Two-dimensional hydrodynamic modeling of overland flow and infiltration in a sustainable drainage system

Abstract: As a part of the GrönNano project at Luleå University of Technology, a sustainable drainage system, composed of infiltration surfaces and a wale,has been subject to hydrological measurements and modeling. The aim of this study was to identify the conditions under which it is possible to model the hydrological processes of that system adequately, using the two-dimensional hydrodynamic modeling software MIKE 21 equipped with an infiltration and leakage module. To achieve this, a model was set up with site-specific data followed by sensitivity analyses, calibration, validation and finally evaluation against a corresponding model, set up in the integrated hydrological modeling system MIKE SHE. From a sensitivity analysis it was indicated that too large time steps may introduce undesired volume losses when using the infiltration and leakage module. As a consequence, along with limitations of the simple infiltration model, this module and its principles were questioned and recommended to be treated with great care in inland applications. A second sensitivity analysis showed that hydraulic roughness associated with the swale is of great importance. Based on this, a proper two-dimensional representation of the swale was considered to be a critical point for predicting discharge correctly. Therefore it is of interest to further examine the influence on this, of for example the model grid resolution. The MIKE 21 model was successfully calibrated for a selected rainfall event but could not be fully validated for a following longer period. Nor could the model be satisfactorily evaluated against the preliminary version of the MIKE SHE model. However, from this it could be concluded that there were great uncertainties in the accuracy of rainfall and calibration data.