TITLE:
Application of SWAT Model to the Olifants Basin: Calibration, Validation and Uncertainty Analysis
AUTHORS:
Charles Gyamfi, Julius Musyoka Ndambuki, Ramadhan Wanjala Salim
KEYWORDS:
Calibration, Validation, Uncertainty Analysis, Olifants Basin, SWAT Model
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.8 No.3,
March
30,
2016
ABSTRACT: The
application of the Soil and Water Assessment Tool (SWAT) to the Olifants Basin
in South Africa was the focus of our study with emphasis on calibration,
validation and uncertainty analysis. The Basin was discretized into 23
sub-basins and 226 Hydrologic Response Units (HRUs) using 3 arc second (90 m ×
90 m) pixel resolution SRTM DEM with stream gauge B7H015 as the Basin outlet. Observed
stream flow data at B7H015 were used for model calibration (1988-2001) and
validation (2002-2013) using the split sample approach. Relative global
sensitivity analysis using SUFI-2 algorithm was used to determine sensitive
parameters to stream flow for calibration of the model. Performance efficiency
of the Olifants SWAT model was assessed using Nash-Sutcliffe (NSE), coefficient
of determination (R2), Percent Bias (PBIAS) and Root Mean Square
Error-Observation Standard deviation Ratio (RSR). Sensitivity analysis revealed
in decreasing order of significance, runoff curve number (CN2), alpha bank
factor (ALPHA_BNK), soil evaporation compensation factor (ESCO), soil available
water capacity (SOIL_AWC, mm H2O/mm soil), groundwater delay (GW_ DELAY,
days) and groundwater “revap” coefficient (GW_REVAP) to be the most sensitive
parameters to stream flow. Analysis of the model during the calibration period
gave the following statistics; NSE = 0.88; R2 = 0.89; PBIAS = -11.49%;
RSR = 0.34. On the other hand, statistics during the validation period were NSE
= 0.67; R2 = 0.79; PBIAS = -20.69%; RSR = 0.57. The observed
statistics indicate the applicability of the SWAT model in simulating the
hydrology of the Olifants Basin and therefore can be used as a Decision Support
Tool (DST) by water managers and other relevant decisions making bodies to
influence policy directions on the management of watershed processes especially
water resources.