Abstract
Backwater effects in surface water streams as well as on adjacent lowland areas caused by mostly complex drainage structures are not directly computed with hydrological approaches, yet. A solution of this weakness in hydrological modelling is presented in this article. The developed method enables to transfer discharges into water levels and to calculate 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 drainage 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 one to two 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 modelling rainfall-runoff regimes and backwater effects in an exemplary lowland catchment (Hamburg, Germany) with a complex drainage 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
Backwater effects in surface water streams as well as on adjacent lowland areas caused by mostly complex drainage structures are not directly computed with hydrological approaches, yet
The developed method enables to transfer discharges into water levels and to calculate backwater volume routing along streams and adjacent lowland areas by balancing water level slopes
Open demand exists in hydrological modelling of rainfall-runoff regimes in lowlands which are distinguished by complex flow routing in mostly intensively drained catchments by manifold control structures
Summary
Open demand exists in hydrological modelling of rainfall-runoff regimes in lowlands which are distinguished by complex flow routing in mostly intensively drained catchments by manifold control structures. Modelling backwater effects in tidal streams with fast changing water levels in complex drainage systems of lowland catchments directly with hydrological models is not implemented in most hydrological approaches up to now 35 (Waseem et al, 2020). The demand to solve this weakness in hydrological numerical models increases, since in low lying tidal catchments, the pressure on current storm water drainage systems raises due to combined impacts of enlarged urbanisation on the one hand and climate change induced sea level rise in combination with heavy storm events on the other hand (IPCC, 2013b, 2013a; UN DESA, 2018). Studies about the combined risk of high tides (storms) and stormwater events are given by (Lian et al, 40 2013; Nehlsen, 2017; Klijn et al, 2012; Zeeberg, 2009; Huong and Pathirana, 2013; Sweet et al, 2017) These selected examples all show a conformity about the tendency that low lands will face higher pressures to mitigate flooding in the future. State-of-the-art hydrologic approaches reveal shortcomings in modelling the flood routing and retention volume in backwater affected lowland catchments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
