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Water quality modules and improved catchment models

TempQsim has comprised the model development under a pan-European collaboration of 14 participants and is supported by measurement programmes based on eight research catchments across the range of European dryland environments. The models have been applied and tested in the project test catchments and compared with both existing data and additional data collected during the course of the project. The resulting models were to be made available, with technical support, to the research community and end users as a tool for exploring the impacts of land use and climate change scenarios.

The tempQsim project aimed for the first time to make specific improvements to water quality models for application to temporary streams. In this way, tools should be provided to improve the integrated management of water resources in Mediterranean and other dryland river catchments through quantifying the water quality dynamics of these ephemeral and temporary waters and through the development of improved water quality models.

Experience gained during the tempQsim project indicates that the complexity of modelling in dry areas is associated with the high variability in space and time of water flows and pollution sources. The spatio-temporal scale selected for modelling affects the amount of input data required. One way of handling data acquisition and processing is to address different problems at different scales with different modelling tools.

The development of modelling tools addressed both the improvement of coarse scale delivery models as well as detailed in-stream and reach scale water quality models. Specifically, sub-models were designed to account for accumulation, remobilisation and transformation processes for organic matter and nutrients during the dry and wet periods.

The tempQsim tools outlined below are associated with decreasing scales from European scale down to the reach scale. At this smallest scale, describing a part of the stream network, uniformed conditions may be assumed.

PESCAS is devoted to the simulation of sediment and nutrient delivery at regional scale, paying particular regard to difficult data availability at this scale. The PESCAS approach offers a methodology for long term management of water quality, focusing on spatial and seasonal differences at the Mediterranean scale and is designed to operate with a daily time step at the catchment scale. This approach is therefore less demanding in computing resources than a continuous time model running through each event. As land-use and climate are explicit within PESERA and CLINUM the sensitivity of changing environments can be explored.

tempQsim-STREAM is an in-stream water quality model which pays particular attention to transmission losses and mass accumulation during the dry period. It also takes into consideration relevant nutrient transformation and the production/decomposition of particulate matter. Special emphasis is also given mass balance during the onset of flow.

The tempQsim-STREAM model consists of a hydrodynamic model, which includes a non-steady state water quality and a benthic submodel. Instream flow routing is computed via approaches as Kinematic wave, Diffusive wave or Dynamic wave. It is designed especially for modelling problems where water is stored in pools, either naturally or following the input of waste water effluents. Therefore a special focus is given to the dynamic simulation of the change from dry to flowing conditions in the river, and the flood-induced reconnection of isolated pools to the stream. Special algorithms for converting concentrations into mass allow a reasonable treatment of accumulated pollutants during dry periods, retaining mass balance.

Using a specific numerical approach the model is well tailored for non-steady state conditions associated with flash floods and related rapid changes in river condition.

The tempQsim-REACH is a generalised model that can describe the hydrology, sediment transport and biogeochemical processes of temporary rivers at the reach scale. The tempQsim-REACH model simulates process dynamically during wet and dry periods with spatial accounting for the expansion and contraction of the river corridor. The model comprises hydrologic sediment transport and water quality submodels.

Spatially, the reach is represented as zero-dimensional simulating temporal changes in water quality due to biogeochemical processes.

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Reported by

University of Hannover
Am Kleinen Felde 30
30167 Hannover
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