Structural and Non-structural measures for Flood Management

Kazi Nur Kowser Kanon

Dept of Urban and Regional Planning

Jahangirnagar University, Savar, Dhaka 

Introduction

Bangladesh, due to its unique geographical location and topography, is one of the most flood-prone countries in the world. It is affected by flash floods, rain-fed and river floods, and floods due to cyclonic storm surges (Chowdhury, 1987). Approximately 20-25% of Bangladesh’s territory is inundated during the monsoon season. Such flooding provides fertile agricultural land and the floodplains in Bangladesh are densely populated and intensely utilized. On the other hand, during the last half-century at least eight extreme flood events occurred affecting about 50-70% of Bangladesh’s territory with far-reaching negative impacts on human life and the national economy. The programs on disaster management in Bangladesh focus equally on structural and non-structural practices intended for disaster mitigation.

Flooding of different magnitude is a major hazard in Bangladesh like all other deltaic plains of the world. Bangladesh being situated at the confluence of the second largest river system in the world, via the Ganges-Brahmaputra-Meghna river system which has a catchment area of approximately 1.5 million sq. km. is highly vulnerable to recurrent flood (Chowdhury, 1987). The Ganges, Brahmaputra, and Meghna Rivers in India and Bangladesh are some of the most flood-prone river systems in the world Excessive floods present serious risks to the millions of people living in the floodplains. In a normal year an estimated 25 percent of Bangladesh is flooded, and in an excessive flood year, up to 65 percent of the country is flooded (http://www.riverside.com/). About 20 percent of the country is regularly inundated even, severe periodic flooding is common. Since 1954, flooding has covered 37 percent of the land once every 10 years (Chowdhury, 1998). The highest was in 1998 when 68 per cent of the land was inundated.

Nowadays, it is increasingly recognized that disaster management needs to be incorporated as an integral part of the development plans to sustainable development. Bangladeshis and their government are doing their best to prevent and mitigate natural disasters, but there is an overwhelming need to strengthen the structural and non-structural disaster mitigation tools like institutional arrangement, community awareness and warning system as well as disaster preparedness and management capabilities.

However, Flood and other natural disaster cannot prevent but it can be mitigate by disaster management and its damage can be minimized by undertaking appropriate non-structural measures along with structural measures. Disaster management is a very broad term and it includes all aspects of planning and responding to disasters, including both pre-, during and post- disaster activities. It refers to the management of both the risk and the consequences of a disaster.

Objectives:

·         To find out the causes and effects of flood in Bangladesh

·         To evaluate the existing structural and non-structural measures for flood management in Bangladesh

·         To identify the role of structural and nonstructural measures in flood management

Methodology:

It is involves the techniques of the method of conducting survey, map collection, analysis of essential data and information. Most of the data are collected from the secondary sources. The secondary information was collected through the survey of literature on the study and also on through surveying relevant published and unpublished materials such as standing order of disaster management, Annual reports of NDP, books and journals, Unpublished MSc thesis and report relevant to the disaster management etc. Information of flood management is collected from Disaster Management Bureau. Main concern to find out information the structural and non-structural measures of flood management. The problems are identified and solutions are given on the basis of data and information.

Causes of Flood

When it rains or snows, some of the water is retained by the soil, some is absorbed by vegetation, some evaporates, and the remainder, which reaches stream channels, is called runoff. Floods occur when soil and vegetation cannot absorb all the water; water then runs off the land in quantities that cannot be carried in stream channels or retained in natural ponds and constructed reservoirs. About 30 percent of all precipitation is runoff, and this amount may be increased by melting snow masses. Periodic floods occur naturally on many rivers, forming an area known as the flood plain. These river floods often result from heavy rain, sometimes combined with melting snow, which causes the rivers to overflow their banks; a flood that rises and falls rapidly with little or no advance warning is called a flash flood. Flash floods usually result from intense rainfall over a relatively small area. Coastal areas are occasionally flooded by unusually high tides induced by severe winds over ocean surfaces, or by tsunamis caused by undersea earthquakes.

Floods are regular phenomena in Bangladesh during monsoon. Every year during May-October period Bangladesh is generally visited by floods of two types -floods due to gradual rise of water level in rivers and canals, and flash floods due to heavy rains in hilly areas. Due to intensive rains in upstream in Khasia-Jaintia, Garo and Tripura Hill Tracts regions in border areas outside Bangladesh there is sudden upsurge of water in rivers and rivulets resulting in sudden increase of water level inundating river banks thereby creating sudden floods causing immense loss to households, crops and lives and properties. In some areas intensive rainfall locally causes flash floods. 

The location of Bangladesh in the delta coupled with the strong monsoon rain make it extremely vulnerable to recurring floods. The annual rainfall of the country ranges from 2300—5000 mm and 80% of annual rainfall occurs during the monsoon months (Jun-Sep). Eighty percent area of the country is located within the floodplains of three great rivers; the Ganges, Brahmaputra and Meghna, and their tributaries, such as the Teesta, Dharla, Dudhkumar, Surma and Kushiyara. Out of the 230 water courses in the country, 57 are Trans boundary Rivers coming essentially from India and about 93 percent of the catchments areas of the rivers are located outside the country (http://www. wca-infonet.org). Only 7% of their huge catchments areas lie in Bangladesh. The major rivers have a length of 500 to 2500 km and width range from 1 km to 20 km, with very flat slopes

Fig: Flow Distributions in Bangladesh from GBM basins

These factor all together causes flooding in Bangladesh almost every year. However followings are the major cause of flood in Bangladesh-

å  Low general topography

å  Right Embankments and breaches in internal polder embankments and drainage congestion preceded by high flows in the major rivers

å  Flash floods on trans boundary rivers, local intense rainfall, impeded drainage and drainage congestion on the major rivers

å  High inflows through the Ganges and the Brahmaputra and surges

å  Due to landslides in upstream the alluvial soil raises the bed of rivers and canals.

å  Blockade of natural drainage of water due to unplanned population settlement and construction of embankments.

å  Formation of shoals in rivers and sand beds.

å  Increase of sea level and its effect in low-lying areas.

å  Excessive melting of snow in the Himalayas.

å  Human interventions in all the major rivers in the form of building embankments, dams and barrages have shrunk the natural flood plain.

å  The sedimentation has been worsened by deforestation in Nepal and India. It causes more soil erosion and less surface retention of rain by the leaves of the trees and loose ground cover materials.

å  Change in the natural drainage pattern due to development activities. Both the intensity and the duration of flooding might have increased due to unplanned construction of roads and railway tracks. They have compartmentalized the countryside and disrupted the natural flow of water out of the flooded land.

Effect of Flood

Floods can bring a negative impact, including the loss of life and property. Floods not only damage property and endanger the lives of humans and animals, but have other effects as well. Rapid runoff causes soil erosion as well as sediment deposition problems downstream. Spawning grounds for fish and other wildlife habitat are often destroyed. High-velocity currents increase flood damage; prolonged high floods delay traffic and interfere with drainage and economic use of lands. Bridge abutments, bank lines, sewer outfalls, and other structures within floodways are damaged, and navigation and hydroelectric power are often impaired. Each year, financial losses due to floods are considerable. Major negative effects of floods are:

Destruction of agricultural plantations: Crops die in the prolonged accumulation of flood waters in the plantation areas. Rubber, cocoa, palm oil and rice are among the agricultural crops which cannot survive in such conditions. Such damage is a loss for farmers.

Destruction of property: A torrential flood can sink and wash away homes as well as damage various other properties such as electrical goods, vehicles and the like. This is a loss for residents.

Diseases: The worst effect of floods is on one’s health. Floods can cause the accumulation of human waste in the flood waters. These flood waters can spread to other areas, resulting in diseases such as cholera and malaria.

Deaths: Floods often result in loss of life especially in low-lying areas and along river banks.

Loss to Government: Floods damage public property such as roads, buildings, and telephone and electrical infrastructures. Floods can also bring about many kinds of diseases. The responsibility of repairing the damages and subsidizing medical equipment must be borne by the government. All these involve high maintenance costs. The government must also supply basic necessities such as food, drinking water and medicine, and set up temporary shelters for flood victims.

Some of the positive contribution may also be cited below:

i) Land building in the flood plains due to siltation;

ii) Natural fertilization of the flood plain lands;

iii) Increased recharge of the Groundwater;

iv) Availability of abundant soil moisture during post flood period;

v) Increase in production of fish, etc.

In case of severe floods, the negative effects always outstrip the benefits. But normal flood usually contribute to the positive benefits.

Structural Measures

Structural measure refers to those disasters management or mitigation tools which have physical entity such as embankment, flood or cyclone shelter, dam etc. A measure to control the physical process of flooding. Structural measures with adequate appurtenant structures and proper water management practices create condition for increasing productivity from land and other developmental activities. Structural measures aim at protecting an area up to certain level of flooding. It can be divided into five categories: (a) Storage reservoir or basins to restrict overflow. (b) Retarding basins to lower the flow of flooding. (c). Levees and floodwalls to confine floodwaters. (d) Improvement of channel capacity. (e) Some structural measures such as Flood Embankment, Channel Improvement, River Training, Coastal Embankment etc. to combat the flood sufferings. Among these structural measures, construction of embankment is most popular and very old practice in Bangladesh.

There are some options of structural measures-

å  Dams and Reservoirs for impounding excess runoff. Detention basin, Retention Pond to lower the level of flooding downstream. (Not feasible due to topographical limitation.)

å  Embankment, Dyke, Polder, Levee, Bund, or Flood wall to block the movement of water from rivers to floodplain. (most preferred option)

å  Improvement of Conveyance Capacity (planned but not done due to cost element)

å  Flood bye pass, flood diversion ( not feasible)

å  Watershed Management and afforestation (not practiced.)

Non Structural Measures

This option consists of the Flood Plain Zoning & Management; Policies for infrastructure Planning and Development in the flood plains; Flood Proofing; Disaster Preparedness & Response Planning and Flood Forecasting and Warning. Non-Structural Measure to reduce loss or damage by administrative measures. It does not control or affect the process of inundation. Non-Structural measures includes flood forecasting and warning, flood fighting, flood proofing, evacuation and shelter management, flood insurance. Some of the nonstructural measures are: (a) Raised community areas with basic human needs. (b) Home placed at higher elevations and built with flood resistant materials. (c) Flood resistant infrastructure to continue critical services during floods.

Non-structural measures such as flood forecasting and warning were later incorporated as it was felt that structural measures alone could not mitigate flood problems.

Non-structural mitigation measures undertaken by the GoB focus on preparedness and possibilities for action to reduce risks and losses and better co-ordination mechanisms between all actors involved (GO, NGO and community people at grass- root level) during all phases of any disaster. The non-structural disaster management consists of the following tools-

å  Legislation, Policy and Planning

å  Training and Public Awareness

å  Institutional Arrangements

å  Flood Warning System

å  Local Disaster Action Plans

Some non-structural measures

å  Flood forecasting ( done) and warning.(poor practice)

å  Flood fighting (a success around cities)

å  Flood proofing (traditional practice)

å  Evacuation and shelter management ( a success story, standing order of GoB)

å  Flood insurance

å  Floodplain zoning

å  Changes in cropping pattern

FLOOD MANAGEMENT ROLE IN BANGLADESH

The issues of flood management should be considered from different angles of improvement of quality of life, impact on physical environment, socio-economic condition and environmental preservation etc. It is usually found that different methods or techniques are practiced in different parts of the world to tackle the flood problems.

Structural Measures

In Bangladesh it is being some structural measures such as Flood Embankment, Channel Improvement, River Training, Coastal Embankment etc. to combat the flood sufferings. Among these structural measures, construction of embankment is most popular and very old practice in Bangladesh. This is also a very cheap method compared to other structural measures. With the experience over the last few decades, it was observed that the structural measures do not usually bring only blessings. They also have adverse effect. The adverse effects always do not appear shortly after their construction but become apparent with the elapse of time. They are engineering constructions, improvement or change in agronomic practices and watershed management. These options are now being practiced in Bangladesh to modify the flood and to combat the adverse effects of flood. It is found that some of this method is very cheap compared to other methods. Adoption of change in agronomic practices or watershed management requires very high level of community participation. Community awareness campaign is very important in this regard.

Non-Structural

This option consists of the Flood Plain Zoning & Management; Policies for infrastructure Planning and Development in the flood plains; Flood Proofing; Disaster Preparedness & Response Planning and Flood Forecasting and Warning.

Due to increased population pressure it is a typical scenario in Bangladesh that the human habitat is extending more and more towards flood plains, which are vulnerable to recurrent flood. Moreover, more lands of the flood plains are being occupied and converted to habitat and agricultural lands, which were mostly, back swamp. Flood plains are generally regarded as the extended portion of the main river channel. During high flows, the flood plains often act as temporary detention basin as well as conveying excess water to the downstream. Due to increasing occupation of the flood plains for the reason mentioned above, the areas for temporary detention basin as well as conveyance of the flood flow is seriously restricted. As a result, the recurrence of flood is increased along with the flood damage. Flood plain zoning and management is the effective means of regulating habitat construction and agricultural use with minimum interference to the natural condition prevailing in the flood plains.

Due to a swell in population in the flood plains, the governments are bound to undertake more and more development projects in the flood plains. With experiences of construction of different infrastructure in the flood plains, it is often seen that flood vulnerability increases. It is now strongly felt that appropriate policy formulation is needed for infrastructure planning and development in the flood plains to avoid adverse environmental impacts and to lessen the flood vulnerability. Policy formulation should be on the basis of scientific study and research. Bangladesh Government has already finalized Flood Management Strategy in 1995, National Water Policy in 1998 and National Water Management Plan in 2004.

Flood proofing is a measure, which has been found to have less adverse effects. In most of the flood prone areas in Bangladesh, the people used to flood proofing technique in such a way that people build their houses on the built-up earthen mounds. This is being in practice for centuries. Community participation and awareness are very important in the flood proofing measures.

Many of the damages of the floods can be reduced to a great extent through a proper Disaster Preparedness and Response Planning, which is unfortunately lacking in most of the LDC’s (Least Developing Countries) and the Developing Countries. With the increased awareness on this issue, Disaster Preparedness and Response Planning in many countries are being improved. For the Disaster Preparedness regarding the flood, the most important tool is the Flood Forecasting and Warning System. If the flood depth and duration can be forecasted well in advance, the vulnerable communities can be altered beforehand. This will again help the disaster managers and the communities to formulate their own strategies to cope up with the flood. With the current advancement in the information technology and hydrological and hydraulic sciences, it is possible to provide most accurate advance warning. It is now found that if advance warning is not sufficient, the dissemination of information to the people in the flood prone areas is no less important. In this regard assessment of response of the people to the flood warning is very important element in response planning. Disaster Preparedness programme cannot be made successful without proper response planning.

Conclusion:

As Bangladesh is one of the most disaster prone countries of the world, with extremely limited resources; its real development is not possible without the integration of disaster mitigation programs. The existing system for disaster management in the country covers activities at normal times for important disaster management aspects like mitigation /prevention, preparedness, response and recovery. Disaster management has become an event rather than process of development.

Flood management activities should not be a stand-alone approach but rather an integrated approach, Flood management should a combination of both structural and non-structural measures. The process of flood management should be a participatory one; especially communities should be pro-actively involved. Flood management activities should be sustainable. Technical considerations should not preclude socio-economic considerations. Flood management should directly contribute to poverty reduction or alleviation in the developing countries.

Since Bangladesh is a small part of a larger hydrodynamic system that comprises several countries in the region, mutual understanding and cooperation among the co¬riparian countries will be necessary to formulate any long-term and permanent solutions to the flooding problems. However, following key issues should carefully consider for better flood management-

å  Continuous evolution of flood and water management policy

å  Adverse impact of structural flood management measures on agriculture - particularly regarding impact on crop diversification - and fisheries

å  Increased emphasis on non-structural measures and the involvement of communities in flood management activities

Reference

·         Chowdhury, J. U., 1987, Flood Problems of Bangladesh (Proceedings of the US- Asia Conference on Engineering for Mitigating Natural Hazard Damage, Bangkok).

·         A Review of Flood Management in Bangladesh. Retrieved June 4, 2014 from: http://siteresources.worldbank.org/EXTWAT/Resources/4602122-1213366294492/5106220-1213804320899/21.0Flood_Mitigation_Bangladesh.pdf

·         Bangladesh Bureau of Statistics (BBS), 2009. Statistical yearbook of Bangladesh. Statistics Division, Ministry of Planning, Government of the peoples’ Republic of Bangladesh. Dhaka.

·         IOP, 2009.Adaptive measures for coping with increased floods droughts in Bangladesh (IOP Conf. Series: Earth and Environmental science 6, 292001, 2009).

·         Ahmad. M., Lmamuddin. M., 2001, Floods in Bangladesh and their processes (Disaster in Bangladesh: Selected Readings, Dhaka: Disaster Research Training and Management Centre, Dhaka University).

·         Flood Management in Bangladesh. Retrieved June 4, 2014 from:

             http://www.scribd/doc/9865476/flood-management-in-bangladeshp_pdf

·         1998 Flood Damage Assessment of Water Sector Infrastructure (Ministry of Water Resources, Government of the People Republic of Bangladesh, 1998).

·         The World Bank and Bangladesh Centre for Advanced Studies, 1998. Bangladesh 2020: A Long-run Perspective Study ( University Press Limited, Dhaka, Bangladesh).