Variability of furrow infiltration and estimated infiltration parameters in a macroporous soil

Authors: GUZMAN-ROJO, DANIELLE - University Of Mexico; Bautista, Eduardo; GONZALEZ-TRINIDAD, JULIAN - University Of Mexico; Bronson, Kevin

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2018
Publication Date: 12/5/2018
Citation: Guzman-Rojo, D.P., Bautista, E., Gonzalez-Trinidad, J., Bronson, K.F. 2018. Variability of furrow infiltration and estimated infiltration parameters in a macroporous soil. Journal of Irrigation and Drainage Engineering. 145(2):04018041. https://doi.org/10.1061/(ASCE)IR.1943-4774.0001366.
DOI: https://doi.org/10.1061/(ASCE)IR.1943-4774.0001366

Interpretive Summary: Hydraulic analysis of surface irrigation systems requires reasonable knowledge of the infiltration process. Quantifying infiltration for any particular field is challenging because the process is spatially and temporally variable. This is particularly true for furrow irrigation systems. This variability is partly natural, but it is also partially induced by soil and irrigation management factors. This study examines infiltration variability in a furrow irrigated field and develops infiltration parameter estimates for a semi- infiltration physical model. The study used an existing data set and involved 30 furrow evaluations,conducted over 5 irrigation events. As expected, the volume of infiltrated water varied substantially among furrows and also among irrigation events. For each evaluation, the volume of water that infiltrated during the advance and post-advance phase of the irrigation were calculated. On average, the same volume of water infiltrated during the advance phase as during the post-advance phase. However,infiltration variability patterns differed markedly between the two stages. This difference is attributed to the effect of crack / macropore flow. In the presence of cracks, a large volume of water infiltrates during the initial wetting. That flow is largely dependent on crack volume which varies from irrigation event to the next,and mostly independent of the applied flow rate. After the cracks close, infiltration responds to inflow variations along the field, as predicted by porous media flow theory. Estimation procedures were used to determine two parameters of the semi-physical infiltration model, the hydraulic conductivity and the macroporosity term, which is used to model infiltration through soil cracks. The proposed model represented the infiltration process reasonably under the given field conditions, and thus demonstrated the advantages of modeling infiltration in furrows accounting for the effect of variable flow depth along the field and in time, and for crack flow. The estimated hydraulic conductivity values were consistent with values reported in the literature for the soil texture reported for the field experiment. Macropore constant values varied mostly among irrigations for any furrow, and less among furrows for a given irrigation. These results should be of interest to irrigation researchers and practitioners, as it illustrates the use of a recently developed approach for modeling furrow infiltration under field conditions.

Technical Abstract: Understanding the spatial and temporal variations of infiltration in furrows is essential for the design and management of furrow irrigation systems. A key difficulty in quantifying the process is that infiltration depends on the depth of flow, which varies along a furrow and with time. An additional difficulty is that under many field conditions, a large fraction of the infiltrated water flows through cracks and/or macropores. This study examines the spatial and temporal variability of a furrow-irrigated field and evaluates a proposed semiphysical furrow infiltration model that accounts for flow-depth and macroporosity effects. Parameter estimation techniques were used to determine two parameters of the infiltration model, the hydraulic conductivity and the macroporosity term, in addition to the Manning roughness coefficient. The methodology was tested using published data from 30 furrow irrigation data sets collected in six furrows over five irrigation events. The evaluation revealed substantial variations in the final infiltrated volume among furrows and from one irrigation event to the next. Variability patterns differed markedly for infiltration measured during the advance phase in comparison with infiltration measured during the storage phase of the irrigations. Advance-phase infiltration varied systematically between irrigations for all furrows. Interfurrow inflow rate variability contributed to the variability of the infiltration during the postadvance phase, but not during the advance phase. Thus, cracks and/or macropores were an important contributor to the variability of infiltration during the advance phase. The analysis produced reasonable estimates of hydraulic conductivity relative to values reported in the literature. Hydraulic conductivity and post-advance infiltration volumes exhibited similar patterns of temporal variability. Hydraulic conductivity estimates were statistically correlated to the applied inflow rate. Although the reasons for this correlation are not clear, a possible explanation is that they are the result of systematic differences in the applied inflow rate among furrows. As with the advance-phase infiltration volumes, the estimated macroporosity term exhibited greater variation among irrigation events than among furrows during an event. The estimation procedure produced smaller differences between volume balance computed infiltration volumes and predicted values when using the semiphysical infiltration model than when using an empirical infiltration equation. Overall, the results show that the proposed furrow infiltration model represents the infiltration process adequately and that, at least for the studied data sets, the proposed estimation procedure yields a coherent set of infiltration and hydraulic resistance parameter values.