Dryland
Dryland an area where
the rainfall is so low that the soils
remain almost dry throughout the year.
Drylands occupy around 35% of the
continental surface of the earth.
They occur either within the climatic
belts of the lower or middle latitudes,
with an average annual rainfall of
150 to 250 mm. This quantity of rain
is not sufficient to maintain a continuous
plant cover on soils.
The main drylands
of tropical and subtropical regions
cover the vast stretches of the Sahara
and the Libyan deserts in North Africa,
the Arabian and the neighbouring deserts
of West Asia, the deserts of Peru
and Chile in South America and the
deserts of about half of Australia.
A vast area of mid-latitude drylands
is located in Central Asia, and includes
the famous Gobi desert of Turkistan
and the desert of Mongolia. In North
America the drylands encompass sections
of California, Arizona, Nevada and
adjoining areas; in South America
the drylands cover portions of Patagonia
and adjoining areas.
The soils of drylands
are light coloured and are usually
coarse textured. Chemical weathering
is minimal, while physical weathering
is dominant. Rainfall is low and so
also is percolation. The soils of
drylands have been classified as aridisols
in soil taxonomy. They usually have
an ochric epipedon and one or more
of the diagnostic horizons are cambic,
argillic, natric, calric, gypsic and
salic. Aridisols include soils that
are called desert soils, red desert
soils, reddish brown soils etc. Dryland
soil profiles are well oxidised as
is evidenced by their low organic
matter content and lack of free iron
oxide movement.
The southern part
of northwest Bangladesh (rajshahi
and naogaon districts) is the driest
part of the country, where rainfall
is most unreliable in timing and amount.
The general soil types of this region
are characterised by calcareous dark
grey floodplain soils, calcareous
brown floodplain soils, shallow grey
terrace soils etc. These soils are
better suited for the cultivation
of dryland crops. Perennial dryland
crops (such as fruit trees and sugarcane)
require good soil drainage throughout
the year for satisfactory growth.
Annual dryland crops need adequate
soil drainage during their growing
season. Dryland rabi crops may be
grown in the dry season on poorly
drained land which is flooded in the
monsoon. Dryland kharif crops must
be grown on well-drained soils.
Barind Tract
largest Pleistocene
physiographic unit of the bengal basin,
covering an area of about 7,770 sq
km. It has long been recognised as
a unit of old alluvium, which differs
from the surrounding floodplains.
In Bangla, it is spelled and pronounced
as Varendra Bhumi. Geographically
this unit lies roughly between latitudes
24°20´N and 25°35´N
and longitudes 88°20´E and
89°30´E. This physiographic
unit is bounded by the karatoya to
the east, the mahananda to the west,
and the northern bank of the ganges
to the South. A lower fault scarp
marks the eastern edge of the Barind
Tract, and the little jamuna, atrai
and Lower Punarbhaba rivers occupy
fault troughs. The western part of
this unit has been tilted up; parts
of the western edge are more than
15m higher than the rest of the tract
and the adjoining Mahananda floodplain.
The southern part of the main eastern
block of the Barind Tract is tilted
down towards the southwest and passes
under lower Atrai basin sediments
in the south. The Barind Tract covers
most parts of the greater dinajpur,
rangpur, pabna, rajshahi, bogra, joypurhat
and naogaon districts of Rajshahi
division.
The Barind Tract
lies in the monsoon region of the
summer dominant hemisphere. The tropic
of cancer lies south of this region.
The climate of the area is generally
warm and humid. Based on rainfall,
humidity, temperature and wind pressure
the weather condition is classified
into four types, such as, (a) pre-monsoon,
(b) monsoon, (c) post-monsoon and
(d) winter. Rainfall is comparatively
little in this region, the average
being about 1,971 mm. It mainly occurs
during the monsoon. Rainfall varies
from place to place as well as year
to year. For instance, the rainfall
recorded in 1981 was about 1,738 mm,
but in 1992 it was about 798 mm only.
This region has already been designated
as drought prone. Its average temperature
ranges from 35°C to 25°C in
the hottest season and 9°C to
15°C in the coolest season. Generally
this region is rather hot and is considered
semi-arid. In summer, some of the
hottest days experience a temperature
of about 45°C or even more in
Rajshahi area, particularly in lalpur
upazila. In winter it falls to about
5°C in some places of Dinajpur
and Rangpur districts. So this older
alluvium region experiences extremes
that are clearly in contrast to the
climatic condition of the rest of
the country.
Physiographically
this region is divided into three
units. These are Recent Alluvial Fan,
Barind Pleistocene, and Recent Floodplain.
These morphologic units are separated
by long, narrow bands of recent alluvium.
The floodplain of the Mahananda flanks
the west side while the Karatoya delineates
the eastern margin. The punarbhaba,
Atrai and Old Jamuna with headwaters
in the foothills of the himalayas
have cut across the Pleistocene and
their floodplains separate the units.
These and numerous other streams are
responsible for the development of
a broad Piedmont alluvial plain, which
delineates the northern flank of the
Tract. The Tista alluvial fan is located
to the north of the area. This fan
surface of the Himalayan foothills
has a slope of approximately 0.43m/km
and it overlaps the Barind, which
has essentially a flat or somewhat
domed surface. South of the Barind
Tract are the Recent Floodplains,
with a southerly slope of about 0.06m/km.
In the Barind region,
three distinct channel patterns are
observed. In the north there is a
great number of small braided streams,
which have built a broad piedmont
alluvial plain along the foothills
of the Himalayas. The major rivers
of these alluvial plains are the Atrai
and the Punarbhaba, with entrenched
valleys. On the Pleistocene unit,
there are numerous small entrenched,
tightly meandering streams, which
have developed an overall dendritic
pattern and flow into the major north-south
rivers of the Barind unit. There are
some major valleys that separate the
Pleistocene unit into some north-south
elongated units. These valleys are
followed by some major rivers, such
as the Mahananda in the west, the
Karatoya in the east, the Atrai and
the Punarbhaba in between. The largest
unit is bounded by the river Punarbhaba
and the Atrai. Another large unit
is bounded by the Karatoya and the
Little Jamuna. Many small channels,
mostly of dendritic pattern, flow
through the individual units.
However, it is very
interesting that the course of the
Karatoya is controlled by a southeast
trending fault. In the late 17th century,
the major stream of this region was
tista which, near Jalpaiguri, branched
and followed the course of the Depa-Punarbhaba
to the west, the Atrai due south and
the Little Jamuna to the southeast.
All of these rivers discharged into
the Ganges. Of these rivers, the Atrai
seems to have been the major channel
in the late 17th century with the
Punarbhaba as the second most important.
But now the Tista, Karatoya and Atrai
flow into the jamuna (brahmaputra).
The river courses, particularly of
the Tista, changed suddenly in 1787
during a major flood. This change
could have been accompanied by renewed
uplift and tilting of the Barind surface.
At the present time, the Punarbhaba,
Atrai and Little Jamuna still carry
some flood flow but they generally
can be considered as antecedent streams
carrying mainly local runoff water
of the uplifted Barind area.
The Barind Tract,
which is the largest pleistocene terrace
of the country, is made up of the
Pleistocene alluvium, also known as
older alluvium. Tectonically, this
region is situated in the precambrian
indian platform, mostly in the saddle
and shelf area of the shield. This
platform region is covered mostly
by Tertiary and Quaternary sediments
and Recent Alluvium.
The Barind unit is
comparatively at a higher elevation
than the adjoining floodplains. The
contours of the Tract suggest that
there are two terrace levels - one
at 40m and the other between 19.8
and 22.9m. Therefore, when the floodplains
go under water during the monsoon
the Barind Tract remains free from
flooding and is drained by a few small
streams. About 47% of the Barind region
is classified as highland, about 41%
as medium highland and the rest are
lowland. Agricultural land commonly
occupies about 80% of the hill slopes
of Barind unit most of the year. As
this region is generally free from
floodwater, rainwater is the only
major source of groundwater recharge.
Once there were many isolated small
depressions but those have since been
converted into agricultural land.
This landscape modification has affected
the groundwater recharge and has increased
dependence on rainwater. Again, the
channel migration, mainly the shifting
of the Tista and the Atrai and their
distributaries over the last couple
of centuries, has greatly influenced
the climatic conditions of the area.
Geomorphic modifications gradually
turned this area into a hot region.
The Barind is floored
by the characteristic Pleistocene
sediments known as the Madhupur (Barind)
Clay. The madhupur clay is reddish
brown in colour, oxidised, sticky
and rather compact. JP Morgan and
WG McIntire assumed these deposits
to be of fluvial origin. Actually
they were deposited in the late Pleistocene
time towards the end of the last glacial
period. Nearly 18,000 years ago, the
last glacial period reached the peak
of activities. During that time the
sea level dropped to 100m to 130m
below the present-day level. Then
the ice-melt water flowed into the
bay of bengal. Right at that time
the northeast monsoon climatic condition
commenced in the subcontinent. Rainfall
was not then dominating the Bengal
plain. Bengal rivers only flowed with
ice-melt water through their narrow
and incised valleys. Later, 12,000
years ago, the southwest monsoon climate
started dominating the region, and
brought heavy rainfall over the Bengal
Basin. The monsoon rainfall was even
more intense than at present.
The narrow Bengal rivers could not
discharge this huge quantity of water,
supplied by huge rainfall as well
as the ice-melt water from the Himalayan
Range. The rivers spilled over the
banks and deposited sediments over
the large Bengal plain washing the
sediments to the south where the sediments
prevailed in the Barind Tract and
madhupur tract and also in the lalmai
area. Afterwards, climatic conditions
started to change, making temperature
rather hot, which readily influenced
the Bengal river courses, the sea
level started rising again and the
depressed regions began getting more
sediments but these Holocene (Recent
time) sediments could not reach such
a height that they would be deposited
over the earlier Madhupur sediments.
There is another school of thought
that suggests a tectonic origin for
the Pleistocene high terrace. This
school says that the Pleistocene sediments
were deposited in large depressions
of the Barind and Madhupur regions.
After the deposition due to the neotectonic
movement, these regions uplifted and
formed high terraces.
The Barind Tract
is rich in mineral resources as it
rests upon the Precambrian Indian
Shield of the Bengal Basin. Of the
mineral resources, coal, peat, hardrock,
limestone, white clay and glass sand
are very important. Actually these
mineral deposits are found within
the platform area below the Pleistocene
rock units of the Barind Tract. High-grade
bituminous coal deposits have been
discovered in Bogra, Rajshahi, Rangpur
and Dinajpur districts. These are
found in small isolated basins, known
as Grabens, located within the Precambrian
basement below Pleistocene sediments
of the Barind Tract. This coal belongs
to the Gondwana formation of the Permian
period and is of good quality. Limestone
is also found in the shelf area of
the platform located in the southern
part of Barind Tract beneath the Pleistocene
rock units. This limestone belongs
to the Eocene period and is an important
raw material for the manufacture of
cement. Hardrock is another precious
resource of the Barind region. Actually
the whole platform area is composed
of Precambrian igneous and metamorphic
rocks. This hardrock is an essential
building material commonly used for
constructing roads, bridges and other
structures. White clay and glass sand
are generally found in the upper part
of the basement rocks right below
the Barind rock units. These minerals
are widely used for the manufacture
of ceramic wares, electric goods and
many other industrial items.
Rapid population
growth along with modifications of
the landforms of the Barind Tract
has been degrading the biophysical
environment of this region. The climatic
condition in this region has changed.
There is very little rainfall and
the weather remains hot by the daytime
but becomes cooler by late night.
Since rainwater is the main source
of groundwater recharge in this area,
the climatic change that disfavours
abundant precipitation has adversely
affected the groundwater recharge
system. The withdrawal of more groundwater
than its recharge causes the successive
lowering of the groundwater table
of the Barind region. This phenomena
have eventually been greatly affecting
the environmental parameters and if
it persists the environment of the
Barind Tract will become rather unfavourable
for habitation in the near future.
Besides lowering of the water table
another noticeable change is the decrease
in forest area. According to some
reports from the British colonial
times about 42% area of this Tract
was covered by forests in early 19th
century. Statistical reports of the
land survey since 1849 showed that
forests covered about 55% of the Barind
lands. But by 1974, about 70% land
of the region had been changed into
cultivable land.
The Barind almost
became an arid region due to massive
deforestation. Also, due to its extreme
dry nature and relatively low rainfall
the vegetation cover decreased distinctively
and the area could be picked up in
satellite images as a hot and dryland.
As the area was considered a low potential
area for groundwater development,
agriculture used to depend on monsoon
rainwater. As a consequence, there
used to be only one crop and the Tract
was a food deficit area. With initiatives
from local engineers, there have been
new investigations for groundwater
resources and it was found that there
were good aquifers to be developed
for large-scale irrigation.
A project named the
Barind Integrated Area Development
Project (BIADP) was initiated in mid-1980s
to develop groundwater irrigation
in the area. Under this project thousands
of irrigation deep tubewells have
been installed, which facilitated
dry season irrigation for cultivation.
As a result agricultural production
has increased and the area has become
a food surplus area. Apart from providing
irrigation, there have been other
programmes such as tree planting and
excavation of ponds and khals to arrest
the degradation of the environment.
At the beginning, the project generated
a lot of concern among environmental
scientists about sustainability of
the groundwater resources. However,
15 years of its operation has proved
it to be a success. Apart from providing
irrigation, other connected development
schemes such as road development have
had a positive impact on the socio-economic
conditions of the area. Environmental
degradation has also been checked
and positive results such as higher
rainfall and higher vegetation coverage
are evident. The project has been
renamed as the Barind Multipurpose
Development Authority (BMDA) since
the early 1990s and now covers a large
part of the Barind Tract.
Source: Banglapedia,
National Encyclopedia of Bangladesh
Asiatic Society of Bangladesh
