Field values of the shape factor for estimating surface storage in furrows on a clay soil

2009

The two-point method is one of the best known procedures for estimating empirical infiltration parameters from surface irrigation evaluation data and mass balance, mainly because of its limited data requirements and mathematical simplicity. However, past research have shown that the method can produce inaccurate results. This paper examines the limitations of the method, reviews alternatives for improving two-point method results based on data that are collected or can easily be collected as part of a two-point evaluation, and suggests strategies for estimation and validation of results for different levels of evaluation data. Results show the limitations of formulating the estimation problem with advance data only and the benefits of using instead an advance and a postadvance mass balance relationship in the analysis. Because different combinations of parameters can satisfy the mass balance equations, the estimated function cannot be extrapolated reliably beyond the times used in formulating those relationships. While results can be used with confidence to characterize the performance of the evaluated irrigation event, they need to be used carefully for operational analysis and design purposes.

Section: Nonuniformity Of the Datamentioning

confidence: 99%

Structured Application of the Two-Point Method for the Estimation of Infiltration Parameters in Surface Irrigation

2009

“…Previous studies (Esfandiari and Maheshwari 1997) have shown that large field undulations relative to the average slope cause substantial variation in the depth profile. Such conditions may complicate or altogether invalidate the application.…”

Section: Discussionmentioning

confidence: 92%

Improved Surface Volume Estimates for Surface IrrigationVolume-Balance Calculations

2012

This article reviews procedures for estimating surface storage in surface irrigation volume balance calculations. Those procedures are based on the assumption of a power law relationship for flow depth as a function of distance along the stream. The analysis uses zeroinertia simulation and a system of dimensionless variables to examine how the depth profile varies as a function of hydraulic conditions when infiltration is given by the empirical extended Kostiakov equation. Alternatives for approximating the exponent of the depth profile power law (β) are suggested. The magnitude of the resulting errors relative to zero-inertia model predictions is quantified. Results show that the range of variation for the parameter β increases with field slope, with increasing advance length relative to the maximum advance distance, and when infiltration rates are relatively constant with time during the irrigation event. Estimating β as a function of advance distance is most challenging under these conditions. Potentially large errors in the determination of β do not undermine the proposed procedures when the surface volume represents only a small fraction of the applied volume. Users of volume balance procedures need to be aware of conditions in which uncertain surface volume calculations can lead to potentially large volume balance errors and, thus, in which results need to be interpreted carefully.

“…(2) may seem reasonable, such as with sloping open-ended furrow irrigation systems, Vy estimates can be suspect and lead to inaccurate infiltration function determinations (Walker and Kasilingam 2004). Inaccurate determinations arise first, because of the uncertainty in the determination of the Manning roughness coefficient n, and second because Uy is time dependent and not necessarily less than unity, as suggested by field studies (Esfandiari and Maheshwari 1997b). The analysis conducted examines the characteristics of optimal and PIVB infiltration parameter estimates derived from four basin irrigation data sets, and the implications of using alternative infiltration solutions for assessing the performance of the observed irrigation event.…”

Section: Methodsmentioning

confidence: 99%

Optimal and Postirrigation Volume Balance Infiltration Parameter Estimates for Basin Irrigation

2009

Engineering analysis of surface irrigation systems is predicated on reasonably accurate estimates of a field's infiltration properties. Optimal estimation methods pose multiple volume balance equations at various stages of an irrigation event and are assumed to produce the most accurate results among volume balance based procedures. They have the disadvantage of requiring surface volume determinations, which may be difficult to obtain in practice under many field conditions. This study contrasts infiltration solutions from optimal and a simpler postirrigation volume balance method and examines the implications of those solutions on the performance of management strategies with zero-slope and low-gradient basins. With those types of systems, there is little benefit in using optimization over postirrigation volume balance due to the nonuniqueness of solutions and uncertainties of inputs required by the estimation procedures. In addition, system hydraulic characteristics mitigate the insensitivity of the distribution uniformity to reasonable variations in infiltration characteristics from those assumed in the analysis. For the type of systems considered here, management can be optimized based on time needed to infiltrate a target depth, even if the infiltration function parameters are uncertain.