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The research presented in this paper aims at the support tool for generation of multiple networks with preset or randomised properties. To explore particular phenomena, water distribution analysis may require a coherent set of cases. Readily available in the literature are simple synthetic networks used for benchmarking, either real-life cases that are too diverse in size and configuration. The network generation tool (NGT) developed on the principles of graph theory connects any seed of nodes prepared in EPANET modelling software, by avoiding pipe crossings or unnecessary duplications. The pipe properties can be assigned by specifying a range of arbitrary lengths and diameters, by using coordinates to calculate the lengths, or by genetic algorithm optimisation of initial diameters. Equally, the nodal elevations and demands are arbitrarily assigned when not predefined in EPANET. Several sets of networks have been generated, up to 200 junctions. To test robustness of the tool, 13,000 layouts of a 50-junction seed have been generated using different settings. NGT has been proven to be capable of executing this task mostly within a few minutes, producing network layouts that resemble those from practice.

Temporal trends provide a good interpretation of change in stormwater quality over time. This study aimed to analyse trends and influences due to stormflow and baseflow. Grab samples of 18-19 years from 1995 to 2014 recorded at outlets of 7 Tallinn watersheds were analysed for monotonic trend through seasonal Mann Kendall test for long-term, short-term, baseflow and stormflow. Statistically significant downward trends (P-value (p) < 0.05) were found for 6 – hydrocarbon (HC), 1 – suspended solids (SS), 3 – biological oxygen demand (BOD), 4 – total nitrogen (TN) and 2 – total phosphorus (TP) out of 7 sampling outlets over the last 10 years. Less significant decreasing trends (p > 0.05 and < 0.2) for 3 – SS, 1 – BOD, 1 – TN and 1 – TP were identified. Statistically significant long-term upward trends of pH were re-vealed in 5 basins, which reduced to 2 with 5 less significant upward trends over the 10 year period, indicating improve-ments in pH reduction. Härjapea has the highest pH without trend but it includes an upward trend of TN at p = 0.051. The highly possible causes for downward trends are street sweeping, sewer network improvement, decline in sub-urban agri-cultural areas, etc. The upward trend results of pH are related to increased alkalinisation due to acidic rain, weathering of carbonate rocks, sewage discharge and alkaline road dust. In most of the basins, stormflow has more influence on trends than baseflow.

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The nutrient content in streams and rivers depend on many interacting processes such as hydro-geographical conditions and land use practices. The aim of this study was to investigate the current status of Estonian rivers and determine any trends in the concentrations of total nitrogen (TN) and nitrate-nitrogen (NO3-N) between 1992 and 2013. This study involved 43 monitoring sites and 32 rivers in Estonia. The temporal trends were assessed using the partial Mann- Kendall (PMK) test, which was adapted to account for the influence of water discharge. Most of the studied streams and sites did not show any trend in nitrogen concentrations. The statistically significant downward trend in TN was identified at 13 monitoring stations and upward trend at four monitoring sites. The results for NO3-N showed a statistically significant downward trend at three sampling sites while the upward trend was found at nine monitoring stations, particularly at four sites located within the nitrate vulnerable zone (NVZ). Overall, the increasing nitrate content in surface waters can most probably be attributed to the intensification of agricultural activities in rivers catchments during the last ten years. However, there are still many uncertainties in nutrient loss processes. Thus, the national monitoring programmes should be further developed.