6-8 may, 2008 toronto, canada developing a flood warning system: a case study mohammad karamouz...

6-8 May, 2008

Toronto, Canada

Developing a Flood Warning System: A Case Study

Mohammad KaramouzProfessor, School of Civil Engineering, University of Tehran, Tehran, Iran

Azadeh AhmadiPh.D. Candidate, School of Civil engineering, University of Tehran, Tehran, Iran

Ali MoridiPh.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 Study2

6-8 May, 2008

Toronto, Canada

Contents

Conclusion6

Flood Warning Algorithm5

Study Area3

Introduction1

Methodology2

Simulation Models .4


6-8 May, 2008

Toronto, Canada

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.


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Toronto, Canada

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


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Toronto, Canada

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.


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Toronto, Canada

Introduction

Real time flood warning system


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Toronto, Canada

IntroductionThree 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.


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Toronto, Canada

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.


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Toronto, Canada

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.


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Toronto, Canada

Study Area

Persian Gulf

Iran


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Toronto, Canada

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.


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Toronto, Canada

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.


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Toronto, Canada

Study Area

Kajoo Watershed


6-8 May, 2008

Toronto, Canada

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.


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Toronto, Canada

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.


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Toronto, Canada

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


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Toronto, Canada

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.

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120 140t (Min)

Q (

CM

S)

2 2

5 5

10 10

Outflow Inflow


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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.


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Toronto, Canada


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)


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Flood Plan of Kajoo River at 9th and 10th sections (30.4 to 46 Km from end reach) near Oraki village for floods with 25, 50, 100 and 200 years return period


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Flood Warning Algorithm

1 .Determination of proposed stations

2 .Determination of the rainfall and runoff

thresholds 3 .Reservoir management


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Toronto, Canada

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.


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Toronto, Canada

Determination of proposed stations

5 7 . 5 5 8 5 8 . 5 5 9 5 9 . 5 6 0 6 0 . 5 6 1 6 1 . 5

2 6

2 6 . 5

2 7

2 7 . 5

2 8

2 8 . 5

2 9

2 9 . 5

123

4

5

6

7

8 9

1 0

1 1

1 2

1 3

1 4

1 5

1 6

1 7

1 8

1 9

2 0

2 1

2 2

5 7 . 5 5 8 5 8 . 5 5 9 5 9 . 5 6 0 6 0 . 5 6 1 6 1 . 5

2 6

2 6 . 5

2 7

2 7 . 5

2 8

2 8 . 5

2 9

2 9 . 5

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.


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Toronto, Canada

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.


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Toronto, Canada

Determination of the rainfall and runoff thresholdsThe 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.

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120 140t (Min)

Q (

CM

S)

2 2

5 5

10 10

Outflow Inflow


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Toronto, Canada


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 (tc) 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.


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Toronto, Canada


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 (tc)

of each sub-basin.

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

زمان)درصد(

د(صدرن)رابا

Time)%(

Pre

cipi

tatio

n)%

(


6-8 May, 2008

Toronto, Canada

Flood warning system algorithm

.

Defining New StationsNew Weather station: 60 53 Lon. , 26 37 Lat. (Ahooran Station: R5)New Weather station: 60 34 Lon., 26 39 Lat. (Chanef Station: R1)New Weather Station: 60 44 Lon., 26 28 Lat. (Dirak Station: H3)

Monitoring and checking Equipment and Stations

Are they all up and running?

Rep

airm

ent

Reservoir Water Level Control

What month are we currently in?

Water Level Should be below

150 m

February

Max. Allowable Water Level

May: 205 mJun: 183 mJul: 163 mOct: 167 mNov: 164 mDec: 162 mJan: 164 m

Other Months

Discharge in Dirak (H3) Hydrometric Station exceeds of 540 CMS

Ahooran Station (R5)

Cumulative rainfall in 6.5 hrs exceeds

of 15 mm

Cumulative rainfall in 13 hrs exceeds

of 43 mm

Chanef Station (R1)


of 11 mm

Cumulative rainfall in 6 hrs exceeds of

16 mm

Flood Warning to dam officials

Public Warning

Discharge in Chandookan (H1) Hydrometric Station exceeds of 960 CMS


94 m

March


137 m

April


155 m

August


11 mm

Ghasreghand station (R3)


11 mm


14 mm

Warning to Downstream installations and villages of

dam

Open All Dam Gages

Operating Rule- Zirdan Reservoir


41 mm


of 42 mm

0

50

100

150

200

250

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepMonth

Vo

lum

e (

MC

M)

Normal Condition

Flood Condition


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Toronto, Canada

Reservoir ManagementThe 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.

.


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Reservoir Management

.

0

50

100

150

200

250

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Vo

lum

e (M

CM

)

Normal Condition

Flood Condition


6-8 May, 2008

Toronto, Canada

Flood warning system algorithm

.

Defining New StationsNew Weather station: 60 53 Lon. , 26 37 Lat. (Ahooran Station: R5)New Weather station: 60 34 Lon., 26 39 Lat. (Chanef Station: R1)New Weather Station: 60 44 Lon., 26 28 Lat. (Dirak Station: H3)

Monitoring and checking Equipment and Stations

Are they all up and running?

Rep

airm

ent

Reservoir Water Level Control

What month are we currently in?


150 m

February

Max. Allowable Water Level

May: 205 mJun: 183 mJul: 163 mOct: 167 mNov: 164 mDec: 162 mJan: 164 m

Other Months

Discharge in Dirak (H3) Hydrometric Station exceeds of 540 CMS

Ahooran Station (R5)


of 15 mm


of 43 mm

Chanef Station (R1)


of 11 mm


16 mm

Flood Warning to dam officials

Public Warning

Discharge in Chandookan (H1) Hydrometric Station exceeds of 960 CMS


94 m

March


137 m

April


155 m

August


11 mm

Ghasreghand station (R3)


11 mm


14 mm

Warning to Downstream installations and villages of

dam

Open All Dam Gages

Operating Rule- Zirdan Reservoir


41 mm


of 42 mm

0

50

100

150

200

250

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepMonth

Vo

lum

e (

MC

M)

Normal Condition

Flood Condition


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Toronto, Canada

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.


6-8 May, 2008

Toronto, Canada

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.

6-8 May, 2008

Toronto, Canada

Thank you for your Attention

For more information please contact:

Email: [email protected]

Tel: 0098-21-88555884

Fax:0098-21-88701507

6-8 may, 2008 toronto, canada developing a flood warning system: a case study mohammad karamouz...

Documents

introduction flood

flood warning algorithm

early flood warning

flood forecasting

flood events

flood management

flood hydrograph

easiest flood warning