Variation in turbidity with precipitation and flow in a regulated river system – river Göta Älv, SW Sweden

Abstract

Abstract. The turbidity variation in time and space is investigated in the downstream stretch of the river GötaÄlv in Sweden. The river is heavily regulated and carries the discharge from the largest fresh water lake in Sweden, Lake Vänern, to the outflow point in Göteborg Harbour on the Swedish west coast. The river is an important waterway and serves as a fresh-water supply for 700 000 users. Turbidity is utilised as a water quality indicator to ensure sufficient quality of the intake water to the treatment plant. The overall objective of the study was to investigate the influence of rainfall, surface runoff, and river water flow on the temporal and spatial variability of the turbidity in the regulated river system by employing statistical analysis of an extensive data set. A six year long time series of daily mean values on precipitation, discharge, and turbidity from six stations along the river were examined primarily through linear correlation and regression analysis, combined with nonparametric tests and analysis of variance. The analyses were performed on annual, monthly, and daily bases, establishing temporal patterns and dependences, including; seasonal changes, impacts from extreme events, influences from tributaries, and the spatial variation along the river. The results showed that there is no simple relationship between discharge, precipitation, and turbidity, mainly due to the complexity of the runoff process, the regulation of the river, and the effects of Lake Vänern and its large catchment area. For the river GötaÄlv, significant, positive correlations between turbidity, discharge, and precipitation could only be found during periods with high flow combined with heavy rainfall. Local precipitation does not seem to have any significant impact on the discharge in the main river, which is primarily governed by precipitation at catchment scale. The discharge from Lake Vänern determines the base level for the turbidity in the river, whereas local surface runoff and tributary discharge induced by rainfall govern the temporal variability in turbidity. Autocorrelation analysis indicates a temporal persistence in turbidity of about 10 days. The results also show that erosion along the main river, from the river bed and banks, is not a dominant contributor to the suspended sediment transport in the river under normal conditions. Further studies on the correlation between turbidity and suspended sediment transport and its relation to erosion processes are suggested.

Riverine Water Quality Response to Precipitation and Its Change

“…In this paper, two forms of AAP, namely the antecedent AAP and the cumulative antecedent AAP, were considered when investigating the associations of flow and water quality with precipitation, as these two precipitation metrics have been often used in the literature [12][13][14][15][16]. The antecedent AAP is the AAP on a designated antecedent day, while the cumulative antecedent AAP is the sum of AAPs from the current day to a designated antecedent day.…”

“…Precipitation, which produces surface runoff, undoubtedly affects water quantity and consequently water quality indirectly. Many studies have demonstrated the increase of concentrations and/or loadings of various pollutants including total suspended solids (TSS), nutrients, and microorganisms (e.g., E. coli and pathogens) during storm events and extensive rainfalls [12][13][14][15][16]. The linkage between water quality and precipitation is more prominent in heavy rainfalls.…”

Evolution of physicochemical species concentration in streams based on heavy rainfall event data obtained for high-frequency monitoring

“…Heavy rainfall is a common cause for increased turbidity and raising the water level, such as FS2. Göransson, Larson and Bendz (2013) found a positive correlation between turbidity and rainfall in periods with heavy rainfall.…”

Riverbank filtration for the treatment of highly turbid Colombian rivers

“…Generally, the suspended sediment load carried by the rivers during the rainy season is higher than that found during the dry season (Dunlop et al, 2008;Göransson et al, 2013); however, in regulated river systems, seasonal variations in load do not always follow such a trend (Göransson et al, 2013). Shear forces are also seasonally variable, since these forces are a function of the water level (Hubbs, 2006b).…”