The TILE Approach: Closing the hydrologic cycle

English Abstract:

The importance of lateral near-surface flow through weathered bedrock layers in hillslopes or active layers in permafrost regions requires that, to be complete, a hydrologic model, or a land surface scheme must have an interflow algorithm. Conceptual power law extensions of a vertical drainage equation, such as Campbell or Brooks-Corey, generally poorly parameterised interflow. The equations require several parameters that are difficult to calibrate. At the opposite extreme of the complexity spectrum, are numerical solutions of Richards Equation that are too cumbersome for meso-scale modelling.

This presentation will demonstrate a cleaner, easier approach: a power law expression of effective saturation approximates the modeled outflow from a sloping confined aquifer. The solution is a weighted combination of an expression for pure saturated and pure unsaturated flow from the seepage base of the aquifer. The weighting coefficient is determined from the soil pore-size distribution. The result is a Weibull-like expression that requires only SCS texture properties and geometric properties of the slope.

The method, called the Tilted Landscape Element (TILE) approach has been implemented in StandAlone— Modélisation Environmentale–Surface et Hydrologie (SA-MESH). Four parameters are required that SCS sand and clay fractions, along with valley slope and length predict. These parameters are generally available in most models.