One-point method for estimating furrow infiltration

A quick method to estimate parameters of the Philip infiltration function from advance time to the field end, flow rate and flow area were developed using a volume balance principle. By assuming a power advance exponent of 1/2, the volume balance equation resulted in a closed-form integral solution and the infiltration parameters were found from advance to the field end only rather than from two or more points of advance along the field. Average infiltration for a furrow was estimated from intake opportunity time (calculated from advance and recession times) and Philip’s (1957) infiltration function. Model results were compared with more time-consuming volume balance (Philip and Farrell, 1964), neutron probe, and infiltrometer methods. Estimates of furrow infiltration using the one-point method agreed with the standard which was considered to be between neutron probe and field water application estimates. The Philip equation fitted to the infiltrometer data overpredicted for the first irrigation because preferential flow occurred along the perimeter of the bypass infiltrometer. For the latter irrigations infiltration was underpredicted because it was not possible to measure infiltration with the flow-through infiltrometer during the first 10 to 20 min of irrigation when the rate was high. The Philip and Farrell method matched the neutron probe results, and both underpredicted furrow infiltration. For the one-point method, sorptivity, S, was greater and parameter A was lower than predicted from infiltrometer measurements and the Philip and Farrell method, but the parameters compensated for one another and predicted infiltration agreed with the standard. The one-point method can be used to estimate average infiltration of an individual furrow from only advance time to the field end, flow rate, and flow area. Although effective for estimating average infiltration on a heterogeneous field, the one-point method and other volume balance methods did not accurately predict the distribution of water along the furrows with a dramatic change in infiltration properties.