How to green the banks of urban rivers

Posted on October 15, 2015

Because the banks of urban waterways are often highly modified by hard reinforced embankments, streamside habitats can be very restricted.  New ecological engineering techniques can help to improve such habitats by increasing their surface complexity, and thus their capacity to trap sediment particles, organic matter, floating plant seeds and invertebrates.  Coir (the fibrous material around the inner shell of a coconut) is very suitable for straining and retaining seeds and encouraging germination, and coir rolls can be used to establish vegetation on riverbanks.  However, successful plant colonization depends crucially on the available pool of plant seeds in the waterway.  To assess the seed pool and the potential for coir to improve channelized habitats in a highly urban river, rolls of 100 x 25 cm coir sheet were attached to sections of wall at 12 sites along the River Thames in central London.  Coir rolls were positioned around mean high tide level  (± 0.5 m) and were left in place for seven months starting in summer and ending in winter.  Sections of the coir rolls were placed in compost-filled trays, where the retained seeds were germinated and identified to species.   Plants growing on the wall and embankment were also surveyed at each study site.  In total, 104 seed species & 90 wall species were identified.  On average, there was only a low (20%) similarity between the seed and wall plant communities at a given site: 53% of species were found only in the coir, while 27% were found only on the walls.  It seems that coir is a good growth medium for many species that normally find it hard to establish themselves on hard bankside walls.

Reference:  Hoggart, S.P.G. & Francis, R.A.  2014.  Use of coir rolls for habitat enhancement of urban river walls. Fundamental & Applied Limnology 185(1),19–30.