Low flows are a good measure of the waste water recipient self-purification capability. The regional statistical analysis is an objective way of assessment of the required low flows. This paper presents the principles and key phases of the regional statistical analysis. The advantages of this method are a reduction of the outliers influence and the assessment of low flows on ungauged streams and stream profiles. The method is illustrated with the results obtained by the required low flows regional statistical analysis in Serbia (Yugoslavia) with 59 hydrological gauge stations in the scope, which data has the same length of 39 years, from the year 1956 to 1994.

Drought characteristics (minimum flows, drought duration and volume deficit) of the Moraca river near Podgorica, Montenegro (Yugoslavia) are analyzed using the peaks over threshold method based on renewal processes. It is also shown that volume deficit and drought duration are highly correlated.

Withdrawal of water from surface water network should be concerned with preservation of the environment, meaning that the low flow regime in streams should be preserved within the range of natural regime. In order to formulate criteria for minimal allowed flows in streams, it was necessary to perform statistical analysis of low flows in rivers in Serbia (Yugoslavia). The criteria for water withdrawal are proposed on the basis of characteristic ratios between minimum and mean flows. Different criteria are proposed for cold and warm seasons.

Perfluorinated chemicals (PFCs) have been recognised as environmental pollutants that require monitoring. A modified polar organic chemical integrative sampler (POCIS) is able to quantify aqueous PFCs. However, with varying external water velocity, PFC sampling rates (Rs) may change, affecting accuracy of derived water concentrations. To facilitate field deployment of this sampler, two methods of in-situ calibration were investigated: performance reference compounds (PRCs) and passive flow monitors (PFMs). Increased Rs's (by factors of 1.2–1.9) with PFM loss rate (g d−1) were observed for some PFCs. Results indicate PFMs can be used to correct PFC specific Rs's for more reliable estimates of environmental concentrations with a precision of about 0.01 L d−1. Empirical models presented provide an improved means for aquatic monitoring of PFCs. The PRC approach was unsuccessful, confirming concern as to its applicability with such samplers.

Modelling natural attenuation is crucial to managing pharmaceuticals. However, little is known about the mechanism behind their in-stream sorption. To better understand the in-stream attenuation of the highly sorptive antibiotics azithromycin (AZM) and levofloxacin (LVF), we monitored them in a 2.1-km stretch of the Asano River under diverse flow conditions. This stretch receives effluent directly from a sewage treatment plant (STP), which was a dominant source of the pharmaceuticals. Average distribution coefficients between dissolved and particulate phases (Kd,SPM) in the outflow river water were 6.3×105 L/kg for AZM and 7.5×104 L/kg for LVF, while those in the STP effluent were 1–2 orders of magnitude lower. Mass balances in the river stretch calculated by considering only dissolved phase (MBw) and both dissolved and particulate phases (MBs) were 8%–52% and 58%–102%, respectively, for AZM, and 58%–71% and 60%–105% for LVF. MBw<MBs is attributed to an increase in suspended particulate matter (SPM)-mediated mass flows in the river stretch, i.e., in-stream sorption to SPM, which was caused mainly by their much higher river Kd,SPM values than those in the effluent. Their river Kd,SPM values increased on higher-flow days with decreasing effluent content in the river water, resulting in the increase of their in-stream SPM sorption. Their in-stream loss from the entire water column (i.e., 100−MBs), which was attributable to their mass transfer from the overlying water to sediment through sorption, was decreased on higher-flow days by hydrological factors. A key finding is that AZM and LVF mostly entered the river stretch in the dissolved phase of STP effluent, whereas they existed substantially in the particulate phase in the outflow river water, especially on high-flow days.

A recently developed modified polar organic chemical integrative sampler (POCIS) provides a means for monitoring perfluorinated chemicals (PFCs) in water. However, changes in external flow rates may alter POCIS sampling behaviour and consequently affect estimated water concentrations of analytes. In this work, uptake kinetics of selected PFCs, over 15 days, were investigated. A flow-through channel system was employed with spiked river water at flow rates between 0.02 and 0.34 m s−1. PFC sampling rates (Rs) (0.09–0.29 L d−1 depending on analyte and flow rate) increased from the lowest to highest flow rate employed for some PFCs (MW ≤ 464) but not for others (MW ≥ 500). Rs's for some of these smaller PFCs were increasingly less sensitive to flow rate as this increased within the range investigated. This device shows promise as a sampling tool to support monitoring efforts for PFCs in a range of flow rate conditions.

After the year 2000 the issue of a water qualitative and quantitative monitoring increased in importance as a consequence of the provisions of the Framework Directive 2000/60/EC. In this context agriculture is required to use more efficiently the unconventional sources of water. In the enclosures located at the scientific bases from the Danube meadow during the vegetation period from April to September the natural risk factors alternate, being represented by the hydric excess, mainly generated by phreatic excess, and the deficit of humidity from June to August (14, 15). In these conditions the engineering works performed are complex, being required a sizing for mixt task 0 controlled discharge and supply (2, 3, 10, 13). For finding the volume of water resource which transits the drainage works and the capacity of transport it is required to be known first the flow of the absorbent drain.