Maankäytön vaikutus pohjoisten alueiden hulevesiin : esimerkkinä Helsingin kaupunkivaluma-alueet

Land use change and urbanisation changes the environment permanently. Due to the development urban hydrology changes; infiltration decreases, surface runoff increases and previously natural state runoff waters are led away from the catchment area with artificial pipelines. Water discharging from the catchment area affects the receiving aquatic ecosystems condition. In this thesis the impact of land use on storm water quality and quantity is being studied with three urban small catchment area in Helsinki. Veräjämäki represents single-family housing and wide green spaces, Pihlajamäki is an area of suburban housing with fragmented green spaces and Itä-Pasila represents an area of intensive land use ja traffic. The focus of the study is to explore the temporal character and annual loads of storm water. The study was held in period of 1.7.2010-2.1.2012. Winter time storm water is examined as well. Sampling site in the discharge point of each catchment area analyzed the water quality and quantity and took samples continually. Samples were analysed for turbidity, conductivity and discharge. In the University of Helsinki's Laboratory of natural geography samples were analysed for content of soluble elements, such as metals and trace elements. Suspended solids and dissolved material were analysed. In the results indicate variation in both between the catchment areas and in temporal scale. In loads and values of conductivity and turbidity there is clear seasonal variation, and spring time melting period and rainy yet mild autumn 2011 are clearly shown. For annual loads Itä-Pasila's intensive land use areas load was clearly the largest among the studied areas. In Pihlajamäki the discharge from the catchment area was unusually large in relation to the area of the catchment and the weather. It is assumed that the volume of runoff is originated from ground water leakage in the catchment area. In Veräjämäki the springtime melting season was clearly shown in loads. When Itä-Pasila's and Pihlajamäki's melting season began early and lasted for very shortly, Veräjämäki's melting period began later and lasted for longer. When observing the land use it was concluded that intensive traffic areas tended to increase the loads and green spaces tended to decrease both loads and discharge. In Itä-Pasila the loads of metals were large and the winter time de-icing of pavements was evidently shown in storm water concentrations of sodium and chloride. Land use was considered to affect the urban storm water unoff on the basis of three studied catchment areas. It affects the volume and timing of runoff as well as the loads.