Are the Reach numbers hydrologically ordered in the reach files?
Not really. When the EPA constructed their simplly structured RF1 files back in the ’80’s they did attempt to assign SEG numbers in some hydrologic sequence. Even numbers for reaches on the left side of the basin, odd numbers on the right. As the reach files evolved and became more complex, this concept was abandoned. • How were these numbers moved to the 100K hydrography. These numbers were transferred to the 100K-scalehydrography using a conflation algorithm developed by the USGS. After intensively editing the EPA RF2.5 Trace Files to align their beginningand ending nodes on top of the corresponding beginning and ending stream nodes in the 100K-scalehydrography. A routing algorithm then transferred (conflated) the EPA Trace-IDs to the corresponding 100K reaches. With the Trace -ID’s now physically in the 100K-scale hydrography, JOINITEM commands were used to bring across the remaining Trace attributes. A computer program then generated SEG numbers for the remaining un-coded reaches.
