Getting Started with GNAT

Welcome to GNAT! This page documents the General Workflow and directs the user to the appropriate workflow document or tool documentation for more detailed instruction at each step.

Install GNAT Toolbox

1. Download the latest version of the GNAT Toolbox.
2. Unzip the contents to your computer.
3. Open ArcMap and Add the GNAT.pyt to your ArcToolbox.

Prepare GNAT Inputs

Prepare Analysis

This workflow involves preparing the spatial domain of your analysis.

1. Obtain or download the Stream Network Line Feature Class you will be working with. > GNAT was developed for and tested with NHD 1:24K network. Other line networks can be made to work with the GNAT tools.
2. Filter the Network as needed. >Note: at this point in tool development, the network must remain connected. Make sure that through the filtering process that you do not break apart the network.
   1. By NHD attributes (see NHD Builder Tool in FHC Toolbox)
   2. Manually, using other attributes (i.e. spatial domain of a fish species).

Prepare Stream Network

These two tasks involve 1) cleaning the Stream Network to meet processing requirements and 2) generating Stream Branches on the network.

Clean Stream Network

see Clean NHD Line Network for GNAT(In development)

Prepare Network Branches

See Stream Network and Segmentation for background information.

1. Using the Cleaned Stream Network, calculate Stream Order for the network.
2. Generate Stream Branches from the output of the Stream Order.

Generate Stream Channel Polygon

The Stream Channel Polygon (also called Bankfull Buffer Polygon) is a polygon that represents the bankfull stream channel, plus any buffer to account for the active channel as well as uncertainty/error in the line network itself.

see Bankfull Buffer Workflow

Process

1. Use the Bankfull Channel Tool (in FHC Toolbox) to generate a Stream Channel Polygon
2. Review the polygon to make sure it accurately represents the Stream Channel. Since a buffer is applied to ensure that the edges hit the valley bottom polygon during the confinement calculation, it is better to err on having a larger polygon rather than a smaller one.

Generate Valley Bottom Polygon

The Valley Bottom polygon

Process:

1. Use the VBET Tool (FHC Toolbox) to generate the Valley Bottom Polygon.
2. Review and Repair the Valley Bottom Polygon Valley Bottom Editing Guide

Generate Valley Bottom Centerline

The Valley Bottom Centerline represents the center of the Valley. The is used to calculate the Valley Sinuosity and Planform Geomorphic Attributes.

Process

1. Use the Centerline Tool to generate the Valley Bottom Centerline
2. Review and repair the Valley Bottom Centerline.
   1. Remove Extra Dangles
   2. Remove Donuts/Braids?
3. Copy the Stream Branches from the Stream Network to the Valley Bottom Centerline.
   1. Check branch transfer results for errors.
4. Dissolve (by BranchID) and segment as needed for Valley Sinuosity/Planform calculations.

Generate Geomorphic Attributes

Valley Confinement

See Confinement Tool Documentation

Sinuosity and Planform

1. Segment the Stream Network
   • see Segmentation Tool
2. Segment the Valley Bottom Centerline.
3. Run the Sinuosity and Planform Tool

Compile Attributes

see Compile Attributes Tool