The Ramsar Convention's resources on Wetland Restoration

The STRP Expert Working Group on Wetland Restoration

Restoration Approach: Removing Culverts

Wetland type: Tidal wetlands

Background: In many coastal areas, roads have been built across tidal creeks, separating tidal wetlands from the estuary. Frequently, tidal creek flow is maintained by installation of culverts, or pipes, that pass beneath the road. However, these pipes are sometimes too small to allow full tidal flushing of wetlands. Subsequently, the area of tidal wetland that was flooded on each tide before culvert installation is reduced. Furthermore, if a culvert is installed so that the bottom of the culvert is above the creek bed, the culvert will act as a weir, holding water on the wetland. This will cause plant death from waterlogging, and, in some settings, will lead to hypersalinity. Often, culverts can be replaced at a low price with inexpensive bridges. Where roads have been abandoned, culverts can be removed without replacement.

Advantages: Culvert removal can result in immediate re-establishment of tidal flushing with subsequent rapid changes in vegetation and faunal communities. In some settings, improved flushing can reduce mosquito populations.

Disadvantages: After culverts restricted flow, infrastructure (houses, pastures, etc.) may have been built in areas originally flooded by tides, and culvert removal may result in reflooding of these areas. Soils in areas where culverts have restricted flooding may have subsided (because of oxidation of organic carbon in soils and other factors), making them lower than they were before culvert installation, and subsequently resulting in areas too deep to support vegetation after culvert removal. Some soils in areas where culverts have restricted flooding may have become too acidic to support vegetation, through oxidation of potential acid sulfate soils. Culvert removal may lead to erosion, including erosion around bridges intended to replace culverts.

Further information: Streever, W.J. and A.J. Genders. 1997. The effect of improved tidal flushing and competitive interactions at the boundary between salt marsh and pasture. Estuaries 20: 804-815.

Turner, P. and W.J. Streever. 1999. Changes in productivity of the saltmarsh mosquito, Aedes vigilax (Diptera:Culicidae) and vegetation cover following culvert removal. Australian Journal of Ecology 24: 240-248.

Culverts such as this one at Kooragang Island, New South Wales, Australia, can restrict tidal flow, limiting the movement of water on and off of tidal wetlands (photograph for Kooragang Wetland Rehabilitation Project).

Inexpensive bridges, such as this one at Kooragang Island, New South Wales, Australia, can replace culverts, leading to improved tidal flushing (photograph from Kooragang Wetland Rehabilitation Project).

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For further information about the Ramsar Convention on Wetlands, please contact the Ramsar Convention Bureau, Rue Mauverney 28, CH-1196 Gland, Switzerland (tel +41 22 999 0170, fax +41 22 999 0169, e-mail ). Posted 8 January 2001, updated 15 February 2002, Bill Streever and Dwight Peck.