Concept and effects of a multi-purpose grassed waterway

The concept and the effects of a multi-purpose grassed waterway (GWW) were investigated over an eight year period. A GWW, half of it seeded, the remainder left to natural succession, and an intensive soil consevation system in the fields nearby were established in an agricultural watershed (13.7ha). This combination minimized the maintenance in the GWW without sward damaging sedimentation. In consequence the GWW, as well as providing safe drainage for surface runoff, also served additional ecological roles. During the experiment it reduced runoff and sediment delivery from the watershed by 39% and 82%, respectively. Moreover it improved biodiversity on the research farm and acted as a refuge for beneficial organisms. Soil mineral nitrogen content decreased by 84% after the installation of the GWW, indicating that although infiltration into the GWW was rapid, the risk of groundwater contamination from leached nitrate was diminished. The agricultural assets and drawbacks of establishing GWWs were also studied. We showed that the economic returns were more likely to be improved than reduced. Creating the GWW by natural succession had some advantages compared to seeding with grass.