Eriksmåla road stormwater dams - objectives and obstacles

Abstract

Building wetlands/darns for treating polluted waters is increasingly "in fashion" in
Sweden. Mostly diffuse eutrophication due to agriculture is in focus, but also for
remediation of road stormwater. Draining a four-road roundabout, located 40 km east of
Kalmar, a dam system was designed. The "normal" objectives were to reduce the water
flow and the water's content of mainly nutrients and metals, before the water falls into
river Lyckebyan. A special ambition was to study to what extent this really happens,
depending on biological contents. Therefore a three-dam system was built, of which the
first aimed at lowering high velocity flows and allow some sedimentation. From this,
water was in parallel led to two dams ( each ca 60 m2
), of which one was supplied with
vegetation, the other not.
Throughout almost two years, water flows in the three dams were registered and flowcompensated water samples were taken weekly and analysed. The metals Cd, Cr, Cu, Pb,
Zn were focused, but also total and fractions of nitrogen and phosphorous, P AH, and
suspended solids were monitored. Metals in sediment and dominating plants and
invertebrates were studied. The purpose was to construct a mass balance for at least the
metals in the two main dams, but also to evaluate if the metal levels could reach ''unsafe"
concentrations.
Water metal levels were in several cases "moderate to high", with "through-dam"
reduction figures at 15-30% (Cd however uncertain). Sediment levels were in most cases
and at most times ''very low to low". The overall picture and calculation validity were
however obscured by uncertainties regarding whether a rather substantial additional water
flow entered from an esker besides the dam area. Presently compensatory modelling of
the effect of this flow is taking place.