Stream Reach And Watershed
(c) 2010 by David G. Tarboton
This tool produces a vector network and shapefile
from the stream raster grid. The flow direction grid is used to connect
flow paths along the stream raster. The Strahler order of each stream
segment is computed. The subwatershed draining to each stream segment
(reach) is also delineated and labeled with the value identifier that
corresponds to the WSNO (watershed number) attribute in the Stream Reach
Shapefile.
This tool orders the stream network according to
the Strahler ordering system. Streams that don't have any other streams
draining in to them are order 1. When two stream reaches of different order
join the order of the downstream reach is the order of the highest incoming
reach. When two reaches of equal order join the downstream reach order is
increased by 1. When more than two reaches join the downstream reach order
is calculated as the maximum of the highest incoming reach order or the
second highest incoming reach order + 1. This generalizes the common
definition to cases where more than two reaches join at a point. The network
topological connectivity is stored in the Stream Network Tree file, and
coordinates and attributes from each grid cell along the network are stored
in the Network Coordinates file.
The stream raster grid is used as the source for
the stream network, and the flow direction grid is used to trace connections
within the stream network. Elevations and contributing area are used to
determine the elevation and contributing area attributes in the network
coordinate file. Points in the outlets shapefile are used to logically
split stream reaches to facilitate representing watersheds upstream and
downstream of monitoring points. The program uses the attribute field "id"
in the outlets shapefile as identifiers in the Network Tree file. This tool
then translates the text file vector network representation in the Network
Tree and Coordinates files into a shapefile. Further attributes are also
evaluated. The program has an option to delineate a single watershed by
representing the entire area draining to the Stream Network as a single
value in the output watershed grid.
Parameters
- Number of Processes
Integer
- The number of stripes that the domain will be divided into and the
number of MPI parallel processes that will be spawned to evaluate each
of the stripes.
- Pit Filled Elevation Grid
Raster Grid
- A grid of elevation values. This is usually the output of the "Pit
Remove" tool, in which case it is elevations with pits removed.
- D8 Flow Direction Grid
Raster Grid
- A grid of D8 flow directions which are defined, for each cell, as
the direction of the one of its eight adjacent or diagonal neighbors
with the steepest downward slope. This grid can be obtained as the
output of the "D8 Flow Directions" tool.
- D8 Drainage Area Grid
Raster Grid
- A grid giving the contributing area value in terms of the number
of grid cells (or the summation of weights) for each cell taken as its
own contribution plus the contribution from upslope neighbors that drain
in to it using the D8 algorithm. This is usually the output of the "D8
Contributing Area" tool and is used to determine the contributing
area attribute in the Network Coordinate file.
- Stream Raster Grid
Raster Grid
- An indicator grid indicating streams, by using a grid cell value
of 1 on streams and 0 off streams. Several of the "Stream Network
Analysis" tools produce this type of grid. The Stream Raster Grid
is used as the source for the stream network.
- Outlets Shapefile as Network Nodes
Point Shapefile (optional)
- A point shape file defining points of interest. If this file is used,
the tool will only deliiniate the stream network upstream of these outlets.
Additionally, points in the Outlets Shapefile are used to logically split
stream reaches to facilitate representing watersheds upstream and downstream
of monitoring points. This tool REQUIRES THAT THERE BE an integer attribute
field "id" in the Outlets Shapefile, because the "id"
values are used as identifiers in the Network Tree file.
- Delineate Single Watershed
Boolean
- This option causes the tool to delineate a single watershed by
representing the entire area draining to the Stream Network as a single
value in the output watershed grid. Otherwise a seperate watershed is
delineated for each stream reach. Default is False
(seperate watershed).
Outputs
- Stream Order Grid
Raster Grid
- The Stream Order Grid has cells values of streams ordered according
to the Strahler order system. The Strahler ordering system defines order
1 streams as stream reaches that don't have any other reaches draining
in to them. When two stream reaches of different order join the order
of the downstream reach is the order of the highest incoming reach.
When two reaches of equal order join the downstream reach order is
increased by 1. When more than two reaches join the downstream reach
order is calculated as the maximum of the highest incoming reach order
or the second highest incoming reach order + 1. This generalizes the
common definition to cases where more than two flow paths reaches
join at a point.
- Watershed Grid
Raster Grid
- This output grid identified each reach watershed with a unique ID
number, or in the case where the delineate single watershed option was
checked, the entire area draining to the stream network is identified
with a single ID.
- Stream Reach Shapefile
Polyline Shapefile
- This output is a polyline shapefile giving the links in a stream
network. The columns in the attribute table are:
- LINKNO — Link Number. A unique number associated with
each link (segment of channel between junctions). This is arbitrary
and will vary depending on number of processes used
- DSLINKNO — Link Number of the downstream link. -1
indicates that this does not exist
- USLINKNO1 — Link Number of first upstream link. (-1
indicates no link upstream, i.e. for a source link)
- USLINKNO2 — Link Number of second upstream link. (-1
indicates no second link upstream, i.e. for a source link or an internal
monitoring point where the reach is logically split but the network
does not bifurcate)
- DSNODEID — Node identifier for node at downstream end
of stream reach. This identifier corresponds to the "id"
attribute from the Outlets shapefile used to designate nodes
- Order — Strahler Stream Order
- Length — Length of the link. The units are the horizontal
map units of the underlying DEM grid
- Magnitude — Shreve Magnitude of the link. This is the
total number of sources upstream
- DS_Cont_Ar — Drainage area at the downstream end of
the link. Generally this is one grid cell upstream of the downstream
end because the drainage area at the downstream end grid cell includes
the area of the stream being joined
- Drop — Drop in elevation from the start to the end
of the link
- Slope — Average slope of the link (computed as drop/length)
- Straight_L — Straight line distance from the start
to the end of the link
- US_Cont_Ar — Drainage area at the upstream end of
the link
- WSNO — Watershed number. Cross reference to the *w.shp
and *w grid files giving the identification number of the watershed
draining directly to the link
- DOUT_END — Distance to the eventual outlet (i.e. the
most downstream point in the stream network) from the downstream end
of the link
- DOUT_START — Distance to the eventual outlet from the
upstream end of the link
- DOUT_MID — Distance to the eventual outlet from the
midpoint of the link
- Network Connectivity Tree
Text File
- This output is a text file that details the network topological
connectivity is stored in the Stream Network Tree file. Columns are
as follows:
- Link Number (Arbitrary — will vary depending on number
of processes used)
- Start Point Number in Network coordinates (*coord.dat) file (Indexed
from 0)
- End Point Number in Network coordinates (*coord.dat) file (Indexed
from 0)
- Next (Downstream) Link Number. Points to Link Number. -1 indicates
no links downstream, i.e. a terminal link
- First Previous (Upstream) Link Number. Points to Link Number. -1
indicates no upstream links
- Second Previous (Upstream) Link Numbers. Points to Link Number. -1
indicates no upstream links. Where only one previous link is -1, it
indicates an internal monitoring point where the reach is logically
split, but the network does not bifurcate
- Strahler Order of Link
- Monitoring point identifier at downstream end of link. -1 indicates
downstream end is not a monitoring point
- Network magnitude of the link, calculated as the number of upstream
sources (following Shreve)
- Network Coordinates
Text File
- This output is a text file that contains the coordinates and attributes
of points along the stream network. Columns are as follows:
- X coordinate
- Y Coordinate
- Distance along channels to the downstream end of a terminal link
- Elevation
- Contributing area