Free access to functioning SWAT application of the three river basins

SWAT (Soil and Water Assessment Tool, https://swat.tamu.edu ) was developed to predict the impacts of land management practices on hydrological regimes and the loading of surface waters in complex watersheds over long periods of time. Building a SWAT application is a laborious process. It is of great help to other modelers (researchers and practitioners) if ready applications, in which all the numerous parameters have already been determined for similar areas than that of the user’s own target area. The Bonus Return project produced 3 baseline (no scenarios with e.g. mitigation measures or BMPs) SWAT applications with different parameter combinations for the project’s case study catchments in Finland (Vantaanjoki), Sweden (Fyrisån) and Poland (Slupia). So, the user can start making his/her own scenarios for these areas on top of the baseline applications. As a new contribution to the Syke’s open data, the three SWAT applications of Bonus Return project were compressed into zip-files and stored in the open data repository of the Finnish Environment Institute (Syke), from where anyone with knowledge on SWAT can download the files and start making his/her own runs, simulations and scenarios.

Processing

The SWAT (Soil & Water Assessment Tool - https://swat.tamu.edu ) model setups, calibration and validation for three case study catchments: Vantaanjoki (Finland), Fyrisån (Sweden) and Slupia (Poland) of the Bonus Return project are described here.

The first step of the modelling work was collection and processing of the input data for each case study catchment. These data included digital elevation (DEM), land and use soil maps, as well as meteorological data and information on point sources, agricultural practices etc. Creation of model set-ups was done in a semi-distributed way that enables distinction between areas within the catchments. The numbers of sub-catchments were defined to be high enough for a good spatial representation of hydrological processes, also reflecting the spatial resolution and quality of input data. In general, the level of detail in input data and conducted delineation into spatial modelling units were quite similar between the three catchments in order to enable future cross-comparisons of results.

In the next phase, rigorous model calibration and validation for river discharge (m3 s-1), sediment and nutrient loads (kg day-1) were performed for each case. Here, automatic calibration and uncertainty analysis with SWAT-CUP software (SUFI-2 programme) were carried out. As for hydrology, the results of calibration and validation were good: e.g. for daily data of the Vantaanjoki outlet the model performance measure called Kling-Gupta efficiency (KGE, Gupta et a. 2009) was 0.82 for calibration and 0.80 for validation. Corresponding values for the main gauge on the Fyrisån were 0.86 and 0.83, and for the Slupia 0.76 and 0.85. In the Finnish case (Vantaanjoki), calibration and validation for sediment and nutrients was done against high-frequency (continuous 1-hour measurements aggregated into daily totals) water quality dataset for 6 years’ time-span collected with automatic monitoring system. This gave a valuable insight into the model’s performance in describing rapid changes in water quality. The KGE values for sediment and nutrients in the Vantaanjoki case varied between 0.77–0.81 for calibration and between 0.25–0.67 for validation. In Fyrisån and Slupia only low-frequency (one or two measurements per month) data were available for calibration. For the Fyrisån catchment the KGE values for sediment and nutrient loads varied between 0.62 and 0.75 for calibration and between 0.45–0.7 for validation. In the Slupia catchment KGE ranged between 0.31 and 0.69 in the calibration period and 0.11–0.47 for the validation period.

After calibration and validation, the model applications provided spatially-distributed nutrient loads for the baseline conditions (0-scenarios, reference). In such baseline conditions typical annual total phosphorus (Ptot) and total nitrogen (Ntot) loadings from the Vantaanjoki study catchment into the Baltic Sea are 0.40 kg P ha-1 and 10.2 kg N ha-1, respectively. For the Slupia study catchment the corresponding loadings are 0.47 kg P ha-1 yr-1 and 6.8 kg N ha-1 yr-1, and for the Fyrisån study catchment 0.11 kg P ha-1 yr-1 and 4.4 kg N ha-1 yr-1. The model applications will also provide approximate source apportionment (e.g. agricultural and urban diffuse sources, wastewater treatment plants, etc.) for each case.

IMPORTANT: Before you start using the model, please change the correct path in your computer for the MasterProgress table of the MS-Access file “casename.MDB”. The models were developed with swat2016.exe revision 664.