SOP for Flood Forecasting & Early Warning - UNESCO Islamabad

Table 1.3
S.No.
Flood Limits
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 15 th June to 15 th 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
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