Abstract
AbstractApplying physically based models that include preferential flow (PF) is still very challenging at the catchment scale. A gravity‐driven film flow approach could be a promising concept for modeling PF as it only requires a small number of parameters. We tested if this approach can be used for different soils and land covers within a 247 km2 catchment and if we can find generalizable relationships of the film flow parameters to site or rainfall properties. We used a unique data set from a soil moisture sensor network with 135 instrumented soil profiles in three different geologies (slate, marl, and sandstone) and two land covers (forest and grassland) and fitted the film flow model to around 1,700 infiltration events. The results demonstrate that the physical relationship of film flow was capable to predict wetting front velocity (v) and flow parameters from rainfall input (qs) alone. This relationship was pronounced in grassland sites but weaker for forest sites, probably due to heterogeneity of the rainfall input underneath the canopy. Incorporating the water content into the v‐qs relationship did not improve the quality, but showed that for the film flow the rainfall input and hence gravity is in fact the dominant driver and not capillarity. Furthermore, abstraction of water into the soil matrix during film flow is an important process to be included into the framework with reasonable agreements for marl and sandstone using a multiple linear regression. Film flow and corresponding functional parameter relationships for other regions could improve catchment wide PF modeling in the future.
Highlights
Preferential flow (PF) in the unsaturated zone is a common phenomenon resulting in rapid water flow and solute transport during infiltration (Germann et al, 2007)
We used a unique data set from a soil moisture sensor network with 135 instrumented soil profiles in three different geologies and two land covers and fitted the film flow model to around 1,700 infiltration events
We analyzed in total 1,184 rainfall events at the different sites that led to 1,718 infiltration events of which 1,704 met the quality criteria at 10 cm depth, 395 of those infiltration events produced an usable soil moisture reaction in 30 cm and 136 in 50 cm
Summary
Preferential flow (PF) in the unsaturated zone is a common phenomenon resulting in rapid water flow and solute transport during infiltration (Germann et al, 2007). Soil hydrological models still suffer from difficulties in describing the heterogeneous and complex nature of PF, which often results in higher flow velocities than pure capillary-driven matrix flow (Germann & Hensel, 2006; Nimmo, 2007). Not including these fast flows when modeling infiltration can lead to problems predicting runoff formation (Beckers & Alila, 2004; Niehoff et al, 2002), solute transport (Gerke & Köhne, 2004; Haws et al, 2005) and stable water isotope dynamics (Sprenger et al, 2018). In these dual-domain models the Richards equation was frequently applied for the fast flow domain (Gerke & van Genuchten, 1993)
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