GET THE APP

Flood Risk Reduction of Rupnarayana River, towards Disaster Manag
Journal of Geography  & Natural Disasters

Journal of Geography  & Natural Disasters
Open Access

ISSN: 2167-0587

+44-20-4587-4809

Research Article - (2015) Volume 5, Issue 1

Flood Risk Reduction of Rupnarayana River, towards Disaster Management–A Case Study at Bandar of Ghatal Block in Gangetic Delta

Biplab Das* and Aditya Bandyopadhyay
Indian Institute of Engineering Science and Technology, Shibpur, India
*Corresponding Author: Biplab Das, Research Scholar (PhD), Indian Institute of Engineering Science and Technology, Shibpur, India, Tel: 91-9153015615 Email:

Abstract

The paper discussed the present state of flood at a junction point between two rivers at Bandar of Ghatal block in Gangetic delta and proposed a technological solution to reduced vulnerability of flood. While annual floods have the potential to wreak havoc on unprepared communities, spoil crops and endanger food security, they also play a vital role in agriculture. Flood Management and Mitigation is designed to minimize negative flood-related impacts while preserving the benefits. Flood mitigation involves the managing and control of flood water movement, such as redirecting flood run-off through the use of floodwalls and flood gates, rather than trying to prevent floods altogether. It also involves the management of people, through measures such as evacuation and dry/wet proofing properties for example. The prevention and mitigation of flooding can be studied on a number of levels: individual properties, small communities and whole area or towns or cities. The costs of protection rise as more people and property are protected. The most effective way of reducing the risk to people and property is through the production of flood risk maps. Most countries in the developed world will have produced maps which show areas prone to flooding events of known return periods. By identified areas of known flood risk, the most sustainable way of reducing risk is to prevent further development in those known flood risk areas. It is important for at-risk communities to develop a comprehensive Floodplain Management plan. Those communities that participate in the National Flood Insurance Program must agree to regulate development in the most flood prone areas. Communities should assign a floodplain administrator to oversee the management of the floodplain development permit process. Reduction of erosion hazard we can use by MZWA (Mapping and zoning of watershed area), RZB (Restricted Zone of Build up), various soft engineering techniques and other necessary methods without any negative impacts of natural resources.

Keywords: Flood; Bank erosion; Catchment shape; Sediment; GIS;Model

Introduction

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

Background of the Study Area

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).

geography-natural-disasters-study-area

Figure 1: Map of Study Area.

Objectives

• 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.

Materials and Methods<

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)

geography-natural-disasters-causes

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).

geography-natural-disasters-rainfall

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

       
 Month Rainfall in mm.
2013 2012 2011
January 0 0 0
February 35.6 36.6 37.7
March 128.7 122.7 132.6
April 54 64 56
May 182.2 158.7 147.3
June 333.6 340.6 339.1
July 1092.7 1127 1198
August 356 355 361
September 442.5 338.6 498.6
October 52.8 78.7 69
November 31.6 35 38
December 0 0 10.2

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).

geography-natural-disasters-water

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).

geography-natural-disasters-agricultural

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).

geography-natural-disasters-household

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

YEAR Full damage Part Damage
2010 8 18
2011 3 7
2012 0 5
2013 1 9

Source: B.D.O and field survey

Table 2: Number of households.

YEAR Full damage Part Damage
2010 8 18
2011 3 7
2012 0 5
2013 1 9

Source: B.D.O and field survey

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).

geography-natural-disasters-road

Figure 8: Damage of Road (in Meter).

 Year G.PROAD
(JHAMA)
P.S ROAD
(JHAMA)
KATCHA ROAD(mt)
2010 500 300 1700
2011 300 450 1100
2012 275 212 300
2013 200 250 700

Source: B.D.O and field survey

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).

geography-natural-disasters-image

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).

geography-natural-disasters-population

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

Year SHIFTED POPULATION AFFECTED POPULATION
2000 325 2082
2001 275 1565
2002 272 1365
2003 155 1090
2004 300 750
2005 172 542
2006 135 460
2007 0 45
2008 85 350
2009 132 572
2010 62 350
2011 55 275
2012 42 180
2013 22 150

Source: B.D.O and field survey

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):

geography-natural-disasters-flood

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)

geography-natural-disasters-dwarakeswar

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

Conclusion

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

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.

References

  1. Aylward B, Echeverría J, Allen K, Mejías R, Porras I (1999) Market and Policy Incentives forLivestock Production and Watershed Protection in Arenal, Costa Rica’ IIED Gatekeeper Series.No. 82.
  2. Abbas N, Subramaniam V (1984) Erosion and sediment transport in the Ganges river basin (India), Journal of Hydrology 69: 173-182.
  3. Govt. of West Bengal (1997) Memorandum for Expenditure Finance Committee. Irrigation Dept. (Unpublished) pp. 1 & 15.
  4. MillimanJD, Meade RH(1983)World-Wide Delivery of River Sediment to the Oceans. The Journal of Geology 91: 1-21.
  5. Mukherjee BB (1972) Pollen analysis of few Quaternary deposits of lower Bengal basin (Discussion). inProceddings of Seminar on the Paleopalynology and Indian Stratigraphy,Calcutta.
  6. Poddar BC, Chakrabati C, Banerjee SN, Chakravarti P (1993) Changing geographyand climate of West Bengal since 18000 B.P.,Rec. Geol. Surv.India.121; pp47.
  7. Rao MBR,Sengupta S(1964) Hidden Ridges in the Indo-Ganga Plain.In Advancing Frontiers of Geology and Geophysice. Hyderabad, 152-156.
Citation: Das B, Bandyopadhyay A (2015) Flood Risk Reduction of Rupnarayana River, towards Disaster Management–A Case Study at Bandar of Ghatal Block in Gangetic Delta. J Geogr Nat Disast 5:135.

Copyright: © 2015 Das B, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Top