MODELLING THE IMPACT OF SALINE AND WATERLOGGED AREAS IN KRISHNA CENTRAL DELTA
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Date
2016
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Acharya N.G. Ranga Agricultural University
Abstract
Land, a non-renewable resource, is central to all primary production system. It
is estimated that some forms of land degradation constituting 75% of the earth's usable
landmass affect 4 billion people in the world. About 15% of the world population is
effected by land degradation which is likely to worsen unless adequate and immediate
measures are taken to arrest the degradation processes. Mostly land is affected by wind
and water erosion, which is about 80% of land degradation followed by
salinization/alkalization and waterlogging. Krishna delta irrigates an ayacut of 5.14
lakh ha covering West Godavari, Krishna, Guntur and Prakasam districts of Andhra
Pradesh. Eastern main canal’s command area is about 2.948 lakh ha in Krishna and
West Godavari Districts. Krishna Central Delta is a part of Krishna Eastern Delta that
constitutes the command area of Bandar canal. During monsoon, these lands are
affected by waterlogging and salinity problems.
Hence it is felt appropriate to study Krishna Central Delta with a special focus
to identify the waterlogged and saline lands for reclamation by either drainage system
or addition of amendments like gypsum etc. Under the aforesaid valid and farmers’ felt
research needs, the present post graduate research work entitled “Modelling the
impact of saline and waterlogged areas in Krishna Central Delta” is proposed to i)
to estimate the extent of land under waterlogging and salinity in Krishna Central Delta.
ii) to simulate the effect of waterlogging and salinity on crop yield using a model with
various hypothetic scenarios. iii) to design location specific drainage parameters for
combating waterlogging and salinity.
Krishna Central Delta which is a part of Krishna Eastern Delta constitutes the
command area of Bandar canal which has an irrigated ayacut of 274834.09 acres
(111223.83 ha) in Krishna district. In this study Landsat 8 images and Sentinel-2A
images were used and analyzed using ERDAS IMAGINE 2014 and ArcGIS 10.1
software's. From the literature, different salinity indices were selected to find out the
best suited index for the study area. Salinity indices used to find the salt affected soils
using GIS. Details of ground water quality parameters which were analyzed from the
water samples collected from the observation wells located in the Krishna Central Delta
were collected from Ground water Department, Vijayawada.
Initially for the identified problematic patches, the input parameters some
directly measured, some indirectly were assessed and fed into 'SALTMOD' model.
Without the presence of any drainage systems, simulation for first, fourth, sixth and
tenth year for depth of ground water table and root zone salinity was carried out and the
output parameters were fed into AquaCrop model along with other crop, climate,
irrigation requirement and other related parameters to predict the yields. WaSiM, Water
balance Simulation Model is a physically based, distributed hydrologic model that runs
on a regular grid and uses a modular system of sub-models to offer the possibility of
creating a problem and scale adequate setup. Drain space, one of the modules of
WaSim was used for sub surface drainage design.
Based on the research work carried out, the major conclusions drawn are i)
Normalized Difference Vegetation Index (NDVI) was found to range from 0.72 to -
0.92 in Krishna Central Delta (KCD) region. In KCD region, Normalized Difference
Salinity Index (NDSI) was found the best suitable and it ranged from -0.714 to 0.185
and best correlated with ground truth values. Soil salinity was characterized into five
classes and it was found that highest area was under moderately saline with an area of
68754.01 ha followed by strongly saline, slightly saline, non saline and very strongly
saline. ii) Spatial analysis of water table data revealed that most critically waterlogged
zone was found in post monsoon covering an area of 597.65 km2 which was about
26.27% of the total study area. It was found that critically waterlogged area increased
from 620.12 km2 (27.25%) in pre monsoon period to 1074.02 km2 (47.2%) in post
monsoon period. The area under less critically waterlogged was found to be decreased
from 704.49 km2 (30.95%) in pre monsoon to 163.06 km2
(7.16%) in post monsoon
period. iii) Soil salinity was predicted for future ten years using SALTMOD and
corresponding yield were predicted using Aquacrop. With increase of soil salinity from
0.5 dS m-1
to 6.5 dS m-1
there was about 42.28% reduction in the crop yield and 36.69%
reduction in biomass yield. iv) Using 'Drain Space', a module of WaSim software, by
using the Hooghoudts equation under steady state condition, the drain spacing for
shallow drain depth placement of 0.6 m, 0.7 m and 0.8 m the spacing was arrived as
9.5, 16.6, 22.36 m. For deeper drain depth placements of 0.95, 1.0 and 1.15 m, the drain
spacing was arrived as 30, 32.4 and 38.81 m respectively for a constant desired depth of
water table as 0.5 m to make the root zone free from waterlogging.
Description
D5467
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