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Simulation of Upward Flux from Shallow Water-table Using Upflow Model

Dr. M. H. Ali
SSO
BINA

I. Abustan
Prof.
USM, Malaysia

S. Islam
Graduate student
BAU

Abstract/ Executive Summary:

The upward movement of water by capillary rise from shallow water-table to the root zone is an important incoming flux. For determining exact amount of irrigation requirement, estimation of capillary flux or upward flux is essential. In this study, the performance of model UPFLOW to estimate upward flux was evaluated. Evaluation of model performance was performed with both graphical display and statistical criteria. In distribution of simulated capillary rise values against observed field data, maximum data points lie around the 1:1 line, which means that the model output is reliable and reasonable. The relative error, model efficiency, and index of agreement were found as 27.91%, 85.93% and 0.96, respectively. Considering the graphical display of observed and simulated upward flux and statistical indicators, it can be concluded that the overall performance of the UPFLOW model in simulating actual upward flux from a crop field under variable water-table condition is satisfactory. Thus, the model can be used to estimate capillary rise from shallow water-table for proper estimation of irrigation requirement, which would save valuable water from over-irrigation.

Keywords: Capillary rise, Shallow water-table, Groundwater contribution, Evapotranspiration, Wheat, Simulation model

Location: BINA, Mymensingh

Start Date:

End Date:

Program Area: Resource Development and Management

Non-commodity: Groundwater

Objectives:

To estimate the capillary flux from shallow groundwater to the root zone of wheat crop, and evaluated its performance.

Methodology:

UPFLOW is a software tool developed to estimate the expected upward flow from a shallow water-table in a given soil profile and to evaluate the effects of environmental conditions on the upward flow (Raes and Deproost 2003, Raes 2002). The inputs in the UPFLOW model are: average evapotranspiration (ET) during the time period, initial mean soil water content, average depth of water-table (WT) below the soil surface, crop type, the soil type of various layers and their thickness, and the salt content of the groundwater (if groundwater contains salts). The input data for model run for various conditions (for different water-table depths at various growth stages) were taken from Mridha et al. (2001) [reported in Tables and graphs]. The study was conducted in lysimeter with wheat crop, maintaining different sub-surface water levels e.g. 45, 60, 75 & 90 cm from the surface. Measured quantity of water was added to the lysimeter tanks to maintain the required depth to water level. The soil in the lysimeter was silty clay loam with an average bulk density of 1.5 g.cm^-3.

The daily reference crop evapo-transpiration, ET₀ (for the crop period) was calculated by ET0 software (Raes, 2000), using weather data for the period. The weather data were collected from nearby weather station (600 m apart from the field). Then, mean evapo-transpiration (ET) demand for the particular growth period was computed as:

ET = K_c × ET₀

The model was run stepwise for different growth stages and different water-table conditions. The model simulated outputs were compared with the corresponding measured values reported by Mridha et al. (2001). The following statistics were used to indicate overall model performance: Bias, Mean Absolute Bias, Relative error, Model efficiency, and Index of Agreement.

Source of Information: J. of Natural Resour. and Dev., 03: 123-127, (2013)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Comparison between simulated and observed capillary rise values for different stages of growing period of wheat indicates that the model can estimate actual capillary rise with reasonable accuracy. In distribution of simulated capillary rise values against observed field values, maximum data points lie around the 1:1 line, which means that the model output is reliable and reasonable. Considering the graphical display and statistical parameters, it can be concluded that the overall performance of the UPFLOW model in simulating actual upward flux from a crop field under variable water-table condition is satisfactory.

Knowledge Management: Journal