This article presents a methodology to optimize the integration of local scale drainage measures in catchment modelling. The methodology enables to zoom into the processes (physically, spatially and temporally) where detailed physical based computation is required and to zoom out where lumped conceptualized approaches are applied. It allows the definition of parameters and computation procedures on different spatial and temporal scales. Three methods are developed to integrate features of local scale drainage measures in catchment modelling: (1) different types of local drainage measures are spatially integrated in catchment modelling by a data mapping; (2) interlinked drainage features between data objects are enabled on the meso, local and micro scale; (3) a method for modelling multiple interlinked layers on the micro scale is developed. For the computation of flow routing on the meso scale, the results of the local scale measures are aggregated according to their contributing inlet in the network structure. The implementation of the methods is realized in a semi-distributed rainfall-runoff model. The implemented micro scale approach is validated with a laboratory physical model to confirm the credibility of the model. A study of a river catchment of 88 km 2 illustrated the applicability of the model on the regional scale.
Sophisticated strategies are required for flood warning in urban areas regarding convective heavy rainfall events. An approach is presented to improve short-term precipitation forecasts by combining ensembles of radar nowcasts with the high-resolution numerical weather predictions COSMO-DE-EPS of the German Weather Service. The combined ensemble forecasts are evaluated and compared to deterministic precipitation forecasts of COSMO-DE. The results show a significantly improved quality of the short-term precipitation forecasts and great potential to improve flood warnings for urban catchments. The combined ensemble forecasts are produced operationally every 5 min. Applications involve the Flood Warning Service Hamburg (WaBiHa) and real-time hydrological simulations with the model KalypsoHydrology.
Assessing the performance of future urban drainage management practices requires novel hydrological modelling approaches that can handle a large number of spatially distributed measures, such as sustainable drainage systems (SUDS). This paper presents the implementation of a SUDS modelling approach in a semidistributed hydrological model that enables the simulation of flow among multiple linked SUDS and meso-scale retention spaces and the application of this model to an urban catchment. The objectives of the implemented model are the representation of SUDS as model elements with water redistribution functionality as well as its possible integration into a flood risk management tool. The model was applied to quantify the impacts of socioeconomic and climate change in an urban catchment in Hamburg, Germany, under different future scenarios and combinations of SUDS. The results demonstrate the potential of SUDS and multipurpose retention spaces for flood risk mitigation.
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).
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