THE SULTANATE OF OMAN . Dr - - PowerPoint PPT Presentation

FLOOD STUDIES IN THE SULTANATE OF OMAN

د .ةيشرقلا دوعسم نسح ديسلا يتفم تنب ةشئاع Dr

• Dr. Ai

Aisha a Mufti ti Al Al-Qurash rashi Ex Expert, rt, Floods s and Ar Arid Zo Zone Hy Hydrol

• logy
• gy

Oman Water Society Sultanate of Oman

The 4th Workshop on Tropical Cyclones and Flash Floods 8th - 9th October 2018, Muscat, Oman

Fl Floo

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ds Cha harac acteristics teristics in O n Oma man

• As in rest of the Arabian peninsula countries, normally arid, wadis dry, with

few with continuous wadi flow. Baseflows or continuous flows are rare

• Rainfall is difficult to predict, intense, short lived and extremely variable

in space and time

• Rainfall is generally affected by elevation.
• Avg Rainfall is very low. In Oman, less than 50 mm to above 350 mm, but

can results in high flash floods

• Rainfall is affected by the seasonality
• High evaporation, over 80% of rainfall
• Floods in areas where bare soil, sparse vegetation, steep mountains, can be

flash with very high velocity, and above 10,000 m3/s flood peaks

• Runoff in arid areas tends to vary in space and time, annual average

discharge can be misleading.

• Runoff spatial occurrence varies not only from one area to another, but also

from one event to another.

• Clear wadi paths in mountainous areas, but in plains, no clear paths,

floods spread out over numerous channels, and courses change, so flood assessment difficult

• High transmission loss
• Hydrograph characteristics are different
• Rainfall-Runoff relationship more complex
• Effects of physical characteristics in floods (study carried out in Oman

(1998) found that the floods are affected significantly by the catchment area, slope and the percentage of alluvium, or alternatively percentage of mountain).

• North and south Oman have different climates,(e. g. Khareef and more

cyclones in south) which affects hydrological characteristic and floods, and needs to be considered in hydrological data analysis and selecting the methods

• Occasional cyclones

The Greatest Flood Events Hit Oman

The greatest storm and flood known to Muscat occurred in; 1890 : Just over 100 years ago (286 mm of rainfall was recorded). The storm killed 757 people when it flooded much of Muscat. 1927 : Hit many areas in Oman and upto 9500 m3/s flood peak was estimated using indirect flood measurement 1948 : Hit Dhofar governorate and remained for about a week 1951 : Hit Al-Dakhiliyah Governorate and upto 4130 m3/s flood peak was estimated 1959 : Hit Dhofar for 3 nights causing severe damages. It caused a shipwreck resulting in loss of all 141 ship crewmembers. 1977 : Hit Masira Island (upto 431 mm of rainfall was recorded) and parts of Dofar, Dakhiyah and Sharqiyah (upto 10,600 m3/s in Wadi Ghudon and 8,250 m3/s in wadi Andur were estimated). The storm caused 105 deaths in Masirah island. 1982 : Hit Al-Batinah coasts, Quriyat and Al-Sharqiyah, upto 5190 m3/s was estimated 1983 : Hit Salalah and upto 10,400 m3/s was estimated

1995 : A mansoon depression hit northern Oman, the United Arab

• Emirates. Rainfall reached 300 mm on Jebel Shams mountain in

Oman. 1996 : A tropical storm struck Southeastern Oman, killing one person in a fishing boat, and causing flooding in isolated areas 1997 : Hit different parts of Oman and upto 2760 m3/s was estimated 2002 : Hit Dhofar where upto 434 mm of rainfall was recorded in Aidam 2011: Keila, where the storm dropped heavy rainfall reaching about 700 mm. The storm killed 14 people in Oman and injured 200, mostly in the north from flash flooding 2014 : Nilofar, caused flash flooding in Rustaq in Northeastern Oman, killed four people from its outer rainbands 2015 : June 12, cyclone Ashobaa , hit the east coast of Oman, dropping 231 mm of rainfall on Masirah island in 24 hours. 2015 : November 3, cyclone Chapala, hit Southern Oman

• Gonu in 2007, hit muscat and al-sharqiyah caused the most ever damages to

muscat properties and infrastructure, upto 714 mm of rainfall in 24 hours and upto 1033 mm in 34 hours, and about 8160 m3/s flood peak was recorded. Gonu left US$4 billion in damage and killed 50 people, making it the worst natural disaster on record in Oman

• Phet in 2010, hit al-sharqiyah and muscat, and about 585 mm of rainfall in 24

hours and upto 603 mm in 38 hours, and about 2210 m3/s was recorded.

• Mekunu in 2018, hit Dhofar, upto 449 mm (663 mm was recorded at Shibob

station but needs to checked) for 24 hours, 673 for 48 hours (811 mm at Shibob ), and 714 mm in 72 hours (865 mm at Shibob), with a flood peak of about 4040 m3/s was recorded at Wadi Darbat.

Fl Flood

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Effe fects ts

Fl Floo

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d Effec ects ts

Guno, 2007

Fl Floo

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d Effec ects ts

Mekunu, 2018

Impo mportanc tance e of

• f Fl

Flood

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Studi udies es

• To provide the data and information required for development planning in

flood-prone areas

• Helps to protect existing and future development
• Provide information for progression to the flood plain management
• Determination and implementation of flood control and mitigative measures

in flood prone areas

Mi Misund under erstand standing ings s Ov Over er Fl Flood

• ods
• Difficult to convince developers their land has dangerous flood problems
• Not understanding that their development may endanger others, even if they

are ready to take the risk

• Difficult to persuade others that a 100-year flood can happen any time
• Difficult worldwide to persuade client that if a weir, culvert, flood

embankment, dam, etc. is designed for a 50-year flood, it will be damaged in a rarer flood

• A common misunderstanding relates to dams, normally they reduce flood

peaks, but in the event of a very rare flood, they make almost no difference

Go Gover ernment nment Rol

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Hydrological Analysis:

• Analysis of flood data to assess peaks
• Rainfall analysis
• Wadi flow analysis
• Rainfall – runoff analysis
• Evaporation and evapotranspiration analysis
• Drought / wet periods determinations

Go Gover ernment nment Rol

• le

Flood Management

• Understanding Oman flood characteristics
• Development of guide lines and standards
• Provide nationwide flood frequencies and wadi development locations
• Producing maps showing flood risk zones
• Forming a hydrologic basis for evaluating and controlling current and

future development in flood risk zones

• Providing initial information for planning flood control

Fl Flood

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Guide deline ine Ma Manua nual

Des esign ign St Storm

• rm Ra

Rainf nfall all

• Rainfall intensities for short durations ( 15-minutes to 12- hours)
• Rainfall frequencies for long durations (1-, 2-, 3-days)
• Maximum recorded rainfalls in Oman
• Probable maximum rainfall
• Area reduction factors

Go Gover ernment nment Rol

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Fl Flood

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Guide deline ine

Des esign ign Fl Floo

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ds

• Flood Frequency Analysis ( was carried out using wadi gauge recorded data,

POT series, Station year approach, Semi-log analysis with best fit line)

• Correlation of MAF to catchment parameter
• Growth Factors
• Flood peak frequencies
• Flood Volume Analysis
• Flood Hydrograph Analysis
• Design Flood Approach

Go Gover ernment nment Rol

• le

Cor

• rrelat

relation ion Of Of MA MAF F to Ca

• Catchment

chment Pa Para rameter meter

Correlation of MAF to : Catchment area, Wadi length, Wadi slope, percentage of non mountain (alluvium plain), catchment area

Gr Grow

• wth

h Fa Factors

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Ra Rainfall nfall Fr Freq equency ency Ana nalysi lysis s Ge Gene neral ral

Ra Rainfall nfall Fr Freq equency ency Ana nalysi lysis Pl Plai ain n Are reas as

Rainfall Frequency Analysis Hill Areas

Rainfall Frequency Analysis Mountain Areas

Flood

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Mana nagement gement Pr Prog

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ramme

The nationwide flood study programme of flood- prone urbanized areas

• f Oman was carries for the main towns in early 1990’s to provides:
• Data and information required for development planning in flood-prone

areas.

• Information for progression to the next step, floodplain management, which

involves the determination and implementation of flood control to help protect, existing and future developments.

Fl Flood

• od Risk

sk Ma Maps ps

• The high risk areas (shown in red) are those

being inundated by a flood that on average would occur (1-5 yrs)

• The medium risk area, shown in blue, are

that covered by (6-20 yrs) flood. The 20- year flood is considered the "index" or "design" flood for general planning purposes.

• The low risk area (shown in yellow) being

that covered by the (21-100 yrs) flood.

• Flood frequency curves, the basis for determining the flows for given return

periods, and the catchment areas are the reference.

• The study was based on detailed surveying of wadi channels and hydraulic

structures and computer routing of the expected flood flows using the HEC-2 model (5,6).

• The flood risk maps should be used as a guide for selecting the protection

schemes and in the town planning

Fl Flood

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Mana nagemen gement t Pol

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cies

• Flood control measures are introduced in existing areas of development

which are subject to flooding in order to minimize the effects of flooding and minimize restrictions on redevelopment.

• In areas to be developed, the effects of flooding will be minimized by use of

the aproved standards

• Planning and development controls to minimize the effect of flooding take

into account social, economic and ecological considerations

• Future development should be forbidden in areas subject to flooding

Fl Flood

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ea St Stan anda dards ds

Flood area standard are applied to the following flood areas:

• Floodway areas that are directly in the paths of wadis
• Active flood plain areas which flood when the flow in the floodway exceeds its

capacity

• Areas of passive inundation which are low lying ground and fill with water in

periods of heavy rain

• Areas of sheet flooding which are areas with gentle slopes and non-defined
• channels. The run-off is shallow, at low velocity, and is distributed relatively

evenly over the slopes

10 10-12 12 Ma May y 2002 02 Cyc yclone

• ne in

n Sa Salal alah ah

• Mad. Al-hAq

• Q. Hareiti

• Sal. Airport

Max Rainfall Recorded at Dhofar Rain-Gauges

Rainfall Frequency Analysis

Ma Maximum mum Ra Rainf nfall, all, Go Gonu nu, , 2007 2007, , Ph Phet et, , 2010 10

603 mm 1033 mm

585 mm 714 mm

Rainfall Frequency Analysis Max Rainfall Recorded at Muscat Rain-Gauges

Gu Guno no And nd Ph Phet et Fl Floo

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d Pe Peak aks s Nor

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h Om Oman an

• 2007
• 2010

Flood Peak Frequencies for Muscat

Excluding Gonu

Period Years

• f
• f

Q Record Data MAF 5 10 20 50 100 200 1 Bajariyah Aday FB505467AD 80-2014 35 251 404 650 896 1222 1469 1715 2 Daghmar Dayqah GL060581AD 82-2010 29 623 1289 2115 2942 4035 4861 5688 3 Habubiyah 1 Hayfadh FA777631AD 82-2014 33 102 156 334 511 746 923 1101 4 Hajir 1 Jannah FA580672AD 82-2014 33 70 101 208 315 456 563 670 5 Al Khawd Al Khawd FB104840AD 72-2014 43 256 523 837 1152 1567 1882 2196 6 Hammam Lansab FA395799AD 80-2014 35 62 102 162 222 302 362 422 7 Quriyat Miglas FA877343AD 79-2014 36 262 347 706 1066 1540 1900 2259 8 Hajir 3 Manzariyah FA585595AD 82-2014 33 104 128 192 256 340 403 467 9 Hajir 4 Mayh FA596055AD 81-2014 34 248 331 607 883 1247 1523 1799 10 Dasir Al 'Uqq FA160968AD 80-2014 35 73 130 193 256 340 403 466 11 Dibab Arabiyin GA057335AD 81-2014 34 442 611 1075 1539 2152 2616 3080

Excluding Gonu Data

No. Station Wadi ID No Flood Peak Frequencies - m3/s Return Period - yrs

Period Years

• f
• f

Q Record Data MAF 5 10 20 50 100 200 1 Bajariyah Aday FB505467AD 80-2014 35 251 517 911 1305 1827 2221 2615 2 Daghmar Dayqah GL060581AD 82-2010 29 623 1490 2420 3350 4580 5510 6441 3 Habubiyah 1 Hayfadh FA777631AD 82-2014 33 102 234 512 790 1157 1434 1712 4 Hajir 1 Jannah FA580672AD 82-2014 33 70 140 290 440 638 788 938 5 Al Khawd Al Khawd FB104840AD 72-2014 43 256 572 907 1242 1684 2019 2354 6 Hammam Lansab FA395799AD 80-2014 35 62 127 217 308 427 518 608 7 Quriyat Miglas FA877343AD 79-2014 36 262 536 1200 1865 2743 3408 4072 8 Hajir 3 Manzariyah FA585595AD 82-2014 33 104 213 437 661 957 1180 1404 9 Hajir 4 Mayh FA596055AD 81-2014 34 248 490 1024 1559 2265 2799 3333 10 Dasir Al 'Uqq FA160968AD 80-2014 35 73 135 197 260 342 405 468 11 Dibab Arabiyin GA057335AD 81-2014 34 442 900 1850 2801 4057 5007 5958

Including Gonu Data

No. Station Wadi ID No Flood Peak Frequencies - m3/s Return Period - yrs

Flood Peak Frequencies for Muscat

Including Gonu

Me Mekunu nu, , 2018 18, , Ra Rainf nfall all (mm) m) So South h Om Oman an

Mekunu Rainfall Data (mm), May 2018

Station 1-day 2-day 3-day Madinat Al Haq

83.4 85.8 86.2

Rakbayt

132.4 207.2 222.3

Salalah

233.8 274.2 293.6

Zayk

90 174 188

Awqad

449 543.2 570

Ghadow

354.8 673.2 713.8 Shibob 662.8 811.4 864.8

Meku kunu nu, , 2018 18, , Ghad adow

• w Rai

ainf nfal all l (m (mm) m), Freq Ana naly lysis sis

Duration Rainfall (mm) for the Following Return Periods: days Av 5 10 20 50 100 200 1 9 32 50 68 91 108 126 2 14 46 71 95 128 152 177 3 17 53 79 106 142 168 195 Duration Rainfall (mm) for the Following Return Periods: days Av 5 10 20 50 100 200 1 15 85 138 190 260 312 365 2 19 102 166 229 313 376 439 3 21 110 178 245 334 402 469

Meku kunu nu, , 2018 18, , Sa Sala lala lah Rai ainf nfal all l (m (mm) m), Freq q Ana naly lysis sis

Duration Rainfall (mm) for the Following Return Periods: days Av 5 10 20 50 100 200 1 13 56 87 119 162 194 225 2 17 67 105 142 192 230 268 3 18 71 111 151 203 243 283 Duration Rainfall (mm) for the Following Return Periods: days Av 5 10 20 50 100 200 1 12 36 54 72 96 115 133 2 15 43 65 87 116 138 160 3 16 46 68 91 120 143 166

• f
• f

Me Mekunu nu, , 2018 18, , Fl Floo

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d Pe Peak aks s (m3/s) s) So South h Om Oman an

Rank of Mekunu Flood Peaks compared to the Historical Floods

3351*1 : The second highest record - the higest one was the historical record in 1977 wich was 8250 2410*2 : The highest record even higher than the historical record in 1977 which was 2140 4040*3 : The highest record even higher than the historical record in 1977 which was 1900 1763*4 : The second highest record - the higest one was the historical record in 1972 wich was 4290 582*5 : The second highest record - the higest was record was in 2002 wich was 1122 264*6 : The third highest record - the higest is the historical record only in 1977 wich was 1090 and the second was in 2002 which was 694

Peak

T

Fr Freq eque uency ncy Ana nalysis ysis for

• r Darb

arbat at St Stat atio ion Mek Mekunu nu, , 2018 18

Conclusion

• nclusions
• Hydrologic analysis are very important for good understanding
• f hydrology and flood characteristics of the country. It

includes:

• Rainfall frequency analysis
• Flood frequency analysis
• Rainfall-Runoff relationships
• Evaporation and evapotranspiration determination to assess the losses

Government need to carry out these Analyses and update them periodically

• Flood studies and management are very important for:
• Development planning in flood-prone areas
• Providing information for progression to the flood plain management
• Determination and implementation of flood control and mitigative

measures in flood prone areas

• Helping to protect existing and future development
• Delineation of flooding risk areas,(high, medium, and low) can help in

flood management and town planning and should be updated periodically when required

• Setting special flood standers and policies to be followed in town planning

and developments

• Flood studies and advices for different ministries and organizations when

required Government should be responsible for flood management, setting policies and standards, and review them periodically

THAN THANK YOU K YOU

د .ةيشرقلا دوعسم نسح ديسلا يتفم تنب ةشئاع Dr

• Dr. Ai

Aisha a Mufti ti Al Al-Qurash rashi Ex Expert, rt, Floods s and Ar Arid Zo Zone Hy Hydrol

• logy
• gy