIVE SUMMARY Flood risk management in the City of Skopje – Introduction Historic flood hazard in the City of Skopje Existing flood risk management in the City of Skopje 56 COST-BENEFIT ANALYSIS Flood risk management objectives and principles Benefit analysis Flood hazard and flood risk modelling Cost assessment Flood mapping and flood risk assessment Economic valuation Valuation of flood risk management options Case 1: Flood occurrence in City of Skopje urban zone Identified non-structural measures for flood risk Case 2: Flood occurrence with different return periods/risks in City management of Skopje rural zone Identified structural measures for flood risk management Case 3: Flood occurrence with different return periods/risks along the Lepenec River Case 4: Flood occurrence from torrents in Skopje 30 PROJECT AREA Case 5: Flood protection in Upper Vardar/Rashche Topographic and geographic features Demographic characteristics Hydrological data 64 CONCLUSIONS AND RECOMMENDATIONS Summary of the historical floods in Skopje Vardar’s riverbed through Skopje Upper Vardar/Rashche Vodno torrents 40 HYDROLOGICAL AND HYDRAULIC MODELING Hydrological modeling Rainfall-Runoff model Hydraulic modeling of potential flood events Hec-Ras Software Flash floods in Urban Areas List of figures: Figure 1.Project area: Rashche, Skopje urban with Vodno torrents and Figure 35.Damage factor ........................................................................................52 rural part ...................................................................................................................32 Figure 36.Flood extent and depth-Vodno torrents Q100y ...................................52 Figure 2.Flood in Skopje, River Vardar, 1916.......................................................... 35 Figure 37.Damage factor ........................................................................................52 Figure 3.Flood in Skopje, 1962 ................................................................................36 Figure 38.Flood damage in the urban part of Skopje ...........................................53 Figure 4.Simplified hydrographs for the floods in 1962 and 1979 ..........................37 Figure 39.Probability of occurrence curves and potential peak flood waves ......58 Figure 5.River Vardar in the central part of Skopje ...............................................38 Figure 40.Skopje city – potential peak flood waves Q250 and Q500 (partial over- Figure 6. River Vardar in the city park ....................................................................38 lap) .............................................................................................................................58 Figure 7. Typical cross-section of the Vardar riverbed regulated outside the city Figure 41.Assessed damage area and factors-Skopje rural part; Q100; Q500......58 center .......................................................................................................................39 Figure 42.The flood damages probability distribution (frequency curve) – Skopje Figure 8.Typical cross section of the regulated riverbed of Vardar in the central rural zone.................................................................................................................. 59 urban part ................................................................................................................39 Figure 43.Summary results of cost-benefit analysis – Skopje rural zone ................60 Figure 9.Overview map of Rashche catchments ..................................................40 Figure 44.Assessed damage area -Lepenec river; Q~227m3/s; Q~312m3/s and Figure 10.Overview of Vodno Torrents...................................................................41 Q~400m3/s (left to right) .........................................................................................61 Figure 11.Output HEC-GeoHMS Map for upper Vardar ........................................44 Figure 45.The flood damages probability distribution (frequency curve) – Lep- Figure 12.HEC- HMS basin model for upper Vardar ..............................................44 enec river ..................................................................................................................61 Figure 13.Output HEC-GeoHMS Map for River Lepenec ......................................44 Figure 46.Summary results of cost-benefit analysis – Lepenec river .....................61 Figure 14.HEC- HMS basin model for River Lepenec ............................................44 Figure 47.Assessed damage area and factors-Vodno torrents; Q100 ....................62 Figure 15.Output Hec-GeoHMS for Vodno torrents .............................................44 Figure 48. Flooded area -Rashche area; Q100 ......................................................63 Figure 16.1D modeling of river Vardar, Urban Area ...............................................45 Figure 17.Potential future floods ...........................................................................46 List of tables: Figure 18. Methodology flowchart for flash floods assessment in urban area ...........................................................................................................................47 Table 1.Assessment of the population in Skopje for 2013 ...................................32 Figure 19. Satellite imagery for the urban area ....................................................47 Table 2.Discharges with different probability of occurrence for river Vardar in Figure 20.NDVI image for the urban area, source: Landsat-May 2015 .....................47 Skopje .......................................................................................................................34 Figure 21. Surface flow for urban areas .................................................................48 Table 3. Flooded areas, 1962 ..................................................................................36 Figure 22. Storm water sewers ...............................................................................49 Table 4.Flooded areas, 1979 ...................................................................................37 Figure 23. Storm water sewers with critical points ..............................................49 Table 5.Estimates of damage from the flood in 1979 ..........................................37 Figure 24.Land cover Skopje urban ........................................................................50 Table 6.Damage factors for different land use type .............................................51 Figure 25.Exposure classes/Elements at risk ........................................................50 Table 7.Summary of flooded area for Skopje rural ...............................................60 Figure 26.Land cover Skopje rural part ..................................................................51 Table 8.Summary of flooded area form Vodno Torrents ......................................62 Figure 27.Exposure classes/Elements at risk ........................................................51 Figure 28.Flood extent and depth-Skopje urban part; Q1000 .............................51 Figure 29.Damage factor ........................................................................................51 Figure 30.Flood extent and depth-Skopje urban part; Q500 ...............................52 Figure 31.Damage factor ........................................................................................52 Figure 32.Flood extent and depth-Skopje rural part; Q100y ...............................52 Figure 33.Damage factor ........................................................................................52 Figure 34.Flood extent and depth-Skopje rural part; Q500y ..............................52 List of ANNEXES: ANNEX 1 Project area ANNEX 2 Digital Elevation Model for upper Vardar river basin ANNEX 13 Flood extent and depth-Skopje urban part; Q1000 ANNEX 3 Hydrology model for upper Vardar river basin ANNEX 14 Flood extent and depth-Skopje urban part; Q500 ANNEX 4 Digital Elevation Model for Lepenec river basin ANNEX 15 Flood extent and depth-Skopje rural part; Q544 ANNEX 5 Hydrology model for Lepenec river basin ANNEX 16 Flood extent and depth-Skopje rural part; Q866 ANNEX 6 Hydrology model for Vodno torrents ANNEX 17 Flood extent and depth-Skopje rural part; Q315 ANNEX 7 GUP of city of Skopje ANNEX 18 Flood extent and depth-Vodno torrents Q100y ANNEX 8 Map of Skopje storm water sewers and critical points ANNEX 19 HYDROLOGICAL AND HYDRAULIC MODELING ANNEX 9 CORINE LC for project area ANNEX 10 Land cover for Skopje urban area ANNEX 11 Risk classes for Skopje urban area ANNEX 12 Risk classes for Skopje rural area Project Background Region). The modelling effort, which is expected to generate maps that are compatible with different GIS platforms to be used for development of differ- ent scenarios of eventual future flooding waves, will thus support the flood risk Introduction assessment process through improved preparation of scenarios and plans