Daly
17.2 River outflow from the region

Supporting information

The volume recognised in the water accounting statements (9,698,000 ML) represents the total volume of water outflow from the Daly River to the Timor Sea during the 2011–12 year.

Quantification approach

Data source

Hydstra database.

Provided by

Department of Land Resource Management.

Method

The Daly River is the only river that flows out to sea from the Daly region. The river outflow was estimated using instantaneous discharge data (L/s) collected at the most downstream gauging station nearest to the outlet to the sea along the river (Mount Nancar station). These data were converted to daily volume data (ML) to determine the total annual discharge (in ML) at Mount Nancar during the 2011–12 year.

Assumptions, limitations, caveats and approximations

It is assumed that the river outflow to the sea is equal to the volume of discharge measured at the most downstream station along a river, i.e. there is no adjustment made for the contributing area below the gauging station used to calculate the outflow.

This contributing area below the gauging stations is 6,913 km2, approximately 13% of the total area of the Daly region. Based on a drainage-area ratio equation, estimated outflow is approximately 11,000,000 ML, which is 1.14 times that reported in the Statement of Water Flows (9,698,000 ML).

However, given that the ungauged component of the Daly region mainly lies on the lowlands, which is an area of relatively high rainfall-recharge, it is unlikely that this area will generate such a large amount of runoff. Instead, it is considered that the reported outflow to sea may be underestimated by up to 5–10%.

Uncertainty information

The Department of Land Resource Management assigns quality codes to flow data in accordance with the following table:

 

Department of Land Resource Management quality codes for flow data

Quality code

Description

41

Good rating

91

Satisfactory rating

141

Poor rating

150

Rating under review – (not quality coded)

255

No data

 

The total volume of water that outflows into the sea from the Daly River has a quality code of 91. This quality code indicates the lowest quality of data recorded at the Mount Nancar station during the 2011–12 year.