RESOURCE NOTES

NO. 7 DATE 06/09/99

Tools to Models:

Some Applications

of Automated

Resource Analysis

Tools for Ecosystem

Management.

by Jacek Blaszczynski

Physical Scientist

BLM NARSC

Models are essentially simplified

views of the processes that we

know to occur in Nature. They

often rely on several important

environmental parameters relevant

to the process being analyzed and a

simple “engine” which relates these

parameters to each other. For

example, the Universal Soil Loss

Equation (USLE) model relies on

six primary parameters which

reflect the influence on sheet and

rill erosion of rainfall intensity; soil

erodibility; slope gradient; slope

length; surface cover; and erosion

control practice factors. The values for each of the factors are

either measured or calculated and

fit into an equation developed

from statistical analysis of 104 plot

years of cropland studies. The

USLE model was also modified for

rangeland applications to create

the RUSLE, or the Revised

Universal Soil Loss Equation. The

USLE and the RUSLE are empirical models because their “engine”

is generated from statistical analyses of a large number of actual

experimental results. Other model

“engines” might work differently;

for example, calculating runoff values based on hydrologic equations.

Since models are essentially nothing more than their “engine” and

environmental data, they are

uniquely adaptable to being automated on computers. Then they

can be used to analyze large

amounts of data that otherwise

could not be easily reviewed. 

Whoever utilizes models has to be

aware that they probably will not

predict unique ecological circumstances that can be found on a specific parcel of land but provide

knowledge-based predictions of the

magnitude of the likely processes

that should be occuring in that

area. The accuracy of these predictions is directly dependent on the

quality of data. The most honest

description of modeled information is to present it as a result of a

certain logic and environmental

data combined using this logic

even in choosing our sampling

methods we are already modeling

because we are conceptualizing

what and how specific parameters

should be measured. A model can

be understood as a painting of

reality done with a limited number

of colors which should not be confused with reality itself.

Taking account of these facts,

NARSC is currently engaged in

combining various GIS functions

and tools into models to aid following ecosystem analysis efforts. 

1. Identification of Similar

Terrain Units (STUs)

This project is combining watershed delineation and watershed

morphometric parameter analysis

technology to derive similar areas

based on shape of terrain. It is

understood that particularly in

high relief locations the shape of

terrain has profound impact on

geomorphic, hydrologic, and other

ecosystem processes. Therefore,

subdivision of the land surface

according to terrain characteristics

should aid in finding transitional

zones in terrain and local ecosystems. The methods involve division of the project into miniwatersheds associated with individual reaches of a stream network.

The morphology of each minibasin is analyzed using morphometric parameters that describe each

basin. The basin morphometric

parameter values are then grouped

to indicate which of the miniwatersheds are morphologically

similar to each other.

Morphologically similar watersheds

are grouped in clusters that represent similar terrain characteristics

within the project area. The morphologically similar areas outlined

by groups of analogous watersheds

can be used to study ecologic

processes influenced by terrain

shape. These include the ecosystem processes of soil erosion and

sediment yield, surface and subsurface hydrology, solar irradiation,

and evapotranspiration.

2. Automated Erosion,

Runoff, and Sediment Yield

Models

Terrain analysis tools are directly

utilizable in development of GIS

interfaces to erosion, runoff, and

sediment yield models to aid prediction of the patterns of these

processes on large areas. One of

the main difficulties with application of soil erosion prediction tools

such as the RUSLE has to do with

being able to adequately account

for terrain variability in the modeled area. Various terrain analysis

capabilities, including basic watershed and flow delineation methods, can be utilized to improve the

predictive capability of RUSLE by

permitting measurement of this

variability. Beyond that data integration capabilities of GIS permit

rapid analysis of terrain, soil, and

vegetation data together to develop

Range

GIS and GPS
basin and Hydrologic Response

Unit (HRU) statistics required for

running of the National Resource

Conservation Service Curve

Number (NRCS CN) watershed

runoff model and Modified

Universal Soil Loss Equation

(MUSLE) for watershed sediment

yield prediction. All of these models help us to identify land management measures required to protect soil and water quality, both

major indicators of ecosystem

health.

Soil Survey Enhancement

Methods

Terrain analysis tools are important

for identification of various components of the geomorphic surface

of the landscape, including the

geometry of segments of hillslopes,

locations of stream reaches within

drainage networks, and the morphology of watersheds. Terrain

variability is one of the central factors influencing the development

and evolution of soils, so the soils

developed on different facets of

hillslopes differ from each other

and from soils developed in terrain

depressions or in the floodplains of

streams. Combining terrain information with soil and other multidisciplinary data permits further

refinement of existing soil surveys

which often contain two or more

related types of soils within a single

mapping unit. Mapping the distribution of these components and

inclusions will permit enhancement of existing soil surveys to a

higher degree of resolution. For

more information on soil survey

enhancement, contact Alan Amen,

Soil Scientist, BLM NARSC.

Linked Watershed Modeling

Streams, channels, and hollows

form drainages which are organized into drainage networks or

linked systems of streams and

watersheds usually identified by

their order in the network. A network includes streams and watersheds all the way from a major

topographic divide to the river

delta as it enters the ocean.

Processes within any subwatershed

or reach within a portion of a network can be modeled independently and as part of a linked

watershed system. In this way, it is

possible to subdivide and aggregate

the effects of various watershed

processes (e.g. erosion and sediment yield) throughout the network and calculate their cumulative impact on the landscape within the network. An example of

this type of analysis is provided by

the watershed data preparation

AMLs for the Hydrologic

Modeling System (HMS) of the

U.S. Army Corps of Engineers

which will be described in future

editions of Resource Notes.

We invite further suggestions as to

possible applications of resource

analysis tools and models to your

own projects. For futher information on the efforts describe above

contact:

Jacek Blaszczynski

Physical Scientist

BLM NARSC RS-120

DFC Bldg. 50

Lakewood, Colorado

(303) 236-5263

jblaszcz@blm.gov

Range

Range

Range

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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

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