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| Titel |
Control of mass balance error in a detailed model of surface-subsurface flow interaction |
| VerfasserIn |
Marcello Fiorentini, Stefano Orlandini, Claudio Paniconi, Mario Putti |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093061
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| Publikation (Nr.) |
 EGU/EGU2014-7433.pdf |
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| Zusammenfassung |
| Several process-based catchment-scale hydrologic models have been developed in recent
years to describe the interactions and feedbacks between different components of the water
cycle, but few studies have considered the sources of coupling error in these models. In this
work we analyze the sequential iterative coupling scheme of the distributed model CATHY
(CATchment HYdrology) in order to identify the different sources of mass balance error and
to examine how these are influenced by topography, hydraulic properties, and atmospheric
forcing. A pair of adimensional indices that quantify the degree of coupling and of flux
partitioning is presented. Our analysis shows that mass balance errors increase during the
flood recession limb because of the exchange of information between surface and subsurface
water flow. Surface water propagation is cell centered, while the subsurface flow
equation is solved on the vertices of surface cells. Evaluation of surface pressure
heads and exchange fluxes is critical on this staggered surface–subsurface mesh,
especially during transitions from unsaturated to saturated conditions and vice versa. A
modified version of the flux exchange algorithm is introduced that considers the
effective availability of water on surface cells. The performance of the model is
also improved by introducing a heuristic procedure to control and adapt the time
step interval. Starting from numerical stability and convergence constraints, this
procedure varies the computational interval as a function of the rate of change of
surface saturation via the coupling degree index. A final improvement made to the
sequential coupling scheme in CATHY is to solve the surface routing equation
after rather than before the subsurface module. We find that the modified version
improves the water balance by more than 50% in most of the tests considered for a
simple v-shaped catchment. The results so far obtained for the synthetic v-catchment
indicate the need for a more comprehensive analysis including real catchments. |
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