acknowledgement
TRANSCRIPT
ACKNOWLEDGEMENT
Q am grateful to Professor Sandipan Chakroborty, Dept. of Geography, Presidency
College, Calcutta, for his guidance during the field study in Garhbeta, Midnapore)
^1and for his non stop motivation to carry out studies in the post field work.(His
ideas, remarkable understanding of Fluvial Geomorphology and support has
greatly contributed in carrying out this research work!)
am also indebted to Sri Jayanta Sen, Research Scholar of Vidyasagar
University, Midnapore West Bengal for supplying the useful maps anddocuments?) ^
1 am also grateful to my parents who always inspired me to carry out my
dissertation work.
,/CONTE NTS
HAPTER 1:
a. Introduction
b. Location C. Objectivesc. Methodology
d. Previous Literature
APTER2:
a. Geologyb. Climatec. Natural Vegetationd. Soil I
.CHAPTER 3:a. Progressive growth of gulliesb.Types of water erosionc. The cause and processes of linear erosion
CHAPTER 4:
a. 3 tier gully development!! H b. Shapes of gullies
c. Longprofile of gullies
d. Micro relief features
y<5HAPTER 5:y
a. Information about Garhbeta Badlandb. Impactc. Conclusion
ydHAPTER 6:
Bibliography Annexture
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TRODU
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i near Garhbeta, AMedinipur district, West
Bengal, India has given rise to a mesoscale
badland landscape. Exquisite chromatic
association of land forms and awe-inspiring
character of topography calls for investigation of
geomorphic processes that have dominated the
terrain in the past and are operating even today
in the area.
LOCATION
The Garhbeta Badlands (22° 49'N, 87°
27'E) is situated in west Medinipur district of West
Bengal, India. This area is locally known as
4Ganganir Danga' (Land of Fire). The area lies on
he Howrah-Adra-Chakradharpur route of the
South-Eastern Railway and is located at a distance
of 176kms. from Calcutta and is approachable by
both road & railways.
v/dBJECTIVES
The Specific objectives of the study are - (i)
to delineate the nature and characteristics of
gullies, (ii) to detect the Causes of the
development of rills and gullies of the area; (Hi) to
classify the gullies based on their nature and
extension;
^METHODOLOGY
The entire work has been performed by
different phases and methods are -(I) Pre-field; (ii)
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field method. In Pre-field methods the maps and
data products (digital-imagery) have collected from
different Govt. Sources. In the field, extensive field
work has been done in each sector and phase
according to the levels of development for micro
level study and to observe the nature and
delineate the morphological characteristics of the
study area. In post field work the data have been
processed and analysed by modern Geomorphic
and analytical techniques and ultimately attempt
have been taken to delineate the impact of ravine
development on surrounding.
PREVIOUS LITERATURE
Besides depending on the fieldwork at
Garhbeta, other geomophological data &
informations are taken from different journals of
Bondhopadhyay S, Jayanta Sen, Suman Sen,
Kanailal Das & other's who have done work in this
area.
sy GEOLOGIC DEVELOPMENT
The region around our study area have thick mantle of laterite
occupying the high lands along the bank of river Silai. They are believed to be
of Pleistocene age. The thickness of this laterite capping varies gradually
between 6-25 metres.
The result of exploratory boreholes in the area revealed that there is a
gradual increase in depth of the basement rock (granite gneiss) with
consequent increase in the thickness of the semi-consolidated or loosely
consolidated sediments including the laterite from west to east and southwest
directions. This view also was corroborated by the findings from the
geophysical studies in the area. The palaeontological evidence also indicated
a gradual increase in the base of Pleistosene sediments from 106 to 152
metres to the east (Goswami, 1964-65).
Geology of the area is concealed under a blanket of laterite and laterite
soils. Based on he critical appraisal of the lithological logs and electrical logs of
the boreholes drilled in the area the lithological sequence works out as
follows:-
(i) Laterite Laterites, yellow & mottled clay, furriness sand and silt, yellow clay, gravels.
(ii) Quartzo-feldspathic sand Clay, grey, silty medium to coarse-sand. Grey and brownish grey with intervening clay.
(iii) Ferro-Magnesian sand Clay, grew to brownish grey silt, fine to medium sand, micaceous gravel bed.
(iv) Clay Clay, grey semi-cousolidated contain fossil. Fossil pockets mainly pelecypods and gastropods.
Base unknown
CLIMATE
The climate of the study area has been identified as sub-humid
monsoon type. Hot dry summer season (March - May), wet monsoon season
(June -October) and dry-cool winter (December - January) are the three
important seasons that cover most of the time of the year. During summer, the
maximum temperature increases to 45°C or more. The bare and dark coloured
lateritic surface produces maximum radiation of heat energy during this time.
The area receives an average rainfall of 140cm yr"1. Dry and cool winter
season lasts about three months in a year when minimum temperature goes
down to below 9°C. The seasonal fluctuations of
temperature and humidity have a great impact on laterisation processes and
badland development over the study area.
^NATURAL VEGETATION
Our study are was once covered with mixed deciduous forest and
was a part of Jangal mahal of Rarh upland before independence. Sal
(Shorea robusta) was the most important tree associated with Shimul
(bombax ceibal), Mahua (madhuca indica), Jarul {lagerstroemia
speciosa) etc. Presently, low sub-soil acidity, high subsurface calcium and
absence of organic matter are indicative of poor growth and regeneration of
sal. In most of the places the topsoil has been washed away which is not
favourable to the ecosystem.
|: t/^OIL FORMATION
The region is characterised with loose and dry surface soil with
presence of highly indurated duricrust. The sediments of the area are mostly
concealed under a blanket of duricrust. As laterite is heavily leached tropical
subsoil, when exposed, it dries and gets rock-like due to cementing of
ferruginous concretions by iron oxide colloids (Mallick and Niyogi, 1970). It is
not a fertile soil. At Garhbeta laterite also consists of aluminum
oxyhydroxides with smaller amounts of iron oxyhydroxides and a little bit of a
clay mineral called halloysite. Silica, calcium, magnesium, potassium and
sodium are present in very low amounts of absent. Laterite formations span
several kilometers on the right bank of river Silai. The topography very much
resembles the Australian "breakaways" with a broad flattish and dissected
top and undercut softer materials below (Mallick and Niyogi 1970, Biswas
1987). L
ATERITIC PROFILE AT GARHBETA BADLAND
Sequence Name
Slope Thickness (m) Characteristics
1 Surface Layer
3" or less 0.5 A Surficial cover of red clayey soil, recorded in many places, with some sands, & minute concretions.
2 Laterite duricrust
5U-15° 2.0-4.0 A layer of nodular duricrust, partly cemented containing iron concretions or spaced nodules, which are tabular & sufficiently large to be called pipes often draining out
water, from the solutionai & collapse holes developed on the surface, the highly indurated layer being often cut away vertically by gullies running down to the river.
3 Mottledclaylayer
Nearly 60°
4.0-6.0 A layer of redish & sometimes purplish mottled clay, mired with some five as well as course sand, traversed in places by thin hardpans, cut away by rills & gullies at the scarp face.
4 Palledzonelayer
35° -45° 5.0 A pallied layer of yellowish white clay containing very little of sand somewhat irregular in occurrence, pure clay occuring only in pockets, producing on the break away.
We can also describe the nature of soil and sediment properties in the study
area by the following table >
Nature of Soil & Sediment Properties in the Study area
No Specifications SoilPh
Organic Carbon
%
%0fSand
%of Silt
%ofClay
Textural Class
Available N
AvailableP
S1 Laterite durienst / upland surface
6 8 0.22 51.9 15.8 32 8 Sci 120 20
S-2 Pallid zone surface of western gully fringe
5 5 0 06 499 35.8 14 3 L 32 3.6
S-3 Gullychannel bed / by the sideOf River silat
5 8 Nilm- - -.......„ .
,
927 1.0 6.3 S 25 Trace
S-4 Erosionallateriteuplandcultivableduring wetperiod
5.5t
0 62•
41.8 4.9 16.3 L 401 85.0
QUANTITATIVE ASSESSMENT OF GROWTH OF GULLIES IN
Following Table gives clear indication on progress
of the badland based on estimation of authentic
secondary information viz. Survey of India topographical
maps (1:50,000), Aerial photographs (1:60,000), satellite
data (IRS LISS III Geocoded, 1:50,000; IRS ID PAN
Image - 2001, and ground survey since 1995. It can be
seen that the affected area has increased to about
234.48% during the last 73 years.
SI. Source of Information Year of Observation Affected area km1 SOI Topographical map 1930-31 1.45 km22 SOI Topographical map 1968-69 2.10 km23 IIRS 1C Lisslll Geocoded
Image1995 2.95 km2
4 IRS 1D PAN Image 2001 3.28 km25 Mapping with GPS and
field monitoring2003 3.40 km2
Introduction of Global Positioning System opened up a
new frontier in surveying, with unprecedented accuracy especially
in this terrain which had to be mapped to investigate fluvio-
geomorphological processes so that such spatial database may
assist in adopting necessary reclamation schemes. GPS survey
carried out during 2000-2001, brought about exact extent of
actual present area under badlands, shape and length of the
escarpments, rate of gully headwall retreat, location of micro and
ARHBETA
meso scale geomorphic features, gully networks etc. The GPS
hardware and software used in the survey (Trimble TDC 1 and
TCS-1 receiver with Pro XR antenna and Pathfinder Office V 8.2
software) were capable of providing sub meter accuracy after
post processing of the collected data. Universal Transverse
Mercator (UTM Zone North - 45) projections was used in the
study as this was found to be the most convenient projection
system for transferring the GPS-generated vectors directly to
Geomatica V8.2, the RS/GIS software used for mapping.
Four stages of Gully development at Garhbeta Badland:
EVOLUTION OF GARHBETA BADLANDS IN MEDINIPUR
DISTRICT OF WEST BENGAL
Initially this area was a flat-topped lateritic upland.
Shifting of river Silai towards the upland and erosion along its
concave bank produced a steep escarpment (>20m) revealing 4
to 5 distinct indurated horizons. Gullies dissected the duricrusted
surface and extended headward resulting in rapid scarp retreat.
The badland of Garhbeta have two distinct parts viz. the
less mature Southwestern part (about 0.40 km2) & more mature
North-Eastern part (about 0.85 km2). The maximum retreat of
the gully head was found to be about 60cm/year.
DEFINITION AND CHARACTERISTICS OF BADLAND
'Badlands', as the name implies, are
barren areas of little or no economic value;
generally devoid of vegetation and often
having an extremely rugged terrain, which makes
human access difficult; they are generally regarded
as useless lands. The term can be traced to early
settlers in western North America where scattered
areas of badlands are widely distributed. (Campbell
1989) Encyclopedia of Geomorphology by R. W.
Fairbridge describes badlands as extremely
dissected landscape difficult to cross on horseback
and agriculturally useless. French
Geomorphologists define badlands as areas
dissected by very fine drainage networks and short
steep slopes with narrow interfluves. The slopes
may terminate abruptly in pediments on a miniature
scale and are often completely free of vegetation.
RAINSPLASH EROSION
It occurs when raindrops fall [raindrop fall at
914 cm/s (30ft/s)) on unprotected ground. When
raindrop strikes the ground surface the soil particles
become more loose and splash due to impact force.
A momentary building up of the pressure gradients
towards the edges of the drop disintegrates the soil
and shoots some particles out. The slashed particles
reach to heights ranging up to 2-5cm and horizontally
upto an average of 5cm depending on their size and
slope of the ground at Garhbeta. The important
influencing factors of rain splash are the mass and
velocity of raindrop and the soil character.
SHEET EROSION
At lateritic Garhbeta badland region sheet
erosion result significant surface wash over the
undulating upland surface upto the gully head during
high intensity precipitation events. The western
section is much bare that results tremendous sheet
flow and surface removal. Whereas the eastern gully
section though the gully channels have more width
and length, the upland surface is less undulating and
gradient averages to 2°-5°. Here the sheet or
overland flow becomes active when sufficient rainfall
occurs (100 mm/hr). The surface particles are also
little smaller (<3mm) compare to western gully sector,
which results high ground water percolation and
steady overland flow especially when sufficient rainfall
occurs.
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RILL EROSION
Studies of hydraulic characteristics of the flow
show that change from overland flow to rill flow
passes through four stages at Garhbeta; (i)
Unconcentrated channel flow, (ii) Overland flow with
concentrated flow paths, (iii) Micro-channels without
head cut and (iv) Micro-channels with headcut.
The greatest differences exist between the 1st
and 2nd stage, suggesting that the flow concentration
within the overland flow should strictly be treated as part
of an incipient rill system (Merritt 1984). In the 2nd stage,
small vortices appear in the flow, which, in the 3rd stage,
develops into localised, spots of turbulent characterised
by roll waves and eddies.
Based on the surface slope and velocity of flow
the rill channels on Garhbeta lateritic upland can be
classified into three types :
(a) Small or minor rills, (b) Moderate rills, (c) Major or developed rills.
GULLY EROSION
Gullies are open erosion channels at least
30cm deep which conduct ephemeral runoff and are
frequently characterized by steep sidewalls and a lack
of vegetation. Gullies tend to become deeper with
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n remove vast amounts of soil. Removal of topsoil and
subsoil by fast-flowing surface water creates abrupt
deep and wide gullies, of two different kinds: scouring
gullies and headward erosion. In scouring gulling,
run-off water concentrated in rills or depressions
removes soil particles. Material commonly moved is the
size of fine to medium sand or may be derived from
slaking, when large aggregates disintegrate upon
wetting. Scouring is often associated with gently
undulating landscapes.
THE CAUSE &
PROCESSES OF
LINEAR EROSION (i.e.
Rills & Gullies) IN
GARHBETA
The cause of linear erosion is to be sought in runoff
energy, which depends on runoff volume and its
squared speed.
3 THEORIES OF THE ONSET OF RUNOFF
1. Horton's theory (1945): Runoff starts when rainfall
intensity exceeds soil absorption capacity.
Comparing infiltration to rainfall intensity,! absorption
decreases over time partly because capillary potential falls as the wetting front
penetrates into the soil, and partly because soil structure at the surface
was deteriorated.
2. Soil saturation theory: Runoff starts when all the pores in the soil are
filled with water. In the cause of a simulated rainstorm, if runoff starts
after rain has soaked the soil, it will increase until it stabilizes at a level
corresponding to the absorption capacity of the soil. However if the
rainfall persists (runoff may rise again, reaching a new plateau of
stabilized infiltration. This simply means that the tilled horizon has
reached saturation, so that the macroporous storage capacity of this
horizon is filled to overflowing. If the underlying horizon is totally
impervious, the amount of runoff will correspond precisely to that of the
simulated rainfall; there may, however be a corresponding to that of the
plough pour. When the soil is totally saturated, any drop of rain will runoff
respective of rainfall intensity.
3. Theory of partial watershed surface contribution to runoff: The runoff
measured at the river-level depends on the area of the saturated soil in the
valley bottom. If watershed surface runoff is measured during the dry
season, it is seen that the river reacts very quickly to rain storms whereas
no runoff is seen on the slopes! The volume of is less during this dry period
because only a narrow ship in the valley bottom is saturated - often only
the minor bed. At the end of the winter, however, when the whole soil
cover has been soaked to capacity, the slightest rainfall replenishes the
aquifer, which will spread out sideways, saturating a greater areas of the
valley. As a result, even if there is no runoff on the slope during the rainy
season, the entire watershed well contribute to the volume of flow in the
river through extension of the saturated area, in as much as the ground
water is recharged directly by draining the entire basin.
The stages of weathering and erosion observed in the region are:
1. The Preparatory Stage
During this stage the surface is prepared for sculpturing. Based on seasonal
characteristics of climate such preparatory stage can classified into winter and
summer conditions.
1a. Surface preparation during winter condition (December -
February) : Just after the monsoon the surface moisture is
reduced gradually due to lowering of atmospheric humidity.
Significant fluctuation of diurnal, temperature about 18° -20°C, is
found which results destru :tion of seasonal vegetation mainly
grasses at different stages of the badland sector of Garhbeta.
During December and January when the minimum temperature
further goes down below 9°C and atmospheric moisture goes
down below 65% the surface of the terrain become very dry and
loose and numerous cracks and joints progresses with surface
contraction over the lateritic upland.
The depth to ground water level in the phreatic zone gets
low in winter months and varies between 1.5m to 9metres below
land surface. The winter season persists upto February and
before onset of summer a transitional period occurs for about 15 -
20 days.
1b. Surface preparation during summer condition (March - May):
During summer the atmospheric temperature at daytime at
Garhbeta increases up to 45°C. However, at night, the
temperature goes down to 25°C. This fluctuation encourages
significant processes of mechanical weathering. The bare dark
colored and granular surface of the lateritic upland of Garhbeta
makes suitable conditions for weathering processes to be
maintained. Occasional occurrences of thunderstorms (locally
called Kalbaisakhi) transport loose and unconsolidated surface
materials, which are afterwards washed out more easily by the
surface runoff or sheet wash.
From middle of May up to the 2nd week of June, the
groundwater regime further goes down from 2.8 to 18.0 metres
below land surface. This lowering of groundwater also has
significant impact of laterisation process and surface wash after a
prolonged dry season. Therefore, in the preparatory stage the
seasonal and diurnal fluctuation of air and surface temperature
along with the fluctuating groundwater make suitable
preconditions for fluvial erosion with formation of rills and gullies
during the rainy season.
2. Surface erosion stage / Processing stage
The surface erosion stage at Garhbeta starts from middle of
June at the onset of monsoon rains. The factors that influences
soil erosion by water is the mean annual rainfall and rainfall
intensity. Severe erosion in the badland sector of Garhbeta is
Types and Number of Gully Channels at Garhbeta badland (Eastern Sector)
associated and accentuated with high mean annual rainfall
(about 1400mm and poor growth of vegetation).
v^TIER GULLY DEVELOPMENT
As observed by Bandyopadhyay (1988), a distinct 3-tier
gully development, genetically unrelated to each often, is seen
in the region. Numerous but small (depth : 1-2m) gullies under
the first tier develop above the escarpment, etched on the top
most laterite hardcap. 4 to 5 gullies of the first tier open out into a
single gully of the 2nd tier (depth : 10 - 15m) that extends
headward with basal sapping 3-10m below the top level
duricrust & with the consequent retreat of the escarpment. The
material deposited by the 2nd tier gullies in the erosional plain
created by the retreating escarpment are found to be dissected
by the gullies of the 3rd tier (depth : 0.5 - 1m) which are
unbranched & drain directly into the Silai.
General Classification of gully channels at Garhbeta badland
No. Name TypeSpecifications
Depth (m)
Width (m) Side slope (%)
1 Very small gullies Gi <1.5 <10.0 <82 Small gullies G2 1.5-3.0 10.0-15.0 8-153 Medium gullies G3 3.0-9.0 15.0-18.0 15-454 Deep & narrow gullies G4 >9.0 >18.0 >45
SHAPE OF GULLIES
The riverine gullies of Garhbeta area are characterized
by three common morphological features e.g. gully-head,
gullyneck and gully body. The morphometric properties of a
sample gully draining into the Silai river include 'notched shape'
of gully head with a maximum width of 3.9m and constricted
section of 2.0m width, narrow gully neck of 2.5m thickness and
elongated shape of gully body of 35m length. Besides a few
exceptions, almost all of the gullies are characterized by plunge
pools'. The longitudinal profile of an active gully denotes the
presence of gully heads, gully heads, gully neck, cliff face,
plunge pools, and gully body on the basis of morphological
characteristics the gully heads have been divided into four types
viz. (i) pointed gully head (ii) circular gully head (iii) notched gully
head and (iv) digitate gully head.
The gullies of Garhbeta area vary significantly as regards
their shapes and morphological characteristics and thus they
have been classified into six types e.g. (i) linear gullies (ii) parallel
gullies (iii) gullies (iv) bulbous gullies (v) rectangular gullies and
(vi) mixed gullies represents different morphometric properties of
sample gullies. Linear gullies are long (13.9m to 60m) with
pointed narrow gully heads (ranging in length from 2.2m to 2.6m).
Sometimes, a few very small tributary rills also develop on either
side of the main gully body. It may be pointed out that linear
gullies no longer always remain narrow because their valleys are
broadened and are transformed into bulbous, trellis or mixed
types. They generally develop in the area having highest
concentration of surface run-off through a single channel. They
undergo the fastest rate of advancement through headward
erosion. In a single rainy season, the extension of linear gullies
ranges from 10m to 20m Parallel gullies, which represent group of
linear gullies, have developed on concave side of the Siiai river at
Garhbeta. Trellis gullies have developed on moderately sloping
ground with multiple channel flow of accelerated surface run off. It
is evident that trellis pattern of gullies is characterized by longest
length of gully heads (10m to 28m) and greater depths (8.1m to
15m).
Bulbous gullies have developed in areas having moderate
flow of surface run off with maximum exhumation of soluble
minerals from A horizon of the soil profile B, and B horizons.
Semicircular or amphitheatre like heads of bulbous gullies
generally develop due to buckling down of A horizon fostered by
excessive mudflow
y /
through B horizons. Rectangular gullies have very poorly
developed in the study area.
MORPHOLOGICAL CHARACTERISTICS OF SAMPLE GULLIES
S
■
DETERMINATIO
N OF SHAPE OF
MACRO GULLY
IN WESTERN
SECTOR AT
GARHBETA
Shape of macro gully in western sector
of Garhbeta have been determined from which
idea of gully head, gully floor and gully side
walls can be done. Through the determination
of gully shape the following table can be
represented -
From Gully Head (facing Silai Nadi)
Right Wall Left WallTributary Gully angles
Intervening Spur angles
Tributary Gully angles
Intervening Spur angles
ZB = 130° ZC = 97° ZL= 130° ZQ = 28°ZD = 103° ZE = 76° ZR = 147° ZT = 21°ZF % 70° ZG = 68° ZS = 127° ZW = 56°Zl = 122° ZH= 120° ZU = 60* ZY = 136°ZK= 131° ZJ = 42° ZV = 100° ZZ= 179°ZL = 165° ZM = 87° ZX = 84° ZBt = 130° !
1—
ZN = 178° ZAi = 130° ZB = 59°ZB = 130° ZCi = 110°Average = 128°25'43"
Average = 81°40' Average =111° Average = 79°50'
^/WESTERN AND EASTERN GULLY
As seen before, the badlands of Garhbeta can be classified as
western (or less matured) and eastern (or matured) parts. In the western
part, gullies are short and discontinuous, slope of the gully wall is between
60-90°; their height varies between 18-25m. Whereas in the eastern part,
gullies have greater length; slope is gentle and convex (5-45); height of the
gully wall is below 15m. Our observation shows the orientations of the gullies
are very much integrated with nature and properties of laterite profile. The
profile shows, there are 4-5 distinct horizons and due to differential
sedimentary composition each profile has differential resistance to erosion.
As a result gullies in Ganganir Danga occur in different levels. One set of
gully drain the surface of the lateritic duricrust and the other cut into the lower
horizons originating from the retreating cliff line.
Distinct characteristic difference can be seen between eastern and
western gully channels. V-shaped gullies form in material that is equally or
increasingly resistant to erosion with depth. U-shaped gullies form in material
that is equally or decreasingly resistant to erosion with depth. As the
substratum is washed away, the overlying material loses its support and falls
into the gully to be washed away. Most V-shaped gullies become modified
toward a U shape once the channel stabilizes and the banks start to spell
and slump.
\/CONG PROFILE OF GULLIES
Long profile is the section or line which can be obtained by plotting
the axial line of the channel from source to mouth. As gully slopes are
commonly steep in the headward sides and gentle in the lower reaches
profiles are normally concave upwards.
Here Macro, Meso and Micro types of longitudinal profiles are
determined by the use of clinometer, Abney level and prismatic compass.
While determining the longitudinal profiles an idea can be done of the slope
of longitudinal profile. For e.g.,
cliff slopes are found on escarpment faces. Cliffs are so steep (40° or more)
that the products of weathering for the most part fall immediately to the base.
There is little or no accumulation of detritus on the cliff itself and it is therefore
commonly and meaningfully referred to by geomorphologists as a free-face.
Scree slopes are also found which varies from 35° or more in the
longitudinal profile. Aggradational slopes are seen in the longitudinal profile. It
varies from 20° -35°. Eventually the cliff may disappear entirely to be replaced
by a wholly aggradatinal slope at 20° - 35°. In its lower part, a longitudinal
profile will commonly exhibit a concave section. Rectilinear slope profile is
often observed in the Garhbeta badland area which is straight in profile.
MICRO RELIEF FEATURES IN GARHBETA
On the basis of survey by dumpy level and prismatic compass relief features
are obtained for a gully catchment area. Through this survey in a catchment
area it is found that high relief is found in the Eastern and Southern part.
Based on this variation of relief features serial profiles are drawn and they are
superimposed to identify the micro relief features of the gully catchment area.
Some useful data on Garhbeta badland:
SI Parameters Quantified Units1 Present total area covered by
badlands2 Area occupied by Eastern gully
sectorWestern gully sector
3 Average extension of area under badlands (for the last 8 years)
56.25 sq m
4 Total length of escarpmentRole of escarpment retreat Maximum 85 cm / yr
Average 10-12 cm5 Height of the escarpment Maximum
Average6 Average slope of the terrain
7 Area affected be sheet erosion
14% of total
8 Area affected by rill erosion9 Area affected by gully
erosion72% of total
10 Linear extension of rill channels
Maximum
Average11 Linear / headward extention of
gully channelsMaximum
MinimumAverage
12 Gully channel morphology Slide slope MaximumAverage
Depth MaximumAverage
Width MaximumAverage
Length MaximumAverage
IMPACTS
The impact of Gully Erosion are -
(i) Gully erosion means the loss of large volumes of soil.
(ii) Deep wide gullies, sometimes reaching 30m deep,
severely limit the use of the land.
(t«) Off-site deposition of soil causes water-qualify decline in
streams or rivers.
(iv) Large gullies disrupt normal form operations, creating
access problems for vehicles and stock.
(v) Low soil organic matter levels, lower fertility levels,
changes in soil pH, exposed subsoil and parent material
discourage crop production in gullies and rills.
(vi)
Soil erosion in the badlands of Garhbeta has serious
impact on the surrounding environment by decreasing soil fertility
and land productivity. It also reduces the capacity of soil to absorb
rainfall that often results in increased flooding and reduced
ground-water recharge, augmenting sediment loads in rivers and
streams. This degrades the quality of water supplied downstream
and cause silting of channels and reservoirs, in turn, increasing
risks of flooding and reduction in dry* season water supply. Such
an area was selected by us for study, because all stages of water
erosion, channel initialization, rill and gully development slope
evolution, and other land sculpturing activities are found in this
rather meso-scale topographic unit. Geomorphological
investigation of water erosion on land sculpturing, role of fluvial
action on a specific land and significance of climatic variables on
development of badland topography. The badland though covers
a small area, is a natural plot in itself for carrying out fluvio
geomorphological investigations and research through real time
monitoring techniques.
A greenbelt has been created by the State Agriculture
Department since 1969 to check gully erosion at Gangani. The
green belt is initiated along the divide region to the south of the
badlands mainly using cashewnut (Anacardium occidentale). But
the 2nd tier gullies of Gangani are advancing by undercutting. The
process is operating 4 to 10m below the protected surface. So the
plantation of cashewnuts may not be able to check the gully-
advancement. Trees of other species, such as Sal (Shorea
robusta), which are able to penetrate the root system below the
laterite horizon would perhaps make a better choice (It may be
noted that laterites are indurate only after their exposition to the
atmosphere. At present, the gullies in Gangani are creating
agricultural areas rather than destroying it. Crop-cultivation,
mainly rice & vegetables, is practised in small plots in the
recessional depositional
surface left exposed by the retreating cliff-line.
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