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Super-Charging the NHD with Value-Added Attributes

Super-Charging the NHD with Value-Added Attributes. Cindy McKay, Horizon Systems Jennifer Hill, Horizon Systems Tim Bondelid, RTI International Ian Stack, Indus Sponsored by: US Environmental Protection Agency Office of Water. The Value-Added Attributes:. A set of network characteristics

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Super-Charging the NHD with Value-Added Attributes

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  1. Super-Charging the NHDwithValue-Added Attributes

  2. Cindy McKay, Horizon Systems Jennifer Hill, Horizon Systems Tim Bondelid, RTI International Ian Stack, Indus Sponsored by: US Environmental Protection Agency Office of Water

  3. The Value-Added Attributes: • A set of network characteristics • Provide fast network navigation functions • Based solely on native NHD content • Created with software • Built using the national NHD • Eliminate the use of the NHD flow table • Inspired by the EPA Reach File Version 1

  4. Full NHD

  5. DRAINS - Feature Typing - Confluence-to- Confluence Feature Delineation - Rich Attribution Drains Full NHD

  6. REACHES - Permanent Features with Public Identifiers - Scale Independent - Changes Tracked - Hydrologic-based Delineation - Linear Referencing Framework - Flow Relationships Reaches Drains Full NHD

  7. Why build the Value-Added Attributes? • Keep the best of both Reaches and Drains, while eliminating the disadvantages of each. • Fast and Efficient methods for traversing the stream network. • Provide a time-tested modeling framework.

  8. Stream Order Measure of the position of a stream (defined as the segment between successive tributaries) within the hierarchy of the drainage network. It is the basis for quantitative analysis of the network. “A Dictionary of Earth Sciences,” Oxford University Press 1999 Techniques: Strahler, Shreve, Horton

  9. Strahler Stream Order The smallest permanent streams are called "first order". Two first order streams join to form a larger, second order stream; two second order streams join to form a third order, and so on. Smaller streams entering a higher-ordered stream do not change its order number. Strahler 1964 1 1 2 1 1 2 1 2 3

  10. Strahler Stream Order

  11. Arbolate Sum The sum of all segment lengths that flow to the downstream end of a segment. 4/4 5/5 3.5/12.5 4.5/4.5 2.5/2.5 5.1/22.1 2.2/2.2 2/6.7 1.9/30.7

  12. Arbolate Sum

  13. Path Length The distance from the downstream end of a segment to the network termination point. 4/10.5 5/10.5 3.5/7.0 4.5/7.0 2.5/3.9 5.1/1.9 2.2/3.9 2/1.9 1.9/0.0

  14. Path Length

  15. Start Flag & Terminal Flag Start Flag designates headwater features. Terminal Flag designates a feature that terminates the network (A feature that flows to Atlantic Ocean, Pacific Ocean, Gulf of Mexico, A Great Lake, Canada, Mexico, or the ground.)

  16. Divergence Flag A flag which defines the major and minor branches of a flow split (divergence). 0 0 1 0 2 1 2 0

  17. Divergence Flag

  18. Drain Stream Level Stream level provides the information necessary to determine the main path upstream of each confluence. • Flow Volume • Stream Name • Arbolate Sum 2 1 1 2 2 1 3 2 1

  19. Drain Stream Level

  20. Downstream Level 2/1 1/1 1/1 2/1 2/2 1/1 3/2 2/1 1

  21. Hydrologic Sequence Identifier A nationally unique sequence number that places the stream segments in hydrologic sequence. • Descending sequence = upstream to downstream • Ascending sequence = downstream to upstream. 8 9 7 6 3 5 4 2 1

  22. Hydrologic Sequence Identifier

  23. Level Path Identifier The hydrologic sequence identifier of the most downstream segment on the same level path. 2/8/8 1/9/1 1/7/1 2/6/6 2/3/2 1/5/1 3/4/4 2/2/2 1/1/1

  24. Level Path Identifier

  25. Terminal Identifier The hydrologic sequence identifier for the terminal segment to which this segment flows. 8/1 9/1 7/1 6/1 3/1 5/1 4/1 2/1 1/1

  26. Terminal Identifier

  27. From node/To node 10 9 A set of nationally unique identifiers for the node endpoints of the segments. These ids are independent of the node ids in the .NAT table of NHD workspaces. 8 7 5 6 3 4 2 1

  28. Thinning Attribute An ordinal value designed to allow selection of progressively more dense networks. The least dense network is obtained by selecting Thinner=1.

  29. Thinning Attribute • Provide a control for improving performance in large area displays especially in Web applications. • Assist in the correction of NHD density shifts. • Provide appropriately dense stream networks for National and regional application.

  30. How are the VAAs Computed? • For each Catalog Unit/Sub-basin: • Move Reach Attributes to Drains • Move Reach Measures to Drains. • Compute Drain Flow Relationships based on Reach Flow Relationships and Drain Topology • Run 3 National Passes • Process CUs downstream to upstream (Start and Terminal Flags, Divergence Flag, Arbolate Sum) • Processing CUs upstream to downstream (Drain Level, D/S Level, Hydrologic Sequence ID, Level Path ID, Terminal ID, Path Length, F/T Nodes, Thinner) • Processing CUs downstream to upstream (Stream Order)

  31. Importance of the VAAs • Establish the integrity of the network • Easy answers to network questions • Faster and simpler network navigation • Four ways to navigate the network • Fast, sequential routing • Simple SQL queries • Link Node routing • Flow Table navigation • Provide some commonly used attributes

  32. Questions? Cindy McKayLDM@Horizon-Systems.com

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