Surface water

(the text below is based on the chapter Surface water published in yearbook Prague Environment 2004)

The water quality assessment is every year performed according to the Czech Standard ČSN 75 7221 “Classification of Surface Water Quality” (as amended in October 1998, replacing the Czech Standard 75 7221 of August 4, 1989). The standard was made more exact on the basis of practical experience and at the same time it was closer harmonised with the surface water classification, which is in use in the EU Member States. The standard is focused on a uniform determination of quality class of flowing surface water – the classification, which serves for benchmarking of water quality at various locations and in various times. Surface water is classified into five classes based on quality. Water quality is classified on the basis of check results acquired over a longer continuous period. The shortest period assessed is one year. It is recommended, at monitoring frequency of 12 samples taken per a year, to make the classification of the check results for a two-year period in order to have 24 values measured (1999–2000) at least for the characteristic value calculations. If there are less than 11 values – results of water quality checks – the classification pursuant to the standard mentioned cannot be carried out. The assessment indicators evaluated are sorted into five groups. The indicator of the worst quality determines the entire group value. Then the group of the indicators of the worst classification value determines the overall classification of quality of water in a particular watercourse.

Tab. - Surface water quality classes according to the ČSN 75 7221

Class number	Classification
I.	Unpolluted water
II.	Slightly polluted water
III.	Polluted water
IV.	Heavily polluted water
V.	Very heavily polluted water

Tab. - Groups of surface quality indicators according to the ČSN 75 7221

Group	Indicators
A	General physical and chemical indicators
B	Specific organic substances
C	Metals and metalloids
D	Microbiological and biological indicators
E	Radiological indicators

Water quality assessment

The Czech Hydrometeorological Institute has been engaged in the systematic monitoring of water quality since 1963 within the national network of hydrometric profiles at watercourses important from water management point of view. In 2001 on the territory of the Czech Republic 257 optimised hydrometric profiles were utilised where samples were taken 12 times per a year and given to analyses determining basic physical and chemical parameters, heavy metals, specific organic compounds, and biological as well as microbiological indicators.

The Vltava River and the Berounka River

In 2003 on the Prague territory and its closest vicinity there were four hydrometric profiles monitored as in the previous years, three of them are located on the Vltava River – Vrané, Podolí and Libčice, one is located on the Berounka River – Lahovice. In the last year in total 140 indicators were measued at these profiles. The highest number of the indicators was measured at the profile Vltava – Libčice, 136, the least number at the profile Berounka – Lahovice, 97. The indicators were mostly monitored at frequency of 6–12 samples per year, in some of them the frequency was lower. Water quality could be affected by lower values of flow rate in these rivers last year.

When assessed by the Czech Standard ČSN 75 7221 the classification in chlorophyll was the worst indicator, at Vrané and Podolí class IV, at Libčice and Lahovice class V. The best assessment was found in substances and groups called “specific organic substances” and “Metals and metalloids”, which, with few exemptions, fell into classes I and II.

At the Vltava River – Vrané besides chlorophyll also AOX and IM were assessed as falling into class IV, IM 105 °C, COD_Mn, and total iron and phosphorus fell into class III.

At the Vltava River – Podolí did not show any indicator falling inot class V, aforementioned chlorphyll fell inot class IV only. AOX, IM, IM 105 °C, sum of PAHs, TOC, coliform bacteria, BOD₅, COD_Cr and total cyanides, iron and phosphorus fell into class III.

At the Vltava River – Libčice demonstrated except chlorophyll the mixture of PCBs also classified as class V. AOX and coliform bacteria were in class IV, COD_Cr, COD_Mn, BOD₅, faecal coliform bacteria, IM, total iron and total phosphorus fell into class III. Out of organic substances 1,2-dichloroethane was classified class III.

At the Berounka River – Lahovice similar substances were classified falling inot higher classes as at three profiles at the Vltava River. Besides chlorophyll in class V, these were IM 105 °C, BOD₅, TOC, and total iron in class IV, AOX, COD_Cr, COD_Mn, total phosphorus, coliform bacteria, and lead falling into class III.

Pursuant to the Order of the Government of the Czech Republic No. 61/2003 Code out of the substances enlisted in the Order 50–65 were measured at the aforementioned profiles. While assessing profiles pursuant to the order at the profile Vltava – Vrané the limit value for C95 was attained by 87 % of the total number of 61 substances measured there, at the profile Vltava – Podolí it was 81 % of 54 substances, at the profile Vltava – Libčice it was 78 % of 65 substances, and at the profile Berounka – Lahovice it was 69 % of 51 indicators. At none of the profiles the required limit value of C95 was not attained for total phosphorus, IM 105 °C, for example, and at three profiles the limit values for AOX and total chlorine were exceeded.

The course of annual values of C95 of some of substances against the limit values set in the Order of the Government of the Czech Republic No. 61/2003 Code at selected hydrometric profiles over the last ten years is given in figures below.

Fig. - The course of annual values of C95 of some of substances against the limit values set in the Order of the Government of the Czech Republic No. 61/2003, 1994–2003