**2.1 Descriptions of the study areas**

The river Reka catchment spreads over 30 km2 and is located in the northwestern part of the country (Goriška Brda) (Fig. 1). Altitude ranges between 75 m and 789 m a.s.l. Very steep ridges of numerous hills, which are directed towards the southwest, characterizes the area. The catchment landscape is very agricultural with higher percentages of forest (56 %) and vineyards (23 %). The river Dragonja catchment area spreads over 100 km2 and is located in the far southwestern part of the country (Istria) (Fig. 1). This is a coastal catchment (Adriatic Sea), with an altitude ranging between 0 and 487 m a.s.l. The ridges of the hills are designed as a plateau with flat tops and steep slopes. The landscape is largely overgrown with forest (63 %) and grassland (18 %). Steep slopes allow cultivation only on the terraces.

Fig. 1. The river Reka and Dragonja catchment case areas divided in sub-catchments

Modelling of Surface Water Quality by Catchment Model SWAT 111

Before the modelling a field tour to the research areas and review of available data was carried out (Table 1). Since the available data was insufficient for modelling, we perform additional monitoring of surface water quality at the Reka tributary Kožbanjšček hydrological station Neblo, excavation of soil profiles, laboratory measurements and using established model standards (texture, albedo, organic carbon etc) and water-physical soil

**Data type Scale Source Description/properties** 

Agency

/ Chamber of Agriculture

Mapping Authority of the Republic of Slovenia

Ministry of Agriculture, Forestry and Food of the Republic of Slovenia; Biotechnical Faculty (University of Ljubljana); Faculty of Agriculture (University of Zagreb)

Ministry of Agriculture, Forestry and Food of the Republic of Slovenia; European Environment

and Forestry of Slovenia; Guidelines for expert justified fertilization (Mihelič et al., 2009); Interviews with farmers

Environment Agency of the Republic of Slovenia

Environment Agency of the Republic of Slovenia

Environment Agency of the Republic of Slovenia

Environment Agency of the Republic of Slovenia

Environment Agency of the Republic of Slovenia Elevation, overland and channels slopes,

Spatial soil variability.

lengths

Soil types and properties.

Land cover classification and spatial representation

Crop rotations:

harvesting.

radiation.

planting, management,

Fertiliser application (rates and time)

Daily precipitation, temperature (max., min.), relative

humidity, wind, solar

From surface and groundwater.

Daily flow data (m3 day-1)

P, TP

Registered domestic, Industrial discharge

Water quality (mg l-1): sediment, NO3-

, ortho-

**2.2 Database development for the model build** 

Croatia: 1:50,000

(Graphical Units of Agricultural Land) Croatia: 100m×100m

Reka: 2 precipitation, 1 meteo (wind, temp., rain, humidity, solar)

(CORINE)

Dragonja: 3 precipitation, 1 meteo

46 permits (136 points)

River quality Reka: 0 monitoring

Reka: 2 points Dragonja: 1 point

Reka: 2 stations Dragonja 1 station

station; Dragonja: 1 monitoring station

Table 1. Model input data sources for the Reka and Dragonja catchments

Soils Slovenia: 1:25,000

Land use Slovenia: 1m×1m

Land

Weather stations

Water abstraction

River discharge

Waste water discharges

management

Topography 25m×25m The Surveying and

Flysch bedrock of the case areas was formed in Eocene as a product of the sea sediments and undersea landslides. Flysch consists of repeated sedimentary layers of sandstones, marl, slate and limestone, which can quickly crumble under the influence of precipitation and temperature changes. Brown eutric soils are shallow and due to silt-loam-clay texture difficult for tillage, with appropriate agro-technical measures (deep ploughing, organic fertilisers) they obtain properties for vine or olive production. In case of inappropriate agricultural activities and land management, we can witness very strong erosion processes.

Both areas are characterized by sub-Mediterranean climate (NE Mediterranean) with southwestern winds and warm and moist air. Average annual temperature at the station Bilje (the Reka catchment), for the period 1991−2009, was 13.3 °C, with the highest and lowest monthly average in August (22.8 °C) and January (4 ºC). Average annual rainfall in the period 1992 − 2008, was 1397 mm, with peaks between September and November (max. in September 184 mm). Average annual temperature at the Portorož station (the Dragonja catchment), for the period 1991 − 2009, was 14.1 °C, with the highest and lowest monthly average in August (23.4 °C) and January (5.2 °C). Average annual rainfall in the period 1993 − 2008, was 930 mm, with peaks between September and November (max. in September 130 mm). Both catchments are characterized by fractured aquifer, where water trapped between flysch layers forms surface springs. Alluvial aquifer in the valley bottom overlays impermeable flysch. River network, of the two areas is very extensive. Rivers character is torrential and mediterranean. The river Reka hydrograph recorded (1993-2008) the highest flow rates between October and January with the average flow of 0.98 m3s-1 in November and the maximum 24.50 m3s-1 in October 1998, and extremely low in the summers. Hydrograph of the river Dragonja recorded (1993-2008) the highest flows between November and April with the average flow of 1.41 m3s-1 in January and the maximum 64.70 m3s-1 in October 1993, however in the summer the river dries up every year.

The favourable climate and terrain influences at the higher average temperature, better lighting, soil temperatures, minimal risk of frost, wind prevents diseases development. Viticulture is economically most important agricultural sector in both areas, with important share of olive and vegetable productions in the Dragonja area, and fruit production in the Goriška Brda. Terracing is typical for both areas and depends on natural conditions, steepness of the slopes (erosion), geological structure (sliding) and climatic conditions (rainfall). In Goriška Brda (Reka) is 78% of vineyards terraced while in the Slovenian Istria (Dragonja) about 18%. Vine and olive growing are the sole agricultural sectors, which can withstand the cost of the terraces installation. Terraces in the Dragonja area are characterized by overgrowing, which results in a disordered ownership structure.

The annual average concentration of sediment in the river Reka catchment for one year of research period (July 2008 – June 2009) was 32.6 mg l-1, nitrate (NO3-) 2.7 mg l-1 and TP concentration of 0.109 mg l-1. In the river Dragonja catchment average annual concentration of sediment in the research period (August 1989 – December 2008), was 29.1 mg l-1 (107 samples), NO3- 2.7 mg l-1 (87 samples) and TP concentration of 0.043 mg l-1 (92 samples). In January 2007, the highest sediment concentration measured so far, was 1362 mg l-1. The water quality with exception of sediments does not cause any serious problems in these two study areas. Data shows that sediment concentrations are well in excess of Environment Agency guide level (25 mg l-1).
