Modelling Water Flow and Solute Transport for Horticultural and Environmental Management

During the past 10 years, the simulation model SWAP (Soil, Water, Atmosphere, Plant) was developed by the Sub-Department Water Resources of Wageningen University jointly with the Department Water and Environment of Alterra Green World Research. SWAP simulates vertical transport of water, solutes and heat in variably saturated, cultivated soils at field scale level and during whole growing seasons. Different versions of the model have been applied worldwide in research, education and as a decision support tool in the management of agricultural, horticultural and natural systems water flow in homogeneous and heterogeneous soils with or without the influence of groundwater. The main features of and theoretical concepts behind SWAP are described, in particular soil water flow, solute transport and crop growth

SWAP Version 3.2. Theory description and user manual

SWAP 3.2 simulates transport of water, solutes and heat in the vadose zone. It describes a domain from the top of canopy into the groundwater which may be in interaction with a surface water system. The program has been developed by Alterra and Wageningen University, and is designed to simulate transport processes at field scale and during whole growing seasons. This is a new release with special emphasis on numerical stability, macro pore flow, and options for detailed meteorological input and linkage to other models. This manual describes the theoretical background, model use, input requirements and output tables

Uncertainty in the determination of soil hydraulic parameters and its influence on the performance of two hydrological models of different complexity

Data of soil hydraulic properties forms often a limiting factor in unsaturated zone modelling, especially at the larger scales. Investigations for the hydraulic characterization of soils are time-consuming and costly, and the accuracy of the results obtained by the different methodologies is still debated. However, we may wonder how the uncertainty in soil hydraulic parameters relates to the uncertainty of the selected modelling approach. We performed an intensive monitoring study during the cropping season of a 10 ha maize field in Northern Italy. The data were used to: i) compare different methods for determining soil hydraulic parameters and ii) evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zone) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme. We employed five direct and indirect methods to determine soil hydraulic parameters for each horizon of the experimental profile. Two methods were based on a parameter optimization of: a) laboratory measured retention and hydraulic conductivity data and b) field measured retention and hydraulic conductivity data. The remaining three methods were based on the application of widely used Pedo-Transfer Functions: c) Rawls and Brakensiek, d) HYPRES, and e) ROSETTA. Simulations were performed using meteorological, irrigation and crop data measured at the experimental site during the period June – October 2006. Results showed a wide range of soil hydraulic parameter values generated with the different methods, especially for the saturated hydraulic conductivity Ksat and the shape parameter a of the van Genuchten curve. This is reflected in a variability of the modeling results which is, as expected, different for each model and each variable analysed. The variability of the simulated water content in the root zone and of the bottom flux for different soil hydraulic parameter sets is found to be often larger than the difference between modeling results of the two models using the same soil hydraulic parameter set. Also we found that a good agreement in simulated soil moisture patterns may occur even if evapotranspiration and percolation fluxes are significantly different. Therefore multiple output variables should be considered to test the performances of methods and model

Nieuwe maat voor bodemvochtregime ook geschikt onder toekomstig klimaat

Huidige maten voor zuurstofstress in het wortelmilieu van planten, zoals de gemiddelde voorjaarsgrondwaterstand en het percentage luchtgevulde poriën, zijn niet geschikt voor klimaatprojecties. Dat komt doordat ze correlatief en indirect zijn en geen rekening houden met veranderingen in temperatuur en neerslagpatronen. In natte omstandigheden is de respiratiestress wel een geschikte maat. Met een nieuw model is die nu voor alle locaties in Nederland te berekenen. In de nieuwe maat komen zowel de effecten op de vegetatie van extreme neerslag tot uitdrukking als die van hoge temperaturen. Zuurstofstress door een hevige regenbui op een warme zomerdag zal onder het toekomstige klimaat veel vaker voorkomen. De door het nieuwe model berekende hoge respiratiestress van een dergelijke gebeurtenis zal leiden tot natuurlijke vegetaties van nattere bodems dan de huidige, niet klimaatbestendige maten voorzie

Crop growth

SWAP contains three crop growth routines: a simple model, a detailed model (WOFOST), and the same model attuned to simulate grass growth. The simple model describes crop development, independent of external stress factors. The main function is to provide proper upper boundary conditions for soil water movemen

Water productivity of irrigated crops in Sirsa district, India

Major issues with respect to water management in Sirsa district are waterlogging and salinization in areas with saline groundwater and over-exploitation of groundwater in areas with fresh groundwater. The present crop yield increase of the major crops in Sirsa district is marginal. Recent studies show that water is the main limiting factor to increase the crop yields. In order to identify the main water losses, an extensive WAter PROductivity study (WATPRO) has been performed in Sirsa distric

Soil water - groundwater interaction

SWAP offers eight options to prescribe the lower boundary condition. These conditions are given in this chapte

Reference Manual SWAP; version 3.0.3

SWAP simulates vertical transport of water, solutes and heat in variably saturated, cultivated soils. The program has been developed by Alterra and Wageningen University, and is designed to simulate transport processes at field scale level and during whole growing seasons. This manual describes the theoretical background and modeling concepts that were used for soil water flow, solute transport, heat flow, evapotranspiration, crop growth, multi-level drainage and interaction between field water balance and surface water management. An overview is given of model use, input requirements and output table