Journal of Applied Hydrology

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1 Journal of Applied Hydrology (2) (1) (2015) Journal of Applied Hydrology The use of flood risk map for flood management (Case study: urban area of Nekarood) Abolfazl Mohammadi 1, Abdollah Pirnia 2* 1 M. Sc. Graduate Student in Natural Disaster Management, Sazehpardazi Iran Co. Tehran, Iran. 2 Ph.D. Candidate of Watershed Management, Sari Agriculture Sciences and Natural Resources University, Sari, Iran. Article history: Received: 18 Aug Revised: 26 Sep Accepted: 17Oct Abstract * of Corr. author: pirniaabdollah@yahoo.com Flood is considered as a major threat among natural disasters in the world. This case becomes more important and has a higher risk in urban areas due to the existence of important uses. Therefore, to reduce damages resulted from flood, this phenomenon must be managed and planned using structural and non-structural approaches. Considering the development in Iran has been carried out in high risk areas for flood and great damages entering various uses of the riverbank; so, determination of flood zones and risk assessment seem to be necessary. In fact, the most important step for management and planning in this field is to obtain flood map of the region which is the required condition to provide flood risk maps. Preparation of flood risk maps and the limits of flood design criteria help us to have more confident computations. Generally, determination of high flood risk areas can prevent development of these areas or if development is needed, some management strategies can be considered for construction in these areas. In the resent study, hydraulic simulation of Nekarood flow is accomplished using HEC-RAS, and GIS software and HEC-GEORAS extension. Then, flood zone map of the region is achieved. The equation of flood risk (200 years) is applied for residential, commercial, industrial, public and agricultural uses which causes to prepare flood risk map of the region. Ultimately, the achieved information can be used for flood crisis management. Keywords: Flood Management, Flood Risk Map, Flood Zonation, Nekarood. 1. Introduction Flood occurrence in urban, industrial and commercial areas is much important; since, it will cause great damages if is not controlled. Flood management can be accomplished by various approaches. Generally, flood management includes the processes in flood control which moderate the flood development and its consequent damages. The damages can be analyzed and flood control strategies and reduction of cost and damages can be investigated by study and modeling of high risk regions for flood. Since urban planning is along with constructions and elimination of vegetation covers, in fact, performance of the system components are at opposite point of natural flood flow and consequently, the threat of flood still exists. Neka River watershed is a typical instance of this issue. The watershed is located at the extreme east of Mazandaran Province. Topography of the studied area (Nekarood) is so that, a high potential for flood occurrence and consequently great damages are expected. Neka city is the most important section of the watershed and the position of this city is so that, the flood volume (main and sub-watersheds of this river) becomes heavy

2 22 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) ` while passing this area as this occurrence was observed in the devastating flood of Neka, So, some strategies must be considered to manage crisis resulted from flood occurrence and its damages at various states so optimal engineering options can be proposed for flood control as well as to manage flood caused crisis. Flood management is an important subject which is considered throughout the world. Many studies have been carried out in this field as following: Liang and Mohanty (1997) conducted a flood zonation in Mahan day Eurasia region of India and introduced the food management based on this type of zonation as a useful nonstructural method for flood control. Tate (1998) conducted a study in Water Resources Research Center, University of Texas to combine software models Arc View and HEC- RAS as well as to investigate riverbed privacy of Creek River in Austin, US. He concludes that, this method has many capabilities for hydraulic investigation of flood control structures along the river. Islam and Kimitero (2000) provided flood risk map for the historic flood of Bangladesh in 1998 using remote sensing data and Geographic Information System. Klijn and et all. (2004) proposed an equation for estimation of flood risk as following: R=P.C (1) Where R is flood risk, P is probability of flood occurrence and C is the damage caused by flood. Hill (2001) explained the capabilities of the model HEC-Geo RAS for flood risk zonation as well as the advantages of linking the models Arc View and HEC-GeoRAS. Terry (2002) carried out a study aimed to use GIS tools in hydraulic modeling. They mentioned that, one of the most important advantages of HEC-GeoRAS is to increase precision and cost savings of river engineering particularly in large watersheds and applying the best management strategy in the region. Andam (2003) conducted a study entitled comparison of forest and non-forest river regimes using HEC-RAS software and HEC- GeoRAS extension. He investigated the velocity and Froude number variations in these rivers and compared the effect of vegetation cover on regime and physical behavior of the flow. He concluded that, the use of HEC-RAS model can provide appropriate numerical values to study the regime and other hydraulic traits of the river flow, for the researchers. Todini (2000) and Zenger (2002) conducted some researches on decision making management when crisis occurrence while flooding. Ertug and Kuvel (2001) proposed the use of GIS in flood management when flood occurrence. Smemoe et al. (2000) computed EDA using combination of HEC1 in hydrologic computations as well as HEC-RAS in hydraulic computations. Douglas (1986) and Bikenestoch (2000) made a collection of required information to manage floodplain. Sharma and Dubey (2004) investigated the methods of reducing flood risks caused by dam break, using Mike11 computer mode. In the present study, flood management of urban area is considered the necessity of doing this study seems rational when the watershed has a high flood potential. Determination of the watersheds flood potential needs comprehensive and accurate studies. Francou-Rudier Equation is one of the most common empirical equations applied to describe watersheds flood: log Q 6 k ( 1 ) 10 log A 8 )2( Where: A: watershed area (km 2 ) Q: The maximum instantaneous flood discharge (m 3 /s) K: Regional coefficient of flood of which value varies between 0-6 throughout the world and the value of this coefficient for the hugest floods of the world is 6.5.In the equation above, the food discharge with a 200-year

3 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) return period is 1654 m 3 /s. according to the table above, the flood risk coefficient obtained from Francou-Rudier method is close to the variation range of K coefficient. Therefore, Nekarood watershed can be classified as a high risk watershed for flood. Table1: flood potential in Nekarood Basin K Log A Log Q Q The maximum observed instantaneous flood discharge during index (m 3 /s) A area (km 2 ) 4/08 3/31 3/ / Materials and methods The watershed of Nekarood River is located at extreme east of Mazandaran Province in northern latitude of 36⁰ 28 to 36⁰ 48 and eastern longitude of 53⁰ 15 to 54⁰ 44. The main valley of Neka River is eastern-western despite most of rivers in the region, and 80% of the watershed of this river is covered by forest and pasture. The river is originated from upper Shahkooh highlands located in the south west of Golestan Province. After passing 160 km, the river enters a plain where 15 branches are added to it. The general flow direction of the river is from the east to the west. The flow direction changes close to the city of Neka and a location namely Ablou. The river throws into Caspian Sea after passing Nozarabad village. Generally, flood in Nekarood River flows affected by precipitation occurrence. (Yekom Consulting Engineers Company, 2014) 2.1. Physiographic and geographic properties of Nekarood watershed The area of Nekarood watershed is about 2004 km2. The highest point of the watershed has an elevation by 3500 m and the elevation of the lowest part of the watershed (coastal area of the watershed) is about -10 m. the length of the watershed is 130 m, mean width is about 14.8 km, and longitudinal slope of Nekarood River is 1.9%.City of Neka is the most important part of the river which is located at confluence of the foothills and coastal zone of the Caspian. The river sinuosity is high from the beginning, and the bed slope is 1% averagely. By getting close to the city of Neka, the amount of sinuosity increases and ultimately it is reformed to meandering channel. Neka city has been developed around the meanders of Nekarood River. City of Neka has been located at a mountainous region; so, the flood of main and sub-watersheds of this river passes through this place. Fig.1, shows the location of Neka city Flow discharge The flood discharge was determined for various return periods by conducted investigations on recorded data of Ablou station, a 36-year statistical period since cropping season of to and prolongation and completion of the statistics of the maximum instantaneous flow discharge as below: (Table 2). Table 2: flood discharge for various return periods in Nekarood River T (year) return period P=(1/T) probability of flood occurrence Q (m 3 /s) discharge

4 24 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) ` 2.3. Accomplishment of simulation model of the flow hydraulic The steady flow method was used to do computations of hydraulic simulation of the flow in the area of Neka city; so that, considering the prepared topography maps of the region which have a scale by 1/2000, firstly, the appropriate layers of the maps with numerical value of elevation were transferred to GIS environment, and the topography model was produced as Triangular Irregular Network (TIN). Then, the layers of flow central line, the river bank, and the range of river cross sections were drawn using the extension HEC- GEORAS. Totally, 91 cross sections were extracted from the river topography model. By extracting these cross sections and producing the layer of flow central line, the initial and extractable geometric data were produced from the topography model of the river, and the data were prepared to enter HEC-RAS model. In continue, the required information were considered including cross sections, Manning roughness coefficient, boundary conditions and structural characteristics of the river. Geometric cross sections of Nekarood River Fig. 1: Urban situation of Neka in Nekarood Basin also have been performed using GIS, HEC- RAS software and HEC-GEORAS extension. The figure shows the general shape of the river path and some instance of these cross sections from upstream and downstream of the river. The 10.8 m path of the river has been identified by 91 cross sections. The distance between the cross sections varies from 22 m to 190 m (according to the river position). After model performance, the flood zone map with 200-year return period can be observed as below. According to Fig.2, 3, 4 it can be mentioned that, determination of high flood risk areas can prevent development of these areas or if development is needed, some management strategies can be considered for construction in these areas. About the important uses, the height of constructions must be considered higher than the food depth. Also, the strategies of flood control and management must be considered to prevent damages in high flood risk regions. Therefore, this process is effective to select the location of the future development and engineering measures for constructions as well as reduction of the future floods damages.

5 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) Fig. 2: Flood zonation model (200 year) in Nekarood River using HEC-RAS Legend 5 EG WS 200 Crit 200 Ground Lev ee Bank Sta 50 Elevation (m) Station (m) Fig. 3: Cross section of Nekarood in urban area (using HEC-RAS)

6 26 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) ` Fig. 4: Flood zonation of Nekarood River in urban area (return period 200 years) 2.4. Flood risk map of the region Generally in engineering sciences, if there is any uncertainty about the design, there will be a risk caused by the lack of accountability of the design against inhibiting and destructive factors. The most perfect and best equation for risk is as below (Samuels, P. and Gouldby, B. 2005). Risk = (Hazard vulnerability). In other words, the risk is commensurate with the risk and vulnerability. Source For example: Precipitation, Wind and Sea wave Food is a natural disaster of which risk assessment is a complicated and difficult subject. It is due to the uncertainties existing in various stages of flood risk. At overall state, a simple conceptual model is used for flood risk which has been shown in the figure below. This model is known as SPRC and states a complete and simple definition of risk (Samuels, P. and Gouldby, B. 2005). Pathway For example: Pathway, Dam break and Inundation Receptor For example: People, and Property Consequences For example: Casualties and Financial losses, and Social stress Fig. 5: SPRC model for risk assessment

7 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) According to this conceptual model, the following parameters are needed for risk assessment: P (Probability of Hazard), - E (Exposure of Receptors), S (Susceptibility of Receptors),V (Value of Receptors). Therefore, the risk can be defined as below: Risk = Function (V, E, S, V) In this equation, vulnerability is an auxiliary function which is defined as below: Vulnerability = Function (S, V) Considering that, vulnerability and Exposure to the risk are generally in the phrase risk consequence so: Risk = Function (Probability, Consequence) Each of the mentioned four parameters has some dimensions and passives which increase the freedom degree of the equation above. Now, how can it be used to estimate flood risk? As it was mentioned, risk phenomenon includes the three following parts: 1- Hazard 2- Exposure 3- Vulnerability (In the present study, the risk is the depth of water logging). Exposure to flood and vulnerability depend on the considered use situation). At the simplest state, risk is the product of the three parameters. If the parameters of exposure and vulnerability are combined and then shown by C as consequences of an event with occurrence probability of P, Then, the risk can be shown as the following equation (Samuels and Gouldby,2005). R= C.P If the depth is considered as the risk criterion, so, if the water depth is higher, the amount of risk will be higher too. If susceptibility and vulnerability criteria are introduced for various uses, the risk map of the region is achieved in GIS by multiplying these criteria. The trend above, has been conducted for a 200-year flood of Nekarood which has caused to provide risk map of the region. The map has been given in the figure below. According to the map, the red colored points are considered as high risk points. According to Fig. 6, the high risk points can be diagnosed by the colors sequence. Fig. 6: Risk map of Nekarood urban area

8 28 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) ` 2.5. Flood management strategies There various strategies for flood management which include modification and adaption of one or more approaches depending on the situation and conditions. There are five main strategies in floodplain management and several tools for each of them as below [Tajrishi, M ], [Mahdavi, M ], [Ministry of Energy, Office of Technical Standards and Criteria ]: 1- Reduction of vulnerability against flood 1-1- Setting Rules and Regulations 1-2- Policy making for development and redevelopment 1-3- Readiness for crisis 1-4- Flood forecasting, warning and emergency plans 1-5- Retrofitting against flood and increasing the level of structures 2- Flood reduction 2-1- Flood dams, embankments and walls 2-2- Reservoirs and dams 2-3- Path improvement 2-4- Flood deviation 2-5- Urban network of rainwater harvesting 2-6- Retrofitting the coasts 2-7- Measures for soil improvement 3- Reducing the destructive effects 3-1- Education and awareness 3-2- Flood insurance 3-3- Tax adjustment 3-4- Flood relief 3-5- Financial assistance after disasters 4- Preservation and improvement of natural resources and culture of the floodplains 4-1- Policy making for development and redevelopment 4-2- Regulations 4-3- Education and awareness 4-4- Tax adjustment 4-5- Administrative measures 5- Training on floodplains management 5-1- Publishing books, journals and newspapers 5-2- Technical meetings 5-3- Training meetings 3. Results and Discussion Flood as a phenomenon which has risk and uncertainty in its nature and considering the parameters affecting in the amount of flood caused damages, can be managed much more appropriate and leaves less damages using risk management which has opened a new horizon in modern management. The used techniques and methods in risk management at financial scale needs less investment but, it needs high cost at the scale of individual and social commitments; so that, the plan reaches utilization stage in terms of occurrence probability of various risks with acceptance of a certain risk and based on its occurrence, provided that, all the utilizes consider themselves responsible to the considered occupational and moral commitments (INDI,2001). The results of this study show that, the uses of Nekarood riverside can be exposed to a 200- year flood. According to Fig.4, the obtained flood zonation map can be considered in development projects to reduce the amount of vulnerability of the residents and use damage. Also, flood risk map of the region can be helpful in panning to select safer sections for development in terms of flood. Also, EAP program can be developed when flood occurrence based on the map given in Fig.6. This subject is much important in estimating the expected annual damage (EAD) since, at the first step, preparation of flood zonation map is required and then, this value is obtained by consideration of the riverside uses and the effect of their economic value. 4. Conclusion Considering the situation of the river and its topography in the area of Neka city, and the importance of various uses in urban area of Neka city as well as the bitter past events, studies and designing the Flood Warning System in upstream of Neka city can be considered as a proper option for flood management (non-structural flood

9 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) management) to ensure about flood damage reduction. In the present study, flood risk maps were prepared separately for different land uses (arable lands, gardens and residential areas). By comparison of the maps it is found that, the residential areas have had the highest effect on flood caused damages than the other lands. Although, flood control plans were performed in the region after the devastating floods that occurred in 1999, in fact, it can be mentioned that, this condition is needed but is not enough. By having the water level of the river channel in vulnerable points, the suggestion of protective wall is considerable for flood control. By comparison of the flood zonation and risk maps, it was concluded that, the flood risk maps have more accurate information and more consistency with the nature by which the flood caused damages can be reduced in addition to producing a crisis management plan at emergency conditions of flood. Interaction of the achieved results about the use of flood insurance for various uses can be a great relief in non-structural flood management. In other words, the maps can be used a document for insurers decision making about the amount of insurance of the land uses in high risk zones. References (ATCEC) Abanrood Tadbir Consulting Engineers Company Emergency plan of irrigation and drainage network protection of Neka plain against Neka river floods. (In Persian). Andam, K Comparing Physical Habitat Conditions in Forested and Non-Forested Streams. Thesis of Partial Fulfillment of the Requirements for the Degree of Master of Science Specializing in Civil and Environmental Engineering. University of Vermont.136 P. Birkenstock, T. and Bourget, P Information/Data Needs for Floodplain Management. Building Partnerships: pp doi: /40517(2000)116 Douglas J. L., Hall B Risk Information for Floodplain Management / (ASCE) (1986) 112:4(485), Ertug Gunes A., Kovel J.P., Using GIS in Emergency Management Operations, Journal of Urban Planning and Development, Vol 126 (3). Yekom Consulting Engineers Company Comprehensive engineering studies on the rivers of the East of Mazandaran province. (In Persian). Hekmatifar, H Optimal combination of engineering and management methods of food control (Qarehsou River, Kermanshah, Iran). MSc Thesis, Natural Disaster Management, Faculty of Environment, Tehran University. (In Persian). Hill, M Flood Plain Delineation Using the HEC-GeoRAS Extention for Arc view, Brigham Young University, 514 p. ISCEC Report of the flood hydraulic of Dalaki river improvement project. Iran Sazehpardazi Consulting Engineers Company.102 pp. INCID Committee of comprehensive approaches for flood management, nonstructural flood management methods. Iranian National Committee on Irrigation and Drainage, and National Committee for Natural Disaster Management. Islam, M. D, and Kimitero Sado, Development of Flood Hazard Maps of Bangladesh Using NOAA-AVHRR Images with GIS. Hydrological Sciences Journal, 45(3) pp. Klijn F., van Buren M., van Rooij S Flood Risk Management Strategies for an Uncertain Future: Living Rhine River Floods

10 30 A. Mohammadi and A. Pirnia / Journal of Applied Hydrology 2 (1) (2015) ` in the Nederlands. Journal of the Human Environment 33(3): pp. Liang, S, and C.R.C. Mohanty, Optimization of GIS Based Flood Hazard Zoning A Case Study at the Mohanady Command Area in Cuttack District, Orrisa,India Journal of Chinese Soil and Water Conservation 28 (1) pp Ministry of Energy, Office of Technical Standards and Criteria Publication No (A), the draft of standard guidelines for flood damage assessment. Samuels, P. and Gouldby, B Language of Risk: Integrated Flood Risk Analysis and Management Methodologies, HR Wallingford, Report No. T Sharma D.C., Dubey O.P., Chalisgaonker R Computer Simulated Flood Disaster Mitigation Planning, Irrigation Research Institute, Roorkee, India Shidawara M Flood Hazard Map Distribution Urban Water Journal, 1, pp. Smemoe C., Nelson J., Zundel A Risk Analysis Using Spatial Data in Flood Reduction Studies, World Water Congress, ASCE. Tajrishi, M Flood management in urban areas. Hydrologic-Economic assessment. A project of the Ministry of Housing and Urban Development. Tate E.C, Olivera. F, Maidment. D Floodplain Mapping Using HEC-RAS and ArcView GIS. Center For Research In Water Resources (CRWR), Report No pp. Terry Barr Application of Tools for Hydraulic Power Point Presentation. Gotvand Hydroelectric Power Project Feasibility Study. Todini E An Operational Decision Support System for Flood Risk Mapping, Forecasting and Management. Urban Water Journal, 1, pp. Zerger A., Ingel Smith D Impediment to Using GIS for Real-Time Disaster Decision Suppor. Computers, Environment and Urban Systems, 27, pp.