Quasi Steady‐State Simulation of the Unsaturated Zone in Groundwater Modeling of Lowland Regions

Abstract

A : ME, model effi ciency coeffi cient.S S : V Z M Well-conceived and detailed simula on of soil-moisture processes is a prerequisite for accurate watershed-scale modeling of water quan ty and quality processes. For this purpose, Richards' equa on (and its extensions) is the conceptually preferable op on. Applying the equa on on the watershed scale, however, may overstretch available computer resources. At the other extreme, methods based on lumping are oversimplifi ed. Approaches are therefore needed that are effi cient and just accurate enough, and that provide the required detail in the ver cal column. We have developed a quasi-steady-state model that uses a sequence of steady-state water content profi les for performing dynamic simula ons. The appropriate profi les are-for each me level-selected on the basis of water balances at the aggregate scale of control volumes. The groundwater coupling scheme involves an itera on cycle for the phrea c storage coeffi cient. In the postprocessing stage, the values of state variables obtained using the coupled model are disaggregated, thus delivering pressure heads, moisture contents, and fl uxes at the detailed scale of compartments of a Richards-type model. The plausibility of the simplifi ed approach was tested by comparing its results to those of a Richards-type model. The results appear promising for at least three-quarters of the area of the Netherlands with a shallow groundwater eleva on (within 2 m of the soil surface) and a thin root zone (<0.5 m thick). Customizing the modeling method used to the situa on conserves computa onal resources, allowing more room for doing sensi vity analyses. This could be instrumental for quan fi ca on of model reliability.

Evaluating the use of a gridded climate surface for modelling groundwater recharge in a semi‐arid region (Okanagan Basin, Canada)

“…Across the model grid, precipitation had the potential to evaporate, transpire, infiltrate or move as overland flow based on spatially distributed land cover and soil properties. Unsaturated flow was modelled using Richards' equation, which is considered a rigorous approach to simulate infiltration and deep percolation, and accurately accounts for transient soil moisture retention and upward migration of moisture by capillarity (Scanlon et al , 2002a; van Walsum and Groenendijk, 2008). Results were summarized by varying timeframes (monthly, annually and 3‐month seasons), and by broad soil texture differences (e.g.…”

Impact of Changes in Groundwater Extractions and Climate Change on Groundwater-Dependent Ecosystems in a Complex Hydrogeological Setting

“…AZURE uses MODFLOW for saturated groundwater flow (Harbaugh et al 2000) and MetaSWAP for the unsaturated groundwater zone (Van Walsum and Groenendijk 2008;Van Walsum and Veldhuizen 2011). The input variables in AZURE are designed to be used at a minimal resolution of 25 m, but the model can be run at a coarser spatial resolution.…”

Incorporating Bio-Physical Sciences into a Decision Support Tool for Sustainable Urban Planning

“…The second generation Gaussian plume model URBAIR model (Urban Air Quality) [21] was used to evaluate air quality and dispersion patterns, since it is appropriate for distances up to about 10 km from the source. Finally, the SIMGRO model (SIMulation of GROundwater and surface water levels) [22] was used to produce detailed information on all the hydrological processes present in an urban environment. The different model simulations performed for the BRIDGE case studies, generated outputs like the CO2 flux, CH4 emissions, PM10, O3, SO2 concentrations, sensible and latent heat flux etc.…”