Figure 1 shows the three straightforward GIS processing tasks that the NHD data undergoes.
Figure 1 - Diagram showing NHD stream GIS processing tasks.
The COGO Proportion tool
This video below goes through the above steps using the COGO PROPORTION TOOL
Step 1: Convert the multipart drainage network to a singlepart drainage network. Use the tool “Multipart to Singlepart”
Step 2: The length field needs to be recalculated before moving on to Task 5 (See COGO video above).
Step 1: Create a 100 meter (riparian and upland fringe) buffer using the “Buffer” command under the Geoprocessing Tab. Note: Use End Type “FLAT”
Step 2: Repeat the above step but this time generate a 30 m (bank and channel level) buffer. Note: Use End Type “FLAT”
The video below highlights the simple process of buffering your stream layers for the 30 m and 100 m buffers.
Missing buffer segments from 30m buffer (flat end type)
Step 1: Create a second 30m buffer but this time create a round end type buffer. In your table of contents, place this layer below the flat end type buffer to get an idea where you are no longer missing segments.
Buffer segments from 30m buffer shown in blue (round end type)
Step 2: Run the Erase tool using the round end type buffer as the input feature and the flat end type buffer as the erase feature. Name the output feature class NHD_30m_buffer_filler.
Segments created using erase tool. Note: these are the segments the flat end type buffer did not have
Step 3: To dissolve the semi-circles from the round end type buffer to their respective segment, run the Dissolve tool. The input feature will be the NHD_30m_buffer_filler. *Name the output feature class *NHD_30m_buffer_filler_dissolve. **Uncheck **“Create multipart features.”
Step 4: Open the attribute of the *NHD_30m_buffer_filler_dissolve *and create a new field and label it “Area”. Make the type “Double” and precision 6 and scale 2. Right-click on the field and “Calculate Geometry.” Use meters as your units.
Step 5: To get rid of all the small semi-circles that exist at the upper reaches of the NHD line, we need to start and editing session. First, use the “Select by Attribute” command and set up a query that looks like the following. The values will not be the same. You need to assess what the area is of the majority of the semi-circles and use this value within the query. Once the segments are satisfied, right click on one segment and hit Delete. When satisfied with the edits, save edits and stop the editing session.
Selecting by attribute to remove unwanted semi-circles
Step 6: Run the Merge tool. The input datasets will be the edited NHD_30m_buffer_filler_dissolve and the original flat buffer end type layer. Name the output dataset *NHD_30m_buffer_final. *This will create a more accurate buffer that will not alter the zonal statistics that will be used in the next task.
Final 30m buffer with missing segments