Flood Management in Pakistan

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This report discusses flood hydrology in Pakistan and constraints in management

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Flood Mechanics & Flood Management in Pakistan
Hydrological Outlook 1. Principal River System of Pakistan a. The land mass of Pakistan, measuring 310,400 square miles, is divided into three principal hydrological units, namely Indus River Basin, Closed Basin of Kharan Desert and Makran Coastal Basin. b. Indus, Jhelum, Chenab, Ravi, Sutlej, Beas and their tributaries are the main sources contributing to the surface water potential of Pakistan. Indus and its tributaries rise in the snow-capped hilly terrains of Himalayas and drain the Western Himalayan ranges of Kailas, Karakoram and Hindu Kush. Their upper reaches are in India, part of Tibet and Chinese territories. Heavy rainfall and snowmelt in catchment areas bring about considerable volume of water running down the tributaries of these rivers which pass through the vast flood plains of Pakistan before terminating into the Arabian Sea. c. Indus Basin comprises Indus River and its five left bank tributaries of Jhelum, Chenab, Ravi, Sutlej and Beas, and one major right bank tributary of Kabul. About 75% of the mean annual flows of Indus and its tributaries and diverted into the world‟s largest contiguous Indus Basin Irrigation System (IBIS) of Pakistan. It comprises three major storage reservoirs, 23 barrages/head works, 12 inter-river link canals, 45 canal commands and some 90,000 water courses to irrigate land. Total length of the canal system is about 38,000 miles with water courses, farm channels and field ditches running another one million miles. 2. Causes/Mechanics of Floods a. General. Pakistan has a history of floods which mainly resulted from monsoon incursions, sudden and abnormal releases by India. Besides low floods in isolated pockets, the Country suffered from high floods in 1950, 1956, 1957, 1958, 1963, 1965, 1973, 1976, 1988 and 1992. b. Categories of Floods. (1) With Respect to Their Nature and Location. Most common in this category are Riverine Floods, in main Indus Plain and its adjacent catchments. The hill torrents on either side of Suleiman Range, Baluchistan and Western Punjab (D.G. Khan and Rajanpur) generally result in Flash Floods. Inadequate drainage facilities in urban centres cause Urban “Flooding. Cyclonic activities, which are prevalent before and after the monsoon incursions, produce Coastal Flooding. Climate change and global warming results in excessive retreat of glaciers which builds glacial lakes behind the moraine; These lakes may burst causing Glacial Lake Outburst Flood (GLOF). A recent study (ICIMOD, 2005) found that out of 2420 glacial lakes in the Indus Basin, 52 lakes are potentially dangerous and can result in GLOF) with serious damages to life and property. The study has also indicated that in future global warming can increase the potential of GLOF. (2) With Respect to Weather and Intensity. From weather and intensity/flow point of view, floods are categorized as Category I, II and III. Meteorologically, there are tow situations which may cause floods in Pakistan. (a) For Category-I floods, the seasonal low, a semi-permanent weather system (situated over South Eastern Baluchistan, South West Punjab and adjoining parts of Sindh) intensifies and cause moisture from the Arabian Sea to be brought up to upper catchments of Chenab and Jhelum rivers. (b) Situation for more severe Category-II and Category-III floods in linked with the monsoon low/depression. Such monsoon system which originates in Bay of Bengal and moves across India in generally West/ north-westernly direction to arrive over Rajasthan or adjoining states of India. From Rajasthan, it is nourished from Arabian Sea and turns north over Chenab, Mangla or Khyber Pakhtunkhwa area. It provides rain due to orographic lifting, but sometimes heavy downpour is also due to its interaction with westernly cold winds.

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Flood Limits. In Pakistan, the flood limits are categorized as Low, Medium, High, Very High and Exceptionally High.

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Causes of Floods in Indus Basin Rivers (1) River Jhelum. The intense rainfall in the catchments can produce exceptionally high flood peaks. The 33280 square kms catchment of Jhelum River has produces three recorded floods in excess of 28000 m3/sec in last 75 years, with the latest in September 1992. The estimated Probable Maximum Flood (PMF) for the river various between 48000 to 70000 m3/sec at the recording station. Major catchment area of River Jhelum above Mangla is between 4000-12000 feet above Mean Sea Level. This result in early snow-melt runoff from February, reaching its peak in early June. High floods in the river, however, result from heavy rainfall in catchment area during the monsoon season of July to September. Though, Mangla Dam (with estimated live storage capacity of 4.54 MAF) being an irrigation replacement project does not have any storage specifically allocated to flood control, yet during early part of its filling, till about early August, it can significantly help in flood regulation. (2) River Indus (a) Indus and other snow fed rivers are also likely to experience flooding due to heat wave in early summer. This phenomenon occurred in June 2005 and was followed by early monsoon rains that caused wide spread flooding in KPK. (b) Floods in upper Indus generally result from heavy precipitation in hilly catchment of lower Himalayas and Hindu Kush which have limited valley storage. Superimposed upon significant snowmelt base flow, these conditions cause very heavy floods. (c) Lower Indus receives combined flows of Upper Indus and its left, and right bank tributaries. Floods in this reach may occur from July – October. Tie river can be in high flood for a period exceeding one month. (3) River Chenab. Floods in Chenab generally result from heavy precipitation in the hilly catchment areas in lower Himalayas with limited valley storage. Snow melt flow reach peak in early July. This, however, is not a significant factor contributing to high floods during August and September. Manipulation of hydropower projects by India with significant storage of River Chenab can also result in a flood like situation for a certain period of time affecting significant area adjoining the river course. (4) River Ravi. Flooding in Ravi generally results from excessive rainfall in the mountainous catchments in India and sub-mountainous areas draining into lower river reaches within Pakistan. Snow melt makes no significant contribution to flood peaks in Ravi. The snow melt flows normally occur in the spring, falling off before the monsoon rains begin in June/July. (5) River Beas/Sutlej. Floods in Beas and Sutlej result from intensive rainfall in catchment areas within India. Occurrence and severity of floods in this river is greatly altered by the construction of upstream dams (Pong Dam on Beas and Bhakhra Dam on Sutlej) in India during 1963-1977. However, when these reservoirs are full, some late monsoon rains can still bring down large flood flows into Pakistan. Climate Changes a. The Impact of Climatic Change. The impact of climate change in form of higher temperatures, more variable precipitation and extreme weather events are being felt all over the globe. In South Asia, these changes are likely to cause excessive melting of glaciers in Western Himalayas resulting in increased flooding and depletion of water resources in next two to three decades. International Panel of climate changes (IPCC), in its third assessment report, has reported an increase of 8-24% in South Asian Monsoons which will be variable and intense in time and space.

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Global Warming. Because of extensive reliance on fossil based fuel especially by developing nations, green house gases are being accumulated in atmosphere. This enhances global temperature as indicated at Picture 1 and 2. There is a recorded increase of about 55 ppm of CO 2 concentrate in atmosphere which caused 1.50 C temperature rise in Pakistan and surrounding regions. Effects of global warming are exponentially adverse; it simply gives rise to occurrences of unnatural climatic events such as droughts, floods, wild fires, glaciers melting etc. As concluded in post flood analysis by Pakistan Meteorological Department, recent floods in Pakistan area an outcome of global warming. Recent Trends of Climate Change in Pakistan. Recent trend of climate change in Pakistan based on last 70 years climatic data compiled by Pakistan Meteorological Department in Technical Report No PMD-22/2009 indicates:(1) Rise in mean daily temp of 0.6 to 1.0 degree centigrade in arid coastal areas and arid western/ North-western Mountains.

Picture 1: Trend Observed Over a Span of 32 years (Pakistan Meteorological Department Technical Report No PMD-22/2009)

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Picture 2: Global Temperature Rise in a Decade

10-15% decrease both in winter and summer rainfall in coastal belt. 18-32% increase in rainfall in monsoon zone (sub-humid and humid areas). Further decrease of 5% in relative humidity over arid plains of Balochinstan. 3-5% decrease in cloud cover over central and southern Pakistan resulting in increase in sunshine. (6) Monsoonal Zone of Pakistan (a region that receives almost 65% of total monsoon rains) has shifted 80-100 km from North East (upper Punjab + Kashmir) towards North West (KPK + North West Punjab), therefore, the possibility of occurrence of heavy rainfall events during monsoon season, in the future, would be very likely over North West Pakistan instead of North East. Subsequently, the areas along western river (Indus and Kabul) would be extremely vulnerable to flood episodes as experienced during this season. (7) This trend will give rise to increase in frequency of extreme events such as heavy rains, flash floods, dust/thunderstorms, hailstorms, heat waves, density, persistence of fog etc. Flood Management Mechanics 4. Institutional Arrangement of Flood Management. Flood management is a multi functional process involving federal and provincial department. In this, Federal Flood commission (FFC), is the lead federal agency in providing necessary institutional framework to supplement provincial flood management measures. The Commission has revised flood management policy of the country through two major projects, Flood Protection Section Project (FPSP) I and II. These projects especially FPSP-II has increased flood forecasting capabilities of the FFD to the certain extent. Role of other departments is as under:a. National Disaster Management Authority (NDMA) . NDMA was raised in the aftermath of Earthquake 2005 and has a constitutional cover. The body has been assigned following roles:(1) Lay down guidelines for preparing disaster management plans by all concerned. (2) Provide necessary technical assistance to provincial governments for preparation of disaster management plans in line with laid down guidelines. (3) Coordinate response in the event of disaster. (4) Promote general education and awareness in relation to disaster management.

(2) (3) (4) (5)

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Lay down guidelines for concerned ministries and provincial governments regarding measures in response to any threatening disaster situation or disaster. (6) For any specific purpose or for general assistance, requisition of services of any person(s) and such person(s) shall be a co-opted member and exercise such power as conferred upon him by authority in writing. b. Flood Forecasting Division (FFD). FFD, a subsidiary of PMD, plays a central role in flood forecasting and warning. The department obtains hydro meteorological data from various national and international sources including satellite data to prepare flood forecasts, which are disseminated to various flood management and relief organizations. c. Provisional Irrigation and Drainage Authority . The authority plays a prominent role in flood management through planning, design, construction and maintenance of flood protection works. It also undertakes flow measurements at specific rivers and irrigation canal sites. d. WAPDA. The authority is custodian of Tarbela and Mangla dams and undertakes day to day reservoir management for irrigation flow releases. It helps FFD through provision of rainfall data from telemetric rain guage stations and flood data at various locations in Indus River system. e. Provincial Relief Department. These are headed by Relief Commissioners who coordinate relief efforts during and after floods. The Commissioners also undertake flood preparation actions such as inspection of flood protection measures and establishment of flood warning and flood relief centres at local government level. f. Pakistan Army. Army carries out relief and rescue missions during flood emergency, when requisitioned in „Aid and Civil Power”. It also mobilizes necessary resources for immediate restoration of infrastructure including protective embankment during and after floods. g. Emergency Relief Cell. Emergency Relief Cell is established in Cabinet Division of Federal Government. The relief cell plans for major disasters including floods by stockpiling basis life necessities required by the population affected by flooding. h. Civil Defence Organization. This organization assists local administration / Army in rescue, evacuation and relief efforts and provides manpower for flood management training in rescue and relief work. i. In addition, Provincial health, Agriculture, Livestock, Food, Communication, Works, Planning and Development departments play an important role in flood management. Flood Management. Flood season in Pakistan extends from June 15 to October 15 (4 months). Flood management during this period generally covers following:a. Preparation of flood forecasts and warnings including their dissemination to public and concerned agencies. b. maintenance and operation of various flood protection/control regulating works and management of on-line reservoirs (Tarbela, Chashma and Mangla). c. Evacuation of affected people and relief measures. Structural Measures. Flood management strategy has traditionally relied heavily on the provision of structural measures for flood containment. Structural measures includes construction of embankments, spurs/battery of spurs, dikes/gabion walls/flood walls, dispersion/ diversion structures, delay action dams, bypass structures and channelization of flood water, Approx 5,600 kms of embankments have been constructed along major rivers and their tributaries in Pakistan along with more than 600 spurs to protect these embankments. Non-Structural Measures a. Data collection and dissemination system. b. Real Time rain-fall and river flow data collection. c. Weather radar prediction. Flood Forecasting and Warning a. First step in the process is issuance of a meteorological forecast which is prepared by PMD utilizing satellite could pictures and quantitative precipitation measurements using radar data and

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conventional weather forecasting facilities. In addition, PMD also undertake statistical analysis, using past historical data to predict future occurrences of events comparing the past trends. PMD monitors weather for entire Pakistan as well as neighboring countries. It gives information regarding droughts, precipitation, flood conditions, earthquakes, etc using various sources. It obtains data from satellite images and meteorological around the country. It also obtains data from Chinese satellite exclusively launched for Pakistan by china which remains geo stationary above the region, in addition to exchange of data with Meet Departments of India, Afghanistan, Iran, China, Tajikistan and World met Organization (WMO). All data is obtained, prepared, managed and analyzed by experienced Pakistani scientists. Using various computer models recognized throughout the world. Result of this analysis is forecast of next specified period. Precision of this analysis depends upon the target recipients of weather forecast. For instance weather forecast for aviation should be very precise and should also cover certain altitude. Similarly, forecast for general public and for agriculturists would have relatively low precision but greater accuracy. Parallel to this, climatologists working in PMD cross check results obtained through computer models with classical methods of climatology in order to be certain about the forecast they produce. For quantitative flood forecasting and worming, hydrological data is obtained through the Provincial Irrigation Department, WAPDA and Pakistan Commissioner for Indus Water. Furthermore, improved rainfall-runoff and flood routing models have been developed by National Engineering Services Pakistan (NESPAK) for PMD to provide more reliable and explicit flood information to a flood prone population. WAPDA has two roles in management of floods:(1) Acquisition of flood related data from the upper catchments of River Indus and its tributaries and its transmission/ dissemination to the flood related departments. (2) Regulation and managements of reservoirs.

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Reservoir Management. Flood management of WAPDA through reservoirs in Pakistan in limited to safety of dam structures. According to the Standing Operating Procedures (SOPs) of these Reservoirs following has been observed:a. Mangla. The flood management guidelines of Mangla Dam were revised to avoid flooding in downstream area by reducing the out flow to a safe limit. Guidelines were further modified in 2002. In a model study, recorded floods (4.9 MAF) and the designed floods (4.88 MAF) were routed through Mangla Reservoir in accordance with the Dam Safety Guidelines. The Dam was found safe with the implementation of the modified guidelines. With the raising of the dam, the storage level has now gone up to 1244 feet from currents allowable limit of 1206 feet. b. Tarbela. Tarbela has a catchment of 65,500 square miles out of which 61,500 square miles is snow melt and 4,000 square miles is monsoon fed catchment. Flood history reveals that there have been two events when flood at Tarbela exceeded 600,000 lac cusecs. The historical flood was measured as 820,000 cusecs at Attock on 28 August 1929. The post flood Tarbela data indicates that 33 floods ranging from 300,000 cusecs to 530,000 cusecs have been observed since 1974. Tarbela reservoir with first impounding in 1974 had a gross storage capacity of 11.62 M.A.F. As per hydrographic survey 2009, the storage capacity has reduced to 7.94 M.A.F due to sediment. At conservation level of 1550 feet, the reservoir surface area is 100 square miles. (1) Dam Filling Criteria Safety of structure is the highest priority. Minimum Operating Level 1378 ft ASL Filling of E1 1510 feet Maximum @ 10 feet/Day (inflow>Outflow). (Up to 10 July) Filling E1 1510 feet ASL to 1550 @ 1 foot/Day feet ASL (Upto 20 August)

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Reservoir Drawdown Rate Maximum @3 feet/Day Reservoir Conservation Level 1550 feet (2) Filling Constraints – Tarbela Dam (a) Tarbela Dam has certain structural constraints which necessitate cautious and controlled filling and discharge. Critical areas are listed below:i. Main embankment dam sinkhole at Marginal Bund section. ii. Sinkhole at Auxiliary Dam-1, crossing bund section. iii. Performance of right abutment. iv. Grout curtain at Auxiliary Dam. v. Auxiliary spillway foundation. (b) The sink hole at marginal bund section is sensitive to reservoir fluctuations. The activity in the wash zone is directly related to the rate of filling/ drawdown. The tendency towards stabilization in the wash zone in hampered beyond a certain limit. Similarly excessive loading above the limit may result in development of sink holes in the core at other identical instrumented sections of Main Dam. Chashma. Chashma Barrage is operated in conjunction with Tarbela Dam. On receipt of out flow data from Tarbela and that of Kabul River at Nowshera, floods are routed through Chashma to function as barrage. No attenuation of flood is possible at Chashma due to various hydraulic constraints. As soon as the downstream flow at chashma Barrage rises to the medium flood, flood warning is sent to the downstream area through wireless station installed at Chashma.

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