Oman Water Society Sultanate of Oman FLOOD STUDIES IN THE SULTANATE OF OMAN د .ةيشرقلا دوعسم نسح ديسلا يتفم تنب ةشئاع Dr . Ai Dr Aisha a Mufti ti Al Al-Qurash rashi Expert, Ex rt, Floods s and Ar Arid Zo Zone Hy Hydrol ology ogy The 4th Workshop on Tropical Cyclones and Flash Floods 8 th - 9 th October 2018, Muscat, Oman
Fl Floo oods 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 m 3 /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 m 3 /s flood peak was estimated using indirect flood measurement 1948 : Hit Dhofar governorate and remained for about a week 1951 : Hit Al-Dakhiliya h Governorate and upto 4130 m 3 /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 m 3 /s in Wadi Ghudon and 8,250 m 3 /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 m 3 /s was estimated 1983 : Hit Salalah and upto 10,400 m 3 /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 m 3 /s was estimated 2002 : Hit Dhofar where upto 434 mm of rainfall was recorded in Aidam 2011 : Keil a, 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 m 3 /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 m 3 /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 m 3 /s was recorded at Wadi Darbat.
Fl Flood ood Ef Effe fects ts
Fl Floo ood Eff d Effec ects ts Guno, 2007
Fl Floo ood Eff d Effec ects ts Mekunu, 2018
Impo mportanc tance e of of Fl Flood ood St 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 oods 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
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 ole
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 Go Gover ernment nment Rol ole
Fl Flood ood Gu Guide deline ine Ma Manua nual Des esign ign St Storm orm 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 ole
Fl Flood ood Gu Guide deline ine Des esign ign Fl Floo oods 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 ole
Cor orrelat relation ion Of Of MA MAF F to Ca o 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 owth h Fa Factors ors Oman Regional Flood Frequency Analysis - Regional Growth Curves (GEV Distribution) Comparison Northern Oman & Arid/Semi Arid Regions Worldwide Return Period 5 10 20 50 100 200 500 1000 yrs 40 35 30 Northern Oman 25 Namibia AAR<175 MAF 20 S.W. Saudi Arabia Q / RSA & Botswanna 15 Arid & Semi Arid Worldwide Central Iran A<7500km2 10 Oman Flood Manual (Nov 2000) 5 0 0 1 2 3 4 5 6 7 8 Reduced v ariate y
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 ood Ma Mana nagement gement Pr Prog ogramme ramme The nationwide flood study programme of flood- prone urbanized areas of 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.
Recommend
More recommend
