6-8 May, 2008 Toronto, Canada Developing a Flood Warning System: A Case Study Mohammad Karamouz Professor, School of Civil Engineering, University of Tehran, Tehran, Iran Azadeh Ahmadi Ph.D. Candidate, School of Civil engineering, University of Tehran, Tehran, Iran Ali Moridi Ph.D, School of Civil Engineering, Amirkabir University (Tehran Polytechnic), Tehran, Iran Sina Rassaei Kashuk Graduate M.Sc. Student, School of Civil engineering, University of Tehran, Tehran, Iran

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 2  Contents Conclusion 6 Flood Warning Algorithm 5 Study Area 3 Introduction 1 Methodology 2 Simulation Models. 4

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 3  Introduction Flood is a natural disaster which can cause extensive damages and loss of life. But with appropriate and sound decision making and flood management, the level of damage could be highly decreased and the flood could also be controlled and used as a vital source of water supply.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 4  Introduction Four levels for providing Early Flood warning could be defined as follows: First Level: 4 to 6 months before the flood seasons (January through April) based on a Long Term Precipitation and flood forecasting using Climate Signals and Statistical Downscaling of GCM outputs. Second Level: 1 to 2 months before the beginning of flood seasons based on short term models such as an ANN or ARMAX models. Third Level: Before reaching the probable time of flood occurrance (say February) based on Ensembled forecasts and utilizing any new information in December to January. Forth Level: The start of heavy precipitation that could lead to major floods Flood Monitoring and warning Algorithm will be activated

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 5  Introduction The simplest and easiest flood warning systems in the developing countries are conventional systems. These systems are equipped with simple gages at critical points. In its basic form, they report the data to the system analyst that uses the real time hydro-meteorologic data to estimate flood events through predetermined tables and algorithms. The predictions can include the return period of the flood, the peak discharge of the flood and the time for the flood hydrograph reaches the reservoir, considering the time of concentration of each sub-basins.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 6  Introduction Real time flood warning system

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 7  Introduction Three groups of instruments are needed for developing a flood warning system as follows: The measuring instruments: These instruments are set up in the meteorologic and hydrologic stations and they collect the hydro-metrological data, manually or automatically. The hardware instruments: This group of instruments includes computers, data transfer tools, receiver and amplifier centers. The software instruments: Data banks, data processors, the flood prediction models (including rainfall-runoff and flood routing models), visualization models and user interfaces are included in this group.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 8  Methodology In this study, a flood warning system is developed based on available climatic and hydrometric stations in the study area. Thresholds of the observed cumulative precipitation in the upstream climatic stations and observed flood discharge in hydrometric stations provide early warnings to the area downstream of the reservoir. These thresholds in different time steps are determined using the rainfall- runoff simulation model (HEC-HMS software), flood routing model (HEC-RAS software) and time distribution of the precipitation in the study area.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 9  Methodology The values of rainfall and runoff thresholds for flood warning are recommended for the existing and proposed stations. Different warning levels are set up considering the reservoir storage and the water levels downstream of the reservoir obtained from the simulation model.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 10  Study Area Persian Gulf Iran

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 11  Study Area The Kajoo watershed located in the southeastern part of Iran is considered as the study area. The area of this watershed is about 6800 Km2 and its mean precipitation is about 218 millimeters. Kajoo River is the main river of this watershed and is 254 km long. This river runs from the north to the south of the watershed and entering the Gouatr bay in the Oman Sea.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 12  Study Area The Kajoo River basin has steep areas and is subject to frequent flash floods in the winter and during the Monsoon season in the summer. The base time of the flood hydrograph is short and the peak of the flood events is high. This seasonal river has no base flow most of the year. The arid climate of this region makes the inhabitants to move near the river and take the risk of extensive damages and loss of life due to frequent flood occurrences. Because of the limited carrying capacity of the Kajoo River main channel, yearly floods cause damages in the agricultural fields and in the nearby rural areas.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 13  Study Area Kajoo Watershed

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 14  Study Area Zirdan reservoir located in the middle of the Kajoo river watershed will have considerable effects on flood mitigation. The analysis of cross sections show that the river is too narrow downstream of the reservoir where the carrying capacity of the main river is too low. Therefore the downstream floodplain is too wide and flood control options are needed. In the past fifteen years there have been seven considerable floods in this region, which occurred in the years of 1991, 1992, 1995, 1997, 2005, and 2007.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 15  Simulation models Rainfall-Runoff model A rainfall-runoff model has been developed using HEC-HMS software. Sub-basins of the study area have been characterized and modeled in HEC- HMS software using the SCS method. The hydrograph of the January 1, 2005 flood has been used for model calibration.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 16  Rainfall-Runoff model The SCS curve method has been used for runoff estimation and an average curve number (CN) of 85 has been estimated for the watershed. Observed and predicted flood hydrographs for January 2005

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 17  Flood routing in the Zirdan dam The height of the dam is 53 m and the height of the spillway is about 43m. The maximum discharge of the spillway is about 9634 cms. The reservoir storage at the crust elevation is about 433 MCM and at the spillway elevation is about 207 MCM. The hydrological storage routing method is used for flood routing in the reservoir.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 18  Hydraulic simulation model The HEC-RAS model is used for flood flow routing along the river, downstream of the Zirdan dam. From hydraulic simulation of the river, the safe discharge of the river downstream of the Zirdan dam is calculated. The Safe discharge is the maximum discharge downstream the dam which do not cause damages. The safe discharge is obtained based on land use of the floodplain and hydraulic simulation of flood along the river.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 19  Hydraulic simulation model River section at Km-70 of the river near Taradan Village (Based on Survey of 2002) River section at Km-6 of the river near Polan Village (Based on Survey of 2002)

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 20  Hydraulic simulation model Flood Plan of Kajoo River at 9 th and 10 th sections (30.4 to 46 Km from end reach) near Oraki village for floods with 25, 50, 100 and 200 years return period

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 21  Flood Warning Algorithm 1. Determination of proposed stations 2. Determination of the rainfall and runoff thresholds 3. Reservoir management

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 22  Determination of proposed stations The investigation of the location of existing stations in the study area shows that the existing stations are not sufficient for flood warning purposes. The estimation of runoff, playing an important role in the determination of warning thresholds, has been calculated using the developed rainfall-runoff model in the study area. One of the considered criteria to locate new hydrometric stations is the proportion of each sub-basin to the inflow of the Zirdan dam. First hydrometric station should be constructed after joining the 5 sub-basins named Ahooran, Miani 1 and 2, Kenari and Chanef. This station covers about 48% of the runoff of the study area.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 23  Determination of proposed stations Ghasreghand The storm centers in the study area are identified (one is located at Ghasre-Ghand city) through meteorological studies of the region. Since there is a hydrologic station near this storm center, Ghasre-Ghand station located 20 km downstream of the city, it is considered as one of the stations in the flood warning system.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 24  Determination of the rainfall and runoff thresholds In order to determine the critical threshold of cumulative rainfall in meteorologic stations, precipitations with different return periods have been simulated. The precipitation that causes a flood peak more than the carrying capacity of the river, after the reservoir routing in the Zirdan dam, is considered as the critical threshold of rainfall. As most of the sub-basins in the study area do not have meteorologic station, the isohyets analysis has been used for estimation of each sub-basin's rainfall.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 25  Determination of the rainfall and runoff thresholds The safe discharge is considered based on the importance of the project, economic aspects and the acceptable risk level downstream of the reservoir using a hydraulic simulation of the river for different scenarios. In this study, the 25-year return period flood, with a maximum discharge of about 2500 cms has been considered as the safe carrying capacity of the river. the output discharge peak of the reservoir with a 5-years return period is around 2500 cms.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 26  Determination of the rainfall and runoff thresholds According to the rainfall- runoff model, reservoir and river routing models, the critical cumulative rainfall is 43, 42, and 41 mm for Ahooran, Chanef, and Ghasre-Ghand climatic stations, respectively. This values cause the flood with 5year return period. In order to cross check the flood forecasting results, the control points are considered based on hydrometric stations. The critical discharge in Dirak and Ghasre-Ghand hydrometric stations are 540 and 960 CMS, respectively. The time of concentration (t c ) in each sub-basin and the traveling time of the flood flow in the river is used to determined the pre-warning time of the reservoir and the downstream river.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 27  Determination of the rainfall and runoff thresholds The rainfall pattern includes the dimensionless temporal distribution of cumulative rainfall at meteorological stations which is determined based on the schemes of the historical storms in the region. Thus, the pre-warning times of the reservoir are 13, 12, and 6hr for Ahooran, Chanef, and Ghasre-Ghand climatic stations, respectively. These values are based on time of concentration (t c ) of each sub-basin. Time (%) Precipitation (%)

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 28 Flood warning system algorithm.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 29

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 30  Reservoir Management The decreased peak of floods after entering the reservoir is determined using hydrological flood routing model in the reservoir. The reservoir flood control volume is calculated based on the flood hydrograph after routing in the reservoir and the carrying capacity of the downstream river. Therefore, the needed flood control storage, the extra flood volume and the associated elevation of the reservoir is determined..

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 31  Reservoir Management.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 32 Flood warning system algorithm.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 33  Conclusion In this paper, an algorithm for flood warning in the Kajoo watershed has been developed regarding to the water elevation in the Zirdan dam, the amount of rainfall in proposed and existing stations, and flow discharge at hydrologic stations in different time steps. In the first part of this algorithm, the location of the proposed stations including Ahoran, Chanef and Dirak have been presented. In the next part of this algorithm, the critical precipitation and the pre- warning time for the reservoir from these stations is presented. The values of discharge at hydrologic stations are also used to determine the time of flood warning downstream of the reservoir.

Developing a Flood Warning System: A Case Study 6-8 May, 2008 Toronto, Canada 34  Conclusion The flood warning levels will be changed for a different range of precipitation in each station. These warnings include flood warning to the Regional Water Authority and a warning to the dam operation in order to open reservoir gates to an allowable water level, downstream flood warning and to protect the downstream floodplain.

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