Publications: Guidelines, models and sampling protocols

Sediment assessment methods - protocols and guidelines for assessing the effects of deposited fine sediment on in-stream values

1 January, 2011
CITATION

Clapcott JE, Young RG, Harding JS, Matthaei CD, Quinn JM, Death RG 2011. Sediment assessment methods - protocols and guidelines for assessing the effects of deposited fine sediment on in-stream values. Cawthron Institute, Nelson, New Zealand.

BACKGROUND

Sedimentation is a global issue where land-use change has resulted in excess sediment being delivered to and deposited on the beds of streams, rivers, estuaries and bays. Excess sediment directly affects the health of a waterway, decreasing its mauri or life-supporting capacity.

Deposited fine sediment occurs naturally in the beds of rivers and streams. It usually enters a stream either because of terrestrial weathering processes, or bank erosion and in-stream fluvial processes. Sediment particles are transported and deposited in streams and receiving waters, such as lakes, estuaries and coastal bays, as the result of flowing water.

Because sediment is naturally transported longitudinally through a river network, its state at any given point will be influenced by climate, geology, topography and current velocity. Human activities can impact on this natural sediment cycle by accelerating the delivery of sediment to streams and increasing the quantity of smaller particle sizes.

The effect of excess in-stream sedimentation is recognised as a major impact of changing land use on river health. In particular, sediment alters the physical habitat by clogging interstitial spaces used as refugia by benthic invertebrates and fish, by altering food resources and by removing sites used for egg laying. As such, sediment can affect the diversity and composition of biotic communities.

Excess sediment can also affect the aesthetic appeal of rivers and streams for human recreation. Although there is a general recognition of the significance of sedimentation in New Zealand, there are currently no widely accepted protocols for the measurement of deposited sediments, or guidelines to interpret the results in relation to ecological or recreational values.

A number of regional councils have recognised the need to collect sediment information and have started to include some measure of deposited sediment in their monitoring programmes. However, in the absence of established national guidance, different methodologies are currently being used. This lack of consistency could compromise the validity of any inter-region comparisons, or national state of the environment reporting. Furthermore, the absence of robust and tested methods may also compromise use of the data in any regulatory context (policy development, resource consents, prosecutions).

The protocols and guidelines presented in this document were developed at the request of New Zealand Regional Councils to address a lack of national consistency. The aim of this document is to provide scientifically robust in-stream protocols and guidelines for the measurement of deposited sediment. The document also includes scientific justification and background information on the testing of these protocols.