Learning Objectives

Introduction

Assessing Karst Watercourses

Managing Karst Watercourses

Sinking and Losing Streams

Management Objectives

Karst Management Handbook for
British Columbia

Sinking and Losing Streams

What is a sinking stream?

Sinking streams are streams that disappear underground at a distinct sink point (i.e., swallet).

What is a losing stream?

Losing streams are streams that gradually lose water through an unconsolidated alluvial channel bed, or through a series of indistinct small openings, fractures or sink points.

An important characteristic of some sinking and losing streams

Some sinking and losing streams can spend a large part of the year as a dry stream channel, only flowing when the subsurface karst system backs up and overflows during major storms or runoff events. When these types of streams flow, they can contribute major sources of sediment, organic material and other debris that are readily transported underground. On non-karst terrain, dry channels are generally not considered a major management concern; however, on karst terrain, dry sinking or losing stream channels should be carefully considered for riparian management.

Management objectives

The following are the management objectives for sinking and losing streams. These objectives apply, irrespective of whether the channels carry perennial, ephemeral or intermittent flows.

Maintain water quality and quantity
Limit the introduction of sediment, fine organic material or woody debris into subsurface environments within the range of natural conditions.

Recommended best management practices

Two key recommended best management practices for sinking and losing streams are:

Ensure that reserves and/or management zones along sinking or losing streams completely encircle the recipient karst feature where the water flows underground.
Consider the level of activity in the contributing non-karst catchment area when managing for water quality and quantity for significant recipient karst features.

What are the recommended best management practices for sinking and losing streams?

There are a number of recommended best management practices for sinking and losing streams within cutblock boundaries. The following scenarios are classified according to the width of streams and whether or not the streams flow on karst or non-karst terrain.

Management Scenario: No. 1

The following four scenarios (1-1, 1-2, 1-3, 1-4) refer to sinking and losing streams that are:

Less than 1 metre wide flowing on karst, or
Less than 1.5 metres wide flowing on non-karst.

Each scenario is followed by the recommended best management practices within the cutblock.

Scenario 1-1

A sinking or losing stream contributes water to a significant recipient karst feature located within 250 metres downstream of a cutblock boundary.

What are the recommended best management practices within the cutblock?

The following practices are recommended within an appropriately sized riparian management zone:

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

Scenario 1-2

A sinking or losing stream contributes water to a non-significant recipient karst feature located within 250 metres downstream of the cutblock boundary.

A sinking or losing stream contributes water to a known significant recipient karst feature located more than 250 metres downstream of the cutblock boundary.

A stream does not sink or lose water within 250 metres downstream of the cutblock boundary.

What is the recommended best management practice within the cutblock?

Consult default standards for riparian management as specified in the regulations supporting the Forest and Range Practices Act.

Scenario 1-3

No stream assessment has been carried out.

What is the recommended best management practice within the cutblock?

Assume the stream contributes water to a significant recipient karst feature located within 250 metres downstream of the cutblock boundary. Follow the same management recommendations as in Scenario 1-1.

Scenario 1-4

A stream assessment has been completed and a recipient feature was identified, but not assessed for significance.

What is the recommended best management practice within the cutblock?

Assume the recipient karst feature is significant. Follow the same management recommendations as in Scenario 1-1.

Management Scenario: No. 2

The following five scenarios refer to sinking and losing streams that are:

1 to 3 metres wide flowing on karst; or
1.5 to 3 metres wide flowing on non-karst.

Each scenario is followed by the recommended best management practices within the cutblock.

Scenario 2-1

A sinking or losing stream contributes water to a significant recipient karst feature located within 500 metres downstream of a cutblock boundary.

What is the recommended best management practice within the cutblock?

Establish a minimum 20-metre reserve along the stream, with an adjacent management zone of an appropriate size to protect the reserve from windthrow.

Scenario 2-2

A sinking or losing stream contributes water to a significant recipient karst feature known to be located more than 500 metres downstream of the cutblock boundary.

What are the recommended best management practices within the cutblock?

The following practices are recommended within an appropriately sized riparian management zone:

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

Scenario 2-3

A sinking or losing stream contributes water to a non-significant recipient karst feature located within 500 metres downstream of the cutblock boundary.

A stream does not sink or lose water within 500 metres downstream of the cutblock boundary.

What is the recommended best management practice within the cutblock?

Consult default standards for riparian management as specified in the regulations supporting the Forest and Range Practices Act.

Scenario 2-4

No stream assessment has been carried out.

What is the recommended best management practice within the cutblock?

Assume the stream contributes water to a significant recipient karst feature located within 500 metres downstream of the cutblock boundary. Establish a minimum 20-metre reserve along the stream, with an adjacent management zone of an appropriate size to protect the reserve from windthrow.

Scenario 2-5

A stream assessment has been completed and a recipient karst feature identified, but not assessed for significance.

What is the recommended best management practice within the cutblock?

Assume the recipient karst feature is significant. Establish a minimum 20-metre reserve along the stream, with an adjacent management zone of an appropriate size to protect the reserve from windthrow.

Management Scenario: No. 3

The following four scenarios refer to sinking and losing streams that are:

Larger than 3 metres wide flowing on karst or non-karst.

Each scenario is followed by the recommended best management practices within the cutblock.

Scenario 3-1

A sinking or losing stream contributes water to a significant recipient karst feature located any distance downstream of the cutblock boundary.

What is the recommended best management practice within the cutblock?

Establish a minimum 20-metre reserve along the stream, with an adjacent management zone of an appropriate size to protect the reserve from windthrow.

Scenario 3-2

A sinking or losing stream contributes water to a non-significant recipient karst feature located any distance downstream of the cutblock boundary.

The stream does not sink or lose water along its length.

What is the recommended best management practice within the cutblock?

Consult default standards for riparian management as specified in the regulations supporting the Forest and Range Practices Act.

Scenario 3-3

There has been no stream assessment.

What is the recommended best management practice within the cutblock?

Assume the stream contributes water to a significant recipient karst feature located any distance downstream of the cutblock boundary. Establish a minimum 20-metre reserve along the stream, with an adjacent management zone of an appropriate size to protect the reserve from windthrow.

Scenario 3-4

A stream assessment has been completed and a recipient karst feature identified, but not assessed for significance.

What is the recommended best management practice within the cutblock?

Assume recipient karst feature is significant. Establish a minimum 20-metre reserve along the stream, with an adjacent management zone of an appropriate size to protect the reserve from windthrow.