PERFORMANCE EVALUATION OF Drainmod in A DRAINED AREA OF KRISHNA WESTREN DELTA
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Date
2011
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ACHARYA N. G. RANGA AGRICULTURAL UNIVERSITY
Abstract
Irrigation induced problems of water logging and salinity are noticed in many
canal commands in India. Pilot studies conducted in some of these command areas
demonstrated the potential of subsurface drainage for the control of salinity and water
logging, and the improvement of agricultural productivity. Modeling studies provide
further insight into salt and water balances during the reclamation process and are
useful to make long-term predictions. In this study, DRAINMOD model is evaluated
using a 7-year (2002 to 2009) dataset collected from a subsurface drained
experimental field (7.5 ha) located geographically at about 150 28' N latitude and 800
28' E longitude near Appikatla village in the Krishna Western Delta in Andhra
Pradesh, India. The subsurface drainage system consists of two sub-fields with drains
installed at two different spacing’s of 30 and 60 m. The model was calibrated by using
observed data from the pilot area (7.5 ha) considering an equivalent drain spacing of
50 m during the period from 2004 to 2006 and validated using the observed data from
2007 to 2009. The model predicted variables like drain flow, depth to water table, soil
salinity and relative yields of paddy crop were in good agreement with observed data
as indicated by good statistical model performance measures (Nash-Sutcliffe model
efficiency) EF of 0.57, 0.78, 0.72 and 0.30 and Coefficient of correlation(R) of 0.88,
0.97, 0.90 and 1.00 during calibration period and EF of 0.90, 0.69, 0.64 and -0.42 and
R of 0.99, 0.88, 1.00 and 0.99 during the validation period. The Root Mean Square
Error (RMSE) of 20.7, 13.4, 6.8 and 6.5 and Percent Error (PE) of -4.3, 1.0, 2.01 and
3.7 during calibration period and RMSE of 16.0, 23.2, 10.3 and 40.6 and PE of 15.0, -
3.9, 10.22 and 13.9 during the validation period.
The sensitivity value showed that drain flow was highly sensitive to drain
depth (0.56) followed by surface storage (0.35), drain spacing (-0.26), drainage co
efficient (0.18), distance from surface to impervious layer (-0.15), lateral saturated
hydraulic conductivity of layer III (0.15) and K2 (0.07). There is no effect of initial
water depth on drain flow.
The model has demonstrated potential to reconstruct the pre-drainage situation
at the pilot area. Without drainage system, average (2002- 2009) annual soil salinity
increased by 29.5%, crop yield reduced by 6% respectively. As the drain spacing
increased from 30 m to 70 m, the average (2002-2009) annual drain flow decreased
from 26.54 to 21.13 cm, soil salinity increased from 2488 to 2645ppm and the paddy
crop yield decreased from 95.33 to 93.25% respectively. As the drain depth increased
from 0.6 m to 1.4 m, the average (2002-2009) annual drain flow increased from 19.51
to 28.00 cm, soil salinity decreased from 2643 to 2233ppm and the paddy crop yield
increased from 93.25 to 95.33% respectively.
The DRAINMOD model showed the potential to simulate the performance of
subsurface drainage system at Appikatla
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Keywords
KRISHNA WESTREN DELTA