Calculate Depth to Water Index (DTW) using Surface Parameters

Description

Calculate the depth-to-water index (DTW) from a DEM.

Usage

This tool calculates the depth-to-water index (DTW) from DEM derivative slope and a surface water input. The DTW output can be used as a predictor variable for wetland identification with the WIM workflow. DTW has been shown to accurately indicate saturated areas (e.g., Murphy et al., 2007, 2009, 2011; Oltean et al., 2016; O'Neil et al., 2018; O'Neil et al., 2019; White et al., 2012). Developed by Murphy et al. (2007), DTW is a soil moisture index based on the assumption that soils closer to surface water, in terms of distance and elevation, are more likely to be saturated. This tool uses the Spatial Analyst Surface Parameters tool to calculate the slope component. Like Surface Parameters, this tool gives users the option to implement an adaptive neighborhood size to compute slope. Surface water inputs can be either raster or feature type. Users should derive DTW from a smoothed, high resolution DEM to avoid microtopographic noise, and should use updated surface water data.

Parameters

Parameter Name	Type	Direction	Data Type	Dialog Reference
Input Smoothed DEM	Required	Input	Raster Layer	Full pathname to the input DEM. If DTW Slope raster is given below, this input is ignored.
Input Surface Water Data	Required	Input	Raster Layer or Feature Layer	Full pathname to the input surface water data to be used for DTW calculation. Surface water data should include all streamlines and waterbodies within the DEM extents. Surface water can be entered as feature data or raster data, where all non-water cells are null.
Slope Neighborhood Distance (meters)	Required	Input	Double	The maximum neighborhood length (meters) that will be used by the adaptive neighborhood process for the Surface Parameters method. The adaptive neighborhood process optimizes the window size for which slope is calculated based on local DEM variability. If the neighborhood distance is equal to the cell size of the input DEM, adaptive neighborhoods will not be used. See surface parameters tool documentation. Optimal maximum neighborhood length will vary by use case. Users may begin with a neighborhood length that corresponds to the minimum size of wetlands of interest.
Output DTW Raster (*.tif)	Required	Output	Raster Dataset	Name of the resulting DTW raster. Must be in TIFF format. The output directory will be created if it does not exist.
Save intermediate outputs	Required	Input	Boolean	Option to save intermediate outputs from the DTW calculation: DTW Slope. The output directory will be created if it does not exist.
Output DTW Slope	Optional	Output	Raster Dataset	Output slope raster used for DTW calculation. The output directory will be created if it does not exist.
Input DTW Slope Raster	Optional	Input	Raster Layer	Input slope raster for the DTW calculation. If not given, the tool calculates the slope raster directly from the input DEM. The input slope raster must be in units of m/m (rise/run) and have a very small constant (i.e., 0.001) added to avoid zero-slope cells being used as surface water source locations in the algorithm.