Sinking Watercourses

Definition of a sinking watercourse

To be considered a sinking watercourse, a watercourse must sink into the subsurface at a distinct sink point and possess one or more of the following characteristics:

Poorly or non-defined channels (including flow over an organic bed)
Exhibit no evidence of scouring or alluvial deposition
Flow on the surface for less than 100 metres.

As a minimum threshold, a sinking watercourse must follow a confined, linear drainage course with a distinguishable cross-sectional low point, accompanied by the presence of hydrophytic vegetation (plants that thrive in saturated soils).

Management objectives

Sinking watercourses are considered to be less of a management concern than sinking streams because of their lower potential for impacting significant recipient karst features. For example, sinking watercourses would typically exhibit low-energy water flows, lower transport potential, and intermittent or ephemeral flows. Nevertheless, sinking watercourses have the potential to transport sediment, fine organic material and small woody debris into the subsurface. For this reason, the management objectives for sinking watercourses are the same as those for sinking/losing streams.

Recommended best management practices

Where a significant recipient karst feature receives water from a sinking watercourse, the watercourse should be managed in a manner consistent with the management objectives for sinking and losing streams. The following best management practices are recommended within an appropriately sized riparian management zone:

Retain windfirm trees with roots embedded in the watercourse edge.
Fall and yard away from the watercourse to the fullest extent possible.
Avoid yarding across the watercourse.
Remove slash and debris that inadvertently enters the watercourse.
Retain windfirm non-merchantable trees and other windfirm vegetation (understorey, shrubs, herbs) within 5 metres of the watercourse edge.
Retain windfirm wildlife trees.

These recommended practices, or others deemed appropriate to achieve the management objectives, should be applied for a minimum of 100 metres upstream of the recipient feature, or to the point where the watercourse is no longer readily identifiable, whichever is shorter.