LITERATURE REVIEW

LIST OF PLATES

CHAPTER 3 LITERATURE REVIEW

Some studies have been done on coastal embankment projects in Bangladesh, which are briefly reviewed, hereafter. It is important to note that no study was conducted specifically for coastal embankment in the study area, Chittagong.

3.1 Coastal Embankment Project (CEP) : Engineering and Economic Evaluation (1968)

The hIstory of coastal embankments in Bangladesh traces back as early as during the British Emperor in India. The Zaminders (landlords) used to construct low height embankments to protect agricultural lands from periodic saline water flooding during normal high tides, and the farmers were to pay taxes for it. The embankments suffered from frequent flooding due to their low height and provided partial protection fro~ flood (Williams, 1991).

After the abolishment of Zaminder systems in 1950, the then East Pakistan Water and Power Development Board (EPW APDA) launched a project named 'Coastal Embankment Project', aimed at increasing crop production through protection of agricultural lands from saline water inundation during normal high tides. This project covered 13765 sq.km area of which 71% were agricultural lands. A maximum normal flood of 20-year return period was considered as the design flood. The project extended from the Haribaghna river near India border to the border Makam south .tip of Bangladesh stretching along the 710 km shoreline (EWAPDA, 1968). The project area was divided into three regions. Eastern region cover 1133 sq.km extending from Chittagong to Arakan Hill Tracts.

Central region or estuary is of funnelled apex shape of Bay of Bengal covering 3360 sq.km. The rivers in this region are characterized by their high rate of erosion and siltation. Western region is formed by the deltaic action of Ganges-Brahmaputra-Meghna comprising of an area of 9271 sq.km.

As shown in Table 3.1, under this project a total 4037 km earthen embankment, 1039 drainage sluices were constructed for 108 polders (closed earthen embankment).

Three types of embankments exist in the coastal area of Bangladesh. Larger embankments are situated along the side of Bay of Bengal and major rivers where high waves and currents are expected. Interior embankments are along the bank of rivers where moderate waves and currents persist. Marginal embankments are provided along the bank of small rivers and streams of minor waves and currents.

As shown in Fig.3.1 and Table 3.2, the embankments have dimensional variations in height, width, slopes according to their purposes.

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Typical Sections of Different Types of Coastal Embankments in Bangladesh (Source: EPWAPDA, 1968)

For the selection of embankment height, annual maximum water levels between 1960 and 1968 were analyzed, and a 20-year return period maximum water level during monsoon was used.

Embankments and Drainage Sluices under CEP (EPWPDA, 1968) Table 3.1

Region Regional area (sq.km) Length of Number of sluices

embankment

Eastern Region 1133 523 200

Central Region 3360 542 156

Western Region 9271 2972 683

Total 13764 4039 1039

Table 3.2 Design Features of the Coastal Embankments

g

Embankment type Sea side Country side Crest width Crest level (m) Set back

slope slope (m) distance

Sea dike 1:7 1:2 4.27 x'

+

1.52 76

Interior dike _-- 1:3 1:2 4.27 x

+

0.91-1.52 53

Marginal dike 1:2 1:2 2.44 x

+

1.52 38

x ,s the des, n tlood level

Materials from borrow-pits along the sides of the embankments were used for embankment construction. Sands and organic materials were avoided. A blanket of cohesive earth over the embankment was provided to encourage good turfing and to prevent surface erosion where the embankment materials are not of good condition.

The inner slopes and crest levels of all types of embankments was protected from erosion, due to rainfall, with the use of grass mat. Depending on the purpose, there is a variation in the sea or river facing slope protection work from wave and current erosion. Following are the protection works applied to the embankments facing high wave and heavy currents.

(a) In some places, from the top to the toe of the embankment, pre-cast concrete blocks of size 0.63mxO.63mxO.39m were provided on khoa filter of thickness 0.63m. In some locations, the joint between two successive blocks were kept open while in other locations they were joined with cement mortar. In some other places, embankment was protected by toe wall and in-situ concrete apron blocks of size 1.27mx1.27mxO.6Im. The provisions are for protection of 1:5 slope .

. (b) Slope protection with 3.4 layers of bricks, set with cement mortar between successive layers, was provided. In some places full coverage of protection from top to the toe of the embankment while for other places coverage on only the toe was provided.

20

(c) Some parts of the embankment were protected only with rubble stone.

At planning stage, due to inadequate and lack of environmental data, the probable impact of the project on environment was assessed based on anticipation. Since the assessment of impacts was based on anticipation, the study did not go into the quantification even interms of degree. Thus this is an initial environmental impact assessment on the basis of judgement and anticipation. The study evaluated the project to be feasible to benefit the population in the project area. On the basis of feasibility study, as was made for the CEP project, a short list of environmental consequences has been prepared as presented in Table 3.3. As can be seen from the table, the study found 9 major positive impacts, 3 negative impacts, and 3 having both positive and negative impacts. This is an overall assessment of the project. It is also seen from the table thai the most of the adverse impacts arising out of the project implementation are related to waterlogging. Waterlogging is the problem created due to change in morphology of the river as a result of river erosion and accretion. This impact was not evaluated in the study.

After the construction of the embankments, they brought benefit to the project areas. But in long-term they have been proven to cause harm to the project areas. Some polder areas are left almost without cultivation. Beel Dakatia is one of the polders under 'CEP' in the coastal area where environmental degradation by the project is beyond assessment and imagination. Waterlogging is a permanent problem there and crop cultivation is almost impossible now. This has caused adverse social impacts such as, creation of jobless people, change in public profession, paralysis of normal communication, social culture, human health, collapse of education systems. The socio-economic structure has collapsed in this project area. People in this area cut the embankment at several parts to aid natural gravity drainage. But as with long-term effect flood-regime has already changed, such embanlanent cut is not effective to alleviate waterlogging in the project area. The environmental process is irreversible and irrecoverable. From the environmental point of view all the project areas do not behave similarly.

CEP Environmental Impact Assessment and Present Condition Table 3.3

Parameters CEP Assessment Remarks on the basis of

embankment performance

Climate No noticeable effecl. Change In climate is almost

insignificant due to such regional flood protection.

Cyclone Area can be protected from surge inundation of

Small scale cyclone protection was

marginal magnitude. possible by the embankment.

Embankment gave minimal protection against surge flooding with large scale and through own destruction.

Table 3.3 continued

Parameters CEP Assessment Remarks on the basis of

embankment performance Flood runoff & No significant effect; increase in water levels in Waterlogging in some project area tidal levels confined river channels is anticipated to be less for change in river morphology

than inches. which eventually has paralysed

gravity drainage. In some areas reduction in river/channel waterlevel due to close in river inflow by embankment.

Salinity No significant effect on the pattern or degree of Surface water salinity seems to be incursion salinity. Salinity incursion during low flow reduced by protection of tidal saline

seasOn is expected to be reduced within the flow.

project area.

Depletion of A depletion in upstream flow would increase in Salinity increased due to unusual upstream flow salinity into eastern Khulna and Western withdrawal of surface water from

Bagerhat circles outside the project area upstream.

Water quality Water quality in surface streams will remain Water quality improved as a result of .. unaffected, but within project area would be tidal flood protection and protection

improved because of elimination of salinity of cyclonic surge flooding of

intrusion. marginal scale.

Sedimentation Project work would have ntinor effect upon this In the longterm, sediment and

& erosion element. erosion pattern has changed the river

morphology which has rendered drainage sl u ices/regul ators inoperative causing permanent waterlogging in the project area.

Population Population is expected to rise from 900 persons Population increased in the project per sq.km in 1961 to 1800 persons per sq.km area. Thus after the construction of within 20 years, in the project area. Positive in the embankment, more people are the sense that the project would harbor an vulnerable to surge during cyclone.

increased population in the protected area;

negative in the sense that probable breach in embankment during cyclones would cause damage to more human lives than before.

Soil quality Soil quality is expected to improve as a result of Soil quality degraded in some project tidal flood protection. areas due to permanent waterlogging;

more use of chentical fertilizers, pesticides, herbicides following the project.

Farm size The average agricultural farm size 0.019 sq.km Farm size decreased.

would be reduced due to increase in population.

Food grain Rice production in the project area will increase Crop production increased sharply requirement from 0.8 million tons in 1966 to 1.6 million ton immediate after the project. In

in 1986. longterm some project areas became

uncultivable because of permanent waterlogging.

Salt production Benefit will result from the prevention of high Salt production increased.

tidal flooding.

22

Table 3.3 continued

Parameters CEP Assessment Remarks on the basis of

embankment performance Fisheries A declination in fisheries in the project area is Openwater fisheries declined. Shrimp

expected. culture abruptly increased after the

project which has been an imponant source to earn foreign exchange, although , it caused some social conflicts and damage to crop production.

Transponation Boat communication will be disrupted, but road In some project area road communication will be improved. communication network, in long-

term, completely broke down

because of permanent waterlogging.

In some project area, road communication improved.

Agricultural Current agriculturallanduse of 1000 sq.km will Overall agricultural landuse landuse be projected to 10364 sq.km in future due to increased.

-

improvement in flood condition in the project area.

Crop pattern No significant change except a small increase in Crop pattern remained almost

Rabi crops and fruits. unchanged.

Cropping Cropping intensity will increase from 105% to Cropping intensity in most of the intensity 138% due to more double cropping of Aus project areas increased.

paddy and Rabi crops after the project implementation

Crop yield Crop yield will increase from 102 to 203 tons Crop yield increased due to

per sq.km. cultivation of high yield crops.

3.2 Enviromnental Impact Assessment for Cyclone Protection Project (1992)

The flood due to 1991 cyclonic surge had damaged 14,000 human lives in the coastal area. The government took initiative to save human lives and cattleheads by raising the existing embankment in the coastal areas. An assessment of environmental impacts of the existing embankments was emphasized before raising them. The main objective of this study is to assess the possible environmental impacts of the project. With this objective, the study covered an area of 4000 sq.km under 31 BWDB polders (embankments) (BWDB, 1992). The environmental impact assessment was conducted through collection of data from secondary sources and report reviewing. An overall view of the impacts were discussed rather than impacts for individual polder. This major shortcoming of the study prevented the use of the study results for specific polders individually. The salient features of the study are given in Table 3.4. It can be seen from this table that the embankment project has 7 .negative impacts, 2 positive impacts and 2 having both positive and negative impacts. It can be inferred from the table that the project is not environmentally sustainable. Again it can be note down

that most of the adverse impacts of the project are related to waterlogging which is as a result of change in river morphology as a consequence of longterm erosion and accretion around the polders.

Table 3.4 Presentation of Environmental Impacts as Assessed In the Study 'Environmental Impact Assessment for Cyclone Protection Project'

Parameters Environmental Assessment Comments/Remedies/Measures

Embankment Embankment will save approximately 3.4 Benefit will be only from embankment of million (m) human, 0.8 m livestock, 0.5 m sufficient strength against cyclonic surge.

homesteads, agriculrural crops of 0.6 m tons; Otherwise, damage to human lives and besides, fish farms, fish ponds and open fish canleheads will be more than 'without culture, roads, bridges, culverts, wild and embankment' condition.

aquatic lives from cyclonic storm surge.

Accretion Accretion around the embankments will cause An alternative approach other than a deep pool of water inside the polders drainage regulators/sluices should be causing a permanent waterlogging. adopted to alleviate waterlogging, if such

accretion occurs.

Erosion Erosion around the embankment will cause a River bank protection should be properly .' shifting of embankment. taken to avoid shifting of embankment.

Navigation Due to protection a flood in the project area, Provision for available surface wat~r in a water scarce in the rivers, channels and the rivers/canals through permitting water bodies will cause navigation problems sufficient inflow through regulators/sluices resulting in communication disruption; boat is to be adopted. Otherwise, road communication to the major rivers and communication should be improved as a channels may also be disrupted for the substitute of boat communication.

embankment.

Soil growth A loss in micro-nutrient that used to come This is likely to be insignificant as tidal before embankment may cause to loss in soil saline water is intensively harmful to crop fenility and thus crop yield. Flood protection production. Reduction of soil growth with stops the soil growth on agricultural lands. micro-nutrient can be compensated with better farm management and change in cropping pattern.

Agriculture More crop production through the protection It is only possible when proper flood of the area against saltwater inundation protection is achieved.

during normal high tides and extreme cyclones.

5 h r i mp Positive in the sense, shrimp culture within The existing shrimp culture activities in culture the project area would earn foreign exchange; the coastal area are not good which have

negative in the sense that it may promote caused low yield,a number of social cutting of the embankment illegally for conflicts including forest and crop allowing saltwater intrusion by shrimp damage. Scientific approach should be cultivators, causing an increase in salinity of taken to have high yield per hectare of soil which eventually cause to destroy the land under cultivation. To eliminate social forests, grazing lands for cattle, high conflicts and crop and forest damage, a mortality rare in cattle due to some diseases plan should be taken to identify the most related to salinity increase, agricultural crop effective shrimp culture area where forest and freshwater fish reduction and above all a area are minimum and rhat agricultural severe conflict between the farmers and crop production is low. Area with high

shrimp cultivators. saline water is favorable for shrimp

culture, and such area is not good for crop production.

24 Table 3.4 continued

Parameters Environmental Assessment Comments/Remedies/Measures Irrigation Due to protection against flood, and Irrigation using groundwater can be done water reduction in wet lands, scarcity in surface incase of an area where surface water is

water would cause irrigation problem; scarce. Groundwater availability should be sometimes embankments may be cut for ensured to avoid public cut of irrigation water from major rivers/channels embankment.

outside the polder.

Fisheries Reduction in floodplain though flood A negative impact on fisheries can be protection and scarcity of surface water and compensated by improved shrimp cullUre, water flow disruption will decline openwater and cultivation of other fisheries in the

fisheries. closed waterbodies of the protected area.

Forestry Loss in forestry because of shrimp cullUre, Loss of forestry can be minimized if population migration, more agricultural area shrimp culture area can be properly for the purpose of HYV crop cultivation. identified where forest areas are

minim,um.

Flood The area will be free from flooding. But, due Risk of embankment fail,ure can be to flow confinement, the area outside the minimized by proper design, construction polders would be flooded more, Risk of and maintenance works.

embankment failure leading to damage to human lives and cattleheads as well as to economy.

3.3 Multipurpose Cyclone Shelter Program (1992)

, As reported earlier, the 1991 's cyclone in Bangladesh is a catastrophic havoc to the country. Beside the embankment, to save human lives and cattle heads, the government took a plan to give shelters to the local people in the surge prone areas to save their lives. With this view, BUET and BIDS (1992) jointly conducted a study named 'Multipurpose Cyclone Shelter Program'. The view of the construction of multipurpose cyclone shelters is that they will give shelters to the people of thei~

catchment area during cyclone, and will be used for school and other community purposes during normal time. The main objective of this study is to formulate a plan dealing with identification of mostly and severely cyclonic surge affected areas. Shelters are to be constructed in these areas to save human lives and cattleheads from surge flooding. A number of supporting studies have been carried out to locate the shelters.

The study deals with the delineation of risk zones, hydrometeorological analysis, existing public and private buildings and feasibility of their conservation, methodology for preparation of maps, communication network in the coastal area, methodology for locating of new shelters, initial environmental evaluation, and consultation with the local people in the planning process. The salient features of the hydrometeorological study and delineation of risk zones are illustrated in the following.

The hydrometeorological study incorporated rainfall analysis, determination of rainfree construction period, frequency analysis of cyclonic wind speed, maximum wind speeds, extreme temperature,

maximum surface water levels, and statistical analysis of groundwater level for different important stations in the entire coastal regions. The areas covered with cyclonic surge water are termed as Risk Zone (RZ) and a part of RZ where damage to human lives is likely is termed as High Risk Area (HRA). It is anticipated that as much as the water level below the waist of an adult man, he can move desperately through surge water. So the surge water depth, I m which is equal to the average waist height of an adult is the criterion of the delineation of HRA, i.e, the inland area with upto I m cyclonic surge depth is the HRA. The RZ and HRA delineation are based on the storm surge analysis. The storm surge analysis covers a better understanding of the generation and propagation of cyclonic storm surge in context of Bangladesh. Surge heights for various return periods in different coastal regions have been predicted. The study presents a detail procedure for setting ground floor level of the shelters in the surge prone areas. The study found that although the major embankments along the Bay of Bengal and major rivers are incapable of working against flooding, some interior and marginal embankments protected some areas from flooding of minor rivers during cyclones. This is as a result of reduced surge height and strength after travelling overland. The environmental consequences studied here are out of the implementation of multipurpose cyclone shelters only and so are not discussed here.

3.4 Cyclone Protection Project(1992)

It is important that protection be provided against cyclonic surge flooding. It has been proposed that the existing embankments height be raised to achieve the above objective. 'Cyclone Protection Project' study covers the existing polders in the coastal area. An evaluation of the status of existing embankment alongwith possible damages to the embankment, was studied in this project. The study simulated 7 selected major cyclones and predicted surge heights for the design of coastal embankments that might face cyclonic surge directly (BWDB, 1992). It also predicted the annual normal maximum water levels for different return periods. These results were then used for the evaluation of existing embankment status and for the estimation of different types of possible damages. The study did not go into detail evaluation of the embankments in the study area, Chittagong, and it did not incorporate the environmental consequences of the same embankment. The major findings of this study are that the existing embankments are quit unable to protect cyclonic surge flooding as they were solely constructed for periodic tidal flood protection. Even some of the embankment are unable to protect tidal flooding as they are in very poor condition interms of their low height and slope protection work. They are unjustified to raise their height against surge flooding

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in the point that they were not compacted when constructed and poor construction materials were used in their construction.