The Indus flood of 2010 in Pakistan: a perspective analysis using remote sensing data
Kumar Gaurav, R. Sinha & P. K. Panda
Natural Hazards Journal of the International Society for the Prevention and Mitigation of Natural Hazards
ISSN 0921-030X
Nat Hazards DOI 10.1007/ s11069-011-9869-6
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Nat Hazards DOI 10.1007/s11069-011-9869-6
ORIGINAL PAPER
The Indus flood of 2010 in Pakistan: a perspective analysis using remote sensing data
Kumar Gaurav • R. Sinha • P. K. Panda
Received: 26 January 2011 / Accepted: 27 May 2011 Ó Springer Science+Business Media B.V. 2011
Abstract The Indus flood in 2010 was one of the greatest river disasters in recent history, which affected more than 14 million people in Pakistan. Although excessive rainfall between July and September 2010 has been cited as the major causative factor for this disaster, the human interventions in the river system over the years made this disaster a catastrophe. Geomorphic analysis suggests that the Indus River has had a very dynamic regime in the past. However, the river has now been constrained by embankments on both sides, and several barrages have been constructed along the river. As a result, the river has been aggrading rapidly during the last few decades due to its exceptionally high sediment load particularly in reaches upstream of the barrages. This in turn has caused significant increase in cross-valley gradient leading to breaches upstream of the barrages and inun- dation of large areas. Our flow accumulation analysis using SRTM data not only supports this interpretation but also points out that there are several reaches along the Indus River, which are still vulnerable to such breaches and flooding. Even though the Indus flood in 2010 was characterized by exceptionally high discharges, our experience in working on Himalayan rivers and similar recent events in rivers in Nepal and India suggest that such events can occur at relatively low discharges. It is therefore of utmost importance to identify such areas and plan mitigation measures as soon as possible. We emphasize the role of geomorphology in flood analysis and management and urge the river managers to take urgent steps to incorporate the geomorphic understanding of Himalayan rivers in river management plans.
Keywords Flood disaster Avulsion Embankment breaching Siltation Himalayan rivers Á Á Á Á
K. Gaurav R. Sinha (&) P. K. Panda DepartmentÁ of Civil Engineering,Á Indian Institute of Technology Kanpur, Kanpur, UP 208016, India e-mail: [email protected]
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1 Introduction
Rivers are one of the prime sources of fresh water and have played a major role in the development of human civilization. In recent years, rivers systems have been significantly impacted by human interventions as well as climate change. As a consequence of climatic change, frequency and magnitude of occurrence of disastrous floods in Himalayan rivers have increased in past 2–3 decades (Dutta and Hearadth 2004; Shrestha 2008; Khan et al. 2009). Human interventions through the construction of embankments, barrages, dams, land clearance, and landuse change etc. have also disturbed the river system in terms of sediment load and their run-off, leading to more severe floods (Ali and De Boer 2007; Walling 2008; Sinha 2009). In 2010, heavy and spatially uneven rainfall during the monsoon period resulted in flooding in various parts of Pakistan. Heavy rainfall in the upstream reaches of the Indus River such as the Khyber Pakhtunkhwa region of Pakistan followed by breaches of embankments and canals along the river course devastated most parts of Pakistan. Flood trauma of the Indus started in mid-July of 2010 and continued till early September affecting the lives of more than 14 million people in Pakistan. According to EM-DAT (2010) report, this flooding event of Indus River killed more than 1,961 people and damaged property worth US $ 9,500, 000. The UN estimated that the humanitarian crisis was much larger than the combined effects of the three worst natural disasters in the past decade including the Asian tsunami and the major earthquakes in Kashmir and Haiti. Recent increase in the frequency of floods in this region and large-scale devastation in terms of human lives and loss of property has forced the planners and policy-makers to rethink about the strategies of river management (Sinha 2010). Apart from heavy rainfall, flooding in the Himalayan rivers is strongly influenced by hydrology and sediment transport characteristics. Siltation is a major problem in rivers originating from the mountainous terrain, and the rate of siltation is known to be quite high for the Himalayan rivers (Goswami 1985). Further, flood control strategies on Himalayan rivers are primarily embankment based, which have not only altered the natural flow regime of the rivers but also affected the flood intensity, frequency, and pattern. Apart from the embankments along the river, construc- tion of various barrages across the river, unplanned construction of roads, bunds, and other public utilities in the floodplain has severely affected the natural flow of the river system. As a consequence, rapid siltation of river bed, drainage congestion, and channel discon- nectivity have been reported in these regions (Sinha 2010; Jain and Tandon 2010). In present scenario, the effectiveness of river control strategies through the construction of barrages and embankments along the river, especially for the Himalayan rivers that carry high sediment load is debatable. The Yellow River flood in 1996, the Kosi flood in 2008, and the Indus flood in 2010 are a few glaring examples of the failure of these structures during floods (Sinha 2009; Wang and Plate 2002). Construction of barrages and dams along the river for flow regulation and water diversion has caused serious problem of sediment trapping close to these structures and has also reduced the sediment fluxes in downstream reaches (Walling 2008). One of the major requirements of flood disaster management is the real-time monitoring of maximum flood extent for taking up immediate response, short- and long-term recovery, and future mitigation activities (Wang 2004). The satellite remote sensing data, due their synoptic view and repetitivity coupled with the advent of geographic information system (GIS) techniques, have proved to be extremely effective in flood inundation mapping and monitoring on real-time basis. The availability of a variety of active and passive sensors, operating in the visible, thermal, and microwave
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Nat Hazards range of the electromagnetic spectrum has shown a great promise in the delineation of flood boundary and actual estimation of inundation area in a cost-effective manner (Sanyal and Lu 2004; Smith 1997). A couple of recent studies have highlighted the use of remote sensing and GIS techniques in flood risk evaluation of one of the flood-prone rivers, the Kosi in north Bihar plains, eastern India (Bapalu and Sinha 2005; Sinha 2008) wherein an integrated approach using geomorphology, landuse/landcover, topography, and population density on a GIS platform provided a flood risk map for parts of the Kosi river. This paper presents an analysis of the Indus floods that devastated a large part of Pakistan in July–September of 2010. A systematic analysis of hydro-meteorological data coupled with satellite images and digital elevation models has provided a first-hand doc- umentation of the series of events that led to this disaster. We argue that an integrated river basin approach is crucial for flood management of such rivers, and local engineering interventions cannot provide sustainable solutions.
2 The Indus River
The Indus River (Fig. 1) is one of the largest rivers in the world in terms of its length (3,180 km), drainage area (960,000 km2), and average annual discharge (7,610 m3/s). Out of the total drainage area, about 506,753 km2 of area lies in the semiarid region of Pakistan and the rest lies in mountains and foothills (Hovius 1998; Khan et al. 2009). The Indus originates at an altitude of 5,486 m from the Mount Kailas range in Tibetan plateau on the northern side of Himalaya. The stretch from its origin to Guddu barrage in Pakistan is called upper Indus, and the stretch downstream of the barrage is called lower Indus (Jain et al. 2007). The upper and lower parts of the Indus experience very diverse rainfall pattern and weather condition. The northern part of the Indus basin is mainly characterized by high mountains and glaciers and cold-arid climatic conditions, whereas the lower part of the Indus basin experiences subtropical to tropical climate as it reaches the Arabian Sea (Ali and De Boer 2003). Barring the mountainous region of the basin, the entire Indus valley falls in the driest part of the subcontinent. Much of the flow of the Indus River originates from either glacier melt or monsoon rainfall. Summer monsoon and western disturbance in late winter and early spring are responsible for high precipitation in the Indus basin. The basin receives the highest rainfall during the monsoon season (July–September), and this often causes major flooding in Pakistan (Inam et al. 2007; Ali and De Boer 2007). The average annual precipitation of Indus region varies from 125 mm over the lower plains to about 500 mm in the upstream in Lahore (Khan et al. 2009; Inam et al. 2007). Much of the flow of Indus originates in the mountains of the Karakoram and Himalaya, and the river transports large volumes of suspended sediment. The average annual sedi- ment load of 291 million tonnes/year of the Indus ranks this river as one of the highest sediment load carrying rivers in the world. The sediment-laden water has created many water resource management problems, mainly in the upper Indus basin, and the con- struction of embankments, dam, and barrages has made the situation worse. At many locations, rapid siltation of river bed has been reported in reaches upstream of the barrage. For example, the Tarbela reservoir was accumulating sediments at the rate of 200 million tonnes/year during the nineties (Sloff 1997) (Table 1).
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Fig. 1 The Indus River in Pakistan. Major cities and locations of important barrages along the Indus River are also shown
Table 1 Drainage basin characteristics and hydrology of some Himalayan rivers Parameter Indus Ganga Kosi
Catchment area (103 km2) 960 1,073 101 Total length (km) 3,180 2,700 1,216 Average annual discharge (m3/s) 7,610 15,000 2,236 Annual sediment load at river mouth (million tonnes/year) 291 1,670 43 Discharge/area 8 14 20 Sediment yield (million tonnes/year/km2) 0.3 1.56 0.43
Source: Hovius (1998), Jain et al. (2007), Sinha (2008)
3 Data used and methods
This paper emphasizes the use of geomorphological and topographic data for understanding the causal factors of floods. Given the availability of a variety of satellite-based images and digital elevation data, it is now possible to examine the geomorphological and topographic characteristics of the region, and therefore, such studies must use these data. In the present study, we have used Landsat ETM image of year 2009 to delineate major geomorphological units of the study area. The effectiveness of the Landsat TM and ETM images due to their moderate spatial resolution and wide spectral sensitivity in visible as well as in thermal
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Nat Hazards range of electromagnetic spectrum has been addressed by various authors (Sanyal and Lu 2004; Smith 1997; Townsend and Walsh 1998), particularly in the identification of fluvial geomorphological features, flood inundation mapping, and monitoring. In present study, for the purpose of delineation of floodplain, paleochannels, and other geomorphic features, a combination of band 7 (Thermal), band 5 (SWIR), and band 3 (Red) was used. The special characteristics of complete absorption in SWIR band due to water/moisture proved very useful in discriminating moisture area from the dry land surface. Further, the SRTM digital elevation data were analyzed for understanding topographic distribution and channel network. Topographic sections were generated across the river to compare the relative elevation differences between the river bed and the adjoining floodplain. Using the digital elevation model (DEM) as an input, flow direction, flow accumulation path, and channel network around the Sukkur barrage region were generated using ArcHydro tools in ArcGIS environment. Flow accumulation map was generated with the help of flow direction map, which shows the orientation that water will flow away in any eight possible directions in a single grid (Quan et al. 2010). The basic assumption of flow accumulation grid is that water will flow upward to downward, based on which the algorithm calculates the potential of accumulation of water in each individual grid. The output cell with high accumulation shows the area of concentrated flow, and it was further used to define channel network. This analysis provided important insights to the existing cross-valley gradient vis-a`-vis down-valley gradient along the river.
4 Results and discussion
4.1 Geomorphic analysis
Figure 2 shows a simplified geomorphic map of a part of the Indus River basin downstream of Sukkur barrage prepared from Landsat image of 2009. The river has a moderately sinuous course in this reach and is embanked on both sides barring a large gap along the western embankment. The main channel belt of the Indus River shows frequent abandoned meanders. The embankment on both eastern and western sides runs very close to the present course of the river. The area outside the western as well as eastern embankments has been mapped as inactive floodplain as this is generally not flooded constrained by the embankment. There is a wide floodplain on the eastern side, which is in turn bounded by dry sand field. The western side has a wide floodplain in the upper reaches, but the river runs close to the Kirthar Range in the lower reaches and has not developed any floodplain here. Apart from the river embankments, several canals shoot off from the Sukkur barrage on either sides and run parallel to the river. A highly sinuous channel runs all along the first eastern canal, which is interpreted as a seepage channel. The geomorphic map of the parts of the Indus River plains provides important insights to the river regime. Frequent abandoned meanders and several paleochannels mapped in the active and inactive floodplains suggest a dynamic regime of the river in the past. The present-day floodplain confined within the embankments is much narrower compared with that in pre-embankment stage, and this has significantly modified the river regime. At places, the active floodplain width is less than 5 km (e.g., downstream of the Manchar Lake), and such narrow reaches, apart from the barrages, have caused severe constriction in flow that has in turn led to aggradation in the channel belt. A prominent seepage channel along the eastern canal cuts across the canal at several places and approaches the eastern embankment suggesting its subsurface connectivity with the main Indus River. This
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Fig. 2 Geomorphic map of the parts of the Indus River basin based on Landsat ETM data. Note that the river is embanked on both sides that have constrained the flow significantly connectivity may be significantly pronounced during high flows in the river and may increase the cross-valley gradient of the main river (discussed later) leading to breach of the embankment.
4.2 Hydro-meteorological analysis
The hydro-meteorological data used for the analysis included rainfall (July–August) and flood discharges at barrages. The 2010 flood in Indus started in July and continued till early September following heavy rainfall in the upper catchment. Analysis of the rainfall data published by Pakistan Metrological Department suggests that the rainfall at many stations in NWFP, Punjab, and Sindh regions during the month of July and August of 2010 was much higher than the monthly averages at these locations (Fig. 3). For example, a total of 450 mm of rainfall was recorded in July 2010 in Saidu Sharif area of NWFP that was approximately three times higher than the monthly average at this site. A similar pattern of rainfall was also observed during August in D.I.Khan, Khanpur, and Larkana regions of NWFP, Punjab, and Sindh Provinces, respectively. As a result of such extreme rainfall, the Indus carried very high discharge during this period and flow at several barrages along the Indus, namely Taunsa, Guddu, Sukkur, and Kotri barrages, not just exceeded the discharges at danger levels (typically bankfull levels) but also came very close to ‘designed capacity’ (defined as the maximum dis- charge that is likely to pass through the barrage for a given probability of occurrence) for the barrages. Further, this swollen water of Indus generated a tremendous lateral pressure
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Fig. 3 Spatial distribution of rainfall in various regions of Pakistan during the month of July and August, 2010 (a) NWFP, (b) Punjab, and (c) Sindh (Source: Pakistan Meteorological Department 2010a, b)
on both sides of its embankments. As a result, breaches in embankments and canals occurred at various places, e.g., upstream of Taunsa barrage on 3 August, Tori protective bund between the Guddu and Sukkur barrage on 7 August, and Katcha embankment near Kotri barrage on 24 August (see Fig. 1 for locations). It is important to note that the date of breach matched closely with the period of maximum flow recorded at the barrages (Fig. 4). As discussed earlier, most of these reaches have been aggrading quite rapidly due to high sediment flux and confinement due to embankments and particularly in reaches upstream of the barrages. A decline of *85% in sediment load and annual discharge of the River Indus was recorded between 1930 and 1967 after the construction of Mangla Dam on the Jhelum River (Milliman et al. 1984; Mimura 2008). A similar decline was also observed after the construction of the Tarbela Dam on the main Indus close to Darband in 1974 (Sloff 1997). This decline of sediment load suggests aggradation of the reaches upstream of the barrage thereby decreasing the carrying capacity of the river. Apart from various barrages and dams, the construction of embankments and dyke along the Indus has also contributed in siltation of the main channel. The lower reaches of the Indus is confined between embankments and levees, which has caused aggradation of the main channel and rise of river bed. A recent report (Arifeen 2010) suggests that presently only 52 of 65 gates of the Sukkur barrage are operational due to poor maintenance and heavy siltation near the barrage, and this has reduced the effective design capacity of the barrage from 1.5 million cusecs to 900,000 cusecs only. This has certainly increased the risk of breaching of the embankment and flooding in the reaches upstream of the barrage.
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Tori protective bund (breached on 7 Aug.’10)
Eastern embankment (breached on 3 Aug.’10)
7 Aug.’10 Katcha embankment (breached on 24 Aug.’10) 7 Aug.’10 24 Aug.’10
4 Aug.’10
Fig. 4 Inflow discharges at different barrages on the Indus River on different dates during the month of August, 2010. Major breaches occurred upstream of these barrages close to these dates. Design discharges for these barrages are also plotted along with discharges at danger levels (typically the bankfull level)
4.3 Flow accumulation analysis using SRTM
Figure 5 shows the flow accumulation map for the study window that was generated using the SRTM digital elevation model, which primarily provides the path of concentrated flow in the region. The output cell with high accumulation shows the area of concentrated flow (see dotted lines in Fig. 5) that was further utilized to define channel network (see solid lines in Fig. 5). Flow accumulation analysis for the study area clearly shows a very prominent flow path, apart from the main channel outside the eastern as well as the western embankment close to the Sukkur barrage. On the western side, a couple of potential flow paths exist upstream of the Sukkur barrage (see F1 in Fig. 5), which connect to the Nara Valley Drain running through Larkana, Mehar, and Johi regions of Sindh (See Fig. 1 for locations) before joining the main channel close to Manchar Lake (Fig. 5). It is important to note here that these flow paths are based on the SRTM data acquired in the year 2000. It seems that this flow path became stronger through time, and a part of the Indus channel avulsed into this during 2010 flood after the breach of Tori protective bound between the Guddu and Sukkur barrage. Figure 6 shows the progressive development of the avulsion channel between July 19 and August 7, 2010, which resulted in inundation of the adjacent areas including the important Harappan site and Mohen-jo-daro and finally drained into Manchar Lake. The new avulsion channel was *350 km long and carried a major part of the flow into the lake, which in turn was flooded extensively. Several prominent flow paths are noted outside the eastern marginal embankment immediately upstream and downstream of Sukkur (see F2 in Fig. 5). Some of these connect to the Nara canal, and others are running almost parallel to the main Indus River. With continued aggradation of the reach upstream of the Sukkur barrage, some of these flow paths may become stronger in future and may get connected to the main channel during high floods or due to a breach near the eastern marginal embankment upstream of the
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Fig. 5 Digital elevation model (DEM) of the study area generated from SRTM data. The solid lines show the Indus River and other channels along with the position of the eastern and western embankments. The dotted lines are the flow accumulation paths generated from the SRTM data, and solid lines are the existing channel network
(a) (b) (c)
1. Sukkur Barrage 2. Mehar 3. Dadu 4. Manchar Lake
Fig. 6 The Indus River flooding as seen on successive images between July and September, 2010. A breach occurred on the western flank of the river, and new avulsion channel carried a major part of the flow before draining into the Manchar Lake (Source: NASA Earth observatory 2010)
Sukkur barrage. Under such a scenario, the main Indus water may flank the eastern embankment, and the resulting floods may be disastrous as most of this region is low lying and the cities of Nawabsah, Sanghar, Mirpur-khas, and Kalohi would be threatened. Figure 5 also shows two cross-sections across the river upstream and another downstream of the Sukkur barrage based on SRTM digital elevation data of the year 2000. It is remarkable to note that the river bed is several meters above the surrounding
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floodplain in both the sections although the actual elevation may be debatable due to low resolution of the SRTM data. However, this supports our earlier observation that the river bed has been aggrading fast in recent years. Such rivers are typically referred as ‘superelevated’ rivers (Bryant et al. 1995) and are considered to be prone to avulsion. It is obvious that the present course of the river is strongly constrained by the embank- ments and swings between eastern and western embankments in different reaches. This also explains the development of cross-valley gradient and flow paths transverse to the river.
4.4 Data integration and synthesis
Our first-order analysis suggests that the causative factors of flooding in the Indus River in 2010 can be grouped as: (a) excessive rainfall and overbank flooding, (b) breach of embankment and inundation, and (c) avulsion (rapid shifting) of rivers and flooding. The control of excessive rainfall is more than obvious, and the atmospheric scientists have also termed this as an ‘unusual’ event (Dutt 2010). The influence of engineering structures such as the barrages and embankments certainly compounded the problem. The Indus is a high sediment load carrying river, and these structures have trapped large quantities of sedi- ments within the channel belt thereby raising the river bed considerably during the last few decades. The increased cross-valley gradient created the flow paths on both sides of the embankment, which eventually resulted in breaches at several points. The poor mainte- nance of the embankments could have further worsened the problem. It is important to note here that such breaches could occur at much lower discharges as well, and therefore, the identification of the vulnerable points and their strengthening should be taken up imme- diately. Our flow path analysis based on SRTM data of 2,000 has identified some of the vulnerable points but a high resolution latest topographic data would be extremely helpful to identify such points more accurately. The Indus flood disaster of 2010 has close parallels with the Kosi floods in August 2008, which occurred in the eastern India. Like the Indus, the Kosi flood was also triggered by a breach in the eastern embankment at Kusaha in Nepal, 12 km upstream of the Kosi barrage. This breach, *1.2 km long, resulted in a major avulsion of the channel on to the fan surface, and the maximum shift was recorded to be *120 km (Sinha 2010). Like the Indus, the Kosi also is a very high sediment load-carrying river, the construction of embankment and barrage had resulted in the rise of river bed level, and the river has been flowing in ‘superelevated’ condition in several reaches. As such, the river was close to avulsion threshold at several places, and the poor maintenance of the embankments added to the problem. One major difference between the Indus and the Kosi disaster was, however, that the Kosi breach occurred at much lower discharge (*144,000 cusecs) compared with the design discharge (950,000 cusecs) for the barrage and the embankment. In contrast, the unprecedented rains in the catchment area pro- duced the Indus flood. However, the breach at Kusaha in Nepal still resulted in a flooding of a very large area in Nepal and North Bihar in India, and more than 3 million people were affected by this disaster. In the following year, the local engineers executed a major restoration project was to put the river back into its pre-avulsion course. However, the physical conditions that led to this disaster remain the same. Our efforts to evaluate the flood risk of the Kosi River due to its avulsive nature are continuing, and we are currently pursuing an integrated research to understand the causative factors and to find long-term solutions to this problem.
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5 Concluding remarks
River systems are highly dynamic and integrated system, and any kind of human inter- vention on its natural process can easily propagate and impact the entire system. The recent flood in the Indus was certainly one of the biggest ‘‘human’’ disasters in recent years and was a stark sequel of the Kosi disaster in 2008 in India. These repeated events have sent out a strong signal that our flood management strategies are questionable and our preparedness to such disasters is far too inadequate. Although the extreme rainfall has been cited as the most important causal factor for the Indus floods in the media and elsewhere, it is understandable that a river like the Indus could have easily carried the resulting discharge had there been no major reduction in its carrying capacity due to its confinement within the embankments and obstacles due to the barrages. This disaster has reiterated the urgent need to move from ‘river control’ to ‘river management’ strategies, which necessitates the appreciation of the Himalayan river processes and particularly dynamics of these systems under sediment-charged conditions. We must carefully analyze the impact of engineering structures on river system in terms of natural equilibrium under dynamic conditions. Cost– benefit analysis (long term) of major interventions in the river basins and their utility in the present context should be the next step, including the impact on livelihood and ecology. Alternatives to embankments for flood management must be revisited with an emphasis on the ‘living with the floods’ concept; this may include floodplain zoning and other non- structural approaches. Basin-scale flood risk maps based on scientific data and reasoning are the needs of the hour; such GIS-based, interactive maps may utilize historical data analysis as well as modeling approaches and can be linked to an online database and flood warning system. Future research in this direction should be scientifically rewarding as well as socially relevant.
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