International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com September 2017, Volume 5, Issue 9, ISSN 2349-4476

Floods in Valley –Causes, Effects and Preventive Measures

L Sherjit Singh* and Ibameaihun Dhar Research Scholars Department of Environmental studies, NEHU Shillong

ABSTRACT Floods are the major geo-hazard in many areas of the Imphal valley causing loss of life and destruction of agricultural land and property. They may occur due to high rainfall orriver bank breaching. The amount of water over spilling a river bank or drainage is a measure of the magnitude of a flood. The impact and volume of river floods is determined by the characteristics of the river basin, the channel network and the river channel itself. Many of these are natural factors but others are variable depending to a large degree on the level of human modification in the drainage basin. In this regard, vegetation removal leading to soil and river bank erosion and sedimentation in the river channel affects runoff. Likewise, construction of dams, modification of water courses and urbanization are other important factors in changing the flood hazard in a particular river basin like Imphal valley. We cannot totally solve the problems of floods but we can minimise its ill effects by strengthening river banks, making dams, improving drainage facility and through environment conservational efforts. KEY WORDS: breaching, sediment pollution, land-use, recharging structures, check dam

INTRODUCTION is a small state located in a hilly terrain with a small portion of valley. It has a complex geology, terrain, geomorphology and lithology. Imphal valley is a palaeo-lake basin. Most of the lakes in the basin had now vanished in the course of time. Many natural groundwater recharging structures like ponds, tanks and swampy areas are greatly reduced due to urbanization and change in land-use pattern (Sherjit and Mohon, 2016). Rivers are greatly polluted in many parts of the state. Breaching of river banks, heavy precipitation, inadequate drainage facility and siltation are the main causes of floods in Manipur. Urbanization and changing environment enhances the problem. Floods are among the most common and destructive geo-hazards causing extensive damages to infrastructure, public and private services, environment and economy. The frequency and intensity of floods has grown in the State over the last decades primarily because of the unplanned development and increased encroachment of flood plains.

GEOLOGICAL SETTING OF MANIPUR The geological framework of Manipur including Indo-Myanmar ranges along its eastern frontier is closely linked up with the evolution of Neogene Surma basin, Inner Palaeogene fold belt and ophiolite suture zone. The ophiolite belt occurring along Indo-Myanmar border in Manipur forms a part of Naga-Arakan Yoma flysch trough of Upper Cretaceous-Middle Miocene age. The rock formations consist mainly of flysch sediments of Tertiary ages comprising Disang (thick sequence of splintery shales) and Barail group of rocks (intercalation of shales, siltstones and sandstones). Structurally and tectonically the studied area falls in a zone where the rocks have been evolved as a part of the imbricate thrust system of the Indo-Myanmar Ranges (IMR) during the subduction of the Indian Plate below the Myanmar plate. In the process, the younger litho- units (Barail in the area) have overthrusted the older ones (Disang in the area). The stratigraphy of Imphal valley is given in the following table (table no. 1).

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www.ijetmas.com September 2017, Volume 5, Issue 9, ISSN 2349-4476

Disang Group covers a major part of eastern and central segment of the state. Disang represents a great thick pile of splintery, dark grey to black shales interbedded with siltstone and fine grained sandstones (Mallet, 1876). These rocks occupy major portion of the section. The splintery nature is mainly due to the intersection of bedding and fracture cleavages. The splinters are rhomboid in shape, brown to reddish brown in colour due to weathering. The Disangs sometimes show intercalations of shales, siltstones and fine grained sandstones giving rise to rhythmite bedding. The valley fill of Plio-Quaternary age consists of clay, sand and gravel deposited in a fluvio-lacustrine environment. Table no.1 Stratigraphic succession of Imphal valley (after Soibam et al, 2007)

A BRIEF INTRODUCTION TO DRAINAGE PATTERN OF MANIPUR Imphal valley was formed by the filling up of an ancient Lake which once covered the whole valley. The two most important river basins of the state Manipur are Imphal river basin and Barak river basin. Imphal River and its tributaries drain the central part of the valley and while western part is mainly drain by the Barak and its tributaries. The Eastern ridge line of the western hills forms the water divide between the Barak and the Imphal river basin. The Barak river basin belongs to Brahmaputra river system of the west and the Imphal river basin is a part of the Chindwin-Irrawady river system of the east.

FLOOD PRONE AREAS Floods and flash floods are the regular hazard faced by the State during monsoon. All the major river systems in the State are vulnerable to flooding. The Thoubal River causes breaching of river banks at many places like Thoubal Okram, Sabaltongba, Khekman, Ningombam, Leishangthem, Phoudel and Haokha (MASTEC, 1998). Arong River causes flood in Khangabok, Athokpam and its surrounding areas.The joiningof ImphalRiver and the Iril River at Lilong, makes high volume of water and causing the breach of embankment in Chajing, Haoreibi, Samurou and Lilong area. Khuga River causes flood problem in Kumbi and Ithai Village .The Chakpi River meets the Manipur River at a reverse direction causing flood in surrounding areas of 8 L Sherjit Singh and Ibameaihun Dhar International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com September 2017, Volume 5, Issue 9, ISSN 2349-4476

Sugnu, Serou extending uptoWangoo during rainy season. Most of the embankments are poorly maintained and siltation takes place. Many vulnerable points in Imphal River, Thoubal River, Iril River Nambul River and Nambol River are detected. Nambul River causes frequent flood at Kwairamband Keithel and its adjoining areas like Keisamthong and Sagolband. The rapid increase of urbanisation and lack of proper drainage in the valley areas are alsoimportant factors for the recent floods and flash floods in urban areas.

Fig. 1 Flood Hazard Zonation of Imphal Valley. This map is generated from satellite imaginary of Landsat 8

2015 FLOOD OF MANIPUR 2015 flood of Manipur affects many parts of the state including hill districts. Among them Thoubal district and Chandel district are severely affected. Flood affected areas include Uripok, Sagolband,Lamphel,Khagempalli,khangabok, Athokpam, Heirok,Tentha, Wanging, Serou, Pallel, Kairenbikhok, Wabgai, Sangaiyumpham, Sugunu, Wangoo, Wairi, Chumang, Chairel and kakching KhunouTuibong, Zomunnuam,Kamdou Veng, New Zouveng, Molnom,Kumbirei,, Aimol tampak, Kangoi and Theimungkung, Machi, Pallel, Chakpikarong and Tengnoupal and many more parts of Bishenpur and Imphal East district.

2017 FLOOD OF MANIPUR 2017 flood of Manipur affects many parts of the valley. Districts which are affected by this floods are- Imphal East, Imphal West, Thoubal, Bishenpur and kackching. Number of household affected by this flood is estimated to be about 14000 (Media, IAG Manipur, 2017). River bank breaching was reportse fromBashikhong area, Imphal east and other parts of the state. Over 5000 people have taken shelters in various relief camps. Roads are damages in hilly districts like Kangpokpi and Litan area, Ukhrul district.

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www.ijetmas.com September 2017, Volume 5, Issue 9, ISSN 2349-4476

Fig. 2 Photos showing Floods in Ima keithel and Basikhong

CAUSES OF FLOOD IN IMPHAL VALLEY AND PREVENTIVE MEASURES Jawaharlal Nehru (’s first Prime Minister) believed that dams for irrigation and control flooding.But after making dams, the area affected by floods increases rapidly all over India.Same is true for Manipur also. The causes of flood in Imphal valley includes poor urban drainage, deforestation in catchment areas and other factors include breaching of river banks, improper damming, sediment pollution, siltation of river beds and lakes, heavy precipitation in catchment area, changing land-use pattern, vanishing of traditional recharging structures and water bodies like ponds and tanks. Earlier, the various lakes of Manipur, mostly located in the southern part of the valley, served as effective reservoirs of excess runoff. Most of the lakes are severely degraded in quality to the extent of complete disappearance. Keisampat, Takyelpat, Lamphelpat, Waithoupat are completely disappeared or remain for namesake only. According to Manipur State Disaster management Plan Vol. I and II, the Action Plan of flood in Manipurconsists of the following activities - 1. Declaration of Flood disaster 2. Flood Forecasting and Warning 3. Trigger mechanism 4. Response mechanism and 5. Relief Lack of early warning system and long term plans is one of the factors that often cause problems of flood in Manipur. It multiplies the effects of flooding. The following table shows the causes and preventive measures of flood in Imphal valley. Table no.2 Causes and preventive measures of floods in Imphal valley Sl No. CAUSES PREVENTIVE MEASURES 1 Breaching of river banks Proper maintenance of river banks, and making retaining walls 2 Inadequate drainage facility Drainage facility improvement 3 Improper damming Geo-engineering consideration 4 Sediment pollution, siltation, shallowing of river Minimizing sediment pollution ,siltation and beds and lakes deepening of river banks & lakes 5 Heavy precipitation in catchment area ? 6 Urbanization ? 7 Changing land-use pattern Controlling land-use pattern 8 Vanishing of traditional recharging structures and Restoring traditional recharging structures and water bodies water bodies like ponds, tanks and removing phumdis as far as possible 9 No regulation of flow Check dams to regulate the flow 10 Deforestation and soil erosion Aforestation 11 Lack of early warning system Activation of early warning system 12 Lack of long term action plans for prevention Making long term plans for prevention

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EFFECTS OF FLOODS IN MANIPUR The followings are the effects of floods in Imphal Valley. 1. It damages fields and crops 2. It damages houses and properties 3. Loss of lives 4. Transportation problems 5. Drinking water problems 6. Sanitary problems 7. Spreading of water borne diseases 8. Communication problems 9. Electricity problems 10. It damages farms and pisiculture 11. Disturbance in education 12. Severe reduction in economy etc.

CONCLUSION The magnitude of a natural flood produced by rain is related to the intensity and duration of rain over the catchment area. Floods and Flash floods can occur in urban areas like Imphal East & West Districts due to poor drainage facility.The rate at which water enters river channels depends particularly on vegetation cover and drainage. Large floods occur where there is little vegetation and many soils and paved surface areas those are impervious to water. Such floods are called downstream floods because the effect of flooding increases progressively downstream side of the river. Floods produced by dams tend to be upstream floods which are confined to more limited areas (e.g. Chadong village of Manipur) To minimise the effects of the flood, it is required to strengthen the river bank and deepening the river beds. Drainage facility should be improved particularly in urban areas to prevent flash floods. Environment conservational efforts and check dams are also required to regulate the flows. Geo-engineering consideration when constructing dams and quality control are important to minimise the flooding effects. Making long term plans and activation of early warning system can reduce the hazard. Controlling land-use pattern and restoring traditional recharging structures and water bodies are also equally important.

REFERENCES  “Flood Hazard Zonation In Manipur Valley”, Manipur Science and Technology Council, Central Jail Road, Imphal,1998  Hemanta, RK (2004) “Tectonuic siognificance of minor structures of the rock of Imphal valley” PhD Thesis, Manipur University (unpublished)  L Sherjit Singh and Kh Mohon Singh (2016) “Water crisis in Manipur and Its solution” CGWB Workshop (NER) on “Water conservation, water security, water quality, climate change and best practices in north east India”  Mallet (1876) “On the coalfields of the Naga Hills bordering theLakhimpur and Sibsagar districts, Assam,” Mem. GSI,Vol. 12, Pt. 2.  Manipur State Disaster Management Plan Vol. 1, Government of Manipur, 2013-14,p.30-32  Manipur State Disaster Management Plan Vol. 2, Government of Manipur, 2013-14 p.31-37  Media, Inter Agency Group Manipur, July, 2017  Soibam et al “ Trantentional Basin in Obique Subduction Margin: Imphal Valley An Example” Himalaya(geological Aspects), Vol.5 2007 (Uploaded by Hemanta Singh on 15 October 2015)

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