Conallin, John

Thorn, Paul

Groundwater abstracted near Lejre, Denmark has been a significant source of clean drinking water for the Greater Copenhagen area since 1937. However, this abstraction has had adverse effects on the flows in the streams, especially the summer baseflow within the River Kornerup Catchment, resulting in low flows in the headwater streams and even causing some to go dry in the summer months. These low-flow events are theorised to be a major factor in why the streams within the catchment are having difficulty in supporting healthy self sustaining populations of brown trout. The EU Water Framework Directive (WFD) states that the exploitation of groundwater resources cannot degrade the stream ecosystem so that a “good ecological health” cannot be obtained. This study utilizes the habitat model RHYHABSIM, using brown trout as the indicator species, to predict the stream flows needed to provide the stream habitat required for brown trout, so a “good ecological health” status can be obtained. Furthermore, the model results are compared with the Roskilde County’s method for setting baseflow requirements and a popular method from the USA. The results from all three methods are compared to the current flow regime to determine if the streams are providing these flow requirements. The RHYHABSIM model results show that the three streams investigated require a minimum flow of 35 - 50 l/sec to provide the habitat needed to prevent low flows from negatively impacting on the brown trout population, and a minimum flow of over 100 l/sec to provide the optimal habitat area. The streams are not even close to meeting these objectives; in 1999, 2000 and 2001 flows below 20 l/sec were observed for extended periods of time (over 2 weeks in each year). These low flows severely reduce the available habitat, and would be having serious negative implications for the brown trout. A number of management techniques could be utilized to increase the stream flow to achieve these goals stated in both Danish domestic law and those stated by the WFD. These include both adding water to the streams directly during dry periods, and re-locating the groundwater abstraction sites and rates. The realisation of these management schemes will provide one step in meeting the EU Water Framework Directive by its deadline in 2015.Groundwater abstracted near Lejre, Denmark has been a significant source of clean drinking water for the Greater Copenhagen area since 1937. However, this abstraction has had adverse effects on the flows in the streams, especially the summer baseflow within the River Kornerup Catchment, resulting in low flows in the headwater streams and even causing some to go dry in the summer months. These low-flow events are theorised to be a major factor in why the streams within the catchment are having difficulty in supporting healthy self sustaining populations of brown trout. The EU Water Framework Directive (WFD) states that the exploitation of groundwater resources cannot degrade the stream ecosystem so that a “good ecological health” cannot be obtained. This study utilizes the habitat model RHYHABSIM, using brown trout as the indicator species, to predict the stream flows needed to provide the stream habitat required for brown trout, so a “good ecological health” status can be obtained. Furthermore, the model results are compared with the Roskilde County’s method for setting baseflow requirements and a popular method from the USA. The results from all three methods are compared to the current flow regime to determine if the streams are providing these flow requirements. The RHYHABSIM model results show that the three streams investigated require a minimum flow of 35 - 50 l/sec to provide the habitat needed to prevent low flows from negatively impacting on the brown trout population, and a minimum flow of over 100 l/sec to provide the optimal habitat area. The streams are not even close to meeting these objectives; in 1999, 2000 and 2001 flows below 20 l/sec were observed for extended periods of time (over 2 weeks in each year). These low flows severely reduce the available habitat, and would be having serious negative implications for the brown trout. A number of management techniques could be utilized to increase the stream flow to achieve these goals stated in both Danish domestic law and those stated by the WFD. These include both adding water to the streams directly during dry periods, and re-locating the groundwater abstraction sites and rates. The realisation of these management schemes will provide one step in meeting the EU Water Framework Directive by its deadline in 2015

Groundwater Abstraction, Fresh Water Ecosystems and Low Flows. An Interdisciplinary Study in the River Kornerup Catchment, Denmark

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Roskilde Universitet