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Author: KISHORE, KAMAL × End date: 2020 × Start date: 2020 ×
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    ThesisItemOpen Access
    MORPHOMETRIC EVALUATION AND SOIL LOSS ESTIMATION OF A TRANSECT OF SUBANSIRI WATERSHED IN LAKHIMPUR DISTRICT OF ASSAM
    (AAU, Jorhat, 2020-08) KISHORE, KAMAL; Deka, Bipul
    The present investigation was carried out with the objectives to compute morphometric parameters of the drainage streams of Subansiri river basin and to evaluate soil erosion status in the basin area. The Subansiri watershed is located in the Lakhimpur district which is part of the North Bank Plains of Assam. The studied watershed encompasses 118.67 sq. km area and it lies between 94007’ E to 94018’ E Longitude and 27021’ N to 27036’ N Latitude with the elevation ranging from 86 to 124 m. Based on total variation in satellite data three distinct physiographic units of the studied watershed were delineated which includes: piedmont plain (29.75 sq. km), alluvial plain (63.05 sq. km) and flood plain (25.87 sq. km). The morphometric parameters were evaluated through measurement of linear, areal and relief aspects. The 1st, 2nd, 3rd and 4th order streams had stream numbers of 24, 5, 2 and 2, respectively. The mean bifurcation ratio for the studied area was evaluated to be 2.77. The areal aspects like circulatory ratio (0.70), elongation ratio (0.50), form factor (0.20) and shape factor (5.09) were estimated and the estimated value indicated elongated shape of the watershed. The computed relief aspects viz. relief ratio (0.0015), ruggedness number (0.05) and relative relief (0.082) indicated higher infiltration and lower runoff. Sixty surface soil samples (0-15 cm) along with equal no. of core samples representing all the three physiographic units were collected using handheld GPS of Garmin Etrex 20. The surface as well as core samples were analyzed for various physico-chemical properties. The texture of the studied soils varied from loamy sand to silty clay loam, sandy loam being dominant. There was a decreasing trend of total sand as well as an increasing trend of silt and clay from piedmont plain to flood plain. The bulk density, particle density and porosity of soils of the studied watershed area ranged from 1.01 to 1.61 Mg m-3, 2.19 to 2.88 Mg m-3 and 30.29 to 61.85 %, respectively. The hydraulic conductivity of the soils varied from 0.44 to 5.86 cm hr-1, while the water holding capacity ranged between 5.65 to 49.53 %. The field capacity, permanent wilting point and the available water content varied from 8.03 to 36.46 %, 2.65 to 14.98 % and 0.54 to 24.57 %. Among the physiographic units the piedmont plain soils recorded the highest value of hydraulic conductivity and flood plain showed the highest values of water holding capacity, field capacity, permanent wilting point and available water. The value of macro aggregates, micro aggregates and mean weight diameter of the studied soils varied from 20.20 to 79.54 %, 20.46 to 79.80 % and 1.13 to 3.91 mm, respectively. The pH of the studied soils was extremely acidic (4.15) to slightly acidic (6.69). The organic matter content of the soils ranged between low (5.38 g kg-1) to high (27.83 g kg-1). The available nitrogen, available phosphorus and available potassium content 10 varied from low to medium (137.98 to 464.13 kg ha-1), low to medium (15.96 to 55.25 kg ha-1) and low to medium (35.63 to 331.45 kg ha-1), respectively. Based on the estimated values of soil physico-chemical properties, various soil erodibility indices were computed. In the studied soils, the value of silt/clay ratio, clay ratio and modified clay ratio varied from 0.33 to 4.40, 1.46 to 13.25 and 1.36 to 11.73, respectively. The critical level of soil organic matter of all the studied soils was less than 5 per cent which indicated their vulnerability to soil erosion. The dispersion ratio in the studied soils varied from 0.05 to 0.42 with a mean value 0.26. The values of erosion ratio and erosion index were found to be varying between 0.01 to 0.48 and 0.02 to 0.62, respectively. It was observed that 80.59 sq. km (67.91 %) area had dispersion ratio value more than 0.15 which could be considered as erodible. Nearly 51.64 sq. km (43.52 %) area of the watershed had erosion ratio values more than 0.10 indicating their susceptibility to erosion. The erosion index values were more than 0.18 in about 44.51 sq. km (37.51 %) area. The soil loss of the studied area varied from very slight to very severe (0.87 to 67.95 t ha-1 yr-1) with an average value of 12.38 t ha-1 yr-1. The soil loss showed a significant positive correlation with very fine sand (r = 0.402**) and elevation (r = 0.509**). The soil loss exhibited positive correlation with various erodibility indices viz., silty/clay ratio (r = 0.159), clay ratio (r = 0.251), modified clay ratio (r = 0.249). However, the significant positive correlation of soil loss was noticed with dispersion ratio (r = 0.633**), erosion ratio (r = 0.405**) and erosion index (r = 0.502**). The soil loss along with dispersion ratio, erosion ratio and erosion index exhibited decreasing trend from the piedmont plain to flood plain.
  • Thumbnail Image
    ThesisItemOpen Access
    MORPHOMETRIC EVALUATION AND SOIL LOSS ESTIMATION OF A TRANSECT OF SUBANSIRI WATERSHED IN LAKHIMPUR DISTRICT OF ASSAM
    (AAU, Jorhat, 2020-08) KISHORE, KAMAL; Deka, Bipul
    The present investigation was carried out with the objectives to compute morphometric parameters of the drainage streams of Subansiri river basin and to evaluate soil erosion status in the basin area. The Subansiri watershed is located in the Lakhimpur district which is part of the North Bank Plains of Assam. The studied watershed encompasses 118.67 sq. km area and it lies between 94007’ E to 94018’ E Longitude and 27021’ N to 27036’ N Latitude with the elevation ranging from 86 to 124 m. Based on total variation in satellite data three distinct physiographic units of the studied watershed were delineated which includes: piedmont plain (29.75 sq. km), alluvial plain (63.05 sq. km) and flood plain (25.87 sq. km). The morphometric parameters were evaluated through measurement of linear, areal and relief aspects. The 1st, 2nd, 3rd and 4th order streams had stream numbers of 24, 5, 2 and 2, respectively. The mean bifurcation ratio for the studied area was evaluated to be 2.77. The areal aspects like circulatory ratio (0.70), elongation ratio (0.50), form factor (0.20) and shape factor (5.09) were estimated and the estimated value indicated elongated shape of the watershed. The computed relief aspects viz. relief ratio (0.0015), ruggedness number (0.05) and relative relief (0.082) indicated higher infiltration and lower runoff. Sixty surface soil samples (0-15 cm) along with equal no. of core samples representing all the three physiographic units were collected using handheld GPS of Garmin Etrex 20. The surface as well as core samples were analyzed for various physico-chemical properties. The texture of the studied soils varied from loamy sand to silty clay loam, sandy loam being dominant. There was a decreasing trend of total sand as well as an increasing trend of silt and clay from piedmont plain to flood plain. The bulk density, particle density and porosity of soils of the studied watershed area ranged from 1.01 to 1.61 Mg m-3, 2.19 to 2.88 Mg m-3 and 30.29 to 61.85 %, respectively. The hydraulic conductivity of the soils varied from 0.44 to 5.86 cm hr-1, while the water holding capacity ranged between 5.65 to 49.53 %. The field capacity, permanent wilting point and the available water content varied from 8.03 to 36.46 %, 2.65 to 14.98 % and 0.54 to 24.57 %. Among the physiographic units the piedmont plain soils recorded the highest value of hydraulic conductivity and flood plain showed the highest values of water holding capacity, field capacity, permanent wilting point and available water. The value of macro aggregates, micro aggregates and mean weight diameter of the studied soils varied from 20.20 to 79.54 %, 20.46 to 79.80 % and 1.13 to 3.91 mm, respectively. The pH of the studied soils was extremely acidic (4.15) to slightly acidic (6.69). The organic matter content of the soils ranged between low (5.38 g kg-1) to high (27.83 g kg-1). The available nitrogen, available phosphorus and available potassium content 10 varied from low to medium (137.98 to 464.13 kg ha-1), low to medium (15.96 to 55.25 kg ha-1) and low to medium (35.63 to 331.45 kg ha-1), respectively. Based on the estimated values of soil physico-chemical properties, various soil erodibility indices were computed. In the studied soils, the value of silt/clay ratio, clay ratio and modified clay ratio varied from 0.33 to 4.40, 1.46 to 13.25 and 1.36 to 11.73, respectively. The critical level of soil organic matter of all the studied soils was less than 5 per cent which indicated their vulnerability to soil erosion. The dispersion ratio in the studied soils varied from 0.05 to 0.42 with a mean value 0.26. The values of erosion ratio and erosion index were found to be varying between 0.01 to 0.48 and 0.02 to 0.62, respectively. It was observed that 80.59 sq. km (67.91 %) area had dispersion ratio value more than 0.15 which could be considered as erodible. Nearly 51.64 sq. km (43.52 %) area of the watershed had erosion ratio values more than 0.10 indicating their susceptibility to erosion. The erosion index values were more than 0.18 in about 44.51 sq. km (37.51 %) area. The soil loss of the studied area varied from very slight to very severe (0.87 to 67.95 t ha-1 yr-1) with an average value of 12.38 t ha-1 yr-1. The soil loss showed a significant positive correlation with very fine sand (r = 0.402**) and elevation (r = 0.509**). The soil loss exhibited positive correlation with various erodibility indices viz., silty/clay ratio (r = 0.159), clay ratio (r = 0.251), modified clay ratio (r = 0.249). However, the significant positive correlation of soil loss was noticed with dispersion ratio (r = 0.633**), erosion ratio (r = 0.405**) and erosion index (r = 0.502**). The soil loss along with dispersion ratio, erosion ratio and erosion index exhibited decreasing trend from the piedmont plain to flood plain.