Furrow Geometric Parameters

Abstract

Furrow shape information is required for modeling and evaluating furrow irrigation. Currently used shape models assume the furrow perimeter is rigid so that only the flow depth increases with capacity. Actual furrow perimeters are not rigid and may widen as their capacity increases. If the furrow width increases proportionally with flow depth, the flow cross‐sectional shape remains constant and only the size increases with capacity. This constant‐shape model results in simple generalized relationships between the hydraulic and geometric parameters, which simplifies analysis of the complicated interactions that occur during furrow irrigation. The two shape models are compared conceptually and against field measurements. The rigid‐perimeter model better matches field‐measured furrow shapes and is easier to rationalize conceptually. However, both models match the important relationships between furrow geometric parameters and hydraulic parameters equally well. The most important relationship between flow area and uniform flow section factor is insensitive to both the model and shape. The predictions of both models are more sensitive to the furrow top width‐to‐flow depth ratio than to shape.