Title Distributed Hydrological Modeling at Wadi Samail, Oman

Author(s) Abdel-Fattah, Mohammed; Kantoush, Sameh; Saber,Mohamed; Sumi, Tetsuya

CitationProceedings of the Second International Symposium on FlashFloods in Wadi Systems: Disaster Risk Reduction and WaterHarvesting in the Arab Region (2016): 54-58

Issue Date 2016-10

URL http://hdl.handle.net/2433/228078

Right

Type Presentation

Textversion author

Kyoto University

Distributed Hydrological Modeling at Wadi Samail, Oman Mohammed Abdel-Fattah1,*, Sameh Kantoush1, Mohamed Saber1, Tetsuya Sumi1

1Graduate school of engineering, Kyoto University, Japan 2Disaster prevention institute, Kyoto University, Japan *Corresponding author

Email: abdelfattah_chem@yahoo.com

Keywords: Flash Flood, Wadi, Hydro-BEAM, RRI

Recently, flash floods are frequently occurring in the arid region as Oman, which counter with

various challenges to the management of wadi flash floods. In the past, Oman hit by cyclone

Gonu in June 2007 causing torrential flooding and severe damages where the economic loss

was about 4 billion USD, as well as nearly 50 deaths. Mitigation measures and warning system

have become more critical given the expected increased extreme events due to climate changes.

Oman is an arid country, where the average annual rainfall, in its capital Muscat, is only 100

mm, while the average of the whole country is only 51 mm/yr varying from less than 20 mm/yr

in the internal desert regions to over 350 mm/yr in the mountain areas. Wadi Samail at the

coastal area of Oman is selected as case study for flash flood hydrological modelling. Rainfall–runoff responses predictions in arid climate as wadi system always presents unique challenges.

One of the main challenges beside data limitation is the hydrological models themselves, where

the majority of models developed for catchments that have different characteristics than other

wadi systems. Hence, the need to evaluate the suitability of alternative modelling approaches

for wadi system and its scarce dataset arises. In that regard, two distributed hydrological models

are selected in this study. The first one is the Hydrological River Basin Environmental

Assessment Model (Hydro-BEAM) and the other is the Rainfall-Runoff-Inundation (RRI)

Model. Another aspect of this contribution is to focus on both structural measures for flash

flood retention as dry dams, and water harvesting. The location of such mitigation structures

must be carefully designed to avoid transferring the problems to the developed downstream

area of the wadi. Moreover, mitigation structures should be designed in a coordinated manner,

to assess their overall effect. This study analyzes the wadi flash flood mitigation for three cases:

1) no dams, 2) distributed small dams all over the catchment in the upstream, and 3) proposed

large dam in the middle or downstream area of the wadi. The effect must be quantified through

a comparison of the consequences with and without mitigation structures over the whole wadi.

Various factors are considered to study and improve the assessment methodologies. The

simulated scenarios highlighted significant differences in calculated hydrographs when using

either distributed or concentrated dams scenarios for wadi Samail. This study is expected to

conclude recommendations for hydrological modelling and management at wadi system in arid

environments. The next questions address how to define dam height and reservoir volume. For

better assessment of several dams options, clear quantification of evaluation factors and cost-

benefit approaches should be included in future. Small dry dams are effective structures. Both,

Hydro-BEAM and RRI models are efficient, and emphasizes the importance of taking into

account the variability and spatial properties of rainfall patterns.

54 25-27 October 2016

The Second International Symposium on Flash Floods in Wadi Systems

Distributed Hydrological Modeling at Wadi Samail,

Oman

M. ABDEL-FATTAH 1, Sameh KANTOUSH2, Mohamed SABER2,Tetsuya SUMI2

1 Graduate School of Engineering, Kyoto University

2 WRRC, DPRI, Kyoto University

1

2nd ISFF

Oct., 2016

• Wadi: Arabic term referring to valley.

• Wadi channel is usually dry except during heavy rain events.

• Flash flood: caused by heavy rainfall in short duration< 6 hrs.24/02/2016

2

Wadi System& Flash Floods

Characteristics of Wadi

24/02/2016 3

0

50

100

150

200

250

300

350

400

Dis

cha

rge

(m

3/s

)

SAMAIL CATCHMENT, WILAYAT AL SEEB

WADI AL KHOUDH

Dischareg(m3\s)

Source: A. Al Barwani, Flash Flood Mitigation and Harvesting Oman case study, First International Symposium on Flash

Floods, 2015, Kyoto, Japan

Damages of Flash Floods Disasters

24/02/2016 4

24/02/2016 5

Cyclones History in OmanDate Name& Type Rainfall (mm)

June 1890 Tropical Cyclones

(TC)

285

May 1963 TC 269

Nov 1966 TC 202

Dec 1971 Cyclonic storm 99

Jun 1977 TC 430

Mar 1999 Low pressure-Sur 122

Oct 1999 Deep Low Pressure 69

May 2002 Cyclonic storm 58

Sep 2004 Low Pressure 116

Jun, 2007 Gonu, TC 626

June, 2010 Phet, TC 603

June, 2015 Ashoba, TC 204

Flash Floods Caused By Cyclones

24/02/2016 6•Ryan L. Sriver, 2011

Gonu 2007 Cyclone

50 killed persons

4 billion USD losses

55 25-27 October 2016

The Second International Symposium on Flash Floods in Wadi Systems

26/10/2016 7

Target Research Area of W. Samail

W. Samail location map in Oman, its digital elevation model and the measurements stations.24/02/2016 8

24/02/2016 9

Satellite and Measured RainfallGSMAP Gauges

0

5

10

15

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25

30

35

4:00

AM

5:00

AM

6:00

AM

7:00

AM

8:00

AM

9:00

AM

10:00

AM

11:00

AM

12:00

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1:00

PM

2:00

PM

3:00

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4:00

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5:00

PM

6:00

PM

7:00

PM

8:00

PM

9:00

PM

10:00

PM

Pre

cipit

atio

n (

mm

)

Time (h)

GSMap vs Measured Rainfall (Alkhoud station, Oman)

Meas. Rain GSMap GSMap av. Watershed

Gonu 2007 event

Study Motivation

24/02/2016 10

Wadi Flash Floods

Disaster

Unique Features

Water Resources

Hydrological Modelling

Frequency

Wadi

System

Data

Deficiency

Unsuitable

Models

Objectives

• Proposing innovative methodology for management

of flash floods disaster in ungauged wadis.

• Check the applicability of Hydro-BEAM and RRI

models using available data in W. Samail.

• Comparative study by 2 models Hydro-BEAM&RRI

• To find best scenario of DDR (distributed or

concentrated dams)

24/02/2016 11

Methodology

24/02/2016 12

Da

ta C

oll

ecti

on

& A

na

lysi

s

RRI Model

Fie

ld I

nves

tig

ati

on

Topographic Data Rainfall DataLand Use Data

GIS

& G

oo

gle

Ear

th

Dam Location Detection

Thiessen Interp.Watershed Delineation Hydro-shed Data

Surface RunoffInundation

Flash Flood Mitigation Scenarios

Model Calibration& Validation

Model Sensitivity Analysis

Hydrological Modeling

56 25-27 October 2016

The Second International Symposium on Flash Floods in Wadi Systems

RRI Model

• Rainfall-Runoff-Inundation (RRI) model is a two-dimensional model capable of simulating rainfall-runoffand flood inundation simultaneously (Sayama et al.,2012)

24/02/2016 13RRI model scheme overview (Sayama, T., 2013)

24/02/2016 14

(Sayama et al., 2012)

Mass

Balance eq.

Momentum eq.

h water height from local surface,

Q x, y unit width discharges,

u & v flow velocities,

r rainfall intensity,

H water height from the datum,

ρw water density,

g gravitational acceleration,

τ x and τ y shear stresses and

n Manning’s roughness

k lateral saturated hydraulic

conductivity

d soil depth times effective

porosity

Diffusion Wave approximation

RRI Model

24/02/2016 15

Samail_DEM

Elevation (m)

0 - 299

300 - 415

416 - 531

532 - 676

677 - 908

909 - 2,462

Ü

0 8 16 24 324Km

Topography

• 1 sec void filled SRTM data

Input Data Watershed Delineation

Watershed Delineation

Streams

Wadi Boundary Ü

0 8 16 24 324Km24/02/2016 16

DEM

Flow Direction

Flow Accumulat

ionStream Link

Watershed

Stream Order

Stream To Feature

Sink Check

Watershed modelling using GIS flowchart

RRI Parameter Setting

RRI model major parameter setting for the different land uses showing its default

values and ranges.

Parameter (default) Range Alluvium Igneous Sedimentary

nriver (0.03m-1/3s) 0.015~0.04 0.022 0.022 0.022

nslope (0.3 m-1/3s) 0.15 ~ 1.0 0.3 0.35 0.3

d (0.471 m) 0.15 ~ 1.0 - 0.14 0.3

k (0.1ms-1) 0.01-0.3 - 0.05 0.05

kv(5.56*10-7 ms-1) 6.54*10-5 ~ 1.6710-7 4*10-6 - -

φ 0.3 ~ 0.5 0.475 - -

Sf (0.3163 m) 0.0495~0.3163 0.15 - -

24/02/201617

RRI Model Sensitivity Analysis

24/02/2016 18

Over than 1000 simulations (manually)

57 25-27 October 2016

The Second International Symposium on Flash Floods in Wadi Systems

RRI Model Calibration (Gonu-2007)

24/02/2016 19

0

20

40

60

80

1000

200

400

600

800

1000

1200

1-Jun-07 4-Jun-07 7-Jun-07 10-Jun-07 13-Jun-07 16-Jun-07

Rain

fall

(m

m)

Dis

charg

e (m

3/s

)

Date

Ave. meas. rain (mm)

Meas. flow (cms)

Simulated flow (cms)

(a) (b)

6 June, 2007

1:00 PM

Fig. a) RRI model calibration results (Gonu-2007); b) peak flow spatial distribution.

Discharge

(m3/s)

24/02/2016 20

RRI Model Validation (Phet-2010)

0

20

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80

1000

200

400

600

800

1000

1-Jun-10 4-Jun-10 7-Jun-10 10-Jun-10 13-Jun-10 16-Jun-10

Ra

infa

ll (

mm

)

Dis

ch

arg

e (m

3/s

)

Date

Ave. meas. rain (mm)

Meas. flow (cms)

Simulated flow (cms)

(a)

Fig. RRI model validation results (Phet-2007); b) peak flow spatial distribution.

(b)

4 June/2010

7:00 PM

Discharge

(m3/s)

Model Performance Evaluation

24/02/2016 21

( )

( )1

1

*100n

obs sim

i i

i

nobs

i

i

Y Y

PBIAS

Y

=

=

−=

∑

∑

( )

( )

2

1

2

1

1

nobs sim

i i

i

nobs obs

i mean

i

Y Y

NSE

Y Y

=

=

=−

−−

∑

∑

2 2 21 ( 1) ( 1) ( 1)KGE r α β− − − + −= +

( )( )( )

( ) ( )

2

2 1

2 2

1 1

nsim sim obs obs

i mean i mean

i

n nsim sim obs obs

i mean i mean

i i

Y Y Y Y

r

Y Y Y Y

=

= =

− −=

− −

∑

∑ ∑( )max max

max

*100obs sim

sim

Y YPE

Y=

−

Relative hydrograph peak (PE), Coefficient of determination (squared correlation coefficient) (r2),

Percent bias (PBIAS), Nash-Sutcliffe efficiency (NSE)1), Gupta efficiency (KGE) 2)

where r is the linear correlation, Yiobs and Yi

obs are observed and simulated discharge at time step i, Yiobs ,Yi

obs are the mean observed

and simulate discharge, α is a measure of relative variability and equal to the ratio of standard deviation of the simulated and

observed discharge and β represents the bias and equal to the ratio of the mean simulated and observed discharge.

1) Nash, J. E. and Jonh, V. S. : River flow forecasting through conceptual models part I—A discussion of principles, Journal of hydrology, Vol. 10, No. 3, pp. 282-290, 1970.

2) Gupta, H. V., Kling, H., Yilmaz, K. K. and Martinez, G. F. : Decomposition of the mean squared error and NSE performance criteria: Implications for improving

hydrological modelling, Journal of Hydrology, Vol. 377, No. 1, pp. 80-91, 2009.

RRI model performance evaluation for Gonu-2007 and

Phet-2010 extreme flash floods.

Index (Ideal value) Gonu 2007 Phet 2010

PE (0 %) -1.18 -9.05

r2 (1) 0.96 0.89

PBIAS (0%) -14.3 -12.04

NSE (1) 0.93 0.86

KGE (1) 0.81 0.74

24/02/2016 22

Long Term Flash Flood Simulation at W. Samail

0

50

100

150

200

250

300

350

400

Dec, 2005 Jul, 2006 Jan, 2007 Aug, 2007 Feb, 2008 Sep, 2008 Mar, 2009 Oct, 2009 May, 2010

Dis

cha

rge

(cm

s)

Date

Wadi Flow Simulation using RRI

Simulated Discharge

Measured Dischrage

0

100

200

300

400

6/4/2007 6/10/2007 6/16/2007 6/22/2007

Cyclone Gonu Event

Wadi flow measurement station

Flash Flood Inundation Simulation

24/02/2016 23

Discharge vs Inundation

Wadi Samail Dam

24/02/2016 24

Al-Maktoumi, 2014

Afer Gonu 2007, it was clear that This Dam is not

enough and further mitigation structure is needed

58 25-27 October 2016

The Second International Symposium on Flash Floods in Wadi Systems

Different FF Mitigation Scenarios at Wadi Samail

• Mitigation scenario 1: One big concentrated dam

• Mitigation scenario 2: Three smaller distributed dams

24/02/2016 25

Concentrated

Dam

Distributed Dam

1

Distributed Dam

2

Distributed Dam

3

Location: Y

: X

23.554344

58.103665

23.554344

58.103665

23.371503

58.090958

23.368906

58.157186

Reservoir Capacity

(MCM)

75 40 9.6 25.8

Height (m) 50 40 22 22

Proposed Flash Flood Mitigation Dams

24/02/2016 26

Concentrated DamDistributed Dam 1

Distributed Dam 3Distributed Dam 2

Different Mitigation Scenarios in W. Samail

24/02/2016 27

0

100

200

300

400

01. Jun 07 09. Jun 07 17. Jun 07 25. Jun 07

Dis

ch

arge (

cm

s)

Date

Simulated discharge with concentrated and distributed dam

Without dams

With one concentrated dam

With three distributed dams

Conclusion

• Wadi system have very unique features and should be considered in

flash flood hydrological modelling and management.

• RRI model could be calibrated validated efficiently to be used in

wadi system

• Distributed dams and concentrated dams strategies are efficient in

flash flood mitigation.

• Distributed dams have advantage of upstream protection, local

recharge

• More evaluating parameters for the best mitigation scenarios should

be considered as:

• Optimization of each function of dams

• Economical point of view and maintenance28

24/02/2016 29

59 25-27 October 2016

The Second International Symposium on Flash Floods in Wadi Systems