https://pc-progress.com/documents/jirka/kandelous_simunek_awm_2010.pdf

Numerical simulations of water movement in a subsurface drip irrigation system under field and laboratory conditions using HYDRUS-2D

Due to increasing competition for water resources by urban, industrial, and agricultural users, the proportion of agricultural water use is gradually decreasing. To maintain or increase agricultural production, new irrigation systems, such as surface or subsurface drip irrigation systems, will need to provide higher water use efficiency than those traditionally used. Several models have been developed to predict the dimensions of wetting patterns, which are important to design optimal drip irrigation system, using variables such as the emitter discharge, the volume of applied water, and the soil hydraulic properties. In this work, we evaluated the accuracy of several approaches used to estimate wetting zone dimensions by comparing their predictions with field and laboratory data, including the numerical HYDRUS-2D model, the analytical WetUp software, and selected empirical models. The soil hydraulic parameters for the HYDRUS-2D simulations were estimated using either Rosetta for the laboratory experiments and inverse analysis for the field experiments. The mean absolute error (MAE) was used to compare the model predictions and observations of wetting zone dimensions. MAE for different experiments and directions varied from 0.87 to 10.43 cm for HYDRUS-2D, from 1 to 58.1 cm for WetUp, and from 1.34 to 12.24 cm for other empirical models.

https://link.springer.com/content/pdf/10.1007%2Fs00271-009-0205-9.pdf

Comparison of numerical, analytical, and empirical models to estimate wetting patterns for surface and subsurface drip irrigation.

Subsurface drip irrigation (SDI) systems are increasingly being used in agriculture in attempts to use the available water more efficiently. The proper design and management of SDI systems requires knowledge of precise distribution of water around emitters. We conducted both field and numerical experiments to evaluate the soil water content distributions between two neighboring emitters when their wetting patterns started to overlap. The experiments involved SDI systems with emitters installed at different depths and with different spacings along the drip lateral. The HYDRUS software package was used to analyze the field data, assuming modeling approaches in which emitters were represented as (i) a point source in an axisymmetrical two-dimensional domain, (ii) a line source in a planar two-dimensional domain, or (iii) a point source in a fully three-dimensional domain. Results indicated that SDI systems can be accurately described using an axisymmetrical two-dimensional model only before wetting patterns start to overlap, and a planar two-dimensional model only after full merging of the wetting fronts from neighboring emitters. A fully three-dimensional model appears to be required for describing subsurface drip irrigation processes in their entirety.

/pdf/soil-water-content-distributions-between-two-emitters-of-a-4vwugypk3i.pdf

Soil Water Content Distributions between Two Emitters of a Subsurface Drip Irrigation System

Spatial distribution of soil moisture, soil salinity, and root density beneath a cotton field under mulched drip irrigation with brackish and fresh water

Designing drip irrigation systems involve selection of an appropriate combination of emitter discharge rate and spacing between emitters for any given set of soil, crop, and climatic conditions, as well as understanding the wetted zone pattern around the emitter. The exact shape of the wetted volume and moisture distribution will depend on many factors, including soil hydraulic characteristics, initial conditions, emitter discharge rate, application frequency, root characteristics, evaporation, and transpiration. Multi-dimensional nature of water flow, plant uptake and high frequency of water application increase the complexity in modelling soil moisture dynamics from trickle irrigation. Researchers used analytical methods, semi-analytical methods and numerical methods to Richards’ equation using certain boundary conditions to model the infiltration from point source irrigation for use in design, install, and manage of drip irrigation systems due to their merits over direct measurements. Others developed models based on Green-Ampt equation, empirical models using regression techniques/dimensional analysis techniques/moment approach techniques/artificial neural networks on this topic to describe infiltration from a point/line sources. A review on these models developed under each category is presented in this study. Other knowledge gaps identified include (a) effect of variations in initial moisture content and packing conditions, (b) precision in observing the wetting front and soil–water content, (c) validity of soil surface boundary conditions, (d) effect of crop root architecture and its withdrawal pattern for different input parameters, (e) effects of gravitational gradients, (f) stratification in the soils, and (g) impact of soil hysteresis. The review promotes better understanding of the soil water dynamics under point source trickle emitters and helps to identify topics for more emphasis in future modelling activity.

A review of models for predicting soil water dynamics during trickle irrigation

Using experimental data, the continuity and the cumulative infiltration equations, a new expression for predicting the wetted soil depth was described. Knowing soil hydraulic conductivity K(hf), initial and wetting front water content, this method enables us to calculate the maximum front depth Zf(t), beneath an emitter, by only measuring its radius Rf(t) on the soil surface.

To test this, we used the ADI finite difference method to solve Richards' equation for axisymmetrical water infiltration from a point source on the soil surface. To simulate the evolution of the wetted soil volume dimensions (Rf(t) and Zf(t)), proper conditions were fixed for the wetting front boundaries.

The Zf(t) predicted values were compared with those computed and measured during an axisymmetric water infiltration test on a silty soil for three different discharge rates. The results obtained showed good agreement between predicted, computed and measured data. Copyright © 2002 John Wiley & Sons, Ltd.

Approach for predicting the wetting front depth beneath a surface point source: theory and numerical aspect

An easy, empirical and reliable new approach for predicting the wetted soil depth underneath trickle irrigated crops is proposed. The approach was adjusted using field measurements of the maximum wetting front depth Z (t) and lateral spread R (t) in both tomato and sweet melon plots. Within each plot, ff measurements were made for distinguished initial water contents and using different emitters' discharges. For all cases, results showed that Z (t) is strongly correlated (r > 0,92) with R (t). An empirical exponential ff relationship was inferred. Knowing the lateral wetting front spread (in situ measured), the proposed approach enables to predict for instance the correspondent maximum wetted soil depth. The only two empirical parameters could be easily fitted by in situ measurements. Because of its simplicity and its feeless, the proposed approach could be a practical helpful tool for trickle irrigation management, deep water percolation and fertilizers leaching control.

/pdf/an-empirical-concise-approach-to-predict-the-maximal-wetted-sas8w7iig5.pdf

An Empirical Concise Approach to Predict the Maximal Wetted Soil Depth under Trickle Irrigated Crops

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Approach for predicting the wetting front depth beneath a surface point source: theory and numerical aspect

An Empirical Concise Approach to Predict the Maximal Wetted Soil Depth under Trickle Irrigated Crops