Exercise 4 supplementary material

Reference Material

This is a list for extended reading giving papers cited in the lecture and that may be of interest.  You are not expected to read this before doing the homework, or even at all in its entirety.  You should be willing to search in this material for help or clarification when necessary. Some of these are online and require Acrobat Reader which can be obtained from Adobe.

Installation.

This may require system administrator help (or at least permission) for networked configurations.  First check if TARDEM is already installed.  TARDEM programs are DOS style programs run from a command line, so open a MS-DOS Prompt  (Start/Programs/MS-DOS Prompt).  In this DOS window type 'flood'.  If you get the message "bad command or file name" then the programs are not (properly) installed.  If you get the message "Usage: ..." then the programs are installed.  To install download and save to disk tardem.zip.  This file contains several *.exe files that should be placed in any convenient folder, e.g. c:\tardem\myexec.  To use these programs this directory needs to be on the system search path.  Since these programs use the ESRI gridio library this library also needs to be on the system search path.  Both these requirements can be met by including the following line in the autoexec.bat file.
    Windows 95/98
    SET PATH=C:\TARDEM\EXEC;C:\ESRI\AV_GIS30\ARCVIEW\BIN32

    Windows NT
    path=c:\tardem\exec;c:\esri\av_gis30\arcview\bin32

There may be other path entries on your system depending on the software you have.  You should leave them alone and only add the entries involving TARDEM and ARCVIEW.  Once these changes have been made the system should be rebooted.  Make sure there are no blanks or trailing blanks in these paths or it won't work. The autoexec.bat file can be edited from the Windows Start Menu Start/run/sysedit.

Additional notes on TARDEM programs.

From tdprepro and aread8 you sometimes get a warning message saying "Value Range exceeds 100000 and number of unique values exceeds 500, please use BUILDVAT if a VAT is required.  You may ignore this warning message. We do not need a VAT.  This message occurs because the contributing area has a large number of different integer values - too many for ArcView to treat as attribute table categories.   The programs could also have been run on the ASCII grid file using
    tdprepro reydem.asc    (you do not need to do this)
If you do this ignore the 'invalid grid item syntax' message.  This is saying the program could not open the grid as an ESRI grid at which point it reverts to reading it as an ASCII file.  This will be a bit slower because ASCII input/output is used.

The programs may also be run individually using the commands

    flood reydem   (you do not need to do these - they were done by tdprepro)
    d8 reydem
    aread8 reydem
    gridnet reydem
This is useful if there was a problem part of the way through and you do not want to rerun work already done, or if you know you will be using a channel network delineation approach that does not use some of the output, e.g. the constant support area method does not use gridnet output.

Following are the suffixes for the grid files produces and what they contain:
no suffix.  Elevation data.
fel Pit filled elevation data.  produced by flood input to D8, Dinf, netsetup
p D8 drainage directions.  produced by D8 input to aread8
sd8 D8 slopes.  produced by D8  input to netsetup, some methods
ad8  D8 contributing area’s, units are number of grid cells. produced by aread8 input to netsetup
slp Dinf slopes. produced by Dinf
ang  Dinf flow directions.  produced by Dinf  input to areadinf
sca  Dinf contributing area’s, units are specific catchment area, i.e. number of grid cells times cell size. produced by areadinf
plen  Longest path length to each grid point along D8 directions. produced by gridnet
tlen  Total path length to each grid point along D8 directions. produced by gridnet
gord  Strahler order for grid network defined from D8 flow directions.  produced by gridnet
src Network mask based on channel source rules.  produced by netsetup
ord  Grid with Strahler order for mapped stream network.  produced by netsetup
w Subbasins mapped using subbasinsetup.  produced by subbasinsetup
fdr Flow directions enforced to follow the existing stream network  produced by streamtogrid optional input to flood
fdrn Flow directions enforced to follow the existing stream network after cleaning to remove any loops  produced by flood optional input to d8, dinf
The .asc extension is used if the data is ASCII.

The complete set of methods for defining channel networks via netsetup are

  1. Catchment area threshold A >= p[0].
  2. Area-Slope threshold A S^p[1] >= p[0].
  3. Length-Area threshold A >= p[0] L^p[1]. Here L is the maximum drainage length to each cell in the plen file.
  4. Accumulation area of upward curved grid cells.  The DEM is first smoothed by a kernel with value p[0] at its center, p[1] on its edges, and p[2] on diagonals.  The Peuker and Douglas (1975) method is then used to identify upwards curved grid cells and contributing area computed using only these cells.  A threshold, Auc >= p[3] on these cells is used to map the channel network.
  5. Grid order threshold  O >= p[0].
  6. Use existing channel networks specified in a *fdrn file [fdrn file created from fdr file by flood.  fdr file created from shape file by streamtogrid]
Experiment with a few of these.  You may want to rename the files reydemtree.dat and reydemcoord.dat between runs to save them, as each new run overwrites the old ones.  My favourite is method 4, with parameters  .4 .1 .05 20.

Method 6 extracts watersheds following a given EPA reach file (vector data).  Flow directions are forced to follow along the given streams. To use this option run

    streamtogrid reydem reystreams [The last argument is the file name of the shape file of streams.]
    tdprepro reydem reydemfdr
    netsetup reydem -m 6 -xy ** ** [You will have to identify a new outlet that is on one of the streams]