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Exception rules were applied in preference to the algorithm rule. They were:·
Named streams were retained. After the algorithm was run, a search for any named streams not included (including those under 750m in length), was done manually. These features were then added.
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When required to visually maintain straighter or more cartographically represented streams, varying angle distances from watercourse line segments were trialled, rejected, or accepted.
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In braided stream networks, and data in areas of bifurcation, a manual review and upgrade was required. These anomalies were later referred to as areas of loops or circles.
Feature Manipulation Engine (FME) was used to carry out the automatic processing for the assignment of the stream order working via drainage basins. A digital elevation model (DEM) of the drainage basin was used to determine headwater and downstream. Once the automation was complete, various manual corrections and updates were made, and ongoing maintenance of the dataset continues to improve and enhance the dataset.
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Strahler, A. N. (1957), "Quantitative analysis of watershed geomorphology". Transactions of the American Geophysical Union, 38, No. 6, 913–920.