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Development of Infiltration Equation Using Field Data from Border Irrigation System

M.N. Islam
Department of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

A.A. Hassan
Agncultural Engineering Division, Bangladesh Institute of Nudear Agriculture, Mymensingh-2202, Bangladesh

K.K. Dey
Post Graduate Student, Department of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

A general infiltration equation was developed using different irrigation trials (discharges) in border irrigation system under different soil physical conditions at Bangladesh Agricultural University farm soil. Volume balance and Cylinder infiltrometer methods were used to evaluate the infiltration characteristic constants of the farm soil. First three trials (12.42,2.21 and 5.19I/s) were conducted in non-vegetative border and last trial (5.19 I/s) was conducted in vegetative border (Maize crop). For cylinder infiltrometer method, the average initial and final infiltration rate were 3.46 and 0.73 cm/hr. respectively. While in volume balance method the rates were 5.25 and 1.98 cm/hr, respectively. The average values of infiltration characteristic constants a,b,c,by cylinder infiltrometer method were 0.284, 0.525 and 0.319, respectively and for volume balance method these were 0.319, 0.627 and 0.356, respectively. Thus ,it was observed that the values of cumulative infiltration, infiltration rate and infiltration characteristic constants obtained by Volume balance method were higher than that of Cylinder infiltrometer method for all the trials.

Keywords: Infiltration equation, Border irrigation, Field data.

Location: Bangladesh Agricultural University, Mymensingh

Start Date: 01-01-1998

End Date: 31-12-1998

Program Area: Crop-Soil-Water Management

Commodity: Water management

Objectives:

To develop a general infiltration equation and evaluate some of the infiltration characteristic parameters of border irrigation system under non-vegetative and vegetative condition in a silty loam soil of Bangladesh Agricultural University farm.

Methodology:

Two plots were selected for the experiment. Border width of each plot was 8 m and border length was 40 m. Two border-strips were prepared by keeping 1 m gap between the adjacent levees. Levees were roughly 30 cm wide and 20 cm high. The slope of the experimental plots and elevation at different points were determined by dumpy level. These elevations at different points of the plots were used for levelling by cutting or filling so that there is no cross slope along the plots. To avoid outward seepage at the first trial of irrigation polythene sheets were vertically placed at 20 cm depth below the surface along the side of the levees of the two plot. The bed of the earthen canal from cutthroat flume to the delivery point at the head-end of the plots was completely covered with a piece of polythene sheet ensuring no loss of water in between. Maize crop was used as a vegetative cover. Line to line and plant to plant distance of maize crop was 30 m and 15 cm, respectively. During water supply to the plots three openings were made for each plots at the upstream side. The openings were 2 m apart with a dimension of 10 cm x 10 cm. Before each irrigation trial bulk density and soil moisture were determined using core sampler and gravemetric method (oven-dry method), respectively for each experimental plot. Cumulative infiltration was measured using cylinder infiltrometer . method and volume balance method. In cylinder infiltrometer method, the cylinders are 25 cm deep and formed of 2 mm rolled steel. Diameter of the inner and outer cylinder are 30 cm and 60 cm, respectively. The cylinders were installed about 10 cm deep in the soil. The average depth of water maintained in the cylinders was 7 to 12 cm. Rate of fall of water level in the inner cylinder was noted at 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 minutes from the start of experiment. Before each irrigation trial, infiltration behaviour of the soil was studied at two places, one approximately at the middle point of the upper half and the other at the middle point of lower half of the plots. By averaging the two mathematically fitted infiltration curves for a particular trial, time shows the infiltration characteristic for the whole irrigated area. In the volume balance method infiltration was measured per unit width of border at every instant of time. In this method, different advance time, advance length and average depth of flow are needed to measure infiltration. For measuring depth of flow on the border length meter scales were used. The least count of meter scale was 0.1 cm. These meter scales were tied with bamboo sticks in such a way that zero marking of the scale was leveled with the field surface. The depth of flow was measured at three points (2 m apart) across the border by meter scales after every 5 m interval from the upstrem end of the border. In this method infiltration was measured by subtracting volume of water applied to the volume of water stored at different times and d.fterent lengths of the border.

Source of Information: Bangladesh J. Agril. Sci. 26(1): 133-140; January, 1999

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The average values of infiltration characteristic constants a,b,c,by cylinder infiltrometer method were 0.284, 0.525 and 0.319, respectively and for volume balance method these were 0.319, 0.627 and 0.356, respectively. Thus, it was observed that the values of cumulative infiltration, infiltration rate and infiltration characteristic constants obtained by Volume balance method were higher than that of Cylinder infiltrometer method for all the trials.

Knowledge Management: Journal