Mølle å stream and the Raadvad industrial site
Mølleå is a 30 km long stream, originating West of Ballerup lake and flowing eastward towards the Baltic sea (Øresund). Mølleåen drains a catchment of ca. 126 km2, in a typical geological setting of eastern Denmark (gytjja and mixture of sand, gravel, clay till below). It is considered a small to median stream in Denmark, with a median flow of ca. 400 l/s and width ranging between 8 and 15 m in its most downstream stretch. In these last kilometers, the stream flows through the former industrial site of Raadvad, runs through the “Deer park” (Dyrehaven) protected area before discharging into the Baltic sea.
The site of Raadvad was primarily used over the past two centuries for metal manufacturing activities, and is the location for a well-known knife factory that produced domestic metal wares until 1972. In addition to metal works, the site has hosted a number of other factories including a bronze foundry and metal workshop. The site today houses various professions including offices, residential houses and a Nature school offering a variety of activities for children.
As a legacy of these previous industrial activities, the site and shallow groundwater are contaminated with metals, hydrocarbons and chlorinated compounds used for steel processing (NIRAS, 2012). Some of these contaminants are seeping from the shallow groundwater to the Mølleå stream, in a very dynamic and complex manner (Lemaire et al., 2020, submitted).
Map of Raadvad industrial site, showing the two channels and the confluence
RIVERSCAPES activities
Riverscapes activities in Raadvad are centered at the confluence of the two channels in the downstream part of the industrial site (See Figure 1). The main objective at this site is to better understand how contaminants (discharging from a contaminated site to a stream) are transported, spread and mix in surface waters under realistic conditions.
The measurement campaign at Mølleå stream consists in tracer experiments, in which an optically active substance is released in a control manner and its concentration monitored along the stream using a Riverscapes package (UAVs+ hyperspectral camera). The application of this technology will facilitate the data acquisition and capture of the relevant contaminant mixing processes, as opposed to more traditional ground measurements that are expensive, time consuming and spatially constrained.
The outcome of these experiments will improve the understanding of the mixing and transport of contaminant in small streams, ubiquitous in Denmark. Additional post treatment of the data will allow the extraction of relevant parameters and help refining an existing model for the fate of the contaminant in streams. This model, already made available for the different Danish Regions and public (DTU, 2018) will be relevant for the future risk assessment and prioritization of remediation of contaminated site impacting stream.
References:
DTU. 2018. Risikovurdering af vandløb.
Access at: http://www.sara.env.dtu.dk/modelvaerktoejer/risikovurdering-af-vandloeb
Niras. 2012. Videregående undersøgelser på Raadvad knivfabrik 3-19 OG 4-50,
2800 KGS. LYNGBY. Consulting report for Capital Region of Denmark
Lemaire G., McKnight U.S., Schulz, A. , Roost S., and Bjerg P.L. 2020. Evidence of spatio-temporal variations in contaminants discharging to a peri-urban stream. Submitted in : Groundwater Remediation and Monitoring.