PART 5

Soil Moisture Monitoring

5.1. Data collection methods

 The soil moisture data collection methods in hydrological year 2000 on both sides remained the same as in the previous years. Measurements on the Slovak side are performed by neutron probe down to a prescribed depth or to the depth of the ground water level. Measurements on the Hungarian side are performed by a capacity probe to the prescribed depth. The observation objects were put in the soil layer, down to the underlying gravel layer. The soil moisture on both sides is expressed by the total soil moisture content in volume percentage recorded in 10 cm depth interval for each measurement during the year. The observation points are situated on different monitoring areas. Measurements on the Slovak side are performed on 12 forest monitoring areas, on 5 biological monitoring areas and on 3 agricultural areas – Tab. 5-1. Measurements on the Hungarian side are performed on 9 forest monitoring areas and 5 agricultural areas - Tab. 5-2. The situation of observation objects is shown on Fig. 5-1.

Table 5-1: List of monitoring stations on the Slovak side

Table 5-2: List of monitoring stations on the Hungarian side

5.2. Data presentation methods

 Both Parties use the same presentation principle of soil moisture content values: figures showing the average soil moisture content in volume percentage for the depth interval from 0 to 100 cm and from 110 to 200 cm. A small difference is at Hungarian data where the value for depth interval under the 110 cm represents the average value for the rest of total measured depth. The soil moisture time distribution for the whole measured depth is presented on colour figures. The graphical presentation of the whole set of measured data is given in the Slovak and Hungarian National Annual Reports.

5.3. Evaluation of results on the Hungarian side

 Measurements of soil moisture contents on the Hungarian side were conducted at forestry monitoring sites as well as at agricultural monitoring sites. The results of evaluated year were affected by moisturising conditions different from those of the year 1999. Soil moisture values at all monitoring points were lower than in the previous year. This was caused by less precipitation during the vegetation period (61 % of several year’s average). Besides this the soil layer thickness, composition and the depth of the ground water level primarily influence the soil moisture conditions.

 Forestry monitoring sites

All soil moisture monitoring point on forestry areas, except the site No. 9972 was characterised by that fact that both up to 1 m depth and below 1 m the average maximal and minimal values of the soil moisture content were lower comparing to the previous year. The maximum average soil moisture content in 1 m depth was recorded on 2^nd of December at four monitoring sites, at the other four monitoring points it was recorded at the beginning of the year. The minimum values were recorded in July at seven monitoring sites, and at one point in August.

The maximum of average soil moisture contents in the depth below 1 m were recorded in April and May, the minimum was recorded on the 25^th of February at four monitoring points, on the 2^nd of December at two points, and on the 24^th of August at monitoring point No. 9972.

Regarding the effect of ground water on soil moisture content, differences can be observed at monitoring points.

As a result of the water supply the ground water moisturised the soil at monitoring site No. 9355, 9994 and 9995 at various depth. At observation point No. 9997 the ground water fluctuated in the gravel layer. The covering layer is shallow and the water supply in this place is not sufficient. At the monitoring site No. 9996 the ground water level was generally found in the gravel bed as well, but during flood events in March, April and August it raised and moisturised the lower part of the soil layer. The soil moisture content in the soil layer at the monitoring site No. 9994 was balanced, but generally lower than in previous year.

Monitoring site No. 9452 is situated close to the river arm supplied by water, on the flood-protected side, hence the ground water constantly moisturised the soil layer. The observation point No. 9972 lying next to the Danube and is under strong drainage effect. The ground water did not reach the 160 cm thick soil layer during the evaluated hydrological year. The ground water level at monitoring site No. 9998 is affected by the water level fluctuation in the Danube. The ground water level all the year fluctuated in the 275 thick soil layer, moreover during flood events it rose close to the surface. ( Fig. 5-2, Fig. 5-3, Fig. 5-4.).

 Agricultural monitoring sites on the flood protected side

Precipitation dependent moisturising was similar to that observed at the forestry monitoring sites. Monitoring points No. 2630 and 2653 can get water only from precipitation because the ground water level is situated deep in the gravel bed. Monitoring points No. 2605 and 9443 lying on areas with thick covering layers, the ground water moisturised the bottom of soil layer from March till end of August or September. At the monitoring site No. 7920 was the ground water situated in favourable range of the soil profile from February till June, while from September due to the low discharges in the Danube a significant lowering of ground water level occurred. However the ground water still moderately moisturised the thick covering layer.

5.4. Evaluation of Slovak results

Monitoring sites on the Slovak side are situated in the inundation area and flood protected agricultural area (Fig. 5-1).

According to the soil moisture observation at monitoring sites situated in the agricultural area it can be stated that the soil moisture content during the whole observed period remained unchanged (Fig. 5-5). The position and fluctuation of ground water level remained unchanged as well. The ground water level at the monitoring site No. 2716 fluctuated in the depth of 3-4 m, at site No. 2717 in the depth of 2.5-3.5 m and at site No. 2718 in the depth of 2-3 m.

The fluctuation of soil moisture content in the depth interval from 0 to 1 m mostly depends on climatic conditions. In the depth from 1 to 2 m the soil moisture fluctuation is partly influenced by the ground water level. The soil moisture content in the depth to 1 m mostly fluctuated in the range from 20 to 30 %, in the depth between 1 and 2 m the soil moisture content varied from 12 to 35 %.

The situation in the inundation area is more complex. The changes of the soil moisture content depend mainly on the location of the monitoring site in respect to the Danube, in respect to the river branch water supply and to the soil profile thickness.

The soil moisture is besides the ground water level and precipitation highly dependent on artificial floods. In hydrological year 2000 there was a small flood simulated in June, which helped the moisturising of the lower part of soil layers.

In the inundation area around Dobrohošť and Bodíky is the thickness of the soil profile, similarly to the Hungarian side, is low - monitoring sites No. 2703, 2764, 2763, 2762 and 2760. The ground water level in hydrological year fluctuated only in the gravel layer. This was characteristic already before damming the Danube. The average values of the soil moisture content in the depth to 1 m significantly fluctuated and highly depend on the climatic conditions. The soil moisture values in the depth interval from 1 to 2 m are less dependent on the short periods of extreme precipitation or temperature. The ground water supplied this layer only at higher discharges in the Danube or during the artificial flood (Fig. 5-6a, Fig. 5-6b and Fig. 5-7). The maximum average soil moisture content occurred at the end of February. During the vegetation period, except the artificial flood, the soil moisture content continuously decreased and the minimum values reached during August and September. At the end of the year the soil moisture content, influenced by precipitation, started to rise up.

The thickness of the soil profile in the middle part of the inundation area is higher. The ground water regime in this region is influenced by the water supply of the river arms, introduced in May 1993. Moreover, the artificial floods are with high influence on the ground water level. The ground water level fluctuates mostly above the boundary between the soil profile and gravel layers - monitoring sites No. 2704, 2705, 2758, 2759, 2761 (Fig. 5-8). The lack of precipitation in 2000 resulted in continuous decrease of the soil moisture content in the second half of vegetation period in the upper part of the soil layer. The ground water significantly supplies the soil profile in the depth interval from 1 to 2 m.

In the lower part of the inundation area, downstream of the confluence of river branch system and the Danube (2706, 2756, 2755), the ground water level fluctuates around the boundary between the soil profile and the gravel layer. The average values of the soil moisture significantly fluctuate. The minimum and maximum values are related to the minimum and maximum ground water levels respectively. The soil moisture in this area highly depends on the ground water level position. In 2000 the soil moisture was positively influenced by the high discharges in the Danube in March and April (Fig. 5-9a, Fig. 5-9b). In the second half of vegetation period, when discharges in the Danube dropped down, the soil moisture content rapidly decreased.

The soil moisture contents at monitoring sites No. 2707, 3804, 3805, located in the inundation below the confluence of the tail-race canal and the Danube, are highly influenced by the discharge regime in the Danube. In the year 2000 maximum values occurred during the spring, while the minimum values occurred in the second half of the vegetation period because of lower discharges in the Danube and lack of precipitation.

Fig. 5-1 Monitoring network of observation objects agreed in the frame of the Joint monitoring		Fig. 5-2 Soil moisture monitoring Dunakiliti		Fig. 5-3 Soil moisture monitoring Hédervár
Fig. 5-4 Soil moisture monitoring Lipót		Fig. 5-5 Soil moisture monitoring Bodíky - Šulany		Fig. 5-6a Soil moisture monitoring Horný Bar - Šulany
Fig. 5-6b Soil moisture          Horný Bar - Šulany		Fig. 5-7 Soil moisture monitoring Dobrohošť		Fig. 5-8 Soil moisture monitoring Horný Bar - Bodíky
Fig. 5-9a Soil moisture monitoring Gabčíkovo - Istragov		Fig. 5-9b Soil moisture     Gabčíkovo - Istragov