A state-dependent parameterization of saturated-unsaturated zone interaction

The relevance of groundwater as an important source of root zone moisture by means of capillary rise is increasingly being recognized. This is partly reflected in many current land surface schemes, which increasingly replace a one-way (i.e., downward) drainage of water by a two-way interaction flux between the root zone and a groundwater system. A fully physically correct implementation of this two-way saturated-unsaturated interaction flux requires transient simulations using the highly nonlinear Richards' equation, which is a computationally demanding approach. We test a classic simple approximation that computes the root zone¿groundwater interaction flux as the net effect of a downward drainage flux and an upward capillary rise flux against the Darcy equation for quasi steady state conditions. We find that for a wet root zone and/or shallow groundwater, the errors within this approximation are significant and of the same magnitude as the interaction flux itself. We present a new closed-form parameterization of the Darcy equation¿based fluxes that accounts both for root zone soil moisture and depth to the water table. Parameter values for this parameterization are listed for 11 different, widely applied soil texture descriptions. The high numerical efficiency of the proposed method makes it suitable for inclusion into demanding applications, e.g., a Monte Carlo framework, or high spatial resolution

A Conceptual Framework for Integration Development of GSFLOW Model: Concerns and Issues Identified and Addressed for Model Development Efficiency

In Coupled Groundwater and Surface-Water Flow (GSFLOW) model, the three-dimensional finite-difference groundwater model (MODFLOW) plays a critical role of groundwater flow simulation, together with which the Precipitation-Runoff Modeling System (PRMS) simulates the surface hydrologic processes. While the model development of each individual PRMS and MODFLOW model requires tremendous time and efforts, further integration development of these two models exerts additional concerns and issues due to different simulation realm, data communication, and computation algorithms. To address these concerns and issues in GSFLOW, the present paper proposes a conceptual framework from perspectives of: Model Conceptualization, Data Linkages and Transference, Model Calibration, and Sensitivity Analysis. As a demonstration, a MODFLOW groundwater flow system was developed and coupled with the PRMS model in the Lehman Creek watershed, eastern Nevada, resulting in a smooth and efficient integration as the hydrogeologic features were well captured and represented. The proposed conceptual integration framework with techniques and concerns identified substantially improves GSFLOW model development efficiency and help better model result interpretations. This may also find applications in other integrated hydrologic modelings

Krylov subspace approximations for the exponential Euler method: error estimates and the harmonic Ritz approximant

We study Krylov subspace methods for approximating the matrix-function vector product φ(tA)b where φ(z) = [exp(z) - 1]/z. This product arises in the numerical integration of large stiff systems of differential equations by the Exponential Euler Method, where A is the Jacobian matrix of the system. Recently, this method has found application in the simulation of transport phenomena in porous media within mathematical models of wood drying and groundwater flow. We develop an a posteriori upper bound on the Krylov subspace approximation error and provide a new interpretation of a previously published error estimate. This leads to an alternative Krylov approximation to φ(tA)b, the so-called Harmonic Ritz approximant, which we find does not exhibit oscillatory behaviour of the residual error

Some aspects of soil physics applicable to trickle irrigation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Soil Science at Massey University

Irrigation of crops is one of the more widely used techniques to increase yeilds. Trickle irrigation is one such method and is more suited to horticultural crops. In New Zealand, with horticulture assuming more importance, appropriate methods of design and operation of trickle irrigation systems are required. In this study a simple approximation to Wooding's solution for steady infiltration from a shallow ponded source, much like that found under trickle emitters is examined. This may aid in irrigation design and practice. The approximation also allowed for the development of a method to concurrently measure the saturated hydraulic conductivity and sorptivity from simple field infiltration measurements with a minimum of soil disturbance. Saturated hydraulic conductivities and sorptivities are of great use in soil water studies in general. A commercial trickle irrigation system was also examined to determine the suitability of such irrigation systems to particular soils, and to examine the present irrigation scheduling. The approximation to Wooding's solution was found to perform well in the field in many respects, particularly in determining steady ponded zone sizes. Ponded zone sizes are important in that they control the volume of soil wetted by irrigation to a large degree. Much of this agreement is due to the use of parameters determined by the simple field method developed from this theory. Sorptivities and saturated hydraulic conductivities obtained by this method were found to be more realistic for trickle irrigation than those determined by other existing methods. Systematic errors in these other methods, mainly soil disturbance and the concomitant creation of continuous flow paths for water, as well as soil smearing, are thought to be the main cause of this difference. Temporal and spatial variation in soil physical properties are however, found to hinder the use of soil physics theory in the field. Macropores (due to soil biological activity) were found to profoundly influence infiltration processes and soil-water distribution. These effects were particularly marked for the site with a commercial trickle irrigation system. Here the efficiency of the present system is thought to be low, and evidence indicates that irrigation was in excess of plant requirements. The utility of Wooding's solution, and the method to measure soil physical parameters developed from this, is further demonstrated in this orchard

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