The growing availability of multi-temporal satellite data has increased opportunities for monitoring large rivers from space. A variety of passive and active sensors operating in the visible and microwave range are currently operating, or planned, which can estimate inundation area and delineate flood boundaries. Radar altimeters show great promise for directly measuring stage variation in large rivers. It also appears to be possible to obtain estimates of river discharge from space, using ground measurements and satellite data to construct empirical curves that relate water surface area to discharge. Extrapolation of these curves to ungauged sites may be possible for the special case of braided rivers. Where clouds, trees and floating vegetation do not obscure the water surface, high-resolution visible/infrared sensors provide good delineation of inundated areas. Synthetic aperture radar (SAR) sensors can penetrate clouds and can also detect standing water through emergent aquatic plants and forest canopies. However, multiple frequencies and polarizations are required for optimal discrimination of various inundated vegetation cover types. Existing singlepolarization, fixed-frequency SARs are not suAcient for mapping inundation area in all riverine environments. In the absence of a space-borne multi-parameter SAR, a synergistic approach using single-frequency, fixed-polarization SAR and visible/infrared data will provide the best results over densely vegetated river floodplains. #1997 John Wiley & Sons, Ltd.

Satellite remote sensing of river inundation area, stage, and discharge: a review

The effects of dams on downstream geomorphology are reviewed and a typology is devised, consisting of nine cases. The classification can be seen as a further development of Lane's balance between water discharge, sediment load, grain size, and river slope. Depending on changes in released water flow and changes in released sediment load, relative to the transport capacity of the flow, it is possible to estimate resulting cross-sectional geomorphology. The longitudinal extent of changes and their variability with time, and the tributary response to altered mainstream cross-section changes, are also discussed.

Classification of geomorphological effects downstream of dams

In this article we investigate the complex relationship between environmental risk, poverty, and vulnerability in a case study carried out in one of the poorest and most flood-prone countries in the world, focusing on household and community vulnerability and adaptive coping mechanisms. Based upon the steadily growing amount of literature in this field we develop and test our own analytical model. In a large-scale household survey carried out in southeast Bangladesh, we ask almost 700 floodplain residents living without any flood protection along the River Meghna about their flood risk exposure, flood problems, flood damage, and coping mechanisms. Novel in our study is the explicit testing of the effectiveness of adaptive coping strategies to reduce flood damage costs. We show that, households with lower income and less access to productive natural assets face higher exposure to risk of flooding. Disparity in income and asset distribution at community level furthermore tends to be higher at higher risk exposure levels, implying that individually vulnerable households are also collectively more vulnerable. Regarding the identification of coping mechanisms to deal with flood events, we look at both the ex ante household level preparedness for flood events and the ex post availability of community-level support and disaster relief. We find somewhat paradoxically that the people that face the highest risk of flooding are the least well prepared, both in terms of household-level ex ante preparedness and community-level ex post flood relief.

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Socioeconomic vulnerability and adaptation to environmental risk: a case study of climate change and flooding in Bangladesh.

The conventional means to record hydrological parameters of a flood often fail to record an extreme event. Remote sensing technology along with geographic information system (GIS) has become the key tool for flood monitoring in recent years. Development in this field has evolved from optical to radar remote sensing, which has provided all weather capability compared to the optical sensors for the purpose of flood mapping. The central focus in this field revolves around delineation of flood zones and preparation of flood hazard maps for the vulnerable areas. In this exercise flood depth is considered crucial for flood hazard mapping and a digital elevation model (DEM) is considered to be the most effective means to estimate flood depth from remotely sensed or hydrological data. In a flat terrain accuracy of flood estimation depends primarily on the resolution of the DEM. River flooding in the developing countries of monsoon Asia is very acute because of their heavy dependence on agriculture but any flood estimation or hazard mapping attempt in this region is handicapped by poor availability of high resolution DEMs. This paper presents a review of application of remote sensing and GIS in flood management with particular focus on the developing countries of Asia.

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Application of Remote Sensing in Flood Management with Special Reference to Monsoon Asia: A Review

A growing number of cities are preparing for climate change impacts by developing adaptation plans. However, little is known about how these plans and their implementation affect the vulnerability of the urban poor. We critically assess initiatives in eight cities worldwide and find that land use planning for climate adaptation can exacerbate socio-spatial inequalities across diverse developmental and environmental conditions. We argue that urban adaptation injustices fall into two categories: acts of commission, when interventions negatively affect or displace poor communities, and acts of omission, when they protect and prioritize elite groups at the expense of the urban poor.

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Equity Impacts of Urban Land Use Planning for Climate Adaptation: Critical Perspectives from the Global North and South

Bangladesh, situated on the delta of the Ganges, the Brahmaputra, and the Meghna rivers, experiences two distinct types of inundations: (a) river floods resulting from excessive runoff contributed by monsoon precipitation and (b) coastal floods induced by storm surges of tropical cyclones. The river floods are normal annual events and human settlements and agricultural practices have adapted admirably well to their regimes. Abnormal floods that occur once in every few years cause serious damage to crops and properties. To minimize flood losses, a number of modern engineering projects have been constructed within Bangladesh. However, the successful solution of the problem would probably require some international collaboration for basinwide unified systems planning, since large parts of the drainage basins of Bangladesh lie beyond its borders. In the absence of such collaboration, internal resources should be utilized for the construction of smaller public projects, such aspolders, and for encouraging and reinforcing various types of indigenous adjustments to floods. There are very few successful indigenous adjustments to coastal floods. Most of the structural solutions, such as community shelters and higher embankments, are expensive public projects that are probably beyond the means of the internal resources of the country.

Flood problems in Bangladesh: Is there an indigenous solution?

EVERY year, almost one-third of Bangladesh is flooded. However, because of topographical characteristics, the regions of the country experience varied degrees of flooding; some parts may be under deep floodwater, others unaffected. Flooding is beneficial only within certain limits of timing, duration, and magnitude (Paul 1984; Rasid and Paul 1987). A normal flood, known as borsha in Bangladesh, generally is associated with monsoon rains that occur between June and October. The residents adjust to it as a part of life. Indeed, although normal floods may cause some damage to crops and properties, they are widely considered a blessing for agriculture, because floodwaters provide soil moisture and plant nutrients from both nitrogen-fixing blue-green algae and decomposing plant remains (Brammer 1990b, 164). Abnormal floods, known as bonna, occur once every few years and, because of their unpredictability, also inundate houses and cause serious losses to life and property. Villagers regard a bonna as undesirable (Islam 1980; Alam 1990). Although the people of Bangladesh have evolved numerous adaptive strategies to benefit from normal flooding, an abnormal one surpasses their ability to adjust. The extent of damage caused by both normal and abnormal floods varies not only spatially but also from year to year. Several studies have examined the extent of crop damage caused by flooding (Montgomery 1985; Brammer 1990a), but they have virtually ignored the temporal dimension of flood damage. The objective of this article is to study the spatial patterns of damage to rice crops resulting from flooding during a specific period, 1962 to 1988. The disastrous floods of 1987 and 1988 generated much international and national interest in finding a permanent solution to the chronic flood problem in Bangladesh. Soon after the 1988 flood, four reports were commissioned by the French and Japanese governments, by the United Nations Development Programme, and by the United States Agency for International Development (Boyce 1990, 425). At the request of the government of Bangladesh and several donor countries, the World Bank assented to coordinate the various flood-control initiatives suggested by those reports and prepared a five-year plan of action to extend from 1990 to 1995. This program, known as the Flood Action Plan (FAP), was approved in 1989 and currently is being implemented by the Bangladesh Ministry of Irrigation, Flood Control, and Water Development. FAP essentially focuses on heavy-engineering solutions. Under the plan, the two main rivers, the Brahmaputra and the Jamuna, would be embanked on both sides; later, the Padma and Meghna rivers could be similarly embanked (World Bank 1989, 93). However, opposition to a structural solution to the flood problem is strong in Bangladesh (Miah 1988; Islam 1990). Many independent experts and concerned Bangladeshi have criticized FAP because of its structural emphasis, its use of scarce land for embankment, and its ecological effects. The fear is that FAP will transform Bangladesh into a "land without water" (Islam 1990). The debate between the multitude of citizen groups and the donor agencies sponsoring FAP is yet to be resolved. FAP comprises a phased program of flood-control activities supported by surveys, special studies, and pilot projects. Different environmental and social studies have been undertaken. The next two years will be devoted to project preparation; construction of embankments will not commence until the final year. The research reported here may not influence any component of FAP, but it might suggest whether the construction of huge embankments is absolutely necessary in view of the possible long-term crop loss due to flooding. Construction of embankments will cost the equivalent of U.S.$10 billion and will require some twenty years to complete (Bingham 1989, 42); additionally, annual operating costs are projected at some U.S.$500,000. Because the lion's share of the Bangladesh national budget comes from foreign sources, the embankment proposal would require a further rise in the already severe foreign-debt burden. …

Flood Damage to Rice Crop in Bangladesh

Eliciting public preferences for municipal water supply options

This article presents the methods and results of visual interpretation of NOAA AVHRR imagery for mapping flood areas in Bangladesh. Color composites of channels 1 and 2 for 18 August 1987 and 10, 15, and 24 September 1988 were interpreted visually for delineating flood boundaries. On such imagery flood areas appear in dark tones and are separated from land (light tones) owing to the absorption of near infrared by water and its reflectance by land and non-waterbodies. Visual interpretation was aided by the use of ground information, such as physiographic and river maps, previous flood maps, newspaper reports, and other published and unpublished documents on the 1987 and 1988 floods. Interpreted flood areas on selected images ranged from 31% to 43% of the total area of Bangladesh. Visual interpretation overestimated flood areas by 5%–10%, compared to the digitally analyzed data. The main advantage of visual analysis lies in the cost effectiveness of AVHRR photographic products, which make them more accessible than the digital image analysis of computer-compatible tapes.

Visual interpretation of satellite imagery for monitoring floods in Bangladesh

This paper presents the methods and results of visual interpretation of satellite imagery for estimating areal extent of the 1988 flood in Bangladesh. The main limitation of this method was that cloud-free images were not available for the peak flood period in the first week of September. Relatively cloud-free images on three selected dates in the last three weeks of September showed that areas of inundation on those dates ranged from 44000 to 60000 km2 ± 5% (31 to 42% of Bangladesh). The Government of Bangladesh official estimates of the areal extent of flooding were tentative in nature, since these were based on a choropleth map of relative proportions (percentages) of flooding in different parts of the country. The official estimate of the maximum extent of flooding was 82000 km2 (57% of Bangladesh), i.e. 15 to 26% larger than the area shown on satellite imagery. The actual extent of flooding was certainly larger than the estimates from satellite imagery but, perhaps, smaller than the official estimates, since a reduction of 15 to 26% of flood area in one to three weeks seemed unlikely. An alternative method of mapping flood-affected areas by using newspaper-interpreted data was attempted, but the method had limited values because of reporting bias.

Harun Rasid

Papers

Flood problems in Bangladesh: Is there an indigenous solution?

Flood Damage to Rice Crop in Bangladesh

Eliciting public preferences for municipal water supply options

Visual interpretation of satellite imagery for monitoring floods in Bangladesh

Areal extent of the 1988 flood in Bangladesh: How much did the satellite imagery show?