AH 503 Wichmeier

8/11/2019 AH 503 Wichmeier

1/67

1

Ke^


2/67

U . S .

Departmentof

A f ^ '

Nat ionalAgricuJturalL..

Division

o f

L en d i n g

PRFDirTINC

^ ^ ' ^ ' ^ ' ' ^ ^ ' ^ ^ ' ^ ' ^

R A I N F A L L

E R O S I O N

LOSSES

A

GUIDE

TO

CONSERVATIONPLANNING

S u p e r s e d e s

AgricultureHandbook

N o .

282,

' 'Predict ing

R a i n f a l l - E r o s i o nLo s s e sF r o mC r o p l a n dE a s to f

the

R ocky

M o u n t a i n s

Sciencea n d

d u c a t i o n

Administration

UnitedS t a t e s

Department

of

Agriculture

in

o o p e r a t i o n

with

P u r d u e

griculturalxperiment

t a t i o n

U S D A

olicy

o e s

o t

ermitiscrimination

e c a u s efg e ,a c e ,o l o r ,

a t i o n a lrigin,e x,r

religion.nye r s o nho

e l i e v e s

e

r

he

a s

e e n

i s c r i m i n a t e d

g a i n s t

n

n y

SDA-related

activity

s h o u l d

write immediately

to

the

Se c r e t ar y

of

Agriculture, Washington, D. C. 20250.


3/67

A B S T R A C T

Wischme ie r ,

W.

.,

n d

mith,

.D .

978.

r e dict ing

a i n f a l l

ros ion

o s s e s a

g u i d eoo n s e r v a t i o nl a n n i n g .

.S.e p a r t m e n tfgr icul ture,griculture

H a n d b o o k

N o .

537.

The

Universal o il

os squation

USLE)

nables

lannerso

predictheaverageateofsoil

erosion

or a c h

easible

alter-

nativeombination

f

cropystemndmanagement

ractices

in

ssociation

with specifiedoil

ype,

ainfall

attern,

nd

topography.When

h e s e

redicted

osses

re

ompared

with

given

oil

os solerances,

hey

rovidepecificuidelines

or

effectingrosion

ontrol

within

pecified

imits

he

quation

groups

he

umerous

nterrelated

hysical

nd

anagement

parameters

hatnfluence

rosionatender

six

major

actors

whosesite-specific

values

can

e

expressed

numerically.

A

half

century

ferosionesearch

n

many

tates

a s

supplied

nfor-

mationromwhich teastpproximate

alues

f

heS LE

factors a n

e

obtainedorspecifiedarmieldsorothersmall

erosion

rone

reas

hroughout

he

United

tates.

ables

nd

charts

presentedn

his

handbookmake

his

nformationeadily

available

or

ield

s e.

ignificant

imitations

n

he

vailable

dataare

identified.

The

S LEs

an

rosion

model

designed

o

computeongtime

average

oilo s s e sromheetand

ill

rosionnderspecified

conditions.

t

s

also

useful

or

construction

i tes

and

other

non-

agricultural

onditions,

ut

t

o e s

ot

redict

eposition

nd

d o e sotcomputesediment

yields

rom

gully,

streombank,

and

streambederosion.

K e y w o r d s :

Conservationpractices,conservationillage,construc-

tion

i tes,

crop

canopy,

crop

e q u e n c e ,

delivery

atios,

ero-

sion

actors,

erosionndex,

rosionrediction,

rosionol-

erances,

rosivity,r o s s

rosion,

minimumillage,

o-till,

rainfall

characteristics,

ainfall

data,

esidue

mulch,

unoff,

sediment,

ediment

elivery,

lopeffect,

wateruality,

soilerodibility.

Forsaleby

theSuperintendent

ofDocuments,

U.S.

GovernmentPrintingO f l B i c e


4/67

C O N T E N T S

U.S.

i^gnT-*--.

/ . ..

NaionaM

''' W

D V i s i o nof''^^^'^

eitsWIie

..

Purpose

f

andbook

History

f

o il

o s s

quations

S o i llo s solerances

S o i l

o s squation

Rainfallnd

runoffactor

R )

Rainfall

erosion

index

Raluesorhawndnowmelt

SoilerodibilityactorK )

Definition

factor

Values

f

or

pecific

o i l s

S o i l erodibility

nomograph

0

Topographic

actor

(LS)

2

Slope-effect

chart 2

Slope-length

effect 4

Percent

slope

5

Irregular

slopes

6

Changes

ns o i lypeor

cover

along

he

slope

6

Equationoro il

etachment

o nuccessive

segments

of

a

slope

7

Coverndmanagement

actor

C ) 7

Definitionfactor 7

Cropstage

periods

8

Quantitative

valuations

f

crop

nd

management

effects

8

S o i lo s satios

0

E r o s i o nindexistribution

ata

1

Procedure

orerivingocal

alues

8

Support

racticeactor

P )

4

Contouring

4

Contourtripcropping 6

Terracing

7

Applying

he

o ilo s squation 0

Predictingroplando il

o s s e s

0

Determining

lternative

and

s e

and

reatment

combinations

2

Construction s i t e s 4

Estimating

upslope

ontributions

owatershed

ediment

yield

5

Accuracy

f

SL Eredictions

7

References 8

Appendix 0

Estimatingercentages

of

canopy

nd

mulchovers0

Probability

alues

fEl

n

he

nitedStates 0

Computingheerosion

ndexrom

ecording-rain

age

ecords

0

Conversion

to

metric

ystem

1

D 5


5/67

T A B L E S

1

. C o m p u t e d

values

or

oils n

erosionesearch

stations

2.Approximatevalues

of

he o ilerodibilityfactor,K,or 0benchmark

soi ls

nHawaii

3.Values of

he

opographicactor,

LS,

or

specific

ombinations of

lope

ength

and s t e e p n e s s

2

4.~Estimated

relative

oil losses

rom

u ccess iv eequal-length

egments

f niform

slope ......5

5.Rat io

of

soil

oss

from

cropland

o

corresponding

oss

from

continuous

fallow

2

5 A . - ~ A p proximo

te

soil

ossatiosorcotton 5

5- - B. Soi l

oss

atiosorconditions

not

evaluated

nable 6

5 C S o i l

ossatiospercent)forcropstage

4

whenstalksarechopped

and

distributedwithout

soil

illage

5- - D. Fac tors

o

credit

esidual

f fects

ofurned

o d 6

6. Perc entagesofheaverageannual lwhich

normally

ccu r s

between

January

and

he

ndicated

ates.Computedorhe

eographic

areas

hown

n

igure

.

8

7.MonthlydistributionofElatse l ec ted

ain

gageocations

9

8 . S a m p l e

working

able

or

derivation

of

otation

C

value

0

9. Mul c hactorsand

engthimits

orconstruction

lopes 1

10.Factor

C

value

or

permanent

pasture,

ange,

and

dle

and

2

1 1 .FactorC

valuesfor

undisturbed

orest

and 3

12.-Factor

Cor

mechanicallyprepared

woodland

i tes

4

13.Pvaluesandslope-length

imits

orcontouring *

14.P

values,

maximumstrip

widths,andslope-length

imits

or

contourstripcropping6

15.Palues

or

ontour-farmed

erracedields 7

16.Maximum

ermissible

C

values

T/RKLS)

or

R

= 80 ,

K=0.32,

and1

=

5

3

17.Observed

ange

and

0-,0-,

and ercent

probabilityvaluesoferosion

indexat

a c h

f

81

key

ocations

2

18.Expected

magnitudes

ofsingle-storm

Elndex

values 4

19.Kineticenergy

of

ainfall

expressed

noot-tonsperacrepern c hofain6

20.Kineticenergy

ofainfall

xpressed

n

metric

on-meters

er

ectare

er

entimeters

ofain

.6

F I G U R E S

1.Average

annual

alues

of

he

ainfall

rosion

ndex

map)

e

tween

ages

and

2. Est i matedaverageannualvalues

of

herainfall

erosionndex

n

Hawaii

3,The

soilerodibilitynomograph

1

4.Slope-effect

chart topographic

actor,

S ) ...

3

5.Influence

of

vegetative

canopy

n

effective

El

values

9

6.Combined mulchnd

anopy

f fectswhenaverageall

istancef

rops

from

canopy

o

he

ground

s

about

0

nc hes

9

7.Combinedmulchndanopy

f fects

whenverage

all

istance

f

rops

fromcanopyohe

ground

sabout

0

nc hes 9

8.Typical

l-distribution

curves

orhree

ainfall

atterns 7

9.Keymap

or

selectionof

applicable

El-distribution

data

romable 7

10. Rel a t i on

of

percent

coverodryweightof

uniformly

distributedesidue

mulch0

11. Sl ope- ef fec t

chart

or

metric ystem 8


6/67

PREDICTING

R A I N F A L L

EROSION

LOSSES

A

GUIDE

TOC O N S E R V A T I O NP L A N N I N G

WaiterH.

Wischmeier

ndDwight.Smith ^

PURPOSE

FA N D B O O K

Scientific

lanningoro ilndwateronserva-

t i o n

equires

nowledge

of

he

elationsetween

t h o s e

actors

hat

causeo s sofo ilndwaterand

t h o s e

hatelpo

educe

uch

o s s e s .

ontrolled

studiesnieldlotsndmallwatershedsave

supplieduch

aluable

nformationegarding

these

omplexactor

nterrelations.ut

he

reat-

e s t

ossibleenefits

rom

uchesearch

an

e

realized

nly

when

he

indings

re

onverted

o

sound

ractice

n

he

umerousarmsandther

erosionrone

reashroughouthe

ountry.

pe-

cificuidelinesre

eeded

orelectinghe

on-

trol

ractices

est

suited

o

he

articularneeds

f

each

site.

The

o ilo s s

rediction

rocedure

resented

n

this

andbook

rovides

uch

uidelines.

he

ro-

cedure

ethodically

ombines

esearchnforma-

t i o n

rom

any

o u r c e soevelop

esign

ata

forach

onservation

lan.

Widespread

ield

x-

perience

or

more

han

wo

decades

as

roved

t

highlyaluable

as

a

onservationlanninguide.

Theprocedure

is

founded

o n

anempirical

s o i lo s s

equation

hatselieved

o

e

pplicable

wher-

everumericalaluesftsactorsrevailable.

R e s e a r c h

has

uppliednformationrom

which

t

least

pproximate

alues

of

hequation'sactors

can

e

btainedor

pecific

arm

ieldsr

ther

small

and

reas

hroughoutmost

fhenited

States.

ables

nd

harts

resented

n

his

and-

book

make

his

nformation

eadily

vailable

or

field

u s e .

This

evision

fhe

965andbook64)pdates

the

content

and

ncorporates

newmaterial

hat

has

been

vailable

nformally

r

rom

cattered

e-

search

eports

n

rofessionalournals.

ome

f

theriginalhartsnd

ablesreevised

oon-

form

ith

dditional

esearch

indings,

nd

ew

ones

re

eveloped

oxtendhe

sefulness

f

theo ilo s squation.n

ome

nstances,xpand-

ing

able

orchart

ufficientlyomeetheeeds

for

widespread

ieldpplication

equiredrojec-

tion

fmpirical

actorelationships

ppreciably

beyond

he

hysical

imitsf

he

ata

romwhich

the

elationshipswere

erived.

stimates

btained

in

his

manner

re

he

est

nformation

vailable

for

heonditions

hey

epresent.

owever,

he

instances

re

dentifiednheiscussions

f

he

specificrosion

actors,

ables,ndharts.Major

research

eedsreuggested

yhese

iscussions

and

ere

ecently

ummarized

n

n

vailable

publication

y

Stewartandthers42).

HISTORY

F

OIL

OSSQ U A T I O N S

Developing

quations

o

alculate

ield

o il

o s s

beganbout

940

n

he

ornelt.heo ilo s s

estimatingrocedure

eveloped

nhat

egion

between 1940

and 1956 has been generally re-

^

Retired.ormer

esearch

tatistician

water

anagement).

ci -

ence

nd

ducation

dministration

SEA),

nd

rofessormeritus,

agriculturalngineering,urdueniversity,

est

afayette,nd.;

and agricultural

engineer,

SEA,

Beltsville,

Md.

ferred

o

as

he

lope-practice

method.

ingg

64)^

publishednquationn

940elatingo il

o s s

rateoengthandercentageof

slope.

The

ollow-

ing

ear.

mith38,

9)

dded

rop

and

onserva-

tionracticeactors

nd

he

oncept

fpecific

s o i ll o s simit,

oevelop

raphical

methodor

Numbers

n

arentheses

refer

o eferences

p.

8.


7/67

UNITED

T A T E S

EPARTMENT

F

GRICULTURE,AGRICULTURE

ANDBOOKUMBER37

determiningonservationracticesnhelbynd

associated

o i l s

f

heMidwest.

rowningnds-

sociates

)

dded

o ilnd

anagement

actors

and

repared

e tof

ables

o

implifyields e

of

he

quation

n

owa.

esearch

cientistsnd

operationsersonnel

f

he

oilonservation

Ser-

vice

S C S )n

heorthentral

tates

workedo-

gether

n

eveloping

he

lope-practice

quation

for

u s ethroughout

theCornBelt.

A

ational

ommittee

et

nhion

946

o

adapthe

Corneltquationoroplandnther

regions.

hi s

ommittee

eappraised

heorn

elt

factoraluesnd

dded

ainfall

actor.

he

resulting

ormula,

enerally

nownsheus-

grave

quation

31),

as

een

idelysed

or

estimatingrossrosionromwatershedsnlood

abatementrograms.

raphical

olutionf

he

equation

wasublished

n

95219)

andsed

y

the

SC S

n

he

Northeastern

States.

The

o ilo s s

quation

resented

nhisand-

book

as

ecome

nown

sheniversaloil

L o s s

quation

U S L E ) .

egardless

f

hetherhe

designation

sully

ccurate,

he

ame

oes

is-

tinguish

his

quationrom

heegionallyased

s o i lo s sequations.TheSL Ewasdevelopedathe

National

unoffndoil

o s s

ata

enter

stab-

lished

n954y

he

cience

nd

ducation

d-

ministration

formerlygricultural

esearcher-

vice)

n

ooperation

with

urdueniversity.

ed-

eral-State

ooperative

esearchrojects

t

9o-

c a t i o n s ^

ontributed

more

han

0,000

plot-years

of

basic

unoff

ndo ilo s s

ataohisenter

or

summarizingnd

verall

tatisticalnalyses.

fter

1960,

ainfall

imulators22)perating

rom

ndi-

ana,

Georgia,

Minnesota,

andNebraska

were

used

onieldlots

n16

states

o

fillome

of

hegapsn

the

ata

eeded

or

actor

valuation.

Analysesfhisargessemblyfasic

ata

provided

everal

major

mprovements

orhe

o il

l o s squation

53):a)

ainfallrosion

ndex

evaluated

rorn

ocal

ainfallharacteristics;b)

quantitativeo ilrodibilityactor

hat

sevaluated

directly

rom

o ilroperty

data

andsndependent

of

opography

nd

ainfallifferences;

c)

method

f

valuating

ropping

nd

management

effectsnelationo

ocal

limaticonditions;nd

(d)

method

f

ccounting

or

ffectsof

nterac-

tions

etween

rop

ystem,roductivity

evel,

ill-

age

ractices,

ndesiduemanagement.

Developmentsi n c e

965

haveexpandedhe

u s e

of

he

o il

o s s

quation

y

roviding

echniques

for

stimating

ite

alues

f

ts

actors

or

ddi-

tionalands e s ,

limatic

conditions,

ndmanage-

ment

ractices.

hese

avencluded

o il

rodi-

bilityomographor

armland

nd

onstruction

areas

58);

opographic

actors

or

rregular

lopes

(72,5);

over

actors

orangendoodland

(57);

over

ndmanagementffects

fonserva-

tion

illage

ractices54);rosion

redictionn

construction

reas61,4,

5);

stimated

rosion

indexalues

or

he

Western

tates

ndawaii

(5,

,

5);o ilrodibilityactors

or

enchmark^

Hawaiio i l s9);and

mprovedesignand

valua-

tion

of

rosioncontrol

support

practices

7,6).

Research

s

ontinuing

with

mphasisonobtain-

ing

etternderstanding

f

he

asicrinciples

and

r o c e s s e s

f

water

rosion

nd

edimentation

and

evelopment

fundamental

models

apable

of

redicting

pecific-stormo il

o s s e sndeposi-

tion

y

verland

iow

JO ,

7,

2,

6,

2).

he

fundamental

modelsave

eenelpful

or

nder-

standing

heactors

nhe

ield

o il

o s s

quation

and

or

nterpreting

he

plotdata.

SOIL

O SS

O L E R A N C E S

The

erm

soil

o s solerance

enotes

hemaxi-

mumlevelfo ilrosion

hatwillermit

igh

level

of

crop

productivity

to

be

sustained

eco-

nomicallyandndefinitely.

^

The

ataereontributed

y

ederal-Stateooperativee-

searchrojects

the

ollowing

ocations:

atesville,

rk.;

ifton

and

atkinsville,

a.;

ixon

prings,

oliet,

nd

rbana,II.;a -

fayette,

nd.;

larinda,

astaa,eaconsfield,ndependence,nd

Seymour,owa;

ays,

ans.;aton

ouge,

a.;

resque

sle,

Maine;

Bentonarbor

nd

a s t

ansing,

ich.;

orris,

inn.;

olly

Springs and State

College,

M i s s . ;Bethany

and

McCredie, Mo.;

Hastings,

ebr.;

eemerville,

arlboro,

nd

ew

runswick,.J.;

Ithaca,

eneva,

nd

Marcellus,

.Y.;

tatesville

nd

aleigh,

.C.;

Coshocton

nd

anesville,

hio;herokeenduthrie,

kla.;

Stateollege,a.;

lemsonnd

partanburg,

.C.;adison,

S.Dak.;

noxvillend

reeneville,

enn.;emple

ndyler,

ex.;

Blacksburg,

a.;ullman,

ash.;

aCrosse,

adison,nd

wen,

Wis.;and

Mayaguez,

.R .


8/67

PREDICTING

AINFALLROSION

OSSES-A

GUIDE

O

ONSERVATION

PLANNING

The

major

purposeofthe

o il

o s sequation

s

o

ethodical

ecisionmaking

n

onservation

n ite

asis.he

quation

nables

lanner

oredict

he

verageate

fo il

or

ach

f

arious

lternative

ombina-

ofcrop

system,

management

echniques,

and

ractices

on

any

particular

site.

When

hese

o s s e saneompared

with

o ilo s s

or

hat

ite,

hey

rovidepecificguide-

or

ffectingrosionontrol/ithinhepec-

imits.nyroppingnd

managementom-

orwhichhepredictederosion

rate

se s s

he

olerance

ayexpected

orovide

rosion

ontrol.

rom

heatisfactory

ndicated

y

his

rocedure,

he

ne

uitedo articular

arm

r

thernter-

may

thenbeselected.

S o i l

o s s

olerances

ranging

rom

5

o

2

t/A/year

heo i l s

fhe

nited

tates

wereerived

y

cientists,

gronomists,

eologists,

oil

on-

nd

ederal

ndStateesearch

ead-

rst

ix

egionalorkshops

n

96 1nd

962.

onsidered

n

defininghese

imits

ncluded

epth,

hysical

ropertiesnd

therharac-

ffectingootdevelopment,ully

reven-

n-field

edimentroblems,

eeding

o s s e s ,

rganicattereduction,

nd

lantutrient

eep,medium-textured,

moderately

er-

o il

hat

as

ubsoil

haracteristics

avor-

or

plant

growthhasa

reater

olerance

han

withhallow

oot

ones

righ

ercentages

hale

t

he

urface.idespreadxperience

shown

heseo ilo s solerances

o

eeasible

enerally

dequate

or

ustaining

igh

ro-

evels

ndefinitely.

omeo i l s

with

eep

favorable

oot

zones

mayexceed

he5-tolerance

without

o s sof

sustainedroductivity.

Soil

o s s

imits

re

ometimesstablishedri-

marily

or

water

uality

ontrol.

he

riteriaor

definingieldo il

o s simitsor

his

urpose

re

not

heames

hose

or

olerances

esigned

o

preserve

roplandroductivity.

oilepth

s

ot

relevantor

ffsite

ediment

ontrol,ndniform

limits

nrosionateswillllow

ange

nhe

quantities

f

ediment

er

nit

rea

hat

re

e-

livered

oa

iver.

Soil

material

eroded

rom

a

ield

slopemayedepositednhe

ieldoundaries,n

terracehannels,nepressional

reas,

r

nlat

or

vegetated

areas

raversed

y

he

overland

low

before

t

reaches

a

iver.

The

erosion

amageshe

cropland

n

hichtccurs,

utedimente-

posited

eartslaceoforiginsotdirectlyele-

vant

for

water

quality

control.

Ifhe

o il

o s s

olerance

esigned

orustained

cropland

roductivityails

o

ttain

he

esired

water

quality

standard,

lexibleimitshat

consider

otheractorshouldeeveloped

ather

han

uniformlyoweringheo il

o s s

olerance.

hese

factorsncludeistancefheieldrommajor

waterway,heediment

ransport

haracteristics

of

he

nterveningrea,

ediment

omposition,

needs

f

hearticular

odyf

waterbeingro-

tected,andheprobablemagnitude

of

luctuations

in

ediment

oads

42).

i m i t s

f

ediment

ield

wouldrovide

ore

niformater

uality

on-

trol

han

oweringheimits

no il

ovement

fromield

lopes.

hey

wouldlso

equire

ewer

restrictions

nropsystemelectionor

ieldsrom

which

nly

mallercentages

f

he

roded

o il

becomeoff-farmsediment.

SOIL

OS S

Q U A T I O N

Therosionate

tiven

ite

setermined

he

articular

way

n

which

he

evels

n

u-

hysical

ndanagementariables.

are

that

ite.

hysical

easurementsf

o s sorach

f

he

arge

numberf

ossible

n

which

he

evelsf

hese

ariable

an

ccur

nder

ield

onditions

would

ot

eeasible.o ilo s squations

were

evelopedo

onservationlannersorojectimited

ata

o

he

many

ocalitiesndonditions

aveoteen

irectly

epresentednhee-

TheSL E

snrosion

model

esigned

o

re-

dict

he

ongtime

verage

o il

o s s e s

n

unoff

frompecific

ield

reas

n

pecified

ropping

nd

management

ystems.

idespread

ield

s eas

substantiated

ts

sefulnessndalidity

orhis

purpose.

tslsopplicable

or

uch

onagricul-

tural

conditionss

onstruction

i t e s .

With

ppropriateelection

f

ts

actor

alues,

theequationwill

ompute

he

average

o ilo s s

or

amulticropsystem,oraarticular

cropyearn

rotation,or

for

a

articular

cropstageperiodwithin

a

rop

ear.

t

omputes

heo il

o s s

oriven


9/67

UNITED

TATES

E P A R T M E N T

F

G RICULTURE,G RICULTURE

ANDBOOK

U M B E R37

site she

product

ofsixmajor

actors

whosem o s t

likely

alues

t

articularocationan

e

x-

p r e s s e d

umerically.

rosion

variableseflected

by

these

actors

varyconsiderablyaboutheirmeans

from

torm

otorm,ut

ffects

f

he

andom

end

o

verage

ut

ver

xtended

periods.e c a u s e

f

he

npredictable

hort-time

n

he

evels

f

nfluential

ariables,

hov/ever,

resent

oilos s

quations

re

ubstan-

essaccurateor

prediction

f

specificevents

or

redictionfongtimeverages.

The

soillossequation

is

A=:RKLSCP

0)

s

hecomputed o iloss

per

unit

area,express-

edn

he

units

elect ed

or

K

andor

he

peri-

od

elect ed

or

.

n

ractice,h e s e

ares u -

allyoelect edhat

heyompute

n

o n s

percreer

ear,

utthernitsa ne

select ed.

he

ainfallandunoff

actor,s

henumberof

rainfallrosion

ndex

nits,lus

actor

or

runoff

rom

snowmelt

or

applied

water

where

s uch

unoff

issignificant.

K,

heo ilrodibility

actor,

s

heo ilossate

per

rosion

ndex

nit

or

specified

o il

s

measured

n

nitplot,

which

sdefined

s

a

2.6-ft

ength

f

niform

-percentlope

continuouslyn

clean-tilledallow.

,

he

lope-length

actor,s

heatio

f

o ilos s

from

hefieldslopeength

o

that

from 2.6-

ft

ength under

denticalonditions.

,

helope-steepnessactor,

she

atio

f

o il

loss

rom

he

field

slope

gradiento

hat

rom

a-percentlope

nder

therwise

dentical

conditions.

he

over

nd

managementactor,

she

atio

ofsoil

os s

rom

n

areawith

pecified

cover

and

anagement

ohat

rom

n

dentical

area

nilledcontinuousallow.

he

upport

ractice

actor,

s

he

atio

fo il

loss

with

upportractice

ike

ontouring,

stripcropping,

rerracingohatith

straight-rowarming

p

andown

he

slope.

The

oil

os s

quationnd

actor

valuation

charts

ere

nitially

eveloped

n

ermsfhe

Engl i shnits

commonly

s e d

nheUnited ta tes.

Theactordefinitions

arenterdependent,

ndi-

rec tonversionfc r e s ,ons,n c h e s ,nd

eeto

metricunitswouldnotproducethekindofintegers

thatwouldeesirableor

an

xpression

f

he

equation

n

hat

s y s t e m .

Therefore,

only

the

Engl ish

unitsre

s e d

nhenitial

resentation

f

he

equation

ndactorvaluation

aterials,

nd

their

counterparts

nmetric

units

are

given

n

he

Appendix

nder

o n v e r s i o n

o

etr icy s t e m .

Numericalaluesor

ac hf

heix

actors

were

erived

rom

nalyses

f

he

ssembled

e -

searc h

ata

nd

rom ational

Weather

ervice

precipitationecords.

or

most

onditions

nhe

United

ta tes,he

pproximate

aluesof

he

ac-

tors

or

anyparticular

it e

may

e

obtained

rom

charts

nd

ables

nhisandbook.ocalitiesr

countrieswhere

he

ainfallharacteristics,oil

types,

opographic

eatures,

r

arm

ractices

are

substantially

eyond

he

ange

fresent.S .

data

willind

h e s e

charts

nd

ables

ncomplete

anderhapsnaccurateorheir

conditions.

ow-

ever,

hey

will

provide

guidelines

hat

a n

educe

the

mount

f

ocal

esearch

eeded

o

evelop

comparable

charts

andables

or

heirconditions.

The

subsectionn

P r ed i ct i ngC r o p l a n d

Soi lLo s s -

e s ,age

0

llustrates

ow

o electactor

values

from

he

ablesandcharts.Readerswho

have

had

n o

experience

with

he

o il

oss

equationmay

wish

toeadhat ect ion

irst.

After

hey

have

eferred

to

he

ablesnd

igures

ndocated

he

alues

u s e d

n

hesample,heymay

move

eadily

o

he

intervening

etailed

iscussions

f

he

quation's

factors.

The

soil

os s

rediction

rocedure

s

more

valu-

able

s

guide

forselectionofpracticesif

the

s er

ha s

eneral

nowledge

f

he

rinciples

nd

factor

nterrelations

n

hich

he

quation

s

based.

Therefore,he

significance

of

a c h

actor

s

d i s c u s s e d

efore

resentingheeference

abler

chart

rom

which

ocalaluesmaye

btained.

Limitationsof

he

data

available

orevaluation

of

s o m e

ofhe

actors

are

also

pointed

out.


10/67

PREDICTING

R A I N F A L L

E R O S I O N L O S S E S - AGUIDEO

O N S E R V A T I O N PLANNING

R A I N F A L LANDU N O F FA C T O R

R )

Rillsnd

ediment

eposits

bserved

ftern

unusually

ntensestorm

ave

sometimes

e do

he

c onc l us i onhat

he

significanterosions

associated

withonly ew

storms,

or

hatt

s

solely unc-

tionfeak

ntensities.

owever,morehan0

years

of

measurements

n

many

S t a t e s

have

shown

that

hiss

othe as e

5 1 ) .he

atashow

hat

a

ainfall

actor s ed

oestimate

average

nnual

soil

ossmustncludehe

cumulative

f fectsofthe

many

moderate-sized

storms, swell she f fects

o fthe

occasionalsevereo n e s .

The

umerical

alue

s edor

n

he

oil

oss

equationmust

quantifyhe

aindrop

mpact

effect

a n d

must

alsorovide

elativenformation n

he

amount

ndate

of

unoff

ikelyo

e

associated

withhe

ain.

he

ainfall

rosionndexerived

by

Wischmeier49 )

appearso

meet

h e s e

equire-

m e n t s

etter

han

ny

ther

f

he

many

ainfall

parameters

nd

roupsf

arameters

ested

against

he

ssembled

lot

ata.

he

ocal

alue

of

his

ndexenerallyquals

or

he

o il

oss

equationndmay

ebtained

irectlyrom

he

map

n igure. owever,he

ndex

o esotn-

cludeheerosiveorcesofunofffromhaw,

snow-

melt,

r

rrigation.

rocedureor

valuating

for

ocations

wherehis

ypeofunoffssignificant

will

e

iven

nderheopic V a l u e s

or

Thaw

andS n o w m e l t .

Rainfall

r o s i o n

ndex

Th e

esearch

ata

ndicate

hat

when

actors

other

han

ainfall

re

eld

onstant,

torm

oil

lossesrom

ultivated

ieldsre

irectly

ropor-

tionalo ainstorm

arameter

dentified

s

he

El

defined

below)

49).

he

elation

f

soil

os s

o

thisarameter

s

inear,nd

ts

ndividualtorm

V alues

aredirectlyadditive.

he

u m

fhe

storm

E l

alues

or iveneriods umericalmea-

su r eofheerosive

otentialof

he

ainfall

within

thatperiod.

The

average

annual

otal

of

he

storm

E l

valuesn particularocality

s

heainfallero-

s ionndexor

hat

ocality.

e c a u s e

fpparent

cyclical

patterns

n

ainfalldata

33),

he

published

rainfallrosion

ndex

alues

wereasedn

2 -

yearstationrainfallrecords.

Rain

howersfes s

han

ne-half

nc hnd

separated

rom

therain

eriods

ymorehan

6

ours

eremittedrom

he

rosion

ndex

computations, nless

s

m u c h s0.25

nofain

ell

in

5

min.ExploratoryanalysesshowedhatheEl

values

or

uc h

ains

re

sually

oomall

or

practical

ignificance

nd

hat,

ollectively,

hey

have

ittle

ffect

n

onthly

ercentages

f

he

annual

l.

heo s t

f

bstracting

nd

nalyzing

4,000

ocation-yearsofainfall-intensity

atawas

greatly

educedy

adopting

he.5-in

hreshold

value.

ElParameter

By

efinition,

he

value

f

lor

iven

ain-

stormquals

he

roduct,

otal

torm

nergy

E)

times

he

maximum

0-min

ntensity

I30)/

where

is

n

undreds

f

oot-tons

er

acre

nd

3 0

s

n

inch eser

our

in/h).

ls

n

bbreviationor

energy-times-intensity,

andheermhouldot

e

considered

imply

an

nergyparameter.

he

data

show

hatainfall

energy,

tself,-is

not

ood

n-

dicatorferosive

otential.

he

torm

nergy

n-

dicateshe

olume

f

ainfall

nd

unoff,

ut

long,slow

ain

may

ave

he

a m e value s

shorter

aintu c h

igher

ntensity.aindrop

erosion

ncreases

with

ntensity. he

3 0component

indicates

he

rolonged-peak

ates

f

etachment

and

unoff.

heroducterm. l,s tatistical

interactionerm

hat

efiects

howotal

energyand

peak

nensityre

ombinedn

a c h

articular

storm.Technically,tndicates

how

particle

detach-

ment

scombined

withransportcapacity.

Th energy f ainstorm

s

unction

f

he

amount

of

ain

nd fall

he

torm's

omponent

intensities.edianaindrop

iz e

n c r e a s e sith

rain

ntensity

2),

nd

erminal

elocitiesof

ree-

falling

waterdrops

ncrease

with

ncreasedrop-

s ize

7 3 ) .

ince

he

energy

of

given

m a s s

n

o -

tion

sroportional

o

elocity-squared,

ainfall

energy

s

irectlyelatedo

ain

ntensity.he

relationship

sexpressed

y

heequation,

E=:

916+3 3 1

ogio,

(2 )

where

s

inetic

nergynoot-tons

ercre-

inchnd

s

ntensity

nnc hes

er

our62).

limitof n/h

smposed

n

y

he indinghat

median

ropsize

o e s

otontinueo

ncrease

whenntensitiesexceed n/h

7 ,5 ). he

energy


11/67

FIGURE1 . ^ A v e r a ge

n n ua l

v a l u e s

f

hea i n f a l l

rosion

n d e x .


12/67

UNITED

TATES

E P A R T M E N T

F

G RICULTURE, AG RICULTURE

ANDBOOKUMBER

37

of

ainstorm

s

omputed

rom

ecording-rain

gage

data.

Thestorm

sdivided

nto

uc c ess i ven-

crements

f

ssentially

niformntensity,

nd

rainfallnergy-intensity

able

erived

rom

he

above

ormula

app.,

able 9)

s

s e d

o

compute

the

energyore a c hncrement.B e c a u s ethe

energy

equationndnergy-intensity

ableave

e e n

frequently

ublished

ith

nergy

xpressed

n

foot-tonser

cre-inch,

hisnit

was

etained

n

table

9.

owever,

oromputation

f

lalues,

storm

energy

s

expressed

n

hundreds

of

oot-tons

peracre.

Therefore,

energies

computed

by

the

pub-

lishedormula

or

able

9must e

dividedby 00

before

multiplying

by3 0

o

compute

E.)

I s o e r o d e n tMaps

L o c a lvalues

f

he

ainfall

rosion

ndex

may

be

taken

directly

fromhe

soerodent

maps,figures

I

nd

.

he

plotted

ines

n

he

maps

are

called

isoerodentse c a u s e

heyonnectoints

f

qual

rainfallerosivity.Erosi onndex

valuesfor

ocations

between

heines

re

obtained

y

inearnterpo-

lation.

Thesoerodent

map

n

heriginalersionf

this

handbook(64)

was

developed

from

22-year

s t a-

tion

ainfall

ecordsbycomputingheElvalueor

e a c h

torm

hatmet

he

previously

definedhresh-

old

criteria.soerodents

were

then

ocated

between

t hese

point

valueswithhe

help

of

published

ain-

fall

ntensity-frequency

ata

47 )

and

opographic

maps.

he

1

estern

tatesweremitted

rom

thenitial

ap

e c a u s eheainfall

atterns

n

this

ountainous

egion

re

poradic

nd

ot

enoughong-term,

ecording-rain

age

ecords

wereavailableoestablish

aths

of

equal

erosion

index

values.

The

soerodent

mapwasextendedohe

Paci f ic

Coast

n

97 6

y

s e

fon

estimating

rocedure.

Resultsofnvestigationsatthe

Runoff

and o il os s

DataCenter

at

Purdue

Universityshowedhathe

known

erosion

ndex

alues

n

he

Western

Plains

and

orth

Central

tatesouldepproximated

with

easonable

ccuracy

yheuantity

7 . 3 8

p2.i7^

where s

he

-year,-hainfall

mount

(55) ,

his

elationship

as

s e d

ith

ational

Weatherervice

sopluvial

maps

opproximate

erosionndexalues

or

he

Western

tates.

he

resulting

soerodents

areompatible

with

he

ew

pointvalueshatade e n

stablished

withinhe

II

Western

tatesand

a n

rovide

helpfulguides

foronservationlanning

n

iteasis.

ow-

ever,

hey

re

ess

recise

hanh o s eomputed

forthe37-Statearea,

wheremoredatawereavail-

able

nd

ainfall

atterns

re

ess

rotic. lso,

linear

nterpolations

etween

heines

willot

alwayseccuratenmountain

egionse c a u s e

values

f

he

rosion

ndexmay

hange

ather

abruptly

with levationhanges.he

point

values

thatwereomputed

irectly

rom

ong-term

ta -

tion

ainfallecordsnhe

Western

tates

re

n-

cludedn

able

7 ,

s

eference

points.

Figure

waseveloped

y

computing

hero-

s ionndex

forfirst-order

weatherstations

inHawaii

anderivinghe

elation f

h e s ealues

o

a-

tional

Weather

Service

ntensity-frequencydata

or

the

ive

ajorslands.

When

heresent

hort-

term,

ainfall-intensityecordsave

e e n

uffi-

cientlyengthened,

more

pointvalues

of

the

ndex

should

be

computed

by

the

tandard

procedure.

Figure

howshatocal,verage-annualal-

uesof

he

rosion

ndexn

he

8

onterminous

Sta tesangeromesshan0

omorehan0 0.

Th e

erosion

ndexmeasureshecombined

effect

of

rainfall

ndts

ssociated

unoff.fheoil

nd

topography

were

xactly

heameverywhere,-

averageannual

oilo sse s

rom

lotsmaintained

incontinuous

allow

would

differndirectpropor-

tion

o

heerosion

ndex

values.However,

his

po-

tential

ifference

sartiallyffsetyifferences

in

soil,

topography,

vegetative

cover,

and

esidues.

On

ertile

oils

n

he

ighainfall

reas

f

he

Southern ta tes,

ood

egetaloverrotects

he

soilurfacehroughout

o s t

fhe

ear

nd

heavy

lantesiduesmayrovideexcellent

cover

also

uring

he

ormant

e a s o n .

n

heegions

whereheerosionndexsextremelyow,ainfall

is

seldom

adequateorestablishingannualmead-

owsand

hecover

providedby

othercropss

often

for

elatively

hort

eriods.enc e,erious

oil

erosion

azardsxist

n

semiaridegionsswell

as

n

humid.

F r e q u e n c y

i s t r ibut ion

The

soerodent

opsresent

2-year-average

annualvalues

of

Elor

the

delineated

areas.

How-

ever,bothhe

annual

andhemaximum-stormval-

uesat

aparticularocationvary

from

year

to

year.

Analysis

f

81tation

ainfallecords

howed

thathey

end

oollow

og-normal

requency

dis-

tributions

hat

are

usually

well

defined

bycontinu-


13/67

PREDICTING

AINFALLROSION

LOSSES-A

GUIDE

O

ONSERVATIONPLANNING

us

ecords

from

0

o25

ears

49).

ables

f

probabilities

of annual andmaximum-

R

V a l u e s

o r

Tha w

Thetandard

ainfall

rosion

ndexstimates

rosive

orces

fhe

ainfall

ndtsirectly

runoff.nhePacificNorthwest,asmuch

s

0

ercent

fhe

rosion

n

he

teeplyolling

asbeenstimated

o

derive

rom

un-

ssociated

s ^ i t h

urface

hawsnd

nowmelt.

ypefrosion

s

otccountedor

y

he

rosionndex

ut

s

onsidered

ither

pre-

or

appreciable

nmuch

ofhe

Northwest

n

ortionsfhe

entral

Western

tates.

recipitationelationshipwouldotccount

peak

o s s e s

n

earlyprinigecause

a s

he

win-

rogresses,

heo il

ecomes

ncreasingly

more

as

he

o il

moisture

rofile

s

eing

illed.

storm

l

alues

t

he81

locations

re

resented

in

theappendix

(tables

17

and

18).

a n dn o w m e l t

the

urfacetructure

seing

rokenowny

repeated

reezing

nd

hawing,

nduddling

andurfaceealingreakinglace.dditional

researchfhe

rosion

r o c e s s e sndeansf

controlnder

heseonditions

s

rgentlyeeded.

In

he

eantime,

hearly

pring

rosion

y

runoff

rom

nowmelt,haw,

r

ightain

n

ro-

zen

o ilmay

e

ncluded

nhe

o il

o s s

computa-

tionsy

dding

ubfactor,g ,

oheocation's

erosion

ndex

obtain

R.

nvestigationsofimited

data

ndicatedhatnstimatef

g

may

e

b-

tainedyaking.5

imes

he

ocal

ecember-

through-March

recipitation,easured

snches

of

water.

F o r

example,

a

location

in

the

North-

M A U l

K A U A I

O A H U

MOLOKAI

FIGURE

2 . E s t i m a t e d

v e r a g e

n n u a l

al ueso f

he

a i n f a l l

ros ion

n d e x

n

a w a i i .


14/67

NITED

TATE SEPAR T MEN TF

G R I C U L T U R E ,

A G R I C U L T U R E

A N D B O O K

U M B E R

37

hatas

n

rosion

ndex

f0

fig.

)

verages

2nfrecipitation

etween e-

ndMarch1wouldhave

an

estimated

annual of.5 (1 2)

+

20 ,or

8.

This

type

of runoff

may

also

be

a

significant

factornhe

orthern

ier

of

Centralnd

astern

Sta tes.Wherexperiencendicates

his

o

e

he

c a s e ,

t

hould

e

ncluded

n

nd

lso

n

he

erosion

ndex istributionurves

s

llustrated

n

p a g e

27.

SOILRODIBIUTYA C T O RK)

Th e

eaning

f

heerm

soil

rodibility"

s

different

rom

hatof

he

ermsoil

ero-

he

ate

f

o ilrosion.

,n

he

oil

os s

maye

nfluenced

morey

and

lope,

haracteristics,

over,

nd

management

y

nherentroperties

f

heoil.

owever,

oils

rodemore

eadily

hanthers

ven

ll

theractors

re

he

a m e .

his iffer-

aused

yroperties

f

he

o il

tself,

s

e -

osheo il

rodibility.everal

arly

t-

were

made

o

determine

criteria

or

c i en-

lassifications

foilsccording

o

rodibility

,

8,28 ,

5 ),

ut

classifications

s e d

orerosion

were

only

elative

ankings.

Differences

nheatural

susceptibilities

of

oils

Definit ion

Theo il

rodibility

actor,

,

nhe

S LEs

aluexperimentally

etermined.

or

articular

soil,t

s

he

ate

of

o il

ossper

ero-

ndex

unit

asmeasuredon

"unit"

plot,which

as

e e n

arbitrarily

defined

s

ollows:

A

unit

plot

s

2 .6

t

ong,with

uniform

ength-

slopeof percent,ncontinuous

fallow,

illed

nddown

he

slope.

Continuous

fallow,

or

this

s

andhat

as

e e n

illed

and

kept

ree

egetation

ormorehan

ears.

uring

he

eriodof

so i l

oss

measurements,the

plot

splowed

laced

n

conventional

corn

seedbed

condition

pring

nd

s

illed

s

eededo

revent

vegetative

rowthnd

evereurface

rusting.

hen

allof

h e s e

conditionsare

met, , ,C,and

P

a c h

equal

.0 ,

and

equals

A/El.

The 2 .6

tength

and

percent teepnesswere

select ed

s

a s e

alues

or,

,nd

e c a u s e

they

re

heredominant

slope

engthnd

about

the

average

radient

nwhich

ast

erosion

mea-

to

rosion

re

ifficult

o

uantify

rom

ield

b-

servations.

ve n

soil

with

elatively

ow

erodi-

bilityactor

ay

howi gnsf

eriousrosion

whent

c c urs

n

ong

rteepl opesr

n

o -

calities

ithumerous

igh-intensityainstorms.

A o ilwith

high

natural

erodibility

factor, nhe

other

hand,

may

show

ittle

evidence

of

actual

ero-

s ionnder

gentle

ainfallwhen

t

c c urs n

hort

andgentle

lopes,

or

when

he e s t

possible

man-

agement

s

racticed.

he

f fects

ofainfalldiffer-

e n c e s ,lope,

over,

nd

anagementrec -

countedornhepredictionequation

by

hesym-

bols

R, , ,C,and

.

Therefore,

the

o ilerodibility

factor,

,

must

eevaluatedndependentlyof

he

effects

of

the

other

factors.

o f

actor

surements

n

henited tatesade e nmade.

Th e

designated

management

rovides

ondition

thatearlyliminates

f fects

fover,

manage-

ment,

andand

s e

esidual

and

hatc an

edupli-

cated

on

any

cropland.

Direct

easurementsf nell-replicated,

unitplots s

described

efiect

hecombined

f fects

of

allhe

oil

properties

hatsignificantly

nfluence

the a s ewith

which

articular o ilserodedy

rainfall

and

unoff

f

ot

protected.

owever,

s

an

average

valueor

given

soil,

and

direct

mea-

surement

f

heactorequires

o ilos s

measure-

m e n t sor

epresentative

ange

f

tormizes

and

ntecedento ilonditions.

S eendividual

S t o r m oilosses

nder

A P P L Y I N GTHESOILLOSS

E Q U A T I O N . )

o

valuate

or

oils

hat

o

ot

usually

ccurn -percent

lope,o ilos s

ata

from

lotshatmeetall

he

other

specifiedondi-

tionsare

adjustedo

his

a s eby

.

Values

f

o r

pecific

oils

Representative

alues

of

or

o s t

f

he

o il

vailable

r e s e a r c h

information.

These tables are

types

and texture c lasses

c a n be obtained

from

tables

prepared

by

oil

cient is ts

sing

the latest

available

romhe

Regional

Technical

ervice

C e n -

tersr tatefficesfCS .aluesorhexact


15/67

PREDICTING

AINFALLROSION

OSSES-A

GUIDE

O

ONSERVATION

PLANNING

TABLE 1.

Computed

K values

for

soils on erosion

researchtations

Soil ou r c e

of

data

omputed

K

Dunkirkilt

oam

eneva,.Y.O.9

K e e n esiitoam

anesviile,hio48

S helby

oam

ethany,

Mo.41

L o d i

oam l

acksburg,

a.39

Fayette

ilt

oam

aCrosse,

Wis.

38

C e ci l

andylayoam

Watkinsville,

Ga.

36

Marshallil tloam

l

arinda,

owa

33

Ida

iltoam astaa,owa

33

M a n s i cclayloam

ays,

a n s .

32

Hagerstown

ilty

lay

oam tateollege,a..31

A u s t i nlay emple,

ex.

29

Mexico

il t

loam

cCredie,

Mo.28

Honeoyeilt

oam

Marcellus,

.Y.28

C e ci landyoam

l

emson,

.C.

28

Ontario

oam eneva,

.Y.

.2 7

C e ci lclayoam

atkinsville,

Ga.

26

B o s w e l lindandy

oam

yler,ex.

25

C e ci l

sandy

loam

atkinsville,

Ga.

23

Z a n e i s

inesandy

oam

ut

hrie,

kla.

22

T i f t o n

oamy

and

fton,

Ga.

10

Freeholdoamysand

arlboro,

.J.

08

B at hiaggy

il t

oam

with

urface

Arnot,

.Y.

05

s t o n e s

1>

n c h e semoved....

Albiagravelly

loam

eemerville,

.J.

03

*Evaluated from continuous fallow. All others were

computed

f r omowcropdata.

s o i l

onditions

tpecific

ite

ane

omputed

by

s e

f

he

o il

rodibility

nomograph

resented

in

he

nextsubsection.

Usuallyo ilype

ecomes

e s s

rodiblewith

decrease

niltraction,

egardlessf

whether

he

corresponding

ncrease

s

n

he

and

raction

r

the

layraction.

verall,rganic

matterontent

ranked

ext

o

article-sizedistribution

sanndi-

cator

f

rodibility.owever,

oi l 's

rodibility

isunction

ofomplexnteractionsfa

ubstan-

tial

umber

oftshysicalandhemical

roperties

and

ftenaries

within

tandardexture

l a s s .

Values

fetermined

or

3

ajor

o i l sn

which

rosionlotstudiesunder

naturalain

were

conducted

ince

930

re

isted

n

able

.

even

of

hesealues

re

rom

ontinuous

allow.

he

others

re

romrowcrops

averaging

0

lot-years

of

ecord

nd

rownnystems

orhich

he

cropping

ffect

adeenmeasurednthertud-

i e s .Othero i l s

n

which

aluable

rosion

tudies

haveeenonducted^ereot

ncluded

nhe

table

ecause

f

ncertainties

nvolved

n

djust-

mentsofhedata

or

effectsofcroppingand

man-

agement.

Direct

measurementf

herodibility

actor

s

both

ostly

nd

ime

onsuming

nd

as

een

feasible

onlyor

a

ew

majors o i l

ypes.

Toachieve

a

etter

nderstandingfow

nd

owhatx-

tentachfariousropertiesofa

o il

ffectsts

erodibility,

nnterregional

tudy

as

nitiated

in961.hetudyncludedhes e

field-plot

rainfall

imulators

n

at

eastadozenStatesoob-

tain

omparativeata

n

umerous

o i l s ,

abora-

tory

eterminations

of

physical

andhemical

rop-

erties,

ndperation

f

dditional

allow

lots

under

atural

ain.

everal

mpirical

rodibility

equations

were

eported

3,

0),

A

o il

rodibility

nomograph

orarmland

nd

onstruction

i tes

(58)

rovidedoreenerallypplicablework-

ing

ool.pproximatealues

or

0

enchmark

s o i l s

n

awaii

are

istedn

table

2.

*See

ootnote

3,

p..

T AB L E

2.

Approximate

aluesofth esoil

erodibilityfactor,

K,

for

10

benchmarksoils

n iawaii

Order

S u b o r d e r Great

r ou p

S u b g r o u p

Family

Se r ie s

K

U lt is o ls Humults Tropohumults

Humoxic

ropohumults

Clayey,aolinitic,sohyperthermic

Waikane 0.10

O x i s o l s

Torrox Torrox

Typic

Torrox

Clayey,

aolinitic,sohyperthermic

Molokai

.24

O x i s o l s

Ustox

Eutrustox

Tropepticutrustox

clayey,

aolinitic,

sohyperthermic Wahiawa

.17

V e r t i s o l s U s t e r t s Chromusterts TypicChromusterts

Veryine,montmorillonitic,sohyperthermic

Lualualei

Kawaihae

.28

.32

A r i d i s o l s

Orthids

Camborthids Ustollic

amborthids

Medial,sohyperthermic

(Extremelystonyhase)

I n c e p t i s o l s Andepts

Dystrandepts

Hydric

ystrandepts

Thixotropic,

sothermic

Kukaiau

.17

I n c e p t i s o l s

Andepts Eutrandepts

Typicutrandepts Medial,sohyperthermic

Naolehu(Variant) .20

I n c e p t i s o l s Andepts

Eutrandepts

E n t icutrandepts

Medial,sohyperthermic

Pakini

.49

I n c e p t i s o l s

Andepts

Hydrandepts

Typic

ydrandepts

Thixotropic,sohyperthermic

Hilo

.10

I nc ep t iso ls

Tropepts

Ustropepts

Vertic

stropepts

Veryine,aolinitic,

sohyperthermic

Waipahu

.20

SOURCE;l-Swaify

and'

Dangler9).


16/67

10

UNITEDTATESEPARTMENT

F

GRICULTURE,

AG RICULTURE

ANDBOOK

U M B E R37

Soilrodibi l i ty

Thesoil

oss

data

show

hatveryfine

sand

0 . 0 5 -

nn )

s

omparable

n

rodibility

o

silt-sized

ndhat

mechanical-analysis

ata

re

more

valuablewhen

xpressedyannter-

ernrhatdescribes

he

proportions

n

which

and,.silt,

nd

lay

ractions

re

combined

n

soil.

When

mechanical

analysis

dataased

n

tandard

S D A

lassificationre s e dor

he

n

igure3 ,

he

percentageof

very

fine

0.1-0.05mm)mustirst

e

ransferred

rom

sand

ractionohe

silt

raction.The

mechani-

a l

analysis

data

re

hen

effectivelydescribedy

article-size

arameter

M,

which

quals

percent

0.1-0.002

mm)

imesheuantity00-minus-

Where

he

ilt

ractiono es

otx-

0

ercent,

rodibility

aries

pproximately

s

he

.1 4

power

ofhis

parameter,

but

prediction

s

mproved

ydding

nformation

n

matter

ontent,

oiltructure,

nd

rofile

lass .

F or

oilscontaining

es s

han

0

percent

siltand

ine

and,

he

omograph

fig.

)

olves

he

O O

K

=2 .1

M'-'*

(10-')

( 1 2

~a )-f-3 . 2 5 ( b -2 ) +2 . 5 (e -3 )

(3 )

M

=

the

article-size

arameterdefined

bove,

a

=

percent

organic

matter,

b

=thesoil-structurecode

s ed

nsoilclassifica-

tion,

and

c=the

rofile-permeability

lass .

entersection

of

theselect ed

percent-silt

andper-

ines

omputeshe

alue f

M

n

he

orizontal

cale

fhe

omograph.

laynters

nto

he

omputation

s

00

he

percentages

of

sand

and

silt.)

Theata

ndicate

hange

nhe

elation

f

o

rodibility

when

he

ilt

andery

ine

sand

xceeds

about

7 0

percent.

This

change

was

eflected

ynflectionsnhe

ercent-

urves

that

oint

ut

a sotee ne-

y

umerical

equation.

Readers

who

would

ikemore

etailegarding

ata

nd

elationships

nderlyingheomo-

quationmayobtain

his

rom

ournal rti-

( 58 ,

60).

Nomograph

o l u t i o n

With

appropriate data, enter thecale at

he

N o m o g r a p h

leftnd

roceed

o

ointsepresentinghe

oil's

percentand0.10-2.0mm),ercent

rganicmat-

ter,tructureode,

nd

ermeabilitylass

s

l-

lustrated

y

he

otted

ine

nhe

omograph.

Th e

orizontalnd

ertical

oves

must

e

made

in

he

isted

e q u e n c e .

se

inear

nterpolations

between lottedi nes. he

structure

o de

and

per-

meabilitylas s esre

efinedn

he

omograph

forreference.

Manyagricultural

oilshave

oth

ine

granular

topsoilandmoderatepermeability. orh e s e oi ls,

Kmaye

eadrom

he

caleabeled'first

p-

proximationf ,"ndhe

ec ond

lock

f

he

graphsot

needed.

orall

ther

oi ls,

owever,

theroceduremust e

completedo

he o il

erodi-

bility calenhe

s e c o n d

halfofhe

graph.

The

echanicalnalysis,rganic

atter,

nd

structuredata

are

thosefor

the

topsoil.

o r

evalua-

tion

of

Kfor

desurfacedsubsoilhorizons,

hey

per-

tain

ohe

upper

n

ofhe

new o il

rofile.

he

permeabilitylass

she

rofileermeability.

C o a r s e

ragments

are

excludedwhen

determining

percentages

f

and,

ilt,

nd

lay.

f

substantial,

they

may

ave

ermanent

mulch

ffect

which

c a n

evaluated

rom

he

pper

urve

f

he

chartn

mulch

nd

anopy

f fectsp .9,

ig.

)

and

pplied

o

he

umber

btained

rom

he

nomograph

solution.

C o n f i d e n c eimits

In

estsagainstmeasured

K

values

anging

rom

0.03

o .69,

5

percent

ofthenomograph

solutions

differedromhe

measured values

yesshan

0. 02,

nd5

ercent

f

hem

y

es s

han

.04.

Limitedata

vailable

n97 1or

mechanically

exposed and subsoil

.horizonsndicated

bout

comparable

ccuracy

or

h e s e

onditions.ow-

ever,more

ecentdataaken

n

esurfaced

gh-

clay

ubsoils

howedhe

omograph

olution

o

lackhe

desired

ensitivity

o

differences

n

rodi-

bilitiesf

h e s eo ilorizons.

or

u choilshe

contentfreeronnd

luminum

xides

anks

next

oarticle-sizedistribution s

anndicator

of

erodibility

37),o m e

igh-clay

oils

orm

what

ha s

e e n

alled

rreversible

ggregates

n

he

surface

when

illed.

hes e

behave

ike

argerri-

maryparticles.


17/67

PREDICTING

A I N F A L LROSION

L O S S E S - A

U ID EOO N S E R V A T I O N

PLANNING

n

\\\

w\\\

> -

;-X

X

<

V\^

\

V

S.\\VN

X -J

\\

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v

>

XNV

X 5

\\

N

\,

\\\N

x\

\ \

X

5

o

\

>"

^

\X'*^ N

v\

( / )

< \^

V

^ N

X^ X

3

\

x

^

V

^xxx^

V

e

w

w

o oo

:

\\

\\ I^XvXI-X

5.3

S5

i

o

x\

XXX

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x^X

ib

/''

/

UJ

o

t

o

e x

^

2

/

;

> ^ < x

A

^ y

o :

a

o

'Wx

/

//

o

///

'A

p

0

^

p

r

o

p

r

1

a

t

e

d

-

2

.

0

n

m

.

t

t

e

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c

u

r

v

e

s

.

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8

,

s

t

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e

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o

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d

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00

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QNVS

a N I d A d B A4

I

ISiNaodad


18/67

UNITE D

TATE S

E P A R T M E N T

F

G R I C U L T U R E ,


A N D B O O K

UMBER37

T O P O G R A P H I C

A C T O R

L S)

Bothhe

ength

nd

he

teepness

f

he

and

substantially

affect

he

ateof

soilerosion

by

hewo

ffects

ave

een

valuated

ep-

n

esearch

andare

epresented

n

he

soil

loss

quationy

nd

,espectively.

nield

applications,

owever,

onsidering

he

wos

single

opographicactor,

S,

s

more

onvenient.

S l o p e - E f f e c thart

L S

sheexpectedatio

of

soilos sperunit

area

ield

slope

o

hat

rom

72.6-ft

ength

of

-percent

slope

nder

therwise

dentical

his

atio

or

specified

combinations

of

lope

engthnd

niform

radientmay

e

irectly

rom

he

lope-effect

hartfig.

) .Enter n

he

horizontalaxis

with

he

fieldslope

move

vertically

o

he

appropriate

percent-

curve,

ndead

Sn

he

caleat

he

eft.

o r

xample,he

Sactor

or

00-ft

ength f

0-percent

lope

s

.4 .

h ose

who

refer

able

s eable

nd

nterpolate

etween

isted

Toompute

oil

os s

rom

l opeshatre

p-

onvex,

oncave,

romplex,hehart

S

valueseedo

e

adjusted

sndicatedn

he

S

a l u e s

orrregularl o p e s .igure

able

ssume

l opes

hat

ave

ssentially

radient.

he

hart

nd

able

were

e-

ived

by

the

equation

IS=X/72.6) * {65.4] s i n ' 8

+

4.56s in 6-j-0.065) (4)

where

X

=

slope

lengthin

feet;

6 =angleofslope;and

m=

0 .5

f

he

percentslopes

r

more,

.4 n

s l opesof .5

o

.5ercent,

.3

on

l opesof

o

3

percent,

and 0.2 on

uniform

gradients

of

less

than

percent.

The

asis

or

his

equations

given

n

hesub-

sectioniscussinghe

ndividualffects

f

lope

length

nd

teepness.

owever,

he

elationships

expressed

byheequation

were

derived

rom

data

obtainedn

ropland,nder

atural

ainfall,

n

s l opesangingrom

o

8

ercentn

teepness

andabout

0

to

0 0ftnength.

How

ar

beyond

these

anges

n

lopeharacteristics

he

elation-

ships

erived

romheataontinueo

ec c u -

ratea s

ot

e e n

etermined

yirect

oil

os s

measurements.

The a l ouse

egi on f

he

Northwestepresents

TABLE

3.

Values

of

the

topographic

factor,

LS,

forspecificcombinatiorisofslopelength

and

steepness^

Slope

e n g t h

( feet )

^ ^ l o ^ r

^ ^

^

^ ^ ^ ^ ^

^ ' ' ^ ^

0 .2 0.060 0.069 0. 07 5 0.080 0.086

0.092

0.099 0.105

.110

.114

.121 0.126

0.5

73

.083 .090

.096

.104 .110

.119

.126

13 2

13 714 5

.152

0. 8

86

.098 ,107 ,113 .123 .130

.141

.14915 6

16 2

17 1

.179

2 33 .163 .185

.201

.227 .248 .280 .30532 634 437 6

.402

3

90 .233 .264 .287

.325

.354 .400 .437

466

49 2

53 6 .573

4 .230

.303

.357

.400 .471

.528

.62\ .697

76 2

82 092 0 1.01

5

68

,379 ,464 .536 .656 .758 .928 1.07.20

.31

.52 1.69

6

.336

.476

,583

.673

.824

.952

1.17

1.35

.50

.65

.9 0

2.13

8 96

,701

.859

.992 1.21

1.41

1.72

1.98

,2 2.4 3

.81

3.4

10

85 .968 1.19 1.37 1.68 1.94 2.37 2.74

.0 6

.36

.8 7 4.33

12 0 3 1.28 1.56 1.80 2.21 2.55 3.13 3.61

.0 4

.4 2.11 5.71

14

1.15

1.62

1.99

2.30

2.81

3.25

3,98

4.59

.1 3

.6 2

.4 9

7.26

16

1.42 2.01

2.46

2.84 3.48

4.01

4.92

5.68.3 5

.9 5

.0 3

8.98

18

1.72 2.43 2.97 3.43 4.21 3.86 5.95 6.87

.6 8.41

.71

10.9

20 2.04 2.88 3.53 4. 08 5.00 5.77

7.07

8.16

.1 20. 01.5 12.9

^

is=

X/72.6) *

(65.41

s i n '

6-f 4.56in 0-\ -

0.065)

where

X=

s l o p e

e n g t h

n

f e e t ;

=0. 2o r

g r a d i e n t s

5

ercent,

.4

orercentl o p e s ,nd

.3or

3ercentre s s ) ;nd

=

numberfqual-lengthegmentsnto

whichheslopewas

divided.

Fouregments

would

roduce2,3,0,nd5

percent,espectively. egmentNo.

s lways t

the

op

fheslope.

Slope

toe

nfluenced

y

nteractions

withsoil

properties

andurfaceonditions,uthenteraction

ffects

have

not

beenquantified

y

esearch

data.

Neither

are

data

available

o

define

heimitson

he

equa-

tion's

applicability.

Thisquation

an

eerivedrom

he

ormerly

publishedquation

or

.

xpressing

heactors

a

unction f

he

ine

f

he

angleof

lopeather

thanheangent

s

moreccurate

ecause

ain-

drop-impact

orces

long

he

urface

nd

unoff

shear

tress

re

unctions

fheine. ubstituting

100

sin

or

percent

slope,

which

s

00

an ,does

not

ignificantly

ffect

he

nitial

tatistical

eriva-

tionr

hequation'solutions

or

lopes fess

than

20ercent.

utasslopes

ecome

steeper,

he

differenceetween

heine

nd

he

angente-

comes

ppreciable

ndrojections

ar

eyondhe

range

f

he lotata

ecome

moreealistic.

he

numeratorwasdividedyhe

constant

denomina-

tor

for

simplification.


22/67

16 UN IT EDTATE S

E P A R T M E N T

FG R I C U L T U R E ,


A N D B O O KUMBER37

I r regular

S o i los ssalsoaffectedbytheshapeof slope.

ield

l opeseithersteepenoward

he

ower

convex

slope)

or

flatten

oward

he

owerend

lope) .se

f

he

verage

radient

o

igure

or

able

would

underestimate

o il

tothe

oot

of

a

convexslope

and

would

t

orconcave l opes.

rregular

l opes

a n

suallye ivided

ntoegmentshatave

niformradient,uthesegments

cannot

e

valuated

sndependent

l opeswhenunoff

fromone

segment

to

the

next.

However,here

wo

implifying

ssumptions

a n

eccepted,S

orrregular

l opesa ne

erivedyombininge l ec tedalues

he

lope-effecthart

nd

able

5 5 ) .

he

re

hat

1)he

hanges

n

radient

ot

sufficient

to

a u s e

pslope

deposition,and

)

he

rregularslope a n

edivided

nto

small

f

equal-length

egments

nu ch

man-

r

hatheradientwithin

ac h

egmentor

practical

purposes

c an be

considered

uniform.

After

ividing

heonvex,

oncave,rcomplex

nto

qual-lengthegmentssefinedar-

ier,

he

roceduressollows:

is t

he

egment

n

herder

n

which

hey

c c u r

nhe

beginning

at

he

upper

end.

Enter

he

slope-

chart

withhe

otal

slopeengthand

ead

S

ac h fheistedradients.

Multiplyh e s ey

C h a ng e sn

o ilype

r

The

rocedure

or

rregularl opes

an

nclude

fhanges

no il

ype

within lope

length

55 ) .

heroductsofalueselected

rom

origure

and

able

o

evaluate S

or

irregular

l opesremultiplied

yhe

espective

aluesof beforesumming.

ollustrate,

s s u m e

the

alues

or

he

oils

n

he

hree

egments

f

heconvexslopenhe

preceding

example

were

. 27, .32 ,

and

. 3 7 ,

espectively.

he

average

L S

or

heslope

would eobtained sollows:

Slopes

the

orrresponding

actors

rom

able nddd

the

products

o

obtain

S

orhe

entire

slope. he

following

abulation

llustrates

herocedureor

a

400-ft

convex

slope

n

which

heupper

third a s

a

radient

of

ercent;

he

middle

hird,

0

er-

cent ;

and

he

ower

hird,5

percent:

Segmenf

Percent lope Table

Table

Product

1 5

1.07 0.19

0.203

2

10

2.74

.35

.959

3

15

5.12

.46

L S

2.355

=3.517

F or

he

concave

slope

of

he

a m e

ength,with

thesegment

gradients

n

everseorder,hevalues

inhe

hirdolumn

wouldeistedneverse

or-

der.

he

products

would

hen

e

. 9 7 3 ,

.959,and

0.492,

giving

u m

of2,42or S .

Resear ch

a s

ot

defined

ust

ow u c h

radi-

ent

changesneeded

nder

various

conditionsor

deposition

f

soilarticles

f

various

izes

o

e -

gin,

ut

depositional

areas

a ne

determined

y

observation.

henhe

lope

reaks

re

harp

enough

o

a u s e

deposition,herocedure a ne

u s e d

oestimate

S

or

slope

segments

aboveand

below

he

epositional

rea.

owever,t

willot

predict

he

otal

ediment

oved

rom

u ch

n

interruptedlopee c a u s e

t

oe sot

redict

he

amountofdeposition.

C o v e rA l o n ghe

Slope

Withinimits,

he

rocedure

ane

urther

x-

tendedoaccount

or

hanges

n

overalonghe

slopeength

ydding

olumnf

egment

values.However,

t

s

notapplicableorsituations

where

ractice

hange long

he

lopea u s e s

deposition. orexample,

grass

bufferstrip

cr oss

the

oot

of

slope

n

which

ubstantial

erosion

s

occurring

nduces

eposition.he

mount

f

his

deposition

s unction

f

ransport

elationships

(JO)

andannot

e

predictedytheSLE.

Segment

No .

Table

3

Table

4

K

Product

1

1.07

0.19 0.27

0.055

2 2.74

.35 .32

.307

3

5.12

.46

.37

KLS

.871

=

1.233


23/67

PREDICTING

R A I N F A L L

R O S I O N L O S S E S - AGUIDE

O

O N S E R V A T I O N PLANNING

17

Equation

o r

Soil

D e t a c h m e n t

o n

This

rocedure

s

ounded

nn

quation

7 2 )

a n

e

applied

also

when

heslope

segments

eot

of

qual

ength.

o n c e p t s

nderlying

his

includethefollowing:

Sediment

oad

t

ocation

n

lope

so n -

ither

by

he

ransport

capacity

of

he

un-

ndainfall

r

y

he

mount

f

etached

aterial

vailableor

ransport.

henhe

of

detachedmaterial

xceedshe

ransport

deposition

c c ursandhe

sediment

oad

etermined

rimarily

y

he

ransport

apacity

heunoff

at

hatocation.

Where

pslope

de-

Successive

S e g m e n t s

o f

Slope

tachment

a s

ot

qualed

he

ransport

apacity,

sedimentoad

t

iven

ocation

s unctionof

erosion

characteristics

of

heupslopeareaand

a n

be

omputed

yheSLE.

o il

os srom iven

segment

of

heslope a nhen e

computed s

he

difference

between

he

sediment

oads

at

the

ower

and

upper

ends

of

thesegment.

Fosterand

Wischmeier

1 2)

resent

rocedure

forusinghisequationoevaluate Sorrregular

s lopesandoaccountforhe f fects

of

he o il

r

coverage

hanges

long

lope,oongs

he

changesdonot a u s edepositiono c c u r .

COVERND

MANAGEMENT

A C T O RC)

Coverand

management

f fects

ca

AH 503 Wichmeier

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