Geographic Information Systems GIS methods for watershed and stream network delineation are based on

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A tool to delineate watersheds and river networks
for multiple sites spread over large Digital
Elevation Models
Kiran Chinnayakanahalli, David G. Tarboton Civil
Environmental Engineering Department, Utah
State University, Logan, UT John Olson, Ryan
Hill, and Chris KroeberDepartment of Aquatic,
Watershed, and Earth Resources, Utah State
University, Logan, UT Email kiran_at_cc.usu.edu
Abstract
Geographic Information Systems (GIS) methods for
watershed and stream network delineation are
based on the derivation of flow direction and
flow accumulation from Digital Elevation Models
(DEM). This method can be laborious when the
number of watersheds to be delineated is large,
as one has to fill sinks in DEMs, process flow
direction and flow accumulation for each site
being delineated. Further, if the site location
is not exactly on the digital representation of
the stream, GIS based methods will result in the
wrong watershed boundary. Additionally, when
the sites are spread over relatively large
geographical area, DEMs and other raster datasets
necessary for watershed delineation, because of
the chosen resolution, can be large and are not
handled well by the currently available watershed
delineation tools. This work will present a
standalone Windows program based on the
functionalities of ArcGIS and TauDEM that is
specifically designed to delineate multiple
watersheds spread over large raster data sets,
and has functionalities to move the site
locations to the nearest streams based on the
flow direction grid, if they are not already
present on the stream. This tool uses USGS
hydrologic units as regional watersheds to sample
the grids and then delineate watersheds draining
to sites located within each regional watershed
in a batch process. This tool also provides
options to delineate watershed based on
contributing area or a curvature approach that
better reflects variable geomorphology, and can
objectively choose the appropriate threshold to
delineate stream networks based on the constant
drop test. Additional capabilities of this
program include the computation of geomorphic
variables such as hypsometric curve indices,
shape factors, stream network geomorphology
attributes, and average watershed properties from
input grids. This tool is useful in deriving
watersheds, stream networks and watershed
attributes of importance to a variety of problems
in hydrology, stream ecology and geomorphology.
The challenge
-Delineate and derive watershed attributes for a
large number of watersheds -Outlet points do not
always coincide with streams (Fig 1) -DEM too big
for processing all watersheds at once (Fig 2)
-178 sites -at a 30x30m cell size it has 16008 X
18594 grid cells
Fig 1 The effect of the site/outlet off the
stream, on watershed delineation
Fig 2 A typical data set for the use in
Multiwatershed Delineation (MWD) tool
Solution

• Buffer and cut grids (Fig 3) using regional
  watersheds (8 digit HUC)
• Preliminary stream network mapped using support
  area method
• Move outlets down slope to place on nearest
  stream
• Drainage density and stream network mapped using
  constant drop test.
• Delineate watershed boundary
• Compute watershed attributes

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INPUT
Raster/grids -DEM -Sink removed DEM -Flow
direction grid -Flow accumulation grid -Stream
grid
Shapefiles -Regional watersheds (polygons) -Sites
or outlets (points)
Fig 4 Multiwatershed delineation (MWD) program
A standalone program that uses TauDem and
ArcObjects functionalities with a visual basic
interface
Other features -Options for drainage delineation
methods a) Curvature based method b) Support
area method -Constant drop test for objectively
choosing the threshold for delineation -Zonal
statistics tool for sampling other raster
datasets (climate, soil, geology etc) over
multiple watersheds.
Fig 5 Output from the Multiwatershed delineation
program
APPLICATION
We developed this program to allow us to
efficiently derive physical properties for
thousands of watersheds and sample sites. This
tool is used to derive watershed boundaries and
attributes for sites in the Western United States
for -developing statistical models to estimate
stream flow regime variables at ungauged basins
by relating them to watershed attributes (Fig
6) -for classifying streams and rivers using
different classification schemes (ex.
Geomorphologic, geologic, hydrologic etc)