Abstract
Abstract. Backwater effects in surface water streams and on adjacent lowland areas caused by mostly complex drainage and flow control structures are not directly computed with hydrological approaches yet. A solution to this weakness in hydrological modelling is presented in this article. The developed method enables transfer of discharges into water levels and calculation of backwater volume routing along streams and adjacent lowland areas by balancing water level slopes. The implemented and evaluated method extends the application of hydrological models for rainfall–runoff simulations of backwater-affected catchments with the advantages of (1) modelling complex flow control systems in tidal backwater-affected lowlands, (2) less effort to parameterise river streams, (3) directly defined input factors of driving forces (climate change and urbanisation) and (4) runtime reduction of 1 to 2 orders of magnitude in comparison to coupled hydrodynamic models. The developed method is implemented in the open-source rainfall–runoff model Kalypso-NA (4.0). Evaluation results show the applicability of the model for simulating rainfall–runoff regimes and backwater effects in an exemplary lowland catchment (Hamburg, Germany) with a complex flow control system and where the drainage is influenced by a tidal range of about 4 m. The proposed method is applicable to answer a wide scope of hydrological and water management questions, e.g. water balances, flood forecasts and effectiveness of flood mitigation measures. It is re-usable to other hydrological numerical models, which apply conceptual hydrological flood-routing approaches (e.g. Muskingum–Cunge or Kalinin–Miljukov).
Highlights
There is open demand in hydrological modelling of rainfall– runoff regimes in backwater-affected lowlands
Hydrological models are applied to simulate processes in the compartments of the (1) surface–atmosphere interaction, (2) the transition between soil–vegetation–atmosphere, (3) the processes in the vadose zone of the soil and (4) the flood routing in the receiving surface waters
The results show a good reliability of the computed flood-routing and backwater effects in streams
Summary
There is open demand in hydrological modelling of rainfall– runoff regimes in backwater-affected lowlands. The occurrence of backwater effects in such complex lowland river streams and on adjacent lowland areas poses an open research question in hydrological modelling. Adjacent lowland areas in this article are distinguished by a low ground level and connection to rivers. Hydrological models are applied to simulate processes in the compartments of the (1) surface–atmosphere interaction, (2) the transition between soil–vegetation–atmosphere, (3) the processes in the vadose zone of the soil and (4) the flood routing in the receiving surface waters. The last two issues require more detailed considerations because of mostly high groundwater levels and the drainage against fast-changing water levels in tidal streams of complex flow control systems. For simulating the interaction between groundwater and surface water quite a few approaches are available
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