The Transformation of a Danish River System

The Danish action plan for promotion of eco-efficient technologies – Danish Lessons

The transformation of a Danish river system

A focused intervention to change a deteriorating state of the environment in and among the Lilleå river in Aarhus in Denmark totally changed the river and the surroundings. Today the river hosts particular fish species and it has become a popular area for the local population.

The story of the Lilleaa river system in consisted of many, mostly very small and Lilleaa, before it discharged into Gude- Denmark is almost like the famous fairy simple treatment plants among which naa river, was slightly polluted and in an tale by Danish writer Hans Christian An- only some had mechanical treatment acceptable state. dersen about the ugly duckling, which (see fig. 1), and very few had biologi- turned into a beautiful swan. cal treatment. As a result, not only the But pollution was not the only problem main river, but also many of the smaller and the only reason for the deteriorated In the 1970s, the Lilleaa river system tributaries were polluted and unsuitable river environment. Water courses had was heavily polluted by domestic for normal river fauna like trout. been canalized to improve the drainage wastewater, industrial wastewater (from of the river valley for farming. In order slaughterhouses and dairies) and direct The result was that the environmental to preserve drainage capacity, the river discharge of liquid manure from farms. status of the river system was very bad was heavily maintained, including cut- The wastewater treatment infrastructure (see fig. 2), and only the last part of the ting all plants and removing stones and

Langaa Langaa Unpoluted or nearly unpoluted Slightly poluted River Gudenaa 1974 Randers 2005 Randers River Gudenaa Strong poluted Fjord Fjord Very strong poluted Øster Tørslev Å Øster Tørslev Å Randers Randers Grund Fjord Grund Fjord Viborg Nørreå Viborg Nørreå

Alling Å Alling Å Hadsten Hadsten Gudenå Gudenå Hald Sø Bjerringbro Hald Sø Bjerringbro

Tange Sø Lilleå Tange Sø Lilleå Kjellerup Tange Å Kjellerup Tange Å Hinge Å Hammel Hinge Å Hammel Gjern Å Gjern Å Silkeborg Silkeborg

Silkeborg Langsø Lilleå catchment Silkeborg Langsø Lilleå catchment Funder Å Julsø Funder Å Julsø Aarhus Aarhus Århus Aarhus Knud Sø Knud Sø Bay Bay Lilleaa Salten Ravn Sø Salten Ravn Sø Lilleaa Langsø Ry Langsø Ry Salten Å Skanderborg Salten Å Skanderborg Mossø Mossø

Skanderborg Sø Mattrup Å Skanderborg Sø Mattrup Å Brædstrup Brædstrup Hinnerup Hinnerup

Tørring Tørring 1970's 2001

Langaa 0 10 km Langaa Unpoluted or nearly unpoluted Waste water treatment plants: Mechanical treatments and basins Slightly poluted Large dots: more than 5.000 persons River Gudenaa River Gudenaa Biological treatment Medium dots: 1.000-5.000 persons Strong poluted Small dots: 200-1.000 persons Biological treatment and P-removal Very strong poluted

Fig 1: Wastewater treatment plants in the main catchment area of the Gudenaa river and its tributary, the Fig 2: The environmental state (based on macro Lilleaa. fauna) of the Lilleaa before the introduction of ef- Hadsten ficient wastewater treatment.Hadsten

Lilleaa

Hinnerup Hinnerup

1970's 2001 charged into the river system dropped dramatically as shown in fig 3. and at the same time, the load of nutrients was reduced significantly in order to protect Randers Fjord downstream.

Socondly, the number of treatment plants in the catchment area was reduced from approx. 25 in the 1970s to five today.

The surrounding municipalities as- sessed that the advanced treatment would be more stable and cheaper to maintain if it was centralised at several larger plants. Many kilometres of pipe line were constructed together Photo: Jens Skriver Lindenborg. with a number of pumping stations to transport the wastewater from the more gravel. The river was more or less like a The first priority was to get clean water than 25 small plants to the two to three sand desert and only a few tributaries in the river – i.e. to improve wastewa- large new plants and still keep the water were spared and could function as a ter treatment and to prevent discharge balance in the catchment area. refuge for fauna, including fish like the of liquid manure from the farms. The sea trout. management circle was travelled several Fig. 4 shows the effect on river fauna times before the water in the entire river after introducing wastewater treatment A final problem was the numerous system was cleaned up. plants. The fauna is used as an indica- dams, which had been built for use as tor for the level of pollution in the river. watermills, but were no longer used The treatment requirements were so In 2001, the main part of the river was for their original purpose. They made it strict that the best and most advanced only slightly polluted, and the objectives nearly impossible for migrating species technology had to be introduced. This for the river system were fulfilled. In the like eel and sea trout to move freely in had two effects – first and foremost, the last years monitoring results from the the river system. The most important amount of organic matter that was dis- river around the fish farm have shown dam was located by a fish farm in the lower part of the Lilleaa (see fig. 6). This dam made it very difficult for migrating fish like sea trout to reach the few Organic matter BOD spawning areas left in the river system. (kg pr. year) Fortunately, a small stock of original sea 80000 trout was able to maintain the population during the time of deteriorated 60000 environmental state. 40000 So the problems piled up – but where to start? 20000 Planning was a very important tool – 0 planning for water quality on a regional 1982 85 88 91 94 97 00 2003 level, as well as planning for wastewater treatment on a local level.

Fig. 3: Discharge of organic matter into the Lilleaa river system.

2 that the state of the river has improved doing so, they are able to use less water even more since 2001, and probably this from the river. The aim of the project is also valid for much of the rest of the was to document that production could river system. increase without increasing the pollution load, or maybe even reduce the pollu- The fish farm situated in the lower part tion load compared to the previous situ- of the Lilleaa river system was another ation. The pilot projects did succeed in important source of organic matter this, but the investment in this new type Fig 5: Restored tributary to the Lilleaa. and nutrients polluting the river. In the of production is large and, in general, 1970s, when the production was based possible only for larger fish farms. on raw, chopped fish and without any pollution abatement, it was this produc- The next step was to create a more tion that, in particular, put pressure on natural habitat in the river, while simul- the river. In the late 1980s, it became taneously securing drainage of the river compulsory for fish farmers to feed the valley. In the main river, this was done fish dry pellets instead and to construct by constructing a double profile, with ponds or small lagoons for simple treat- a narrow profile for the small summer ment of the effluent water. However, flow and a much wider one for the this regulation reduced the discharge winter flow. only to a certain level. Moreover, fish farmers had no possibility to increase In some places, it was necessary to production. A number of Danish fish restore the river with new meanders and farmers, including the owner of the layout of gravel and stones, as shown farm at Lilleaa, joined in a pilot project in fig 5. In these cases, the land owners concerning the use of other produc- were subsidised because the higher

tion methods and new technology for, water level made it impossible to use Fig 6: The dam at the fish farm – top: before the e.g., physical and biological treatment the valley for normal farming. construction of the by-pass, bottom: the recon- structed part of the river (by-pass) around the fish of the effluent. With the high level of farm. purification of the water, it is possible The last step was to secure the free for farmers to re-circulate water. By migration of fish and other fauna in the have been fulfilled. The habitat for the river system. Therefore, with the help of fauna has been improved and there new designs by-passes were constructed are no significant obstacles left for the Langaa Langaa Unpoluted or nearly unpoluted Slightly poluted River Gudenaa River Gudenaa Strong poluted at the dams, and especially at the larg- migrating fauna, including fish. Today, Very strong poluted est dam as shown in fig 6. The cost of the Lilleaa is the most productive river these projects was paid by the regional system for natural self-reproducing sea Hadsten Hadsten authority (the county). trout in Denmark – and some say maybe among the best in Europe. A number of different parties like municipalities, water consumers, industry The story of the Lilleaa shows the neces-

Lilleaa Lilleaa and fish farmers have contributed to sity of a holistic approach and planning reaching these results. The total cost to restore river habitats. Advanced Hinnerup Hinnerup for wastewater treatment and physical technology has to be applied, and it

1970's 2001 restoration of the Lilleaa is not known. is important to be aware of the fact

Langaa Langaa Unpoluted or nearly unpoluted that entities have to be large to ensure Slightly poluted River Gudenaa What does the beautiful stable results (whether it is wastewater River Gudenaa Strong poluted Very strong poluted swan look like today? treatment or fish farms) and at the same Today, the general state of the Lilleaa time be cost-effective. Fig 4: The environmental state (based on macro fauna) of the Lilleaa river after introduction of ef- river system is very good and the water Hadsten ficient wastewater treatment.Hadsten is clean. The environmental objectives

Lilleaa

Hinnerup Hinnerup

1970's 2001 Photo: Jørgen Kjems.

Many Danish river systems have similar • New technologies used on fish background stories, but they have not farms ensure higher produc- yet reached the same state as the Lil- tion with the same or even lower leaa. The pollution with wastewater is pollution impact, which allows a reduced to an acceptable level in most reduction in the demand for water rivers, but a lot of rivers are still physi- and thus “gives back” the water to cally deteriorated and measures need to the river. be taken before they can live up to the • Clean water is not enough to re- standards in the EU regulation. store the river habitat – the physical habitat must also be improved. Fig 7: A happy man. Lessons learnt: • Even heavily polluted and physically The story also shows that it is not destroyed rivers can be restored – if enough to ensure clean water. The rec- the potential is still there. Contact: reation of at least more natural habitats • Planning is crucial – both for water Poul Nordemann Jensen, Senior Adviser National Environmental Research Institute is necessary to secure a good ecological quality and for wastewater treat- University of Aarhus status in our rivers. ment. [email protected]

• Advanced and stable wastewater Read more: By doing so, nature responds in a posi- treatment changes infrastructure www.ecoinnovation.dk/english – choose Danish Lessons tive manner. dramatically.