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

Analysis of the land surface heterogeneity and its impact on atmospheric variables and the aerodynamic and thermodynamic roughness lengths

The land surface heterogeneity has a very significant impact on atmospheric variables (air temperature T-a, wind speed u, and humidity q), the aerodynamic roughness length z(0m), thermodynamic roughness length z(0h), and the excess resistance to heat transfer kB(-1). First, in this study the land surface heterogeneity has been documented through the comparison of surface reflectance r(0), surface temperature T-0, net radiation flux R-n, and sensible heat flux H partitioning over the different land cover types in the experimental areas of the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment on the Tibetan Plateau (GAME/Tibet), the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project on the Tibetan Plateau (CAMP/Tibet), the Heihe Basin Field Experiment (HEIFE), the Arid Environment Comprehensive Monitoring Plan, 95 (AECMP' 95), and the Dun Huang Experiment (DHEX). The results show that the surface heterogeneity was very significant in the areas of the HEIFE, the AECMP' 95, and the DHEX and that it was less significant in the areas of CAMP/Tibet and GAME/Tibet. Second, the vertical profiles of T-a, u, and q in the near-surface layer and above the blending height z(b) have been analyzed using the atmospheric boundary layer (ABL) tower data, radiosonde data, and tethered balloon data observed during the HEIFE, the DHEX, and the CAMP/Tibet. The results show that the land surface heterogeneity leads in the near-surface layer to different vertical profiles of u, T-a, and q overlying the surfaces of the Gobi and the oasis in the areas of the HEIFE and DHEX. The values of u, T-a, and q become well mixed above a height of about 300 m at the HEIFE and 150 m at the DHEX. z(0m), z(0h), and kB(-1) over the different land surfaces have also been determined in this study. The results show that the land surface heterogeneity leads to different aerodynamic and thermodynamic parameters over the areas of the HEIFE, the AECMP' 95, and the GAME/Tibe

Invloed van grondwateronttrekking voor beregening en drinkwater op de grondwaterstand

De hoeveelheid grondwater die voor diverse doeleinden wordt onttrokken neemt voortdurend toe en heeft tot gevolg dat de grondwaterstand een daling heeft ondergaan. De grootte van deze daling is van belang voor de landbouw, omdat gewasopbrengst en grondwaterspiegeldiepte onder Nederlandse omstandigheden een duidelijk verband vertoont

Compenserende maatregelen bij grondwateronttrekking

Op het beschikbare grondwater wordt door diverse belangengroepen aanspraak gemaakt, zoals de landbouw, natuur, landschap, industrie en drinkwatervoorziening. Een te grote ontttrekking van het grondwater kan resulteren in een belangrij'ke dal'ing van de grondwaterstan:d, dikwijs gepaar'd gaande met schade aan een of meer van de belanghebbenden. Om een daling op te kunnen heffen, zullen compenserende maatregelen moeten worden getroffen. De beschikbare methoden worden hier besproken

Waar blijft het water....

Rede Wageningen, 13 september 199