Australian River Assessment System: AusRivAS Physical Assessment Protocol

Melissa Parsons, Martin Thoms and Richard Norris
Cooperative Research Centre for Freshwater Ecology
University of Canberra
Monitoring River Health Initiative Technical Report Number 22
Environment Australia, 2002
ISSN 1447-1280
ISBN 0 642 54888 9

5 Instructions for the Measurement of Each Variable (continued)

Response Variables (continued)

Extent of bars

A bar is a submerged or exposed ridge-like accumulation of sand, gravel or other alluvial material formed in the channel where a decrease in velocity induces deposition (Armantrout, 1998).

At each sampling site, visually estimate the percentage of the streambed area that protrudes to form a bar of any type (Figure 5.20). Also record the dominant sediment particle size of the bars. Streambed area is equivalent to the length of the sampling site and the width of the wetted channel (under baseflow conditions). Bars can be unattached (e.g. islands) or attached to the banks.

Figure 5.20 Examples of bars in a river channel

Variable derived from the River Habitat Audit Procedure (Anderson, 1993a).

Type of bars

Indicate the presence of one or more of the following bar types along the length of the sampling site:

	bars absent		bars formed around obstructions
	side/point bars VEGETATED		braided channel
	side/point bars UNVEGETATED		infilled channel
	mid-channel island VEGETATED		high flow deposits
	mid-channel island UNVEGETATED

Variable derived from the River Habitat Audit Procedure (Anderson, 1993a).

Channel shape

At each sampling site, examine the overall shape of the channel as one of the following categories:

	U shape Most common natural channel type		Box Commonly encountered with severe gully erosion
	Flat U shape		Wide box
	Deepened U shape May be naturally incised channels		V shaped
	Widened or infilled		Trapezoid Engineered channel shape
	Two stage Lowland channel with one bench		Concrete V Engineered channel shape
	Multi stage Lowland channel with >1 bench		Culvert or pipe

Variable modified from the River Habitat Audit Procedure (Anderson, 1993a).

Bed compaction

After examination of the substratum and the bed along the length of the sampling site¹, assess the overall character of bed sediment compaction as one of the following categories. The term 'dislodge' refers to the ability to pull individual rocks of different sizes from the streambed with the hands. The term 'overlapping' refers to the relative location of rocks on the streambed (ie. whether they sit on top of each other or next to each other).

	Tightly packed, armoured Array of sediment sizes, overlapping, tightly packed and very hard or impossible to dislodge
	Packed, but not armoured Array of sediment sizes, overlapping, tightly packed but can be dislodged with moderate effort
	Moderate compaction Array of sediment sizes, little overlapping, some packing but can be dislodged with moderate effort
	Low compaction (1) Limited range of sediment sizes, little overlapping, some packing and structure but can be dislodged very easily
	Low compaction (2) Loose array of fine sediments, no overlapping, no packing and structure and can be dislodged very easily

¹ In wadeable streams, the bed can be examined visually along the length of the sampling site. In large rivers, the bed should be examined in relation to the range of sediment sizes present at the sampling site (see substrate composition variable). Generally, beds comprised of gravel, sand and silt sediment sizes are not compacted and are easily moved. Thus, these bed types should be allocated to the low compaction (1) or (2) categories.

Variable derived from the River Habitat Audit Procedure (Anderson, 1993a).

Sediment angularity

After visual examination of the substratum and the bed along the length of the sampling site, assess the overall angularity of the cobble, pebble and/or gravel sediment fractions as one of the following categories. Do not include bedrock in the assessment of angularity. Where the cobble, pebble AND gravel fractions are not present at a sampling site (e.g. in lowland rivers), select the 'not present' category.

	very angular
	angular
	sub-angular
	rounded
	well-rounded
	cobble, pebble and gravel fractions not present

Variable derived from the River Habitat Audit Procedure (Anderson, 1993a).