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Volume XV |

The Influence of Extreme Rainfall on Flow, Soil Moisture, Nutrients and Tracer Pathways

Abstract: On two agricultural experimental catchments with different vegetation cover we have carried out experiments with leaching or wash off nutrients due to high artificial rain intensities: grassland after grazing, arable land, river bank covered with grass and during different seasons (spring, summer, autumn). Rainfall total and soil moisture have been automatically recorded in two depths. The concentration of nutrients was analysed in the laboratory. From the results, it is possible to formulate the following conclusions: flow of nutrients during extreme precipitation is high at the beginning of the soil profile saturation and then gradually decreases; increasing concentration occurs in the period just after grazing or after fertilisation with manure; the highest concentration of nutrients occurred in experiments on the field after tillage. The outcomes correspond to results from rainfall-runoff events, when extreme rainfall causes the wash off the soil into the stream. Before and after the experiment the samples of soils have been taken. The change in POlsen (Olsen P) on the pasture slope was less than 1 mg/kg of dry matter of soil while on the catchment used for crops it was larger than 10 mg/kg. Understanding flow pathways in a catchment requires carrying out field experiments with conservative tracers. The contribution brings results from such experiments on a meadow and in forest. Both types of field experiments with sprinkling contribute to the understanding of the flow and nutrient pathways during an extreme rainfall.

Volume XV |

HYDROBOD: obtaining a GIS-based hydrological soil database and a runoff coefficient calculator for Lower Austria

Abstract: In the State of Lower Austria, rainfall-runoff models it is an acknowledged method used when estimating flood peak discharges for small catchments where there are no direct gauging observations. An important input parameter for these models is the volumetric runoff coefficient, which was estimated by rather simple methods until now (for instance the CN-method of the U.S.G.S), which did not provide very reliable results.
The project HYDROBOD intends to provide a solid and homogeneous database of some basic soil hydraulic parameters over the whole state area (over 19.000 km²) and contains a hydrological model for estimation of these runoff coefficients which takes into account some relevant input variables.
In a first step (HYDROBOD I), hydraulic soil parameters are calculated by regionalization methods and assembled for the whole area of Lower Austria, using a GIS-database (ESRI ArcGIS 10.2; at a 50 x 50 m grid). They include soil layer depth, storage capacity, saturated vertical conductivity, plus a classification of the soil reaction types referring to storm events. These data are now available for three soil layers, from top soil down to 1 m below surface. In a second step (HYDROBOD II), a vertical one-dimensional event model was set up which allows to calculate storm event runoff coefficients on a cell-by-cell basis for any given area in Lower Austria.
This model uses the hydraulic soil parameters obtained from HYDROBOD I, plus an estimation of unsaturated vertical pore flux and a soil water storage model with several modules. This model needs the following input parameters: a shape-file with the catchment area, and pairs of rainfall data (duration + rainfall depth).
Results of a calculation process are: runoff coefficients (as an average over the catchment area) for each pair of rainfall data, and for different initial wetness scenarios (from “dry” to “saturated”). Validation of the model is promising.

Volume XV |

Pollution load released into the Bay of Gdańsk by small river catchments in the coastal city of Sopot

Abstract: The purpose of the study is to determine the quantity of wastewater entering the Gulf of Gdańsk, which is part of the Baltic Sea. The study area consists of small river catchments in the city of Sopot, which lies along the Gulf.
The research also aims to determine wastewater release volumes over time, instead of focusing only on spatial distributions. Another aim is to identify main determinants potentially affecting water quality in rivers flowing across the city of Sopot. Land use is also considered as a factor. The study area consists of seven small river catchments in the city of Sopot, each with an open flow channel. The study period was 2014 – 2015. Laboratory tests were performed to determine the concentration of both total nitrogen and total phosphorus. Other metrics in the study included pH, specific conductivity, water temperature, dissolved oxygen content, and suspended matter content. Discharge was also measured for each studied river. Comparisons were then made with local meteorological data. Research has shown that none of the 6 studied rivers experienced concentrations of total nitrogen above the norm accepted in Poland for Class 1 water quality (5 mg·dm-3). Mean annual values ranged from 0.60 to 1.28 mg·dm-3. The Class 1 norm for phosphorus (0.2 mg·dm-3) was also not exceeded in the case of total phosphorus in any of the 6 studied rivers. Phosphorus values ranged from 0.066 to 0.1 mg·dm-3. The annual load supplied by all 6 rivers in the Sopot city area during the study period was 4,295.9 kg for total nitrogen and 370.2 kg for total phosphorus. For the purpose of comparison, the load supplied by Poland as a whole in the year 2012 was: 210,768,000 kg total nitrogen, and 15,269,000 kg total phosphorus. In summary, the 6 small rivers discussed in this paper contribute 0.002% of the biogenic load supplied to the Baltic Sea by Poland as a whole.

Volume XV |

Temporal rainfall properties at events scale in the Curvature Subcarpathians (Romania)

Abstract: Characteristics of rainfall events (RE) play a determinant role in the hydrologic process in a small catchment (e.g., runoff formation, flood elements), water balance and water resource management. The goal was to investigate temporal rainfall properties at events scale. The study was based on long-term properties of rainfall events (e.g., depths, intensities), recorded in the warm semester (the period between 1 April and 30 September; 1980-2010) at Voinești Experimental Basin (VEB), Romania. Rainfall events values were recorded by a pluviograph, production of the former USSR. The rain gauge is situated at the central place of the VEB (altitude 500 m a.s.l.), in Curvature Subcarpathians. A valuable database with 1852 rainfall events characteristics was created. The depths (mm) and durations (min) of each RE were recorded and rainfall maximum and average intensities (mm/min) were calculated. Rainfall events were characterized by small depth (up to 15.7 mm; up to 90th percentile) ~ 93% and they were concentrated (34.4%) in May. Almost half of RE (48.2%), had short duration (up to one hour) and the smallest depth (95% confidence interval, 3.85–4.56 mm), while those with durations longer than 5 hours (10.5%) were specific the September (22.5%). Regarding maximum intensities of rainfall events, just 16 events exceeding 1 mm/min (0.86%), which denote insignificant occurrence – encountered phenomenon in all months, especially in August – and mild torrential character. Insignificant rainfall events correlations between rainfall parameters were observed. Just “time – depth” correlation has been notable (Pearson’s r: 0.631). Absolute frequency of rainfall events parameters in most cases shows a strong density of smallest interval. These results may have important implications for next runoff plot study.