Field monitoring information for the Swift (Ngarradj) Creek catchment Northern Territory
Internal Report 355
Saynor MJ, Evans KG, Smith BL, Crisp E & Fox G
Supervising Scientist Division
About the report
Initial field inspections during the dry season of 1998 (September) were carried out with a view to establishing a field program prior to the 1998/99 wet season. These inspections indicated that the dominant channel erosion processes in the Swift creek catchment were:
- erosion of the outside bank on bends;
- upstream migration of the primary knickpoint at the head of gullies;
- channel widening subsequent to incision by the primary knickpoint;
- bed degradation in the lower gully by the upstream migration of secondary knickpoints downstream of the gully head;
- development of anabranches; and
- erosion of flow-aligned scour pools, similar to those described by Scott and Erskine (1994).
The first four processes are the most important. A rapidly expanding literature has demonstrated that channel sources are an important and often the dominant sediment source on many Australian rivers (Erskine and Melville, 1983b; 1983b; Melville and Erskine, 1986; Erskine, 1992; 1994; 1996; 1999; Erskine and Saynor, 1996a; 1996b; Wasson et al., 1996). To determine the significance of channel erosion as a sediment source in the Swift Creek catchment, it is essential to measure bank erosion and knickpoint migration rates at appropriate sites. The mine site tributaries and Swift Creek should be investigated in detail. The cross sections recommended for determining channel sediment storage are capable of measuring large scale bank erosion only (Wolman, 1959). Erosion pins are needed to measure relatively slow rates of bank retreat (Wolman, 1959; Erskine et al., 1995).
To access changes erosion rates of material being moved through Swift creek, Erskine et al (in Press) made the following recommendations;
- Selectively measure bank erosion rates and knickpoint migration rates (using erosion pins) to determine the significance of in-channel sediment sources in comparison to the sediment yields generated on the mine site;
- Install permanently marked cross sections and use them to monitor the amount of bed sediment storage and/or large scale erosion throughout the channel network;
- Install scour chains at each gauging station to determine the maximum depth of bed scour during each wet season;
The following sections document the location of gauging stations as well as details of the erosion pins, cross sections and scour chains that have been installed along Swift Creek and its tributaries.