Bulk Off-take Project Report

An Audit of the Cap Data Management System by Marsden Jacob Associates concluded that the integrity of water polices like the Cap depends upon the accuracy of measurements of primary diversions from the rivers and recommended among other things the establishment of an open registry of Bulk Off-takes. In response to the Audit, the Commission developed a Registry of Bulk Off-takes in the Basin.

Bulk Off-take registry report Oct 2006 [PDF] 3 Mb

Bulk Off-takes for the purpose of this investigation were defined as sites, which divert or return water from or to the rivers and where the average annual diversions/returns exceed 5 GL.

Key outputs

• A basin-wide database of off-takes/returns was developed. The database include information on off-takes such as their location, type of measurement device annual volume, measurement verification, ownership,. The database is also capable of performing analyses (eg calculating accuracy statistics) and producing Reports by structures and by Cap valleys;
• The accuracy of measurement for sites was assessed;
• Draft specifications, including the accuracy targets, for a national standard of measurement and measurement practices for Bulk Off-takes were developed. The draft specifications have been refereed to the National Water initiative
• Off-takes were assessed for their compliance with draft specifications in terms of suggested accuracy targets and those failing this test were identified.

Key findings:

• Bulk off-takes account for approximately 80% of total Basin diversions. The remaining diversions are made up of small off-takes (less than 5GL per annum);
• Open channels represent 85% of the total bulk off-take diversions;
• Measurement of open channel diversions is made by rating tables (42%), ultrasonic devices (29%) and flow rate equations (12%);
• Conduit structures only represent 15% of the bulk off-take diversions. Propeller meters devices measure the majority of these volumes (10%) followed by electromagnetic meters (1%).
• Currently there is no national or state standard for bulk measurements.
• An accuracy of 5% is considered satisfactory for the Cap purposes and is achievable for almost all types of bulk measurement devices;
• Rating table measurement in open channels is accurate within 5% for most sites;

Actions

• States have been asked to report to the Commission by March 2007 on how they propose to improve the accuracy of off-takes identified as having an unacceptable level of accuracy;
• The Report and the Draft specifications have been made available to the National Water Initiative (NWI) Committee of the Natural Resources Management Ministerial Council for further development as a National Standard for Bulk Off-take Diversion Measurement.