Finding Value in Urban Streams-Throughout many cities, urbanization has had lasting consequences for the waterbodies which now exist as part of an urban landscape. Concrete-channels, rip-rap bank armoring, and channelized sections are just some of the characteristic forms which exist along and in many urban streams. Altered flow regimes from the rapid input of large volumes of stormwater running off impervious surfaces is also another impact of urbanization on watercourses. Management of these altered streams often tends to prioritize moving water as fast as possible off the surrounding landscape, which can spell disaster for the native species that historically lived within the stream corridor, and can encourage the proliferation of exotic species.
It is, however, possible to restore some of the natural ecosystem functions of these urban watercourses. Restoring native riparian vegetation and re-establishing floodplains is a method for helping to improve conditions for native species in urban watersheds. Restoring these aspects of an urban stream can help to give the stream a means of dissipating energy during high flows which can result in reduced streambank erosion and the resulting fine sediment inputs to the waterbody. Healthy riparian vegetation and floodplains can help to catch some of the material such as sediment in the water, allowing for this material to be deposited and contribute again to the dynamic processes of building new banks, point bars, and forming new meanders.
Restoration Efforts Along Ontario’s Hanlon Creek.
Restoring healthy riparian areas and floodplains can be a process that is initiated by something as simple as riparian planting of native live willow stakes in degraded areas which will begin to grow and spread throughout the floodplain. It can also involve solutions as complex as recreating a natural floodplain using heavy machinery. This process is often used when “daylighting” which is a term for removing buried streams from underground pipes or sewers. Where sufficient space allows, a new promising method for restoring the floodplains of streams which have become largely straight, featureless and have scoured down significantly, is to restore conditions conducive for beavers to build and maintain dams and pond complexes which help to reduce peak flood flows, store water to buffer against drought, capture and store excess sediment, and form stream meanders while still allowing for native fish passage. In some areas, urban streams are largely affected by small dams or improperly installed culverts which impede the passage of fish and interrupt the transport of sediment. The removal of these barriers can rejuvenate these areas by allowing for the effective passage of fish and sediment.
Rehabilitation of natural ecosystem functions and the recovery of native riparian and aquatic flora and fauna in urban watercourses is not only achievable in many cases, but it is also becoming increasingly desirable in cities throughout the world. With proper planning and management, urban water bodies can be beneficial to the environmental, social, cultural, and economic sustainability of cities and their inhabitants.
Comments