RESOURCE NOTES

NO. 6 DATE 06/09/99

The Spatial Terrain

Analysis Resource

Toolset (START)

by Jacek Blaszczynski

Physical Scientist

BLM NARSC 

Most of the existing automated terrain

analysis tools are not arranged into any

sort of classes and categories but are available haphazardly as commands on various GIS systems or as software available

outside of commercial GIS systems

because of its specialized nature. In some

cases, the terrain tools are not completely

finalized and they require further software work to cleanly interface with systems like ARC/INFO. To make sense of

these tools we have systematized them

into four major groups based on traditional divisions in geomorphology. These

include tools for hillslope analysis, catchment analysis, and drainage pattern

analysis, as well as physical process modeling tools that simulate the effects of terrain morphology on various physical

ecosystem processes. 

All the tools we are presenting here use

DEMs as their only required data source,

with exceptions that will be noted. They

work primarily in Unix, but it should

also be possible to compile the software

to work on PCs. You should look at the

following list as an early look at capabilities of which most could be made available soon depending on your expressed

interest. We also hope to be able to accept

a few project locations where we could

run the models and develop elevation

derivative data bases and related products. If you email, call, or send in a

response indicating your interest in the

toolset and their products, you will automatically become an informal customer

for the project, part of a potential user

group, and will be kept advised on our

progress and access to the software. We

should remind you that in some cases we

still will need to get into a mutual

arrangement with another agency before

we can distribute their software at BLM.

Hillslope Analysis Tools

• Slope gradient analysis — calculates

slope gradients in degrees or percent

based of Digital Elevation Model

(DEM) data. This data aids in evaluation of soil erosion and landslide

potential, in identification of potential soil types along slope profiles, and

other applications mostly hydrologic

and geomorphic in nature. Available

as an ARC GRID function.

• Slope length analysis — calculates

length of each flowpath on the terrain from any point to a nearest local

elevation maximum identified from

DEM data. A flowpath can be compared to complex cross section of the

slope, or slope profile, made along

the steepest path on the slope.

Therefore, slope length can be useful

in locating a soil type on a hillslope.

Slope length is also useful particularly in erosion and sediment yield calculations. Available as an ARC

GRID function.

• Slope aspect analysis — calculates

the orientation of a slope facet in

degrees from the northern direction

from DEM data, mainly useful to

solar irradiation calculations.

Available as an ARC GRID function. 

• Planimetric curvature analysis —

calculates the curvature of slope that

is parallel to the elevation contours

which can be used to help identify

divergent or convergent flow areas on

the landscape: convergent flow generally indicates higher erosion and

transport potential, while the divergent flow indicates lower potential.

Available as an ARC GRID function.

• Profile curvature analysis — calculates the curvature perpendicular to

the elevation contours from DEMs

which indicates whether any particular point on the hillslope profile is in

an area of convex or concave curvature. This indicates whether the area

is more likely to be erosive or depositional. Available as an ARC GRID

function.

• Neighborhood or focal curvature

analysis — recently developed at

NARSC, this capability permits averaging of negative and positive slopes

over neighborhoods of various sizes

and shapes and is useful in visualization of specific and general hillslope

curvature patterns in map view.

Available as an AML and C software

that imitates an ARC command.

• Fourth-order-of-relief analysis —

this set of methods divides the landscape into the categories of: convex

areas which include crests of convexities and convex slopes; flat areas

(neighborhood curvature=0) which

include sloping flats (curvature=0,

slope>0) and horizontal flats (curvature=0, slope=0); and concave areas

which include concave slopes, open

basins or valleys, enclosed basins or

depressions, and troughs of concavities. The fourth-order-of-relief analysis permits map representation of

hillslope morphology in great detail

and at various levels of generalization

making it easier to identify hillslope

patterns and slope types (e.g. head

slope, nose slope, foot slope, etc.)

Drainage pattern analysis tools:

• Flowpath delineation based on topographic relief aids the identification

of flow patterns across landscape

with relief (STREAMNETWORK.AML);

• Stream order analysis (Strahler and

Shreve methods) permits situating of

stream reaches and related catchments in the context of a hierarchical

framework: aids in multi-scale analysis and in relating our units to

national hydrologic unit frameworks; 

• Analysis of accumulation of water

flow along flow paths throughout the

entire landscape permits delineation

of drainage patterns and aids evaluation of water accumulation in

streams: can be understood as representing catchment area for any point

on the landscape;

• Other drainage network analysis

tools, such as tools for modeling

cumulative effect of runoff across a

connected network of watersheds,

are currently being studied and will

be discussed more closely in future

resource notes.

Range

GIS and GPS
Watershed analysis tools: 

• Delineation of catchments based on:

- Natural divides in the terrain

- User-specified catchment outlets

(MAKESHEDS.AML, SEEDSHEDMODEL.AML)

- Location of stream junctions

(REACHSHEDMODEL.AML)

• Watershed order analysis - based on

stream order analysis using Strahler

and Shreve methods.

• Basin morphometric parameters -

BASINSOFT is an encrypted AML

tool that has been made possible by

some excellent software development

work performed by our colleagues at

the USGS based on century of developments in quantitative geomorphometry. Basin morphometric parameters not only describe the shape of

catchments in a variety of way,s but

many of them have hydrologic significance and can be related to surface

water processes occurring in the

catchment. Although the software is

available only at the USGS (we have

a test version of it), we can perform

the basin morphometric analysis

with their help. A partial list of basin

geomorphometric variables that can

be calculated with this software

includes methods to measure average

basin slope, shape factor, basin rotundity, stream density, relative relief,

constant of channel maintenance,

ruggedness number, and more.

Automated physical process

models:

These models are available in the Terrain

Analysis for Environmental Sciences

(TAPES) software developed primarily

based on work by the late Dr. Ion Moore

and continued by Dr. John Gallant at the

Centre for Resource and Environmental

Studies in Australia and Dr. John Wilson

from University of Southern California

and Montana State University. The software is a set of programs that works both

on grids and contour data to model influence of terrain on various environmental

processes.

• Calculation of solar irradiation

and temperature based on topography is helpful in evaluation of the

geographic distribution of solar

energy input into the landscape;

• Calculation of wetness

index, soil wetness, and

evapotranspiration based

on solar irradiation calculations

and products of other available

modules;

• Calculation of dynamic

wetness index which accounts for

limited time available for water to

drain from upslope areas;

• Spectral analysis of DEM

surfaces to determine their fractal

dimension and, therefore, surface

roughness.

• Calculation of potential soil

erosion index based on several

terrain variables.

This software represents about 20 years

of dedicated research effort and is available as a public domain access with some

limitations. The models can provide estimates of the results of various environmental processes based on DEMs and

auxilliary data such a solar radiation file,

vegetation, and soil data. Preparation of

these additional data inputs is relatively

easy to accomplish based on existing data

sources. If there is enough interest in this

software, it is currently available as C and

FORTRAN source code which we can

compile for the AIX machines at the

BLM for use as contributed resource

analysis software that interfaces with the

ARC/INFO GIS and generates

ARC/INFO data.

At NARSC, we the see the function of

translating research into practical management as a common responsibility of

all the scientists at the BLM, but we also

realize that our various duties might not

give us time to get acquainted with the

latest tools. The START project is the

beginning of our contribution to making

access to these tools easier. For further

information on it and on related efforts

contact:

Jacek Blaszczynski

Physical Scientist

BLM NARSC RS-120

DFC Bldg. 50

Lakewood, Colorado 80225

Tel. (303) 236-5263 Range jblaszcz@blm.gov

Range

Range

Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

necessarily represent those of BLM. Use of trade names does not

imply U.S. Government endorsement of commercial products.

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