The Drentse AA

Meandering streams running alongside heathland, hay meadows and esdorp villages form the characteristic landscape of the Drentsche Aa. This unique and extensive network of streams and tributaries in the provinces of Drenthe and Groningen is home to a wide variety of flora and fauna and is of great ecological and cultural-historical value.

However, due to prolonged drought and increasing periods of hot weather, the area is coming under ever-greater pressure. During dry summers, water levels fall, causing the streams to function increasingly as drainage ditches. This leads to the drying out of the stream valley, erosion of the stream bed and a decline in biodiversity, with vulnerable plant and animal species gradually disappearing.

To restore the ecological quality of the area and make nature more resilient to climate change, the stream bed has been raised at three locations within the Drentsche Aa – the Zeegscherloopje, the Anloërdiep and the Taarlosche Diep – by means of sand replenishment. This measure increases the capacity for water storage during heavy rainfall and helps to retain water for longer during dry periods.

Knoop BV, as a specialist in civil engineering and hydraulic engineering, was asked to develop an innovative construction method suited to the project’s specific circumstances.

The greatest challenge lay in the fragility of the area. The limited load-bearing capacity of the soil, the difficult-to-access banks and the desire to minimise disruption to local residents and landowners made a conventional approach impossible. Knoop BV therefore developed a unique working method specifically for this project, in which sand is mixed with water, transported through the stream via a pressure pipe and deposited precisely at the desired location.

This innovative technique made it possible to raise the stream bed without deploying heavy machinery in the sensitive stream valley. As a result, the ecological impact was kept to a minimum and the natural environment was not only preserved but actually enhanced. This method has been applied on this scale for the first time in the Netherlands and offers a valuable solution for projects in hard-to-reach peatland areas and other ecologically sensitive locations where traditional construction methods are not feasible.