HYDROPHYSICAL PROPERTIES AND ERODIBILITY OF BRAHMAPUTRA RIVER BANK SOILS UNDER GOLAGHAT DISTRICT
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Date
2021
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AAU, Jorhat
Abstract
The study on the hydrophysical properties and erodibility of
Brahmaputra river bank soils under Golaghat district was carried out with the objectives
1) To assess hydrophysical and chemical properties of soils along the bank of
Brahmaputra river and 2) To estimate soil erodibility indices of the studied soils. The
studied area is located in the Golaghat district which is a part of Upper Brahmaputra
Valley Zone of Assam. It encompasses an area of 195.52 sq. km and lies between
93°71' E to 93°99' E longitude and 26°67' N to 26°80' N latitude and with an elevation
ranging from 79 to 84 m. Thirty eight surface soil samples (0-15 cm) both disturbed and
core were collected using handheld GPS of Garmin Etrex 20 upto 5 km from the bank
of Brahmaputra river towards southern direction. The sampling sites were demarcated
across the flow of Brahmaputra river traversing a total distance of 25-30 km from East
to West. The surface as well as core samples were analysed for various hydrological and
chemical properties following the standard procedures. The studied soils exhibited soil
texture ranging from loamy sand to silty clay loam, however, silt loam was the
dominant one. The amount of silt and clay content were found to be somewhat higher
than sand content in the areas away from the river bank and reverse trend persisted in
case of total sand content. The bulk density, particle density of investigated soils ranged
from 1.22 to 1.59 Mg m-3 with a mean value of 1.37 Mg m-3 and 2.31 to 2.65 Mg m-3
with a mean value of 2.47 Mg m-3 respectively. The porosity of the studied soils ranged
between 32.63 to 49.03 per cent, while the hydraulic conductivity ranged between 0.29
to 1.34cm hr-1 . The water holding capacity ranged from 21.45 to 45.01 per cent while
the field capacity, permanent wilting point and available water content values varied
from 17.78 to 33.12 per cent, 4.45 to 13.03 per cent and 6.26 to 24.02 per cent
respectively. The studied soils showed significant positive correlation of water holding
capacity, field capacity with clay which exhibited that dominance of finer particles
increases the capillary pores and maximum surface area to hold water. Hydraulic
conductivity showed significant negative correlation with clay and exhibited high
values of hydraulic conductivity in the soils where clay content is low or finer materials
being migrated due to erosion. The macro aggregates, micro aggregates and mean
weight diameter of the studied soils varied from 41.93 to 84.07, 15.93 to 58.07 per cent
and 0.72 to 3.88 mm, respectively. The studied soils were acidic in nature and the pH of
the soils ranged between extremely acidic (4.45) to slightly acidic (6.74) with a mean
value of 5.56. The organic matter of the studied soil area varied from 0.94 to 2.62 per
cent with a mean of 1.77 per cent. The mean values of available nitrogen, available
phosphorus, available potassium content of soils were 288.42, 44.37, 84.71 kg ha-1
respectively and their status ranged from low to medium.
On the basis of the estimated values of soil physico-chemical properties,
various soil erodibility indices were computed. The silt/clay ratio, clay ratio and
modified clay ratio in the studied soils ranged from 0.75 to 2.43, 1.30 to 7.36 and 1.23
to 6.79, respectively. Among the dispersion ratio, erosion ratio and erosion index,
dispersion ratio ranged from 0.05 to 0.33 with a mean of 0.17, erosion ratio ranged from
0.03 to 0.18 with a mean of 0.08 and erosion index ranged from 0.03 to 0.32 with a
mean of 0.10 respectively. EIROM values ranged from 0.60 to 3.96 with a mean of 1.15
and it exhibited similar trend like EI as showed significant positive correlation with very
fine sand and significant negative correlation with clay content. The values of soil
erodibility factor in the studied soils ranged from 0.09 to 0.12 with a mean of 0.10.
GIS based schematic mapping revealed that among the physical properties total sand
covered highest area nearly 134.64 sq. km (68.86 per cent) of the studied area in the
range of total sand content less than 25 per cent. Silt content range 40-50 per cent
covered the highest area nearly 137.80 sq. km (70.48 per cent) of the studied area which
were away from the river bank. Clay content exhibited highest area nearly 109.86 sq.
km (56.18 per cent) in the clay content range of 30-35 per cent and among the hydraulic
properties , available water content covered highest area i.e 116.55 sq km (59.61 per
cent) in the range of 15-20 per cent, hydraulic conductivity range 0.5-0.75 cm hr-1
covered highest area nearly, 123.70 sq km (63.27 per cent), field capacity values in the
range of 20-25 per cent covered highest area i.e 116.55 sq km (59.61 per cent) of the
studied soil area. Water holding capacity values in the range of 35-40 per cent covered
highest area i.e 116.55 sq km (59.61 per cent) of the studied soil area. Macroaggregates
recorded highest area nearly 147.09 sq. km (75.23 per cent) of the studied area in the
macroaggregate content range 75-80 per cent. Nearly 3.9 sq. km (2 per cent) of the
studied area had dispersion ratio value more than 0.15 which could be considered as
erodible. About 12.05 sq. km (6.16 per cent) of the studied area had erosion ratio values
more than 0.10 indicating their susceptibility to erosion. The erosion index values were
more than 0.15 in about 3.9 sq. km (2 per cent) of the studied area.