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TEMPQSIM Résumé de rapport

Project ID: EVK1-CT-2002-00112
Financé au titre de: FP5-EESD
Pays: Italy

Report of tested water quality models for temporary waters

The models under evaluation within the tempQsim project range from continuous time hydrological models originally designed and suited for application to medium/large scale catchments to rather detailed and complex tools for application to a single slope. Models showed to be rather different in the detail of the output obtained as result of application as well as in the time scale characteristic of the model.

Since the beginning of the project in particular SWAT and HSPF models have undergone a process of improvement by the respective users/developers communities in several aspects. In the same time a coarse scale delivery model (PESCAS), an improved in-stream water quality model (tempQsim-STREAM) and a detailed biochemical reach model (tempQsim-REACH) were established and tested.

Improvements were related to a sub-daily time step for runoff generation and routing of sediment and nutrients (due to the usual fast response time of such rivers), an improved transmission losses calculation (quite critical in rivers with gravel beds), a better quantification of sediment transport along the slopes (to take into account deposition before the runoff enters the river network), an in-stream module that takes into account deposition-resuspension of sediments, the possibility of assimilation of radar weather data to try to overcome spatial variability of rain events.

Within the time boundaries of the project, two developments within the SWAT model took place and have been tested on the Mulargia test site (a) sub-daily time step for water balance simulation and polluting load routing, (b) sensitivity analysis and autocalibration. The adoption of the subdaily time step lead to a significant improvement in the simulation of the peak flow.

The application of the HSPF model to the Krathis River revealed several weaknesses related to heavily modified systems, karstic base-flow, dry-wet/ expansion-contraction dynamics,
first flush effects, biogeochemical processes under changing moisture conditions.

The tempQsim-STREAM model focused on two major features which distinguish the biogeochemical properties of temporary waters from those of permanent waters (a) ongoing biogeochemical processes in pools even after surface flow has ceased, (b) accumulation of organic particulate matter on the channel bed due to transmission losses. Model results show both the significant potential for mass accumulation within the channel system during the dry period, as well as the effects of the first flush.

The consideration of the drying and rewetting impact on biogeochemical processes with tempQsim-REACH was shown to be effective at the Krathis catchment and indicated a sufficient sensitivity regarding resuspension of sediments. Current results for the particular case of the Krathis catchment indicate that changes in nutrient concentrations within the reach are significant during low flow conditions, whilst during the flood events, pollution dynamics are largely driven by the variability of inflow to the reach.

The results of PESCAS show basically a distinct seasonal variability especially for the Krathis and Degebe/Pardiela and the Vène catchment. The model indicated also an added value for upscaling the project results and estimating the relevance of dry streams at an European level.

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