Chapter I

INTRODUCTION

1.1 INTRODUCTION

Rivers are the most prolific land surface sculptors. A variety of aweinspiring landforms

are thus evolved under fluvial processes (river). One of the most dynamic of these

landforms is the floodplain which responds directly and abruptly to the changes

whatsoever to the flow regime of the river. Floodplains are studied for acquiring the

understanding of surface form that affects the passage of flood water as well as ground

water management. Floodplains are a resource of immense value. These are the sites of

most of the settlements and also provide natural resources to support the rural industries.

Floodplains are capable of preserving records of past climatic change. In addition, any

morphological changes in the floodplains due to channel processes have direct bearing on

the land and land use pattern thereof.

Floodplain is defined as the smooth strip of land bordering the river channel, embracing

the river pattern and inundated at the times of high stage (Gregory and Walling, 1973).

In other words, floodplains are prone to inundation. These are best understood in the

context of meandering streams and shifting meanders, which work over the valley

alluvium and erode its outside bends. But deposition of sediments take place only along

the inside bends of the meander. In this way a smooth depositional strip of land is formed

along the length of valley (Dury, 1969).

Processes involved in floodplain evolution and modification are channel aggradation and

degradation (or scour and fill), combined with shifting of a meander. Sediments eroded

from a concave side of meander tend to get deposited on point bar along the convex side

of the next meander downstream. This process is known as lateral accretion. The result of

such type of process is a cross-stratified deposit, with a subdued relief of low ridges and

intervening swales that may record many episodes of meandering channel migration.

Apart from channel deposit, floodplain is produced by over bank deposition i.e. vertical

accretion. The suspended sediments are deposited on the floodplain when the river water

is out on the plain during floods. In such flood condition, the velocity in the over bank

water is very low and the flood waters take long time to recede back into the channel.

1

Deposits precipitated from such type of flooding are usually sand or mud, although splays

from breached channel banks may bring coarse sediments too. The abrupt loss of velocity

at the edge of the flooded channel and the abundant sediment supply commonly cause

coarser deposition on the natural levees, which grade laterally into finer back-swamp

deposits. Thin vertical accretion of alluvium may accumulate slowly on a flood plain if

the river is constrained from migrating laterally. The predominance of either of these two

kinds of depositional environments (lateral and vertical deposit) is dependent upon the

frequency of discharge that inundates the floodplain.

The most significant and characteristic features of the floodplain are the dynamic nature

of both channel and floodplain morphology. Since floodplains are by and large the

product of fluvial processes of channel, any change in these may bring about significant

morphological changes to the floodplain. This also has a direct bearing on the human

activities along the riverbanks. Considering the fact that bordering plains of most of the

rivers often form the fertile agricultural land, the modification and alteration in the

floodplains may affect the livelihood of the region. Therefore, a detailed survey of these

changes and the processes involved therein are essentially needed.

In the tropical region, seasonal inundation of the floodplains is apparent which results in

severe bank erosion as well as large scale vertical and over bank deposition. Floods cause

permanent loss of land, life, property and cause deterioration of land due to erosion, sand

casting and water logging.

This study is oriented towards developing a better understanding of the fluvial processes,

and the hazards precipitated in the flood plain of the lower Rapti river basin in Uttar

Pradesh. This includes the study of alluvial forms of the floodplain and processes that

have brought about changes through sediment deposition, bank erosion and water

logging. Impact and aspects of management and planning is addressed alongside.

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1.2 FLUVIAL PROCESSES IN LOWER RAPTI FLOODPLAIN

The Rapti river is a typical meandering stream. The most prominent features of the lower

Rapti floodplain are ox-bow lakes, alternative channel bars, flood chutes, point bars, swirl

pit, swamps or marshes, natural levee, dry channel and anabranching streams. The

presence of ox-bow lakes (chute and neck cut offs) and the anabranching stream are

indicative of a low surface gradient.

Broken ground and bank slumps are generally determined by a combination of factors i.e.

shearing away of bank materials, variability in bank sediments and the lack of cohesion.

Material slumping into the bed due to caving of bank is more common in meandering

channel just downstream from the axis of the concave bend. The Rapti riverbed has

become shallow due to siltation. Deforestation in the tarai region has increased the

sediment load in these rivers. Sediments get deposited in the riverbed making it shallow

and convert agriculture fields into culturable waste land.

1.3 GEOGRAPHICAL PERSONALITY OF STUDY AREA

The entire Rapti river basin extends from 26° 18' 00" N to 28°33'06" Nand 81 °33'00 E to

83°45'06" E and covers an area of 25793 km2 out of which 44 % (11401 km2) lies in

Nepal and 56% (14392 km2) in Uttar Pradesh. The Rapti river flows in the sub-humid to

humid monsoon region of the middle Ganga plain. It is the largest tributary of River

Ghaghra, which in tum, is a major constituent of the Ganga. It flows through the districts

of Rukum, Salyan, Rolpa, Gurmi, Arghakhanchi, Dang, and Banke of Nepal territory;

and Bahraich, Shrawasti, Balrampur, Siddharthnagar, Santkabimagar, Gorakhpur and

Deoria districts of Eastern Uttar Pradesh (Figure 1.1 ). The SRTM elevation data has been

used to delineate the Rapti river basin with the help of ARC GIS-9.2 watershed

delineation tool. The processed basin boundary is verified using the Landsat TM data of

2005. The division ofRapti river basin is based on the Watershed Atlas of India (1990).

3

8 1°20'0"E 82°0'0"E

z b p ~

z b

~ N

z b

~

Upper

Middle

500 0 SOO Kilometers E3 E'="=3

82°0'0"E

Figure 1.1 Location map of the study area.

Lower

82°40'0"E

83°20'0"E

83°20'0"E

84°0'0"E

N

A

- -- Drainage Network

International Boundary

c:J Rapti River Basin ,------- ~

~ ___ ___ : District Boundary

- Lower Rapti Floodplain

10 20

84°0'0"E

40 Kilometers I

z b

~ N

1.3.1 Physiographic Region

The Rapti river basin is diverse in its physiography. The lofty mountain, inner and outer

tarai and undulating plain regions constitute the topography of the entire basin. On the

basis of relief, the physiography ofbasin can be divided as:

I. The Mountainous Region

II. The Inner Tarai Region

III. The Outer Tarai Region and

IV. The Plain Region or Lower Rapti River Basin (Saryupar Plain)

I. The Mountainous Region

This region consists of the Lesser Himalayas. It extends from the Mahabharat range in

the south to the Lesser Himalaya in the north. To the north, its altitude varies from 1830

m to 401 Om above mean sea level ( amsl). This region is called the Midlands (Sharma,

1974). The mountains run parallel from east to west. It consists of the Rapti, Madi,

Jhimruk, and the Lungri valleys (Figurel.2).

The Mahabharat Range

This chain of mountain runs parallel to the lesser Himalaya from west to east direction.

Altitude varies from 1520m to 3660m (amsl). Some tributaries such as Banganga,

Kunhara and Rohini of the Rapti rise from springs in this range (Sharma, 1974).

II. The Inner Tarai Region

The term 'tarai' literally means moist or wet land (Sharma, 1991). This region is called

the 'Bhitri Madhesh ',which lies, between the Mahabharat mountain in the north and the

Churia hills in the south. Altitude varies from 610m to 1830m (amsl).These mountain

ranges are separated by wide valleys called 'dun', which is a wide and elevated valley.

The Rapti Dun is important which contains alluvial soil but has harsh climate due to the

high level of humidity.

5

28°0'0"N

27°0'0"N

82°0'0"E

Legend

--- Drainage Network

-- Mountain Range

c==J Rapti River Basin

Physiographic Region

~ Mountain

t:.O. :."'<_.J inner Tarai

L~~~d Rapti Dun

~ Outer Tarai

-.:}~ Plain 0

82°0'0"E

25 50

Figure 1.2 Physiographic region of the Rapti river basin.

83°0'0"E 84°0'0"E

Upper

28°0'0"N

27 °0'0"N

Lower

83oo:o"E 84°0'0"E

The Churia Hills

These lie south of the Mahabharat range. These are the foothills of the mighty Himalayas.

Altitude varies from 610 m to 1220m (amsl). These are called the Siwalik range in India.

Landslides are frequent in these hills.

IV. The Outer Tarai Region

The outer tarai region lies between the plain region in the south and Churia hill to the

north, with altitude below 300m (amsl). The tarai is drained by the rivers such as, the

Rapti, Kain, Gholia, Dangmara, Bhainbar, Banganga, Arrah, Ghonghi and Rohini, from

west to east, respectively. A strip of the tarai in the north consists of sandy soil and

pebbles. It is called the Bhaber interspersed by marshes and forests. Due to fall in

gradient from north to south, a number of terraces of alluvial fan origin are found

between the plain and the Siwalik foot hills (Yadav, 1999).

The Dundwa Range

This range lies south of the Rapti dun. It is a longitudinal spur of the Siwalik range (Bose,

1972).

V. The Plain Region (Saryupar Plain)

The plain region is a part of the Saryupar plain which lies south of the tarai region. The

general elevation is 80m (amsl) and generally slope towards the east (Yadav, 1999).

Physical landscape is produced actually by local eminences such as river levees and

bluffs or sand features like Dhus, oxbow lakes, Tats, Chaurs, dead arms or remnants of

the river channels and frequently perceptible notches and slopes carved by the rivers at

the outer edge of the Bhangar tracts (Singh et al., 1971).

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1.3.2 Geology

Geologically, the Rapti river basin may be divided into three zones: I. the northern

mountain zone, II. the tarai zone, and III. the plain zone.

I. The Northern Mountain Zone

The rocks of this zone are tertiary in age and highly folded. The mountain ranges such as

the Lesser Himalaya and the Mahabharata range consist of hard granite and crystalline

rocks and are somewhat older than the Churia hill, which consists of sand, clay and soft

rocks (Sharma, 1974). Thus, the hardness of rocks also varies from north to south.

II. The Tarai Zone

In the northern part of the tarai zone, the alluvial architectural studies on exposed Siwalik

section reveal that the major sandstone bodies are 1 OOOm thick (Khan et al., 1997).

These sandstone bodies are underlain by a major erosional surface and generally are

capped by a palaeo sol. These sandstone bodies are separated by 1OOm thick mudstone

dominated palaeosol bounded sequences, which contain minor sandstone bodies (one to

few meters thick). These sequences are the over bank deposits formed by filling of local

low-lying area through small channels and crevasses followed by progressive shifting

through avulsion (Willis and Behrensmeyer, 1994). This depositional environment is

analogous to the modem interfan areas in the Rapti river basin.

III. The Plain Zone

The large trough called Gorakhpur trough in the southeastern part of the basin is over

8000m deep. It indicates that the entire region has suffered great down warping due to

Himalayan upheaval (Singh et al., 1971). It is formed of sand, silt and clay materials

mostly deposited by the Rapti river and its tributaries. The surface (about 30m) of region

can be divided into two sub zones as:

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A.Bhangar

This zone is formed by the old alluvium. It covers upland tracts beyond the annual flood

limit. It is generally below 1OOm from msl.

B.Khadar

It is formed by new alluvium soil that annually replenishes deposits through overbank

flow. The nodular limestone conglomerate known as Kankar is more abundant in the

Bhangar than in the Khadar alluvium because of riverine character of the Khadar.

1.3.3 Soil

There are five factors such as parent material, climate, topography, organism and time

involved in the soil formation. These factors vary across the Rapti river basin. Thus, the

major soils of the basin are as:

A.Red Soil

In the northern part (mountainous area) of basin the soil is mixed with limestone, granite,

sand, clay etc in some places. Red soil is mainly composed of hard stone, limestone and

mica.

B.Tarai Soil

The tarai soils are found in the inner and outer tarai regions. This type of soil covers the

Rapti Dun and northern part of Bahraich, Gonda, Basti, Sarawasti, Maharajganj and

Siddharthanagar districts of the plain region. These are poorly drained and receive

seepage water continuously from the upper Bhabhar Zone. Soils are highly leached. Clay

soils are suitable for rice cultivation in this zone. The pH value ranges between 6.6 and

7.2 (Yadav, 1999).

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C. Alluvial Soil

On the basis of inundation, alluvial soils of the plain region are divided into two

categories: I. Khadar soils and II. Bhangar soils.

I. Khadar Soils

These are newer in age and cover the flood plains in the vicinity of rivers. Khadar soils

do not have any characteristics soil profile (Singh et al., 1971). They are suitable for the

Bhadai and Zaid crops. Silt is prominent in these soils. The soil of Rapti flood plain

(Khadar) is dated back to <500 years B.P. (Mohindra and Parkash, 1992).

II. Bhangar Soils

These are old alluvium and cover the upland tracts beyond the annual flood limit. These

soils are rich in lime content and suitable for rice cultivation, being sticky and well

drained. The soil of Rapti flood plain (Bhangar) is dated back to 2500 years B.P.

(Mohindra and Parkash, 1992).

Apart from the above classification, the soils of the basin are grouped into three

categories as A. Bhur soil, B. Dumat soil and C. Mattiyar on the basis of the sand, silt

and clay content (U.P. District Gazetteers, Gorakhpur, 1987).

A. Bhur soil: It is grayish in colour. The proportion of sand (65%) is very high as

compared to silt (20%) and clay (15%). It is moderately alkaline and deficient in

organic matter. Jowar, Tarbooj, Sakarkand and Kodon are the typical agricultural

products. These are generally grown near the river.

B. Dumat soil: It is grey to brown in colour. The proportion of silt and sand (40%) is

high as compared to clay (20%). This soil is suitable for wheat, paddy and

sugarcane cultivation.

C. Mattiyar soil: In this soil, the proportion of clay (70%) is very high in comparison

to sand (15%) and silt (15%). It is appropriate for intensive Rabi crop cultivation.

10

On the basis of above details, it can be concluded that the soil structure facilitates good

subsurface flow in the plain region. Poorly drained tarai soil causes considerable seepage

of water, whichjoins the subsurface flow in the plain, resulting in return flow, and during

floods resurges on the surface, thereby, expanding the flooded area.

1.3.4 Climate

Due to difference in altitude, the Rapti river basin has two distinct climatic regions, the

temperate climate prevails in the mountainous region while the plain has subtropical

climate.

1. Temperate climate: The area between the Mahabharat range and the Lesser

Himalayas has a temperate climate. Summers are warm and winters are cool to

severe (Thapa and Thapa, 1969). Temperature varies between 0°C to 37.7°C.

Average annual rainfall is about 170cm (Yadav, 1999).

2. Subtropical Climate: The inner Tarai, the outer Tarai and the plain region

experience typical monsoon type of climate with dry winter season. The weather

is very hot in summers. Daily maximum temperature goes upto 46.5°C. The

western part is hotter than the eastern part. The subtropical climate has four

distinct seasons that are as follows:

A. The Winter Season

The easterly humid winds are replaced by the dry north-westerly winds. The region

receives small amount of rainfall from the western disturbances. Normally, temperature

ranges from TC to 29°C (Yadav, 1999).

B. Summer Season

In this season, the pressure gradient becomes steeper from west to east and wind blows

with increasing velocity (6.4 Km!hour in March to 10 Km/hour in mid-June), with

decreasing humidity and increasing temperature. Wind velocity leads to the formation of

hot winds in this region called 'Loo' (Yadav, 1999).

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C. Southwest Monsoon Season

The southwest monsoon season begins in the middle of June and ends in the middle of

October. The region gets 75% of annual rainfall in this season alone. The average rainfall

of the plain region is approximately 11 Ocm. Rainfall decreases from the northern part to

the west-central part of the basin (Yadav, 1999). These rains are caused by the passage of

low pressure system along the monsoon trough.

D. Post Monsoon Season

This season begins in the middle of October and ends in December and is generally

characterized by decreasing temperature and rainfall.

1.3.5 Vegetation Cover

Different types of vegetation are found in the basin due to variation in climate and

altitude from north to south. The major categories of the vegetation are as:

1. Temperate Coniferous Forest

This type of vegetation is found in the upper northeastern part of the basin i.e., north of

the Mahabharat range. The major tree species of Sallo, Dhupi, Deodar, Gojan, Kalikath,

with Rhododendrons are found at higher elevations (Sharma, 1974).

2. Temperate Deciduous Forest

This type of vegetation is found between the Mahabharat and the Churia ranges. These

trees have broad leaves. Sal, Bamboo, Walnut, Chestnut etc. are the major tree species of

the deciduous forest (Sharma, 1974).

12

3. Tropical Forest

This monsoon forest consists of evergreen trees because of heavy rainfall. It is found in

the southern part of the basin. Most of these forests have softwood, while some have

hardwood. Hardwood trees like Sal (Shorea robust) Shisam (De iberia sisso ), Sankhuwa

etc. and softwood trees like Pipal, Mahuwa, Khair etc. are found in this forest. At some

places, bamboo trees and cane reed are found. In drier parts of the tarai region, Elephant

and Sabai grass are found. The forest in the Bhaber region is very thick.

Some grasses like Bher (zizyphus glaberrima), Moonj (Erianthus moonja), Kans

(Saccharum spontaneum), Jhau etc. are found in Diaras (Yadav, 1999). Babul tree is

found both in Bhangar and Khadar regions.

1.3.6 Population

Figure 1.3 shows the block wise population density (2001) ofNepalese and Indian part of

the basin. Generally it varies from south to north due to variation in physiography,

climate, and soil. In the south-east part of outer tarai of Nepal, the population density

varies from 367 to 2445 personlkm2 while the very low density (16-187 personlkm2) is

observed in the mountainous and Rapti Dun region due to harsh climate.

In the Indian part of the basin, population density generally varies from NW to SE. In the

north-west part, the population density ranges from 339 to 526 personlkm2• This region is

mainly covered with reserved forest of the outer tarai region. In the south-east part, very

high population density (818 to 1240 person/km2) is observed because of mild climate

conditions and availability of arable land as compared to rest of the area.

1.3. 7 Economy

The economy of the basin is based on agriculture. A three-harvest system is prominent.

The major crops of the basin are wheat, paddy, sugarcane, barley, jawar, oilseeds, pulses

etc.

13

z 0 ~ 00 N

z 0 0 0 \0 N

Legend

D Rapti River Basin

- International Boundary

-------- District Boundary

Population Density ( Person/sq.km)

Nepalese Part of Basin

.. 1139-2445

- 574 - 1138

367 - 573

187 - 366

16 - 186

82°0'0"E

Indian Part of Basin

- 990 - 1240

- 818 - 989

- 670 - 817

527 - 669

D 339 - 526

20 40

Figure 1.3: Population density (2001) in the lower Rapti river basin.

80 Kilometers

z 0 0 0 00 N

z 0 0 0 .... N

1.3.8 Flood Prone Area in Rapti River Basin

The flood prone area in the basin was delineated using the Dartmouth atlas of global

flood hazard (2006 and 2007), Landsat TM (2005), Landsat ET~ (2002) satellite

imageries, SRTM elevation data (2000), NATMO maps of Balrampur (2004),

Siddharthnagar (2004), Basti (2001), Gorakhpur (2001) and Deoria (2007) and the

Survey of India topographic sheets (1916-21). Floodplain along the lower Rapti river

were delineated using steady flow data of 100 years return period. HECRAS and

ARCVIEW 3.2a GIS software were applied for the delineation.

Table 1.1 shows the area wise break up of flood prone area in the upper, middle and

lower Rapti river basin. The flood prone area covers 20 per cent of the entire basin area.

The flood prone area covers 38 per cent in the lower Rapti basin while it occupies only

19 and 3 per cent area of the middle and upper basins, respectively. Table 1.2 shows the

break up in district wise flood prone area. Flood prone area covers 49 per cent of

Gorakhpur district (Figure 1.4).

1.4 SELECTION OF STUDY AREA

The study mainly deals with fluvial process and related aspect of arable land in the lower

Rapti floodplain which largely comes under the administrative limits of Gorakhpur

district. This district is one of the worst flood affected district of the basin. The Rapti

river in this particular stretch is very dynamic and frequently inundates considerable area.

As discussed earlier, this part of the basin is densely populated. Area along the river is

extensively cultivated. Therefore, the lower Rapti floodplain is an appropriate area for the

study of fluvial processes and impact of these processes on the arable land. Apart from

this, other factors such as knowledge of regional dialect, availability of data and

conducive working conditions also have played an important role in selecting the area for

this study.

15

Legend

International Boundary .---------,

.__j Rapti River Basin

CJ District

- Flood Prone Area

0 20 40 80 Kilometers

84°0'0"E

Figure 1.4: Hood prone area in the Rapti river basin.

Table 1.1: Flood prone area in Rapti river basin (in km2).

Basin Flood Prone Area Basin Area Percentage of Basin Area to the total Percentage of Flood prone Area to Basin Area Upper 204 6594 26 3 Middle 2441 12959 so 19 Lower 2388 6241 24 38 Total 5033 25793 100 20

Table 1.2: District-wise flood prone area (in km2).

District Country N arne Total District Area District area under Basin Flood Prone Area Percentage Flood Prone Area to District Area Under Basin Gorakhpur India 3321 2944 1437 49 Siddharthnagar India 2895 2839 1171 41 Deoria India 2538 719 271 38 Sant Kabir Nagar India 1646 943 339 36 Shrawasti India 2458 1553 503 32 Balrampur India 3394 2650 741 28 Basti India 2688 182 39 22 Bahraich India 4420 64 12 19 Maharajgan,j India 2952 2210 303 14 Banke Nepal 1477 1428 150 11 Kushinagar India 2906 287 23 8 Dang Nepal 1976 1783 44 2

Source: 1. NA TMO, Dtstnct planrung map of Balrnmpur (2004 ), Stddharthnagar (2004), Basti (200 1 ), Gornkhpur (200 1) and Deona (2007), 2. Census of lndta,

2001, Administrative Atlas of Uttar Pradesh, Vol.II, and 3. The Dartmouth Atlas of Global Flood Hazard, 2006-2007.

1.5 LITERATURE SURVEY

The dynamics of river and associated problems like floods in particular have been studied

extensively by scholars all over the world. Physical based research in the area of fluvial

geomorphology has pointed out the historical trends in fluvial processes and flooding.

Objective of the present study was developed upon previous literature on similar lines.

Pioneering study in fluvial geomorphology by Leopold and Wolman (1957) is the most

noteworthy along with the work of Chorley (1969), Gregory and Walling (1973),

Schumm (1977), Brice (1981) and Hooke (2006). The following section deals with the

literature survey to streamline the present research.

A. Flood Plain Morphology and Sediment Characteristics

Leopold and Wolman (1957) had grouped the alluvial rivers into braided, straight and

meandering on the basis of planform and formulated the characteristics of each of these

patterns. Braided river was found to be the one that flows into two or more anastomosing

channels around alluvial island, and in a winding course.

Chorley et al., (1969) included some consideration of the physical geography of rivers

and drainage basins together with assessment of their significance in socio-economic

framework in geographical analysis.

Bose (1972) the physical, cultural, and economic geography of the Himalaya, had

explained in the backdrop of a detailed account on the Rapti river.

Gregory and Walling (1973) were first, to measure the basin characteristics and runoff,

sediment and solute dynamics, and secondly, with morphology of floodplain, evaluation

of basin form and changes in time and space.

Schumm (1980) while discussing the 'planform of alluvial rivers' he concluded that the

alluvial channels are dynamic and subject to change and suggested that the classification

of alluvial channels should not only be based on channel pattern but also on the variables

that influence channel morphology.

18

Beven et al., (1989) had discussed the areas of flood runoff production, flood hydraulics

and sediment transport, the interpretation of flood sediments and the geomorphological

implications of floods world wide.

Mohindra et al., (1992) had covered the historical geomorphology and pedology of the

Gandak Mega fan. The Gandak mega fan lies in eastern U.P. and northwestern Bihar. The

Gandak river has shifted 8 km to the east in last 5000 years due to tilt in the block

bounded by the Rapti and the Gandak river. Flood plain of the major Rivers such as the

Gandak, the Rapti, the Ghaghara and the Ganga has been demarcated using remotely

sensed satellite data. The soil of Rapti and Gandak flood plains is dated back to <500

years B.P., while the soil of older Gandak flood plain is dated as 2500 years B.P. On the

other hand, the age of soil of oldest Gandak Plain is dated as 5000 years B.P.

Nagarajan et al., (1993) identified the land cover such as ox- bow lakes, high moist area,

arable land, and vegetation cover. Black and white stereo aerial photographs on a scale of

1: 15000 were interpreted to demarcate the water bodies, palaeo channels and floodplain

deposits. A tangent at the point of higher curvature was drawn to get relative angle of

rotation of curvature or meander of two time periods. Based on the angle of rotation and

probability of channel migration, the flooding has been inferred. The Rapti is

characterised by frequent channel avulsion and shifts towards the east.

Simon and Downs (1995) dealt with the modular procedure to assess the magnitude,

distribution and potential for channel instabilities at a large number of sites. The

procedure, based on diagnostic interdisciplinary criteria of alluvial channel morphology

and associated riparian vegetation was presented. The modules include (1) initial site

evaluations, (2) GPS and GIS-based data input and management, (3) ranking of relative

channel stability, (4) identification of spatial trends, (5) ranking of socio-economic

impacts and identification of most "critical" sites, and (6) collection of additional field

data for more detailed evaluation of the magnitude and type of future instabilities and the

effects of proposed mitigation measures.

19

Chen et al., (1996) elucidated on evolution of the palaeochannels on the North China

plain. The palaeochannels were geomorphological expression of abandoned river channel

caused either by human or natural factors based on arial photos and satellite imageries.

These were broadly classified into two categories i.e. surface palaeochannels and

shallow-buried palaeochannels.

Gupta (1998) found the effects of high magnitude floods on the channel forms, erosion

of bed and bank materials and transfer and storage of sediments. The work highlights the

importance of flood studies and records the morphological studies in Indian rivers and

points to the areas that need further studies.

Sinha and Jain (1998) examined the flooding behaviour of rivers draining the plains of

north Bihar. Gemorphological characteristics ofthe Gandak, the Kosi, the Burhi Gandak,

the Bagmati and the Kamla-Balan rivers have been broadly interpreted in order to

develop a better understanding of flooding characteristics of these rivers which record the

highest and frequent flooding in the country. Along with a detailed analysis of

hydrological data, geomorphological factors influencing the overbank spilling of these

rivers have been discussed. Other fluvial processes such as bank erosion, channel

morphological changes and sediment load variation have been also interpreted in relation

to overbank flooding.

Higgit and Waburton (1999) highlighted the applications of DGPS in fluvial

geomorphology. Geomorphic mapping, channel pattern change, bank erosion and

ephemeral flood mapping have been done using DGPS. Ephemeral flood mapping is

based on small scale geomorphic indicators like vegetation trash lines, over bank

sedimentation, flattened vegetation and standing water.

Surian (2002) attempted to analyse the changes of bed material size along the

downstream profile of the Pi ave River (Eastern Alps, Italy) to explain changes in the light

of both natural and anthropogenic factors. Surface material was sampled using the grid­

by-number method. Natural (lateral sediment sources) and anthropogenic factors (e.g.

barrages) were found significant in this river system, which provided explanation for

20

-

most of the observed discontinuities. The barrages produce important changes in

sediment texture. Fining processes of sediments were investigated in the lower part of the

study reach where the lateral sediment sources and the barrages have minor effects on the

bed material.

Jain and Sinha (2003) reviewed the geomorphic setting, fluvial processes and sediment

pattern in the Gangetic plains and illustrated the hydrological and physical characteristics

of the major rivers of the plain as the Gandak, the Ghaghra, and the Kosi, together with

the Rapti river.

Srivastava et al., (2003) studied the late Pleistocene-Holocene hydrologic changes in the

interfluve areas of the Central Ganga plain. Abandoned channel belts, ponds and point

bar deposits of palaeochannels in the region suggest changes in the morphohydrologic

conditions during the late Pleistocene-Holocene period. Oxidised aeolian sand of point

bar deposits of palaeochannel indicates that the channel abandonment possibly occurred

due to the desiccation and aridity. The ponds formed around 8-6 Ka when the channel

activity increased due to tectonic warping and higher rainfall.

Ghosh et al., (2004) studied the spatio-temporal changes in the wet lands ofNorth Bihar

for the period 1984-2002 using satellite data. Surface water bodies including tals were

seen to have decreased in both Ghaghara-Gandak and Gandak-Kosi zones due to massive

sedimentation which probably obliterated the surface waters. On the other hand, there

was a marginal increase in surface water bodies in the western Kosi fan due to west-ward

shifting and frequent spilling of the Kosi river. They conclude that the tals and marshy

lands were the remnants of the active channels in the region.

Kemp (2004) elaborated the flood plain geomorphology and sediment characteristics of

flood plain features of the Lachlan river (southeastern Australia). Both the erosional and

depositional effects of regular large flooding are on the flood plain. The alluvial facies

model shows the variation in sediment size with height and distance from the active

channel. At some distance from the channel, the flood plain is subject to cut and fills by

flood chutes, stripping and swirl pits with fills of mixed textures including coarse flood

21

deposits. The fine flood deposits are deposited in chute bars and crevasse splay during

shallow over bank flooding.

Leece and Pavlowsky (2004) examine the vertical, lateral, and downstream variations in

the grain-size characteristics of historical (post-1830) over bank deposits in the Blue

River watershed, Wisconsin, USA where high rate of accelerated flood plain

sedimentation occurs. Overbank deposits exhibit a coarsening-upward sequence

attributed to historical changes in the sand content of source materials. The average sand

content of near-channel cores increases moderately downstream along two of the reaches

because sandy source materials are increasingly exposed in larger main valleys in the

northern part of the watershed. The two northernmost reaches were coarser overall, but

do not display significant downstream trends. The sand content of surface and early

historical overbank deposits generally decrease laterally as an exponential function of

distance from the channel, suggesting transport by turbulent diffusion.

Sarma (2005) discussed the fluvial processes and morphology of the Brahmaputra River.

The slope of the river decreases suddenly in front of the Himalayas and results in the

deposition of sediment and a braided channel pattern. The Brahmaputra channel is

characterised by mid-channel bars, sidebars, tributary mouth bars and unit bars. The

geometry of meandering tributary rivers shows that the relationship between meander

wavelength and bend radius is linear. The Brahmaputra had been undergoing overall

aggradation by about 16 em from 1971 to 1979. The channel of the Brahmaputra River is

migrating because of channel widening and avulsion. The meandering tributaries have

changed because of neck cut-off and progressive shifting at the meander bends. During

the twentieth century, the total amount of bank area lost to erosion was 868 km2•

Maximum rate of shift of the north bank towards south resulted in an erosion of 227.5

m/year. Maximum rate of shift of the south bank to north resulting in accretion was

331.56 m/year. Shear failure of upper bank and liquefaction of clayey-silt materials were

found to be two main causes of bank erosion.

22

Sinha et al., (2005) attempted, to explain major hydrological and geological controls of

aggradation and degradation in river systems of the Gangetic plains. Stream power and

sediment supply are the two main fluvial parameters that govern the aggradation and

degradation in river systems, which are controlled by the inherent catchment parameters

such as rainfall and tectonics. Aggradation and degradation are the inherent

characteristics of eastern and western Gangetic plains, respectively.

Marren et al., (2006) studied the mud and sand-dominated meanders developed in

close proximity within a floodplain wetland of the Klip River, eastern Free State, South

Africa. They divided the entire reach into three geomorphological zones on the basis of

floodplain gradient (obtained using DGPS) and dealt with the morphological and

sediment characteristics in each zone.

Chabaux et al., (2006) discussed the transfer time of sediments in the Gangetic plain

using 238 U- 234 U- 230 Th disequilibrium in the bank sediments of mountain fed and foot

hill fed rivers. Sediment transfer time of mountain fed rivers like the Ghaghara and the

Gandak are slightly short (100 ka) as compared to foot hill fed river like the Rapti (160-

250 ka). This time scale variation is found to be only due to difference in mineralogical

and chemical sediment evolution in these river systems.

Chandra et al., (2007) discussed the fluvial history of lower Rapti river. Systematic

dating of fluvial sediments from active point bar and occasionally flooded floodplain has

been done using OSL dating technique. The Rapti has had a post-glacial history of

aggradation and avulsion. Aggradational phases were characteristics of the Rapti river

between 11,500 to 5500 years ago, and culminated after 5500 years B.P. by migration of

the river i.e. degradation.

B. Meandering Pattern, Channel Shift and Meander Dynamics

Tower (1904) was first to elucidate the development of cut off meanders. The variables

such as gradient change in water current, disequilibrium between cut and fill were found

to be responsible for the evolution of meander cut-off.

23

Brice (1981) dealt with the meandering pattern of three reaches of the white river system

in Indiana between 1937 and 1968. Centroid of each bend was demarcated in order to

find out the movement in the meanders. Angular movement of centroids versus meander

length was then plotted to find out the potential of erosion in each meander bend. Further,

the eroded area and the meander length were plotted on a scatter diagram to fmd out the

average meander length which triggers erosion. He concluded that the erosion along

straight segments of a highly sinuous channel was negligible.

Thorne (1991) illustrated the bank erosion and meander dynamics of the Red and

Mississippi river in U.S.A. The stability of bank, bank properties and bank failure due to

erosion and mass failure were addressed at length.

Singh et al., (1996) dealt with the neotectonic control on the Gangetic river system of

Uttar Pradesh. LANDSAT MSS (Band 5 and 7) satellite imageries and Sol topographic

sheets were used to identify the lineaments controlling drainage networks. These

lineaments controlled the slope of the region and direction of drainage networks. The

drainage of the north and central part of Gangetic plain was found to be controlled by

newly developed lineaments which formed due to compressional stress of the Himalaya.

While the drainage in the southern part was governed by the reactivated basement

lineaments.

Goswami et al., (1999) covered sequential changes in the position of bank lines of the

Subansiri river using Sol topographic sheets (1920 and 1970) and satellite imageries

( 1990). The entire reach of the river was divided into 10 equal transverse cross-sections

for analysis. The lateral shift in bank line towards east-west direction and the erosion

along cross-section was identified and quantified between 1920 and 1990.

Swamee et al., (2003) discussed the changes in channel pattern of the Ganga between

Mustafabad and Rajmahal. The causes of variation in sinuosity and meanders have been

explained for both the areas i.e. upland and low land.

Raj et al., (2004) analysed the channel shifting of highly sinuous meandering

Vishwamitri river of Gujarat. Satellite, topographic, stratrigraphic, sedimentology and

24

sub surface structural data were used to understand the controls over channel morphology

of the river. The asymmetry of the drainage basin, high sinuosity and entrenched nature

of meander suggested that the tectonics mainly influence channel morphology of the

river.

Mitra et al., (2005) found the channel avulsions in the Sarda river system. Floods

triggered the process of avulsion in this channel. The eastward lateral migration of Sarda

river was found to be related to tectonic tilting of the area during early Holocene.

Sinha and Roy (2005) have attempted to understand the geomorphologic processes in

the Gangetic plain (Farrukhabad-Kannauj area). Detailed geomorphic mapping of the

area suggests that the confluences of the Ganga-Ramganga-Garra rivers had moved both

upstream and downstream between 1970 and 2000, in response to river capture, local cut­

offs and aggradation. Movement of confluence points both upstream and downstream

was mainly caused by local gradient and hydrological fluctuations over a longer time

scale. They found remarkable difference in the fluvial dynamics of this region compared

to the eastern Gangetic plains, where rapid and frequent avulsions were predominant.

They also cited the example of the Rapti river which captured the Bakla river between

1959 and 1974 due to a large scale avulsion upstream.

Hooke (2006) elaborated the spatial pattern of instability and the mechanism of change in

an active meandering river, the Dane. Nearly 100 meandering bends of the Dane river

have been analysed using historical maps and aerial photographs for the period 1981-

2002. More than 20 years of monitoring of these bends provided a unique insight into the

link between erosion, deposition and maximum discharge.

C. Floods, Flood Plain Risk Zoning, Flood Management, DEM and

Land Use

Sears (1957) dealt with the natural and cultural aspects of floods. To him, nature made

floods but man made the flood hazards. The safe evacuation of people from low lying

flood plain to natural levee during rainy season was suggested.

25

Lacewell and Eidman (1972) developed a model to estimate the incidence of

agricultural flood damages in a small watershed of Oklahoma, USA. The model contains

a series of computational steps such as calculation of elevation along a cross-section,

flood depth for specified flood sizes, damage factor as for each sample point in the flood

plain and flood damages. The flood insurance and the optimum cropping pattern were

also discussed.

Rao (1979) elucidated on water resources and floods in India and discussed the causes

and management of floods in the Rapti river basin. The Rapti river which flows in a very

sinuous course with shallow depth and causes heavy flooding in the districts of Eastern

Uttar Pradesh. He suggested that the raising of the villages above the annual flood level

can reduce the severity of floods in the region.

Kayastha and Yadav (1980) elucidated on the impact of flood on socio-economic

development of Mubarakpur village of Deoria district lying in the Ghaghara flood plain,

based on a primary survey.

Kayastha (1983) examined the causes of the floods in India. The flood damage during

1953-69 is discussed and interpreted at length. The flood forecast system and the flood

management measures were also covered in detail.

Kochel and Barker (1982) described carbon dating of slack water flood deposits to

tmderstand the long term flood frequency in the lower Pacos and Devils river. The

physical conditions of slack water deposits have been discussed in detail.

Paul (1984) explained the respondents' perception of floods and agricultural adjustment

which were normal and abnormal. In this study, he observed that normal floods are

beneficial because it enables the harvesting of both aus and aman rice which are major

subsistence to farmers of the Jamuna floodplain of Bangladesh while during abnormal

flood situation, widespread destruction to crops and properties occurred due to high

magnitude of the inundation.

26

Newson (1992) reviewed the evolution of river management and the history of applied

hydrology to contextualise a global study of river basin system and their management

within both physical and social framework.

Kumar and Ram (1995) discussed the synoptic analogue method for semi-quantitative

precipitation forecast (QPF) for the Rapti catchment. They tested the synoptic analogue

of QPF of 1993-flood season with respect to the seven years rainfall data from 1986 to

1992 and found that the systems far away from the catchment predominantly, produce

low rainfall and systems near the catchment areas or active monsoon trough had a

tendency to move towards foot hills producing heavy rainfall in the catchment. On the

basis of this information, fairly accurate QPF could be issued by the forecaster in advance

for the Rapti catchment.

Penning-Rowsell (1996) demonstrated the context of flood hazard reponse is complex

mixture of physical, demographic, political and economic variables. He has discussed

how implementation of sustainable flood alleviation strategy was complicated by the

increase in population and economic restructuring in Argentina.

Miller (1997) explained the cause of floods, flood plain management through structural

counter measures and non-structural flood defence, dam safety and emergency responses,

together with the floods in Bangalesh, China, Mississipi and Central Europe.

Dogra (1997) discusses the flood and water logging problems in east Uttar Pradesh and

north Bihar. He further stated that expenditure on flood control had been increasing

rapidly; the area affected by floods also increased accordingly. Deforestation in Nepal

hills was found to be an important cause of the worsening floods. Haphazard construction

of roads and other development works, which did not provide enough room for drainage

of water, were other important causes. He also addressed the limitation and problems of

embankment in east U.P. and north Bihar.

Kale (1999) discused the temporal patterns of monsoon floods in five large rivers i e,

Mahanadi, Godavari, Narmada, Tapi and Krishna of the Deccan Peninsula. The study

revealed non-random behaviour with respect to distinct periods of high and low floods.

27

The normalized accumulated departure from mean (NADM) plotting methods was

applied to identify the below average (low) and above average (high) floods. NADM also

showed the association between monsoon rainfall and maximum water level.

Yadav (1999) provided a detailed appraisal of floods and flood problems of Eastern Uttar

Pradesh. He illustrated drainage and flood characteristics of the region where due to

highly erratic nature of the southwest monsoon rainfall, all the streams are characterized

by exceptionally high seasonal floods. Both the magnitude and frequency of the floods

had increased due to ecological degradation in the upper reaches of the river. Damage

due to flood, impact of floods on flood plain dwellers and floods management measures

have been discussed in detail.

Parker et al (2000) synthesized research articles on floods and their management, impact

of floods on society, flood plain management of the various countries such as

Bangladesh, U.K., U.S.A., Europe and the Netherlands.

Sinha and Bapalu (2000) attempted to prepare a flood hazard map of Kosi river basin.

They provided flood hazard index using data on population density, distance from active

channels, DEM, land use/land cover and geomorphic features. The river basin has been

classified into low, medium, high and very high flood hazard based on flood hazard index

values. The MODIS flood inundation map wasused for the validation of each flood

hazard zone.

Sarma (2000) attempted the flood risk zoning along the Dikrong river (north tributary of

the Brahmaputra river). DEM, maximum gauge level, agricultural, socio-ecomonic,

communication, population and infrastructure data were used for this analysis. Flood

damages to population, agricultural land and infrastructure at each return period i.e.2, 5,

10, 25, 50, 100 and 200 years have been worked out.

Sivasami (2001) explained the causes of floods in India and its management through

structural and non-structural measures. The flood damage analysis has been worked out

through three years cumulative value for the years 1957 to 1997. The environmental

effect of floods and reservoirs has been discussed in the light of Indian conditions.

28

Thapa (2003) discussed the flood problem of West Rapti river. The 1974 flood of

Gorakhpur is also elaborated. He further remarked that the construction of detention

reservoirs on the Rapti river can protect the life and property of innumerable people

living in the Eastern U.P. Saryu canal controversy and the locational characteristics of

West Rapti high dam were also addressed in the study.

Haq and Bhuiya (2004) had aimed to delineate the flood zones of tangail District of

Bangladesh using Radarsat-WIFS and satallite imageries of 1:50,000 scale. Three types

of flood zones were demarcated and the flood plain morphology, flood intensity,

periodicity, seasonality and its spatial-temporal variations and flood damages in each

zone also analysed.

Trinh et al., (2005) Studied the land use dynamics and soil degradation in Tamduong

District of Vietnam using landsat images (Landsat MSS in 1984 (4 bands), TM 1992,

1996 and 2000 (6 bands) were used for creating maps of the color composite and band

ratios. From these images, bare and degraded soils were identified and extracted.

Classified maps of the Band Ratios G/R and R/NIR for the year 2000 were established on

the basis of new soil maps and ground data. The best band ratio, R/NIR, was selected for

further processing and classification base on visual interpretation. The classified map of

degraded soils, based on the RINIR band ratio, matched well with the soil survey map

and the field checks.

Wang et al., (2005) analysed the water volume, length, total area and inundation area of

the three gorges reservoir of China at different gauge level using the Shuttle Radar

Topographic Mission Digital Elevation (SRTM DEM) data. The voids of the DEM were

removed through void-removal method.

Chandran et al., (2006) attempt to prepare the flood map of 2004 flood in Baghmati

river (Bihar) using Airborne Synthetic Aperture Radar (ASAR) images. Land use map

(LISS III) and DEM data were used to calculated flood affected agricultural area.

Sanyal and Lu (2006) used the GIS based hazard mapping at block and revenue village

level in the Gangetic West Bengal. They used number of flood occurrences, population

29

density, road density and access to safe drinking water for flood hazard mapping at block

level. While number of flood occurrence, population density and highest elevation of

each village were used at revenue village level. A knowledge based hazard ranking

method was applied to achieve a rational scenario of flood hazard in the study area.

1.6 OBJECTIVES

In the light of above research themes the following objectives have been drawn to:

1. Study the occurrence of floods, and to delineate the floodplain of lower Rapti

River Basin.

2. Map the flood plain morphology of the lower Rapti river.

3. Study the dominant processes viz. Channel shift, Meander dynamics, lateral and

over bank deposition which collectively modify the flood plain and flow pattern.

4. Study the impact of fluvial processes on arable land.

5. Study the trend in flood damages.

6. Analyse human adjustment and response to flood and associated problems.

1.7 DATA BASE

The secondary data base used in this study are:

o National Atlas oflndia, Vol. II, 1981.

o Watershed Atlas of India, 1990.

o Monthly Rainfall data ofGorakhpur (1901-1970), Bansgoan (1901-1968), Basti

(1901-1968), and Gonda (1901-1967) obtained from: http://www.ngdc.noaa.gov

o Monthly Rainfall data (1971-2000) of Gorakhpur, Bansgoan, Basti, and Gonda

were obtained from the National Data Centre, IMD, Pune.

o Monthly rainfall data of Gorakhpur, Bansgoan, Basti, and Gonda, (2000-2006)

were collected from IMD, Lucknow.

o Monthly data (1901-2006) of All-India and East Uttar Pradesh Region were

obtained from the Indian Institute ofTropical Meteorology, Pune.

30

o Flood Appraisal Report, Monsoon Season-2002, 2003 and 2008, Govt. of India,

CWC, Lucknow.

o Flood Report, 2008, Irrigation Department of Uttar Pradesh.

o District Disaster Management Plan, Gorakhpur, 2001 and 2009-10.

o The Dartmouth Atlas of Global Flood Hazard (2006 and 2007), E80N30 obtained

from http://www.dartmouth.edu/~floodslhydrography/E80N30.jpg

o Regional Divisions of India: A Cartographic Analysis, Census of India, Uttar

Pradesh Series-1, Vol. XXII, 1989, p.29.

o Estimated discharge and sediment load data (2006-2007) of Rapti river were

collected from CWC, Gorakhpur.

o Estimated Monthly Runoff data of Rapti River at Gorakhpur is obtained from:

http://www.dartmouth. edu/-jloods/AMSR-E%20Gaging%20Reaches/209.htm

o HMG of Nepal, Ministry of Science and Technology, Hydrological Records of

Nepal Stream Flow Summary, Kathmandu, Nepal, April1998.

o Census of India 2001, Primary Census Abstract, Gorakhpur, Santkabir Nagar,

Maharajganj, and Deoria 2001.

o Population Census 2001- VDC Municipalities, Central Bureau of Statistics

Thapathali, Kathmandu, Nepal.

o Block wise population data, 2001 was obtained from Jila Sankhyikik Patrika

(District Statistical Bulletin), Bahraich, Balrampur, Siddharth Nagar, Basti,

Santkabir Nagar, Maharajganj, Deoria and Gorakhpur, 2007.

o Topographical Sheet Nos. 63J/13, 14, 63Nil, 2, 5, 6, 7, 9, 10 and 11 on a scale

1:50,000 published by Survey oflndia, 1916-21.

o Topographical Sheet No. NG44-8 on a scale 1:250,000 prepared by Army Map

Service (RMBM), Corps of Engineers, U.S. Army, Washington, D.C, 1955.

o Landsat MSS P153/R041, 16th December, 1972.

o Landsat MSS P 153/R041, 25th February, 1975.

o Landsat TM Imageries, P142/R041 and P142/R042, lOth November, 1990.

o Landsat ETM+ Imageries, P142/R041 and P142/R042, 4th February, 2002.

31

o Landsat TM P142/R04I and P I42/R042, 19th November, 2005.

o Landsat TM PI42/R04I and P 142/R042, 5th October, 2006.

o Aster Data, 3I st July, 2008. Scene description is given as:

AST _LIB_ 003021 0200405I25I_ 2008073I074125 _24744.hdf

AST LIB 00303I5200805I759 20080731074105 23332.hdf - - - -

AST LIB 00303I5200805I808 20080731074205 26036.hdf - - - -

AST LIB 00304092008051204 2008073I074205 26038.hdf - - - -

AST LIB 00304092008051213 2008073I0742I5 26370.hdf - - - -

o Landsat TM P142/R041 and P I42/R042, 27th September, 13th October, and 16th

December, 2009.

o The map of Saryu command area was accessed on 8th July, 2010 from

http:/ /irrigation. up .nic.in/ptr/ saryu.htm

o SRTM data 03 Arc Second, February 11-22, 2000 was accessed on 24th

September, 2008 from http://srtm.csi.cgiar.org.

o GEOTOP030, 30Arc Second, 1996 was accessed on 24th September 2008 from

http://eros.usgs.gov/#/Find Data/Products and Data Available/gtopo30/e060n4

Q

Primary data used for this study are:

o Ground verification of floodplain features was done using Garmin hand held

GPS-76CS.

o Lagging exposed section along the bank was done using measuring tape and

ranging rode.

o Human response to fluvial processes and adjustment to agriculture were executed

through inventory and questionnaire survey in November and December 2008.

32

1.8 METHODOLOGY

a The normalized accumulated departure from mean (NADM) plotting method was

used to filter short-term fluctuations and to highlight the long range variability in

maximum water level and annual monsoon rainfall. The NADM is the

accumulated departure from mean (ADM), divided by the largest number

(absolute) in order to plot between -1 and + 1.

a The Pearson correlation coefficient ( r ) was used as an index to show the degree

of correspondence between two or more different NADM curves.

a Log Pearson Type III method was used for recurrence Analysis

a Floodplain along the Rapti river was delineated using HECRAS and HEC­

GEORAS software.

a Ground verification and Visual interpretation of topographic maps and satellites

imageries were done to identify the floodplain features such as ox bow lakes, clay

plugs, point bars, swales, Channel bars, natural levee, crevasse splay, abandoned

and anabranching channels.

a The entire stretch of the channel was divided into 8 reaches on the basis of

curvature to calculate the sinuosity index (SI).

a

a

a

a

a

SI = (Channel length I Straight line valley length)

Midpoint of the axis of meander was defined as centroid to analyse the channel

shift.

Lithologs along the Rapti river bank were prepared to know the composition of

the bank materials using ranging rode and measuring tape.

The trend in flood loss was interpreted by three years cumulative value.

Land use classification was done using supervised classification of satellite

imageries.

The Historical Migration Zone (HMZ) of the selected reach was demarcated using

ARC GIS 9.2 software. This migration zone covers the collective area of the

channel occupied in the historical records (1916-21 to 2009). The section of

33

HMZ, where embankment physically controls channel migration, has not been

considered in HMZ.

a Data logger and channel migration predictor extension of ARC VIEW 3.2a GIS

software were applied to predict the future channel course.

a Visual interpretation of the satellite imageries (1972-2009) has been done to map

and identify the sand casting and waterlogged areas.

a Width and length of gullies were directly measured during the field surveys

(November-December 2008).

a The size composition of soils was done by 'texture by feel' analysis as elaborated

by Northcote (1979).

a On the basis of the water depth associated with the 100 years return period,

selected part of the lower Rapti floodplain was divided into three classes i.e.,

high, medium, and low flood depth zone. Subsequently, proportionate random

stratified sampling was applied for collecting data for each zone.

a Special Package for the Social Sciences (SPSS-14.0) software was used to cross

tabulate different variables and analyse the frequency of different variables.

a Knowledge based risk ranking method was applied to prepare the composite

index of flood risk.

In addition, a detail description of methodology used for the analysis has been given in

each chapter.

1.9 ORGANISATION OF MATERIAL

The entire work has been organized into seven chapters. First chapter is the introduction

that includes geographical personality of the study area, literature survey, objective, data

base, methodology and practical utility of the study. Second chapter discusses drainage

pattern, flow characteristics and floodplain delineation. Third chapter covers the analysis

of floodplain morphology and channel characteristics. Fourth chapter dealt with the

channel shift and meander dynamics. Fifth chapter covers the impact of fluvial processes

on arable land. Sixth chapter contains the human responses to fluvial processes and

34

aspect of management. Seventh chapter summarizes the entire work along with

conclusion of the study.

1.10 APPLIED ASPECT OF THE STUDY

The present study has high degree of practical utility as it takes into consideration both

fluvial processes and human adjustment. This study would provide basic guidelines for

administrators and planners to:

• Access to flood risk map for any eventuality.

• Mobilise the people living along the shifting river bank in the face of any flood.

• Raise the villages located in the high flood risk zone and connect them to nearby

Highway (State and National) in order to evacuate the people prior to

exceptionally high flood.

• Have a provision for quick availability of sand and cement bags to villages

located near the embankments which are vulnerable to breaches.

• Introduce appropriate paddy varieties which are best suited to certain flood water

depths.

• Devise the mechanism for crop insurance when and where affected, based on

flood risk map.

35