76

76

Appendix two – Tunnel Erosion brochure

Pote

nti

al

imp

act

s o

f tu

nn

el

ero

sio

n

reduce

d p

roduct

ivit

y

soil

and n

utr

ient

loss

fro

m p

roper

ty

inju

ry t

o liv

esto

ck

dam

age

to f

arm

equip

men

t

har

bor

for

rabbit

s an

d w

om

bat

s

sedim

enta

tion o

f dam

s an

d w

ater

way

s

the

pote

nti

al t

o t

urn

into

hig

hly

act

ive

gully

er

osi

on (

Figure

s 3

& 5

)

neg

ativ

e im

pac

t on t

he

Gip

psl

and L

akes

’ w

ater

qual

ity.

Publis

hed

by

the

Dep

artm

ent

of

Prim

ary

Indust

ries

.©

The

Stat

e of

Vic

tori

a, July

20

04

This

public

atio

n is

copyr

ight.

No p

art

may

be

repro

duce

d b

y an

y pro

cess

exce

pt

in a

ccord

ance

wit

h t

he

pro

visi

ons

of

the

Cop

yrig

ht

Act

19

68

.R

evis

ed July

20

09

.A

uth

ori

sed b

y th

e V

icto

rian

Gove

rnm

ent,

1 S

pri

ng S

tree

t, M

elbourn

e,

Vic

tori

a, 3

000.

ISBN

1

-74

10

6-6

50

-6

Dis

clai

mer

: T

his

pub

lica

tion m

ay b

e of

assi

stan

ce t

o y

ou b

ut

the

Stat

e of

Vic

tori

a an

d its

em

plo

yees

do n

ot

guar

ante

e th

at t

he

pub

lica

tion is

wit

hout

flaw

of

any

kin

d o

r is

wholly

app

rop

riat

e fo

r yo

ur

par

ticu

lar

purp

ose

s an

d t

her

efore

dis

clai

ms

all liab

ilit

y fo

r an

y er

ror, loss

or

oth

er c

onse

quen

ce w

hic

h m

ay a

rise

fro

m y

ou

rely

ing

on a

ny

info

rmat

ion in t

his

pub

lica

tion.

For

furt

her

info

rma

tion

ab

ou

t D

PI vis

it t

he w

eb

site

at

ww

w.

dp

i.vic

.gov.

au

or

con

tact

th

e D

PI

Cu

stom

er

Serv

ice C

en

tre

on

13

6 1

86

.

Kn

ow

n s

usce

pti

ble

are

as

Mit

chel

l R

iver

esc

arpm

ents

Gle

nal

adal

e

Mel

wood

Mount

Tayl

or

Clif

ton C

reek

Bruth

en

Kal

imna

Stra

tford

DEP

ART

MEN

T O

FPR

IMA

RY IN

DU

STR

IES

An

earl

y i

den

tifi

cati

on

g

uid

e f

or

East

Gip

psla

nd

Tunnel

Ero

sion

CC

09

/tl0

9_0

62

00

9

Figure

5:

Illust

rati

ng p

oten

tial dam

age

of t

unnel

ero

sion

.

77

Tunnel erosion in East Gippsland

77

Tunnel e

rosio

n is

....

....

. a n

atu

rally o

ccurr

ing pro

cess -

A p

roce

ss w

her

e th

e su

bso

il is

ero

ded

by

wat

er f

orm

ing u

nder

gro

und t

unnel

s.

It is

oft

en

asso

ciat

ed w

ith s

oils

that

hav

e a

har

d-s

etti

ng

top s

oil

ove

r a

subso

il (c

lay)

whic

h m

ay b

e st

able

when

dry

but

read

ily d

isper

ses

when

wet

(F

igure

4).

Iden

tify

ing t

unnel

ero

sion

in t

he

earl

y st

ages

is

difficu

lt a

s in

dic

atio

ns

are

smal

l are

as o

f cl

ay

dep

osits

and/o

r hol

es in

the

surf

ace

soil

on lo

wer

sl

opes

. As

mor

e su

bso

il is

was

hed

dow

n t

hro

ugh

the

‘tunnel

s’ f

an s

hap

ed c

lay

dep

osits

or fl

um

es

form

as

show

n in

Fig

ure

1.

As

mor

e su

bso

il is

was

hed

aw

ay, t

he

tunnel

s dee

pen

and w

iden

until t

he

roof

of

the

tunnel

ca

nnot

suppor

t its

own w

eight

and c

olla

pse

s fo

rmin

g h

oles

. At

this

sta

ge

the

ero

sion

is a

lrea

dy

w

ell a

dva

nce

d. E

ventu

ally

mor

e tu

nnel

s co

llapse

fo

rmin

g a

n a

ctiv

e gully

(Fi

gure

2, 3

and 4

).

Earl

y det

ection

of

tunnel

ero

sion

will

incr

ease

th

e ch

ance

s of

succ

essf

ul c

ontr

ol m

easu

res,

re

duci

ng t

he

repai

r co

sts

and li

mit t

he

dam

age

to

pro

duct

ive

farm

land a

nd t

he

Gip

psl

and L

akes

.Pro

duct

ivit

y a

nd w

hole

farm

assets

are

th

reate

ned b

y t

unnel ero

sio

n.

Earl

y s

ign

s o

f tu

nn

el

ero

sio

n

Smal

l hole

s an

d/o

r in

den

ts a

ppea

ring in

the

pas

ture

.

Wat

er ’s

pouti

ng’ f

rom

sm

all hole

s in

the

gro

und f

ollo

win

g h

eavy

rai

n.

Cla

y par

ticl

es d

eposi

ted in a

fan

shap

e on

the

pad

dock

surf

ace

(Fig

ure

1).

‘Dry

ing o

ff’ l

ines

in p

astu

re c

ause

d b

y sh

allo

w s

oil

dep

th (

Figure

2).

Colla

psi

ng s

urf

ace

soil

crea

ting e

longat

ed

dit

ches

, usu

ally

runnin

g d

ow

n a

slo

pe

(Fig

ure

3).

DEP

ART

MEN

T O

F PR

IMA

RY IN

DU

STR

IES

Figure

2:

Part

ial co

llapse

of

tunnel

wit

h d

ryin

g o

ff

lines

vis

ible

.

Figure

1:

Cla

y dep

osit

s ri

sing t

o th

e su

rface

thro

ugh a

n

outl

et,

crea

ting a

‘fan’ s

hape.

Figure

3:

Tunnel

col

lapse

and s

urf

ace

cla

y dep

osit

s.Fi

gure

4:

Start

of

gully

for

mati

on.