Jan Boll

Low-dimensional modeling of hillslope subsurface flow: Relationship between rainfall, recharge, and unsaturated storage dynamics

[1] We present a coupling between the one-dimensional Richards equation for vertical unsaturated flow and the one-dimensional hillslope-storage Boussinesq equation (HSB) for lateral saturated flow along complex hillslopes. Here the capillary fringe is included in the flow domain as an integral part of the Boussinesq aquifer. The coupling allows quantitative investigation of the role of unsaturated storage in the relationship between rainfall and recharge. The coupled model (HSB coupled) is compared to the original HSB model (HSB original) and a three-dimensional Richards equation (RE) based model (taken to be the benchmark) on a set of seven synthetic hillslopes, ranging from convergent to divergent. Using HSB original, the water tables are overestimated and the outflow rates are generally underestimated, and there is no delay between rainfall and recharge. The coupled model, however, shows a remarkably good match with the RE model in terms of outflow rates, and the delay between rainfall and recharge is captured well. We also see a clear improvement in the match to the water tables, even though the values are still overestimated for some hillslope shapes, in particular the convergent slopes. We show that for the hillslope configurations and scenarios examined in this paper it is possible to reproduce hydrographs and water table dynamics with a good degree of accuracy using a low-dimensional hydrological model.

Modeling the hydrological effect on local gravity at Moxa, Germany

Abstract A superconducting gravimeter has observed with high accuracy (to within a few nm s−2) and high frequency (1 Hz) the temporal variations in the earth’s gravity field near Moxa, Germany, since 1999. Hourly gravity residuals are obtained by time averaging and correcting for earth tides, polar motion, barometric pressure variations, and instrumental drift. These gravity residuals are significantly affected by hydrological processes (interception, infiltration, surface runoff, and subsurface redistribution) in the vicinity of the observatory. In this study time series analysis and distributed hydrological modeling techniques are applied to understand the effect of these hydrological processes on observed gravity residuals. It is shown that the short-term response of gravity residuals to medium- to high-rainfall events can be efficiently modeled by means of a linear transfer function. This transfer function exhibits an oscillatory behavior that indicates fast redistribution of stored water in the upper...

A semianalytical solution of the Saint‐Venant equations for channel flood routing

[1]xa0A semianalytical solution for channel hydraulic routing has been derived from the Saint-Venant equations. The Saint-Venant equations were converted into a nonlinear diffusion equation by introducing the Froude number. Subsequently, the mixing cell method is used to discretize a nonlinear diffusion equation in space, transforming it into a first-order nonlinear ordinary differential equation where the optimal space interval is obtained to be the same as the characteristic reach length. The nonlinear ordinary differential equation was solved by integration with respect to time to achieve a nonlinear implicit algebraic equation. The resulting implicit equation is practical and easy to program on a computer. This method is based on the results of a numerical simulation using the Lambda scheme which indicates that the Froude number is only dependent on the channel roughness and bottom slope. The method was tested with numerical examples and compared with the Lambda scheme and observed data. The hydrographs produced by this method were of comparable accuracy.

Comparison of WEPP and SWAT For Watershed Hydrology and Erosion Prediction

Prediction of hydrology and erosion at the hillslope and watershed scale are needed for placement of conservation practices as well as for understanding implications of land use change. Modeling approaches are continually being improved for such purposes. This study compares a modified version of WEPP with the SWAT model in Town Brook watershed in New York (Figure 1). Model comparison includes observations at the watershed outlet as well as major hydrological flow paths, and initial predictions of sediment yield at the watershed scale. Despite fundamentally different modeling approaches the agreement between observed and simulated streamflow was comparable using both WEPP and SWAT. SWAT simulated a flashy hydrograph that agreed better with observations than WEPP however sediment yield was over-predicted by SWAT. Simulated hydrographs by the WEPP model were poorest in the fall, which appears due to misrepresentation of transpiration changes in deciduous forests. Although stream channel erosion was not simulated by WEPP, sediment yield predictions from hillslopes suggest that the majority of sediment delivered at the outlet of the stream is derived from streambanks. Overall, WEPP appears to be better suited for hillslope applications whereas SWAT is more appropriate for large scale applications. Improvements in stream channel algorithms in WEPP are needed for further comparison of these models.

Education and Research in a Horticultural Irrigation Project in El Salvador

In September 2008 a government financed project was initiated to increase water availability for vegetable production in Chalatenango, El Salvador. CATIE (Centro Agronomico Tropical de Investigacion y Ensenanza, Turrialba, Costa Rica) and the University of Idaho (Moscow) teamed up for a multi-level educational effort to train local technicians and farmers in water management, and to support undergraduate and graduate student experiences in water management in developing countries. The project objective was to increase farmer incomes through crop area expansion, where water availability had been the limiting factor in vegetable acreage. University students were tasked with the introduction of monitoring techniques, and implementation of tools for the evaluation of water use efficiency. They were also exposed to field level problems of achieving and evaluating efficiency. Farmers and technicians were provided with water monitoring techniques, and tools for evaluating irrigation efficiency. Many of these techniques were developed for use on computers, and innovations were necessary to make these available to farming areas where computers were not generally available.