The Power of NHD as a Reach File

What can you do with Reaches?  Linking Information to the NHD Linear Referencing to the Network Areal Referencing to Waterbodies  Modeling – Upstream/Downstream Cause Determination – Look Upstream Impact Analysis – Look Downstream In-stream Water Quality Computations

Linking Information to the NHD   Permanent Identifiers – Reach Codes subbasin + sequential number = On Transport, Coastline, and Waterbody Reaches   Addresses along Transport Reaches Proportional numbering from downstream to upstream Link to points and stretches along a reach   Permanent Features

Reach Codes as Permanent Surface Water Identifiers

Adding a Start (Headwater) Reach

Adding a Sub-Network of Reaches

Adding a Divergent Channel Reach

Permanent Reach Codes - Except   When the hydrography changes Building or removing a dam Flooding The guy with the backhoe  Mapping Errors Reach Code Cross Reference

Old Reach Code Old Reach Date New Reach Code New Reach Date Change CodeProcess subbasin + segment yyyy + mm + dd subbasin + segment yyyy + mm + dd A – Add D – Delete 11 – One-to-one 1P – One-to-partial (merge) P1 – Partial-to-one (split) PP – Partial-to-partial (split & merge) SA – Shoreline to artificial path (RF3  NHD only) A six character code for the process that effected the change

NHDReachCrossReference Table

Addresses on Linear Reaches  Each linear reach is one addressable unit - a ‘street’  Addresses are proportional ‘street’ numbers from bottom to top

Example - Linear Transport Reach Reach Addresses (Similar to Street Addresses) Street NameAnd Number 2 Program Reach Begin End Description System ID ID Position Position 3 TMDL-B 303(d) Listed TMDL-B WQS-C Water Quality WQS-C Standard WQ-A WQ Monitoring WQ-A