"Soil, Water, Atmosphere and Plant"

Lizenz: kostenfrei

SWAP simulates transport of water, solutes and heat in unsaturated/saturated soils. Swap is the successor of the well known Swatre model which originates from 1978. It results from a long lasting cooperation between groups of the Centre for Water and Climate, which is part of Wageningen University and Reseach centre . The groups that developed the SWAP model are: the team Integrated Water Resources Management and the Wageningen University Soil Physics, Ecohydrology and Groundwater Management Group .

The program is designed to simulate the transport processes at field scale level and during entire growing seasons.

The model offers a wide range of possibilities to address both research and practical questions in the field of agriculture, water management and environmental protection.

1 General

SWAP (Soil, Water, Atmosphere and Plant) simulates vertical transport of water, solutes and heat in unsaturated/saturated soils. The program is designed to simulate the transport processes at field scale level and during entire growing seasons.

2 Atmosphere

Basic, daily meteorological data are used to calculate daily, potential evaporation according to Penman-Monteith. If basic meteorological data are not available, potential evaporation or reference evaporation can be input. Precipitation may be provided either at a daily basis or at actual intensities. Short-term rainfall data allow the calculation of runoff and preferential flow.

3 Crop

Crop growth is simulated by the code WOFOST. The processes considered include rate of phenological development, interception of global radiation, CO2 assimilation, biomass accumulation of leaves, stems, storage organs and roots, leaf decay and root extension. The assimilation rate is affected by water and/or salinity stress in the root zone. If simulation of crop growth is not required, the user should prescribe leaf area index, crop height and rooting depth as function of development stage.

4 Irrigation

Irrigation gifts can be prescribed or are calculated. The user may choose various timing and depth criteria in order to optimise irrigation application.

5 Soil water movement

SWAP employs the Richards' equation for soil water movement in the soil matrix. The Darcy equation is used to calculate infiltration and evaporation fluxes at the soil surface. A physical description rather has been chosen beyond a parametric description of water flow, as it allows the use of soil physical data bases and the simulation of all kind of management scenario's.

6 Root water uptake

Root water extraction at various depths in the root zone is calculated from potential transpiration, root length density and possible reductions due to wet, dry, or saline conditions.

7 Preferential flow

In cracked clay soils the shrinkage characteristic is used to determine crack volume, area and depth. Water collected in the cracks will infiltrate according to Darcy at the crack bottom. In the clay matrix the Richards' equation applies. The program will calculate solute leaching by fast moving crack water from top-soil to sub-soil.

Flow and transport in water-repellent soil is based on the concept of a mobile and an immobile soil volume. The actual mobile volume is derived from the soil layer and the soil water pressure head. In the mobile volume the Richards' equation and the solute transport equation apply. Solute difusion between mobile and immobile volume is taken into account.

8 Drainage

Drainage is calculated with the Hooghoudt or Ernst drainage equations, which allow evaluation of drainage design. Also the user may specify a drainage resistance or tabular values of the drainage flux as function of groundwater height.

9 Surface water systems

The program offers the possibility to simulate the management of a surface water system.

10 Bottom boundary

Options offered include flux, groundwater height, flux as function of groundwater height, free drainage and lysimeter with free drainage.

11 Solute transport

SWAP simulates convection, diffusion and dispersion, non-linear adsorption, first order decomposition and root uptake of solutes. This permits the simulation of ordinary pesticide and salt transport, including the effect of salinity on crop growth. In case of detailed pesticide transport or nitrate leaching, daily water fluxes can be generated as input for the models PESTLA and ANIMO.

The program calculates the residence time of the solutes in the saturated zone analogous to mixed reservoirs. In this way solute breakthrough to surface water is derived.

12 Heat transport

The program calculates heat conductance and temperatures in the soil. Soil temperatures have a large affect on solute decomposition. Either an analytical or a numerical solution can be used. The numerical solution uses the ambient air temperature as upper boundary condition.

13 Siehe auch

14 Weblinks

Kategorien: Modelle

Letzte Änderung dieses Artikels: April 01, 2009, at 03:49 PM