Decision makers worldwide face a difficult challenge in developing an effective response to the threat of water-induced disasters. After prayers to the rain gods, answered in excess in parts of our country, now the focus has shifted to floods. Many states in our country are flood prone due to heavy rain or otherwise. The flood causes loss to human life and wide spread damage to property. Unimaginable damage to agriculture takes place affecting the States planning and upset the financial budgeting there by slowing down the whole economy of the country. People not affected by the flood tend to ignore the event thinking that it does not affect them so why bother? Flood is not unique to India. Floods come in different parts of the world. Floods are the biggest cause of loss of life every year throughout globe. Majority of countries do not document or map floods methodically. Flood affects many areas of national economy. Following are some of the areas needing attention from government bodies [1].

• Agricultural Damage

• Commercial and Industrial Damage

• Residential Properties Damage

• Transportation Damage

• Man and Livestock Damage

• Flat Land

River Silabati and Dwarakeswar meet at Bandar, and the combined flow is named as Rupnarayan, which joins river Hoogly at Geonkhali covering a distance of 78 km. The study area extends between 22039’30’’N & 87046’12’’E and 22039’30’’N & 87047’15’’E to 22040’50’’N & 87046’12’’E and 22040’50’’N & 87047’15’’E at Bandar, Paschim Medinipur, West Bengal, India. The catchment area of both the tributaries has typical tropical monsoonal type of climate with an average rainfall of 1320 mm to 1630 mm. Annual temperature ranges from 11°C to 45°C. The angle of junction of river Silabati and Dwarakeswar with respect to river Rupnarayan are 230 and 360 respectively. The gradient of Dwarakeswar (0039’52.56”) is more than Silabati (0011’55.03”) and Rupnarayan (009’25.16”). The average elevation of the junction is 12 m. from mean sea level. The junction area is characterized by a sequence of pools and riffles. Semi-diurnal tide is active here and tidal impulse penetrates a little beyond Bandar. Tidal bore of lower magnitude is an important phenomenon at that junction (Figure 1).

Figure 1: Map of Study Area.

• To find out the main causes of flood and it’s effect on the ecogeo- environmental condition.

• To generate and apply eco-friendly technological solutions and arrangements supported by local technical knowledge and materials for flood risk reduction.

Floods vary in degree of severity in terms of areas extent or magnitude and in depth. They are, thus, classified as minor or major flooding. In a minor flooding, inundation may or may not be due to overbanking. When there is no bank overflow, flooding is simply due to the accumulation of excessive surface run-off in low lying flat areas. Floodwaters are usually confined to the flood plain of the river along the channel, on random low-lying areas and depressions in the terrain. Floodwater is usually shallow and there may not be a perceptible flow.

During a major flood, flooding is caused by the overflowing of rivers and lakes; by serious breaks in dikes, levees, dams and other protective structures; by uncontrollable releases of impounded water in reservoirs and by the accumulation of excessive runoff. Floodwaters cover a wide contiguous area and spread rapidly to adjoining areas of relatively lower elevation. Flooding is relatively deep in most parts of the stricken areas. There is a highly perceptible current as the flood spreads to other areas.

While floods take some time, usually from 12 to 24 hours or even longer, to develop after the occurrence of intense rainfall, there is a particular type which develops after no more than six hours and, frequently, after an even less time. These are what are known as flash floods.

Causes of flood in the study area (Figure 3)

Figure 3: Causes of flood of the Study Area.

Main causes of the flood at Bandar of ghatal block are -

Meteorological: High rain fall in monsoon season is main causes for flood at Bandar area of Ghatal block.

Month wise rainfall chart (Silabati development authority) (Table 1 and Figure 4).

Figure 4: Month wise rainfall in various year of the Study Area.

Table 1: Month wise rainfall chart ( Silabati development authority).

Catchment size: Badar is a junction point of dwarakeswar and silai river and the combined flow is named as Rupnarayan. So in a monsoon season two rivers carry on huge amount water and when meet the junction point of Bandar, water is overflow. Because catchment size of river is not enough here (Figure 5).

Figure 5: Depth of water in river at Bandar.

Catchment shape: The actual width of the river Silabati and Dwarakeswar is 50 m., but it is 80 m for Rupnarayan. The expected width of Rupnarayan is 66.66 m [9]. The increase volume of water due to tidal effect is one important cause for the extra width of Rupnarayan River at junction. This sudden widening causes flow separation leading to increased sedimentation.

Effects of flood

Flooding can be very dangerous – only 15 cms of fast-flowing water are needed to knock you off your feet! Floodwater can seriously disrupt public and personal transport by cutting off roads and railway lines, as well as communication links when telephone lines are damaged.

Floods disrupt normal drainage systems in cities, and sewage spills are common, which represents a serious health hazard, along with standing water and wet materials in the home. Bacteria mould and viruses, cause disease, trigger allergic reactions, and continue to damage materials long after a flood. Floods can distribute large amounts of water and suspended sediment over vast areas, restocking valuable soil nutrients to agricultural lands. In contrast, soil can be eroded by large amounts of fast flowing water, ruining crops, destroying agricultural land/ buildings and drowning farm animals.

Agricultural loss: Agricultural land is the vital resource for the people living in study area specially those who live in land, total agricultural production of that particular land and labour force engaged in that occupation. The poor had less amount of land to support their family. Almost 62 percent of the total population lives on agriculture (Figure 6).

Figure 6: Agricultural loss.

Loss of households: Last few years some residential house is partly or completely damaged by flood and an erosion of the selected area (Table 2 and Figure 7).

Figure 7: Damage of household (No. of Household).

Table 2: Number of households.

Table 2: Number of households.

Loss of road: Last four years every year 1.5 to 2.5 km average road is destroyed by flood of the selected area (Table 3 and Figure 8).

Figure 8: Damage of Road (in Meter).

Table 3: Damage of road in mt.

River bank erosion: River bank erosion put enormous stress to the people who reside along with riverbanks as they lost their homestead, agricultural lands and overall agricultural production (Figure 9).

Figure 9: An image of river bank erosion.

Damage of population: Unfortunately many family or person is affected by flood or shifted of the selected area in last decade (Table 4 and Figure 10).

Figure 10: Affected and shifted population during flood in various year.

Table 4: No. of population.

Flood risk reduction management

Flood control refers to all methods used to reduce or prevent the detrimental effects of flood waters. Some of the common techniques used for flood control are installation of rock berms, rock rip-raps, sandbags, maintaining normal slopes with vegetation or application of soil cements on steeper slopes and construction or expansion of drainage channels. Other methods include levees, dikes, dams, and retention or detention basins. There are two types of measures to mitigate the flood damage: structural mitigation measures and non– structural mitigation measures.

Structural mitigation measures:

• Reduction of flood peak by storage reservoirs

• Storage reservoirs and detention basin

• Confining river flood by embankments

• Flood wall

• Channel improvement works

• Cut – off

• Diversion of flood water: floodway

• Construction of higher earthen platform in low – lying flood prone area

• Sluices

• Ring bund

Non-structural mitigation measures (Figure 11):

Figure 11: Flow chart of flood management.

• Drainage linkage system (DLS)

• Prepared RZB (Restricted Zone of Buildup)

• Prepared MZBA (Mapping and Zoning of Basin Area)

• Connection of rivers with source

• Flood forecasting or warning

• Flood proofing

• Weather modification

• Mathematical modeling

• Flood insurance (Figure 12)

Figure 12: Flowchart of Managerial action for Flood Reduction Process of Dwarakeswar-Silabati-Rupnarayan river.

Irrigation and Waterways Department (I & WD) Govt. of West Bengal has already taken up distillation works in some major reaches of the river. However, the progress is not up to the mark and there is no comprehensive project to solve the problem. Finally I thing long term sustainable development is ideal development for any type disaster management including flood.

Acknowledgements

The author is grateful to thousands of flood-erosion-victims in study area who shared their experiences and rendered hospitality during field work. Thanks are due to Soumen Baral and Jayashree Sen who has taken all the photographs. The author is also grateful to Professor Dr. Aditya Bandyopadhyay for having discussion and guidance on the research.