SOP for Flood Forecasting & Early Warning

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  • c:\documents and settings\administrator\desktop\cd material nust\international training workshop\session 5\2_sop pmd_51 pages.doc

  • c:\documents and settings\administrator\desktop\cd material nust\international training workshop\session 5\2_sop pmd_51 pages.doc

    LIST OF ABBREVIATIONS

    S. No

    1. SOP Standard Operating Procedure

    2. PMD Pakistan Meteorological Department

    3. FFD Flood Forecasting Division

    4. FFC Federal Flood Commission

    5. NDMA National Disaster Management Authority

    6. PMF Probable Maximum Flood

    7. PMP Probable Maximum Precipitation

    8. WAPDA Water and Power Development Authority

    9. PID Provincial Irrigation Departments

    10. PIDA Provincial Irrigation and Drainage Authority

    11. RDFF Routine Daily Flood Forecast

    12. GMT Greenwich Mean Time

    13. PCIW Pakistan Commissioner for Indus Water

    14. ERC Emergency Relief Cell

    15. UNDP United Nation Development Programme

    16. ADB Asian Development Bank

    17. APT Automatic Picture Transmission

    18. RTT Radio Telegraphic Transmission

    19. H & WM Hydrology and Water Management

    20. FWC Flood Warning Center

    21. RC Relief Commissioner

    22. SWH Surface Water Hydrology

  • c:\documents and settings\administrator\desktop\cd material nust\international training workshop\session 5\2_sop pmd_51 pages.doc

    Introduction

    Planes of Pakistan have quite often been swept across by severe flood. In fact out of all the natural

    hazards floods are the single most devastating natural hazard in Pakistan. Statistically every five

    years a flood of exceptionally high level occurs in the Chenab, which is the flashiest channel out of

    all the five major rivers. Every ten years a major flood of exceptionally high level passes through

    all the five rivers. Even 15 years a super flood of 1988 or 1992 type occurs. Loss of life and

    property associated with floods has been colossal. In the year 1973 more than 3 million homes

    were destroyed and 160 persons lost their lives. The 1976 flood demolished over 10 million houses

    while 425 lives were lost with losses amounting to Rs. 6 billion. In 1988 an unprecedented flood

    occurred towards the end of September inflicting Rs. 17 billion worth of damage to the country.

    The super flood of 1992 surpassed all previous records with the damage estimated at Rs. 50

    billion.

    The modern flood fighting strategy is always a blend of engineering as well as non-engineering

    measures. This is because the meteorological phenomena causing the floods is outside the purview

    of the human activity and thus the occurrence of the rainfall and floods cannot be checked.

    However advance information of occurrence of meteorological events can be used to forecast

    floods and adopt safety measures well in time.

    The flood mitigation planning in Indus basin consists of both the engineering as well as non-

    engineering measures. Watershed management above the rim station (the first gauging stations on

    rivers after they enter in Pakistan) forms the starting point of the planning. Below the rim station,

    several flood protection works have been provided to protect the facilities. Most important part of

    the flood mitigation planning is the establishment of a reliable flood early warning system so as to

    afford the timely evacuation of people from the threatened area, use of Mangla and Tarbela

    reservoirs on the basis of the forecast of the expected in flows (through improved flood forecasting

    facilities) is also an important aspect of the flood mitigation process for reducing the downstream

    flood damages by phasing out the flood waves at the confluences.

    The SOP contains the procedure of the flood forecast, early warning the stakeholder for data

    collection, transmission and dissemination of the flood forecast and warning. Classifications of

    floods, flood limits and travel time (from one headworks/sites to other all the agencies involved in

    flood management process in Pakistan. Chapter I describes the causes of flood in Pakistan and the

  • c:\documents and settings\administrator\desktop\cd material nust\international training workshop\session 5\2_sop pmd_51 pages.doc

    three categories, which cause flooding in the catchments of the Indus basin river system and its

    tributaries. The flood management process is also described in this chapter. The early warning and

    flood forecasting system is covered in chapter 2. The responsibilities of the stake holders involved

    in the management process are indicated in chapter 3. The process of flood forecast and flood

    warning dissemination system is described in chapter 4 of this SOP.

  • c:\documents and settings\administrator\desktop\cd material nust\international training workshop\session 5\2_sop pmd_51 pages.doc

    Chapter 1

    Flood Causes & Management

    1.1 Define Floods

    Flood is defined as the high stage of a river at which the stream channel gets filled up and above

    which it overflows its banks and inundates the adjoining areas.

    1.2 Classification of Floods

    In Pakistan, floods are classified into five levels, shown in Table (1.1).

    Table 1.1 Classification of floods

    S.No. Classification Detail

    1. Low Flood It is that flood situation when the River is flowing within

    deep channel(s) but is about to spread over river

    islands/belas.

    2. Medium Flood The river is called in Medium Floods when River flows is

    partly inundating river island/belas but below half of its

    highest flood level

    3. High Flood When the water level of the River is almost fully

    submerging islands/belas and flowing upto high

    banks/buds with encroachment on freeboard.

    4. Very High Flood When the water level of the river flows is between high

    banks/bunds with encroachment on freeboard.

    5. Exceptionally High

    Flood

    It is that flood situation where there is imminent danger of

    overtopping/breaching or a breach has actually occurred or

    high bank areas become inundated.

    1.3 Flood Limits of the River/Nullah

    The limits of the flood in different rivers/nullahs at different places are shown in

    Table 1.2 & 1.3

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    Table 1.2 Flood Limits (In Lacs of Cusecs)

    RIVER SITE DESIGN

    CAPACITY

    LOW MED HIGH VERY

    HIGH

    EX.

    HIGH

    INDUS TARBELA 15.0 2.5 3.75 5.0 6.5 8.0

    ATTOCK - 2.5 3.75 5.0 6.5 8.0

    KALABAGH 9.5 2.5 3.75 5.0 6.5 8.0

    CHASHMA 9.5 2.5 3.75 5.0 6.5 8.0

    TAUNSA 11.0 2.5 3.75 5.0 6.5 8.0

    GUDDU 12.0 2.0 3.5 5.0 7.0 9.0

    SUKKUR 9.0 2.0 3.5 5.0 7.0 9.0

    KOTRI 8.5 2.0 3.0 4.5 6.5 8.0

    JHELUM KOHALA - 1.0 1.5 2.0 3.0 4.0

    MANGLA 10.6 0.75 1.1 1.5 2.25 3.0

    RASUL 8.5 0.75 1.1 1.5 2.25 3.0

    CHENAB MARALA 11.0 1.0 1.5 2.0 4.0 6.0

    KHANKI 8.0 1.0 1.5 2.0 4.0 6.0

    QADIRABAD 8.07 1.0 1.5 2.0 4.0 6.0

    TRIMMU 6.45 1.5 2.0 3.0 4.5 6.0

    PANJNAD 7.0 1.5 2.0 3.0 4.5 6.0

    RAVI JASSAR 2.75 0.5 0.75 1.0 1.5 2.0

    RAVI SYPHON 4.5 0.4 0.65 0.9 1.35 1.8

    SHAHDARA 2.5 0.4 0.65 0.9 1.35 1.8

    BALLOKI 2.25 0.4 0.65 0.9 1.35 1.8

    SIDHNAI 1.5 0.3 0.46 0.6 0.9 1.3

    SUTLEJ SULEMANKI 3.25 0.5 0.8 1.2 1.75 2.25

    ISLAM 3.0 0.5 0.8 1.2 1.75 2.25

    KABUL WARSAK 5.4 0.3 0.45 1.0 2.0 4.0

    NOWSHERA 0.45 0.47 1.0 2.0 1.0

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    Table 1.3 Flood Limits

    S.No. NAME OF

    NULLAH PLACE

    LOW

    FLOOD

    MEDIUM

    FLOOD

    HIGH

    FLOOD

    VERY

    HIGH

    FLOOD

    EXCEPT

    HIGH

    FLOOD

    1. BEIN Chak Amru 1300 7000 20000 30000 35000 & above

    2. BEIN Shaker Garh 1600 3000 24000 26000 43000 & above

    3. AIK Ura 2000 9000 13000 16000 33000 & above

    4. BASANTAR Jassar 4100 4700 7500 11600 17800 & above

    5. DEG Q.S. Singh 3600 7500 15000 30000 35000 & above

    6. PALKHU Wazirabad 2500 3100 5000 25000 26000 & above

    1.4 Causes of Floods in Pakistan

    Pakistan has unique flood forecasting problems, which can be appreciated only if the

    meteorological causes of the floods are first understood. Floods in Pakistan are mainly caused by

    the heavy monsoon rains during the summer monsoon period from July to September. Officially,

    the flood season extends a little further to cater for any possible exceptions and covers the period

    form 15th

    June to 15th

    October. There are two situations which cause flood producing rains in the

    upper catchments (Annex-1) of the rivers. The two meteorological situations in relations to

    different conditions of intensity and movement of monsoon low/depression may produce three

    categories of floods as described below.

    i) Meteorological Situation For Category-I Floods

    This is the situation when the seasonal low, which is a semi permanent weather system generally

    sitated over south eastern Balochistan, south western Punjab and adjoining parts of Sindh gets

    occasionally intensified (due to the passage of a westerly wave) and thus causes the moisture from

    the Arabian Sea to be brought up to the upper catchments of Chenab and Jhelum rivers resulting in

    the heavy downpour along the windward slopes of the mountain ranges due to the orographic

    lifting of the moist air mass. Rainfall is generally short lived and occurs either in the late

    afternoon/evening or during the early morning lasting for a maximum period of about six hours.

    Floods under this condition are the Category-I floods, which may cause a short peak ranging from

    3 to 5 lac cusecs under extreme conditions. Most common1y, the peak is limited to within 3 lac

  • c:\documents and settings\administrator\desktop\cd material nust\international training workshop\session 5\2_sop pmd_51 pages.doc

    cusecs only. This should pose no serious flood management problem for the Mangla reservoir due

    to short Rhiration and thus less volume. Tarbela is affected to a much lesser degree.

    Annex-2 depicts this condition, wherein the south westerly wind flow from the Arabian sea and the

    south easterly air current from the Bay of Bengal are indicated reaching the upper catchments of

    the Sutlej, Ravi, Chenab and Jhelum rivers.

    ii) Meteorological Situation for Category-II & Category-HI Floods

    The second flood generating meteorological situation is the one linked with a monsoon

    low/depression. Such monsoon systems originate from the Bay of Bengal region and then moving

    across India in a general west/north westerly direction arrives over Rajasthan or

    any of the adjoining states of India. After this the monsoon depression may take any one of the

    following three courses.

    a. Continue moving straight west causing heavy wide-spread rains over Sindh/Balochistan.

    However, no river flooding shall occur in this case.

    b. Recurve in the north east direction towards the upper catchments of Sutlej, Ravi and Chenab

    rivers causing extremely heavy rainfall and consequently the floods first across the border in

    India and then (within hours) at the rim stations in Pakistan. This is the Category-II flood

    situation as depicted in Annex-3. Under this situation floods first occur in river Chenab due to

    its peculiar topographic features which provide the most favorable conditions for the

    orographic lifting of the south west/south east monsoon currents. Ravi and Jhelum are affected

    next in sequence, followed by river Sutlej.

    The control structures over Sutlej & Ravi rivers in India significantly delay the arrival of

    flood wave in Pakistan. Floods in Jhelum under this situation may be significantly greater

    than the Category-I floods and may thus cause some flood management problem for the

    Mangla reservoir. However, the problem can be safely resolved by resorting to safe (minimum)

    pre-flood releases corresponding to the lower side of the forecast inflow range. Generally the

    flood peak at Mangla is limited to below 5 lac cusecs, but may reach 7 lac cusecs under an

    extreme condition.

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    c. Continue moving in the northerly direction under the effect of a strong westerly wave over the

    plains of Lahore/Gujranwala Divisions to finally ending up over Rawalpindi/Hazara Divisions.

    The upper catchments of Chenab, Jhelum and Indus rivers come under its influence.

    Extremely heavy rains may occur over Mangla and/or Tarbela catchments under this situation,

    depending upon the final position of the depression causing extremely heavy floods

    (Category-III), as shown in Annex-4. The probable maximum flood (PMF) is an extreme case

    of Category-III flood. These are the most threatening floods for Mangla reservoir, a typical

    example of such floods was the 1992 flood. Forecasting of such floods at least 24 hours in

    advance should pose no problem, specially when 'S' band weather radars at Lahore and Mangla

    are available for system identification. Close coordination between FFD and WAPDA shall be

    necessary for the safe routing of such floods through the Mangla reservoir. WAPDA, after

    1992 catastrophic flood in Jhelum & Chenab rivers has devised an SOP for the routing of

    category I, II & III situation to safely pass the high inflows in Mangla. The SOP for Mangla is

    annexed as (5A, 5B, 5C).

    The meteorological factors linked with each situation are generally well known and 24-hours

    advance prediction should be quite possible in each case. In fact tracking of the depression is

    commenced from the Bay of Bengal and its position is reported on continuous basis in the

    daily flood forecast bulletin issued by FFD. Once a depression reaches Rajasthan, an extremely

    close watch is started using meteorological charts, and satellite cloud pictures. As the

    depression advances towards Pakistan and comes within the meteorological range of the

    Lahore Radar, an intensive watch would be started and color coded Met Alerts are issued as

    applicable.

    1.5 Flood Management Process

    (i) Flood management process in Pakistan is multi-functional involving a number of different

    organizations. The very first step in the process is the issuance of the flood forecast/warning. This

    function has been assigned to the Pakistan Meteorological Department (PMD) since the basic

    cause of the floods in Pakistan is the rainfall which can be best predicted and monitored by PMD

    utilizing the satellite cloud pictures and the quantitative precipitation measurement radar data, in

    addition to the conventional weather forecasting facilities. For quantitative flood forecasting the

    hydrological data is obtained (through the Provincial Irrigation Department and WAPDA.

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    WAPDA's telemetric system is an important source of hydrological data for the flood forecasting

    purposes.

    (ii) This is supplemented by the manually observed data from the Surface Water Hydrology

    Project of WAPDA. In addition to data measurement sites at the main rivers, the Irrigation

    Department also maintains limited network of manually observed hydrological stations at barrages

    and important nullahs. T...

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