Plug/dam canals or trenches: freshwater marshes

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects, on vegetation, of plugging/damming canals or trenches in freshwater marshes. The study was in the USA.


  • Overall extent (1 study): One replicated, site comparison study of backfilled canals in freshwater marshes in the USA reported that emergent marsh vegetation coverage was greater within the channels of plugged than unplugged canals, after 6–60 months. However, coverage on former spoil areas did not significantly differ between plugged and unplugged canals.




About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, site comparison study in 1983–1984 of five backfilled canals in freshwater marshes in Louisiana, USA (Neill & Turner 1987) reported that emergent marsh vegetation coverage was greater within plugged than open canals, but that coverage was similar on the adjacent former spoil areas. Statistical significance was not assessed. After 6–60 months, emergent vegetation coverage was 15% within plugged canals (vs <1% in open canals) and 35% on the former spoil areas alongside plugged canals (vs 35% alongside open canals). Methods: In 1983 and 1984, vegetation was surveyed in three freshwater canals that had been plugged with earth or seashell dams at one end, and two canals that had not been plugged. Coverage of emergent marsh vegetation was estimated from aerial photographs. All canals, originally dug by the oil and gas industry, had been backfilled with adjacent spoil between 1979 and 1984.

    Study and other actions tested
Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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