avon lymington beaulieu bartley cadnam hampshire water ...€¦ · life 02 nat/uk/8544 new forest...

LIFE 02 NAT/UK/8544 New Forest Wetland Management Plan

Tab

le 3

-4: G

eolo

gic

al C

har

acte

rist

ics

Peri

od

Qu

ater

nar

y

Tert

iary

Epo

ch*

Rec

ent

25,0

00 y

ear

BP

Plei

sto

cen

e1

mill

ion

year

s B

P

Olio

gen

e40

mill

ion

year

BP

Eoce

ne

60 m

illio

nye

ars

Dri

ft &

So

lidG

eolo

gy

Shin

gle

Allu

viu

m

Peat

Val

ley

Gra

vel

Bri

ckea

rth

Plat

eau

Gra

vel

Hea

do

n B

eds

Bar

ton

San

ds

Bar

ton

Cla

y

Bra

ckle

sham

B

eds

Bag

sho

t B

eds

Key

Ch

arac

teri

stic

s

Fou

nd

alo

ng

co

asta

l fri

ng

es o

fLy

min

gto

n c

atch

men

t in

clu

din

g H

urs

t Fo

un

d l

inin

g m

od

ern

day

riv

erfl

oo

dp

lain

san

d v

alle

ys

Flin

ty in

ch

arac

ter

wit

h a

co

mp

lex

mix

of

gra

vel,

san

d a

nd

cla

y.U

nst

rati

fied

mix

ture

of

fin

e-g

rain

edq

uar

tz s

and

or

flin

t. L

aid

do

wn

as

flo

od

dep

osi

ts a

lon

g y

ou

ng

er r

iver

terr

aces

an

d m

ay h

ave

a p

arti

ally

aeo

lian

(w

ind

blo

wn

) o

rig

inC

om

po

sed

alm

ost

exc

lusi

vely

of

flin

tw

ith

so

me

peb

ble

s o

f sa

rsen

(si

licif

ied

san

dst

on

e) la

id d

ow

n o

n o

ld r

iver

terr

aces

Hea

ldo

n f

orm

atio

ns

dep

osi

ted

infr

esh

wat

er la

go

on

co

mp

risi

ng

sh

elly

clay

s, s

ilts

and

san

ds

Lyn

dh

urs

t m

emb

er d

epo

site

d in

bra

ckis

h o

r m

arin

e co

nd

itio

ns

and

com

pri

ses

mo

re s

and

y se

dim

ents

.U

pp

er H

ead

on

fo

rmat

ion

is s

hel

lysa

nd

. Sa

nd

s o

f m

arin

e o

rig

inC

lay

dep

osi

t la

id d

ow

n in

dee

p w

ater

.M

arks

sta

rt o

f B

arto

n g

rou

pFo

ssil

rich

dep

osi

ts la

id d

ow

n in

war

m,

mar

ine

and

fre

shw

ater

co

nd

itio

ns.

San

dy

bed

s o

f co

arse

, po

rou

s m

ater

ial

Avo

nLy

min

gto

nB

eau

lieu

Bar

tley

Cad

nam

Ham

psh

ire

Wat

erA

von

Tr

ibu

tari

es✓

✓✓

✓✓

✓✓

✓✓

✓

✓✓

✓✓

✓ ✓✓

✓✓

✓✓

✓✓

✓

✓✓

✓✓

✓

✓✓

✓✓

✓✓

✓

✓✓

3.7


3.8

Tab

le 3

-5:S

ites

of

Geo

log

ical

or

Phys

iog

rap

hic

Inte

rest

Riv

er B

asin

Ham

psh

ire

Avo

n

Trib

uta

ries

Ham

psh

ire

Avo

n

Trib

uta

ries

Ham

psh

ire

Avo

n

Trib

uta

ries

Cad

nam

Lym

ing

ton

Lym

ing

ton

Lym

ing

ton

Site

of

Spec

ial

Geo

log

ical

or

Phys

iog

rap

hic

Inte

rest

Stu

dle

y W

oo

d

SU 2

27 1

58

Cra

nes

Mo

or

SU 2

47 0

69

Wo

od

Gre

en

Gra

vel P

it

SU 1

72 1

70

Shep

her

d’s

Gu

tter

SU 2

63 1

53

Park

Hill

Incl

osu

re

SU 3

16 0

59

Mar

k A

sh W

oo

d

SU 2

47 0

69

Hig

hla

nd

Wat

er

SU 2

72 0

73

SU 2

39 1

23

Key

Fea

ture

s o

f In

tere

st

Pro

lific

Ter

tiar

y lo

calit

y ex

po

sin

g t

he

on

ly c

om

ple

te e

xpo

sure

of

the

silt

y H

un

tin

gb

rid

ge

Form

atio

n o

f th

e B

rack

lesh

am

Gro

up

, rem

arka

ble

fo

r it

s m

ollu

scan

fau

na

and

th

e n

um

ber

of

spec

ies

limit

ed t

o t

he

form

atio

n.

Nu

mer

ou

s co

rals

, sca

ph

od

a,

biv

alve

s an

d g

astr

op

od

s m

ake

it a

n o

uts

tan

din

g E

oce

ne

loca

lity

of

gre

at in

tere

st in

stu

die

s o

f Te

rtia

ry s

trat

igra

ph

y an

d

pal

aeo

nto

log

y.

A la

rge

mir

e co

mp

lex

set

in a

sh

allo

w b

asin

co

nta

inin

g s

ign

ific

ant

pea

t ac

cum

ula

tio

ns

dat

ing

bac

k to

Dev

ensi

an la

te g

laci

al

tim

es.

A k

ey r

efer

ence

sit

e fo

r p

alyn

olo

gic

al a

nd

pal

aeo

eco

log

ical

stu

die

s in

so

uth

ern

En

gla

nd

. Als

o u

nu

sual

fo

r th

e

app

aren

tly

rap

id a

ccu

mu

lati

on

s o

f p

eat

in t

he

Bo

real

Per

iod

an

d is

th

us

imp

ort

ant

for

the

stu

dy

of

earl

y im

mig

rati

on

an

d

exp

ansi

on

of

flo

ra in

po

st-g

laci

al t

imes

.

The

pit

exp

ose

s g

rave

l, d

epo

site

d b

y th

e R

iver

Avo

n, r

ich

in p

alae

olit

hic

art

efac

ts.

Pala

eolit

hic

ass

emb

lag

es p

rovi

de

maj

or

evid

ence

fo

r th

e su

bd

ivis

ion

of

the

terr

ace

seq

uen

ce in

th

e So

len

t B

asin

, wh

ere

they

are

par

ticu

larl

y im

po

rtan

t o

win

g t

o

a d

eart

h o

f p

alae

on

tolg

ical

sit

es.

The

site

als

o h

as s

ign

ific

ant

po

ten

tial

to

elu

cid

ate

the

com

ple

x h

isto

ry o

f th

e R

iver

Avo

n

gra

vels

an

d t

he

evo

luti

on

of

The

Sole

nt

Riv

er.

Loca

lity

ren

ow

ned

fo

r it

s ri

ch T

erti

ary

mar

ine

fau

nas

, kn

ow

n t

o g

eolo

gis

ts s

ince

th

e m

id 1

9th

C. S

ho

ws

a se

ctio

n t

hro

ug

h

the

Sels

ey F

orm

atio

n o

f th

e B

rack

lesh

am G

rou

p, o

f M

idd

le E

oce

ne

age,

an

d in

clu

des

sev

eral

mo

llusc

-ric

h h

ori

zon

s an

d

on

e ki

nd

of

Nu

mm

ulit

es c

orr

elat

able

wit

h t

he

Isle

of

Wig

ht

and

Bra

ckle

sham

sec

tio

ns.

A k

ey lo

calit

y fo

r sh

ow

ing

co

rrel

atio

ns

bet

wee

n c

lass

ic E

oce

ne

loca

litie

s o

f th

e H

amp

shir

e B

asin

, an

d f

or

its

pro

lific

mo

llusc

an f

aun

as.

On

ly e

xpo

sure

in

En

gla

nd

ou

tsid

e th

e Is

le o

f W

igh

t to

sh

ow

up

per

mid

dle

Hea

do

n B

eds.

Th

e o

ccu

rren

ce o

f C

erit

hid

ea

ven

tric

osa

an

d o

ther

mo

llusc

a in

th

e H

ead

on

cla

ys a

llow

s co

rrel

atio

n w

ith

th

e ty

pe

of

sect

ion

s o

f th

e Is

le o

f W

igh

t.

The

fau

na

of

wel

l-p

rese

rved

sh

ells

an

d f

ish

rem

ain

s m

akes

th

is o

ne

of

the

rich

est

Tert

iary

fau

nal

loca

litie

s o

n t

he

mai

nla

nd

.

Als

o a

n im

po

rtan

t si

te f

or

its

pal

aeo

nto

log

y an

d f

or

corr

elat

ion

s w

ith

in t

he

Tert

iary

Ham

psh

ire

Bas

in.

A v

alle

y m

ire

com

ple

x o

f co

nsi

der

able

imp

ort

ance

fo

r p

alyn

olo

gic

al a

nd

pal

aeo

eco

log

ical

stu

die

s. P

eat

gro

wth

at

the

site

dat

es f

rom

th

e ea

rly

par

t o

f th

e D

even

sian

late

-gla

cial

to

th

e su

b-A

tlan

tic

Peri

od

. Als

o c

on

tain

s o

lder

po

st-g

laci

al p

eats

in

the

New

Fo

rest

an

d is

exc

epti

on

al f

or

hig

h a

ccu

mu

lati

on

rat

es d

uri

ng

late

-gla

cial

tim

es.

Mac

rofo

ssil

and

po

llen

an

alys

es

hav

e yi

eld

ed s

om

e o

f ea

rly

Bri

tish

po

st-g

laci

al r

eco

rds

of

bry

op

hyt

es. S

ite

also

imp

ort

ant

for

trac

ing

ear

ly p

ost

-gla

cial

imm

igra

tio

n a

nd

exp

ansi

on

of

flo

ra in

po

st-g

laci

al t

imes

.

Un

iqu

e ar

ea d

emo

nst

rati

ng

a c

om

bin

atio

n o

f lo

w m

anag

emen

t an

d lo

w h

um

an im

pac

t o

n f

luvi

al p

roce

sses

. Th

e h

ydro

log

ical

and

flu

vial

ch

arac

teri

stic

s o

f H

igh

lan

d W

ater

are

typ

ical

of

tho

se t

hat

fo

rmer

ly o

ccu

rred

in m

uch

of

sou

ther

n E

ng

lan

d.

The

site

pro

vid

es v

alu

able

op

po

rtu

nit

y to

stu

dy

bo

th t

he

role

an

d in

flu

ence

of

veg

etat

ion

in h

ydro

log

ical

an

d f

luvi

al

pro

cess

es a

s w

ell a

s th

e ef

fect

of

deb

ris

dam

s.


3.3.2 Geomorphology

The New Forest can be viewed as a plateau dipping gently from north to south. The steeperwestern escarpment is flanked by the broad Avon Valley while the lower valley of the RiverTest and Southampton Water provide a boundary to the to east. The gently sloping southernflank is bounded by the Solent. The smaller tributaries and streams draining the Forest haveeroded down through the plateau to create gently sloping valleys between flat-topped hillsgiving rise to an undulating topography (Figure 5). The highest point in the Forest isaround 125m OD to the north of the Forest along the watershed between basin of theCadnam and Hampshire Avon Tributaries.

The main Forest watershed runs approximately north to south and separates the HampshireAvon tributaries from the other five main river basins. The Blackwater and Cadnam Riversdrain east into the lower end of the River Test and Southampton Water respectively. TheLymington, Avon Water and Beaulieu all drain in a southeasterly direction to the Solent.

The Hampshire Avon tributaries have cut deeply incised U-shaped valleys, which are separatedby long, narrow, gravel-capped ridges. Their short, steep profiles have evolved in responseto recurrent down cutting by the River Avon whose course has remained reasonably stablethrough recent geological history.

In contrast, the drainage networks east of the main watershed seem to have evolved inresponse to a retreating river or shoreline. The Cadnam, Bartley and Lymington rivers allhave their sources close to the watershed in the north east of the forest around the 90m OD.The Beaulieu rivers rises at a lower level (46m OD) toward the middle of the Forest atLyndhurst while the Avon Water rises to the south of Burley (50m OD).

3.3.3 Soils

The soils of the New Forest have been mapped by the Soil Survey of England and Wales at1:250,000 scale and are described in Bulletin No. 15 Soils and their use in South-EastEngland. Ten different soil associations can be found across the river basins as summarisedin Table 3-6. More detailed soil surveys have been carried out for the Inclosures (Pyatt 1964)as shown in Figure 6.

The majority of soils are seasonally waterlogged as indicated by the soil wetness class.However, drainage in many parts of the Forest has improved the drainage characteristics.The humose, waterlogged surfaces of the many soils are highly susceptible to poaching andstructural damage during the winter months.

3.9

Tab

le 3

-6:S

oil

Ch

arac

teri

stic

s

(So

urc

e: J

arvi

s et

al 1

984)

* F0

r d

escr

ipti

on

of

Soil

Wet

nes

Cla

ss r

efer

to

Ap

pen

dix

K

Soil

Ass

oci

atio

n

Wic

kam

3 (

711g

)

(42m

OD

)

Bo

lder

wo

od

(64

3c)

(On

rid

ges

ab

ove

43m

OD

)

Ho

liday

s H

ill (

643a

)

25m

OD

Shir

rell

Hea

th 1

(631

c) 9

5m O

D

Sou

tham

pto

n (

634)

47m

OD

Bu

rsle

do

n (

572j

)

40m

OD

Hu

rst

(841

b)

20m

OD

Shab

bin

gto

n

(841

d)

Isle

ham

1 (

861a

)

(121

m O

D)

Effo

rd (

571s

)

Ch

arac

teri

stic

s

Typi

cal s

tagn

ogle

y so

il. F

ine

loam

y or

fin

e si

lty

drif

t ov

er c

laye

y pa

ssin

g to

slo

wly

per

me-

able

clay

or

mu

dst

on

e. D

uri

ng

hea

vy w

inte

r ra

in e

xces

s w

ater

is d

isp

ose

d o

f b

y la

tera

l

flo

w. I

n N

ew F

ore

st s

oils

oft

en h

ave

thin

hu

mo

se s

urf

ace

ho

rizo

ns

and

po

ach

eas

ily

Wat

erlo

gg

ed f

or

lon

g p

erio

ds

du

rin

g w

inte

r b

ut

mo

der

atel

y d

rou

gh

ty d

uri

ng

su

mm

er

Ver

y ac

id S

tag

no

gle

y-p

od

zols

. O

ccu

r w

her

e ri

ver

terr

ace

dri

ft a

nd

Pla

teau

Gra

vel

cove

r Te

rtia

ry c

lays

, lo

ams

and

san

ds.

Co

arse

loam

y, f

linty

, ho

rizo

ns

ove

r cl

ayey

sto

nel

ess

dri

ft. S

ub

soil

pan

s an

d o

ther

slo

wly

per

mea

ble

laye

rs im

ped

e ve

rtic

al w

ater

mo

ve-

men

t ca

usi

ng

sea

son

al w

ater

log

gin

g. E

xces

s w

inte

r ra

in is

ab

sorb

ed s

low

ly a

nd

po

nd

s

on

su

rfac

e b

ut

ther

e is

litt

le r

un

-off

. Su

rfac

es a

re w

et a

nd

mu

dd

y in

win

ter

and

hu

mo

se o

r p

eaty

to

pso

ils a

re s

lipp

ery

and

vu

lner

able

to

ero

sio

n.

Stag

no

gle

y-p

od

zols

wit

h p

erm

eab

le s

and

y su

rfac

e h

ori

zon

s p

assi

ng

to

loam

y an

d

slo

wly

per

mea

ble

laye

rs b

elo

w. W

et a

t th

e su

rfac

e fo

r lo

ng

per

iod

s in

win

ter

wit

h

thin

hu

mo

se o

r p

eaty

su

rfac

e h

ori

zon

s d

evel

op

ing

un

der

hea

thla

nd

. At

risk

of

po

ach

-

ing

& c

om

pac

tio

n in

win

ter.

Ver

y ac

id, s

and

y-h

um

o-f

erri

c p

od

zols

. Per

mea

ble

an

d w

ell d

rain

ed a

nd

dro

ug

hty

in

sum

mer

Pala

o-a

rgill

ic p

od

zol w

ith

ver

y st

on

ey, v

ery

acid

, san

dy

soils

Stag

no

gle

yic

arg

illic

bro

wn

ear

ths

wit

h f

ine

loam

y h

ori

zon

s p

assi

ng

to

cla

y an

d s

and

.

Seas

on

ally

wat

erlo

gg

ed

Typ

ical

arg

illic

gle

y so

ils w

ith

co

arse

loam

y h

ori

zon

s o

ver

no

n-c

alca

reo

us

gra

velly

dep

osi

ts, d

evel

op

ed in

riv

er t

erra

ce g

rave

ls.

Wat

erlo

gg

ed b

y g

rou

nd

wat

er f

or

mu

ch

of

the

win

ter

wit

h s

ho

rt p

erio

ds

of

win

ter

flo

od

ing

. C

an b

e d

rou

gh

ty in

su

mm

er.

Arg

illic

gle

ys d

evel

op

ed in

loam

y d

rift

wh

ich

var

y in

sto

nin

ess

and

co

mm

on

ly r

est

on

bed

ded

san

dy

or

gra

velly

mat

eria

l at

dep

th. F

ou

nd

in r

iver

ter

race

dri

ft. T

end

to

be

affe

cted

by

hig

h w

ater

leve

ls a

nd

are

sea

son

ally

wat

erlo

gg

ed.

Typ

ical

hu

mic

-san

dy

gle

y so

ils d

evel

op

ed in

per

mea

ble

, san

dy,

so

met

imes

sto

ney

dri

ft

fou

nd

in v

alle

y b

ott

om

s an

d d

epre

ssio

ns.

Pe

ren

nia

lly w

ater

log

ged

an

d s

up

po

rt m

uch

bo

gg

y ve

get

atio

n.

Arg

illic

bro

wn

ear

ths

wit

h w

ell d

rain

ed b

row

n f

ine

loam

y so

ils a

sso

ciat

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3.11

3.3.4 Geological, Geomorphological & Soil Issues

a) Susceptibility of the soil to damage

In certain areas of the Forest, the waterlogged nature of some of the soils makes themsusceptible to structural damage (compaction and erosion) when working with machinery.It is often not feasible to work with heavy machinery on soils during the late autumn, winterand early spring months (unless the ground is likely to be frozen for an appropriate lengthof time) which significantly limits the time period available to carry out certain restorationworks. Even in summer, heavy rainfall events have resulted in machinery standing idle toprevent undue damage to the soil structure which can add to the final project costs.

These limitations require careful planning of the timing of the works and an appreciationthat periods of poor weather can result in increased project costs.

Further Reading

Institute of Geological Sciences. Lymington Sheet 330 1:50 000 SeriesBournemouth Sheet 329Ringwood Sheet 314

Jarvis M.G., Allen R.H., Fordham S.J., Hazelden J., Moffat A.J. & Sturdy R.G. (1984).Soils and their Use in South East England, Harpenden 1984

Melville R.V. & Freshney E.C. (1982) British Regional Geology – The HampshireBasin and adjoining areas. Institute of Geological Sciences

Soil Survey of England & Wales, Soils of England and Wales - Sheet 6 South EastEngland Scale 1:250,000


3.4 HYDROLOGY & DRAINAGE

3.4.1 Introduction

The six main river basins are drained by a complex network of rivers, streams and drains asshown in Figure 7 and Table 3-7. Although many have different local names, for the purposesof this Plan they are referred to by the names cited on the New Forest 1:25,000 OrdnanceSurvey map.

A significant amount of data exists for the Lymington Catchment as this has been studiedfor many years by Southampton University and has been subject to specialist studies for theLife 3 Project . However, the majority of watercourses within the New Forest are not classifiedas Main River and data is limited for many of the streams. The locations of Monitoring andGauging Stations are also shown in Figure 7.

Since the 1870’s, well over half the total length of main streams and first order tributarieshave been modified to some extent by drainage schemes to improve areas for forestry orgrazing. For example, 78% of surveyed channel in the Black Water and 44% along theHighland Water have been modified in the past. Even so, the rivers and stream still representan excellent example of a relatively undisturbed lowland river system.

3.4.2 The River Basins

Lymington River Basin

The Lymington River Basin is the largest basin (127km2) in the New Forest and comprises adense network of steams and tributaries draining a highly wooded catchment. The highesttributaries (Highland Water & Bratley Water) rise at 100- 110m OD around Ocknell Inclosurejust to the north of the A31. Highland Water is joined by Bagshot Gutter at SU263 084before continuing south east via Millyford Bridge and the A35 (SU 276066) to join the mainRiver Lymington at Bolderford Bridge (SU291041)

Bratley Water rises at 98m OD from spring lines around the valley occupied by SluftersInclosure, to the north of the A31. It flows south through North Oakley Inclosure where itbecomes the Blackensford Brook (SU237066) and on through Anderwood Inclosure to meetthe Black Water just upstream from Dog Kennel Bridge (SU 241052).

The small network of tributaries feeding the Warwickslade Cutting rise around 75-55mODin the area of Mark Ash Wood, Wooson’s Hill Inclosure and Holidays Hill Inclosure to thenorth of Bolderwood Arboretum Ornamental Drive. The Warwickslade Cutting joinsHighland Water at SU282051.

The Black Water rises around 68m OD to the outside edge of South Oakley Inclosure andflows south-east via Dog Kennel Bridge and Dames Slough Inclosure to pass under the A35at Blackwater Bridge (SU244047) and Rhinefield Ornamental Drive before flowing througha long, straightened reach known as Fletchers Water. Fletchers Water joins Highland Waterat SU 287044

3.12


Mill Lawn Brook rises at 90m OD from Ridley Bottom just to the south of the A31. It is fedby additional tributaries rising from Harvest Slade Bottom before flowing through Burleyand then eastward via Markway Bridge (SU 250039) and Puttles Bridge (SU278 028) whereit becomes known as Ober Water. The Silver Stream draining Redhill Bog also enters OberWater at Puttles Bridge. The Ober Water continues to flow eastwards to the north ofBrockenhurst where it joins the Lymington River at Bolderford Bridge (SU 291 041). TheWeir Stream rises from White Moor at SU275019 and flows eastwards through Brockenhurstbefore entering the Lymington River at SU 304031.

From Bolderford Bridge the Lymington River is classified as main river . It continues to meandersouthwards through woods and agricultural land before passing to the east side ofLymington where it enters the sea. The normal tidal limit extends to Walhampton(SZ329963). Tidal flaps control the flow at its outfall.

Beaulieu River

The Beaulieu River has its source at Pikeshill on the north side of Lyndhurst rising at 55mOD. It flows south-eastwards draining predominately open heath and woodland exceptwhere it flows through the agricultural land holdings of Decoy Pond Farm and Ipley Manor.The river leaves the perambulation at North Gate (SU384047) from where it meanderssouthwards through fields and woodland before reaching its tidal limits at Beaulieu (SU 387 024)where tidal flaps control the flow. It then follows a long tidal estuary for approximately 8km toreach the sea.

Shepton Water rises at 14mOD at Penny Moor and flows eastwards via Shepton Bridge tojoin the main river at North Lane (SU 384044). Worts Gutter rises at 41m OD at the edge ofStockley Inclosure and flows eastward where it becomes the much straightened PenerleyWater. The Shepton Water and Penerley Water converge at SU 375046.

A number of shorter un-named tributaries also join the Beaulieu throughout its length.

Bartley Water

Bartley Water is one of the smallest river basins. It is fed by two main tributaries – The MillSteam and Fleet Water. The Millstream rises at 99m OD in Ringwood Ford Bottom anddrains south-eastwards via Leominstead Pond before turning north east to converge withBartley Water at SU305105. Fleet Water rises near Stoney Cross at around 109M OD andflows south-eastwards through wooded and agricultural areas before passing through MillPond and converging with the Mill Steam at SU 298102.

Outside the New Forest perambulation the Bartley Water is joined by a series of un-namedtributaries which drain a large part of its catchment south of the M27. This part of thecatchment is semi - rural interspersed with fields and settlements. The Bartley Water passesthrough the National Park Boundary to flow through Totton and enter the sea at the upperend of Southampton Waterr.

2 Main river classification mean that the Environment Agency has permissive powers to maintain the drainage capacity of the

channel and may also carry out works to limit the risk of flood from the river subject to technical, environmental and eco-

nomic feasibility and to the availability of funding.

3.13


Cadnam

The Cadnam is another small river basin draining the north-eastern corner of the Forest.The Cadnam River rises to the north-east of Minstead around 55m OD and drains north andnorth eastwards via a dammed lake at Paultons Park and Ower Bridge (SU 326167) to jointhe River Blackwater at SU 338171.

Avon Water

The Avon Water basin is a small basin draining the south-west edge of the Forest. It riseswithin the southern confines of Burley and flows eastwards where it drains Holmsley Bog.The river continues its journey following the edge of Wootton Coppice Inclosure andBroadley Inclosure where it appears to have been significantly straightened before passingthe perambulation boundary at SZ 266984. From this point it flows through farmland viaSway Lakes and passes to the western side of Lymington before entering the Solent atKeyhaven. Tidal Flaps control its outfall to the sea.

Hampshire Avon Tributaries

The Hampshire Avon tributaries draining the Forest comprise a south-eastern sub-basin ofthe main Hampshire Avon. The tributaries comprise a series of small streams draining thewestern side of the Forest.

The most northerly stream is un-named but drains Deadman Bottom, Millerford Bottom andHale Purlieu.

Black Gutter rises around 108m OD. Where the stream bends southwards at Stone QuarryBottom it becomes the Ditchend Brook. It enters the River Avon at SU 148134.

The Latchmoor Brook rises at 115m OD at Picket Corner and flows south westwards throughIslands Thorns Inclosure, Amberwood Inclosure and Alderhill Inclosure before entering theOpen Forest. Around Ogdens the stream is known as the Huckles Brook where it flowsthrough farmland before entering the River Avon at SU149106

The Dockens Water rises around Fritham at 115m OD and flows south westwards throughthe Open Forest passing close to the northern edge of Holly Hatch Inclosure, BroomyInclosure and Linwood. After passing through the National Park Boundary it flows betweengravel pits and Blashford Lakes Nature Reserve before joining the River Avon at SU 144064.Hampshire Wildlife Trust has carried out some restoration work on the Dockens Waterwhere it flows through Blashford Lakes Nature Reserve.

Linford Brook rises at 94m OD and flows through Milkham Inclosure, Roe Inclosure,Greenford Bottom and Linford Bottom. After the perambulation boundary it passesthrough farmland and between gravel pits to the north of Ringwood before entering theRiver Avon at SU147058.

Smaller un-named tributaries drain Foulford Bottom and Cranesmoor to the south of theA31.

3.14


Table 3-7: Principal Watercourses & Tributaries

Principal Length Named Guaging/MonitoringWatercourse (km) Tributaries Stations

Avon Water 18.5 ✓ (Flexford)

Lymington River 15.0 Bagshot Gutter

Warwickslade Cutting

Longbrook

Highland Water ✓ (Highland Water 1 & 2, Brockenhurst

Bratley Water

Blackensford Brook ✓ (Blackensford Brook, Blackwater 1)

Blackwater ✓ (Blackwater 2)

Fletchers Water ✓ (Blackwater 3)

Silver Stream

Mill Lawn Brook

Ober Water ✓ (Ober Water 1)

Etherise Gutter

Passford Water

Beaulieu River 26.0 Worts Gutter Hartford Bridge (ultrasonic)

Shepton Water Beaulieu Gates

Penerley Water Penerley Farm

Bartley Water 12 Millstream Ashurst Bridge

Fleet Water Totton (Tidal)

Cadham River -

Hampshire Avon Millersford Bottom

Black Gutter

Ditchend Brook

Latchmoor Brook

Huckles Brook

Dockens Water ✓ (Dockens Water)

Linford Brook

3.4.3 Channel & Floodplain geomorphology

Channel and floodplain form is a result of the processes of erosion, deposition and sediment transport over

time. The processes are naturally constrained by the geology and topography of the catchment and the way

in which the river responds to changes in climate and hydrology.

The natural form of many New Forest streams is a sinuous meandering channel of variable width and depth

that is laterally, relatively stable and contains pools, riffles and debris dams (except in flood). However, a num-

ber of streams throughout the Forest catchments have been modified by straightening, deepening and

removal of debris dams.

3.15


The gradient of most of the streams is relatively low ranging from 1% - 0.6%. The majorityof channels are less than 5m wide with shallow flows. Channels wider than 7m and morethan 1m deep are limited to the lowest reaches of the Lymington & Beaulieu rivers. Thestreams with the steepest gradients are generally the Hampshire Avon tributaries whichdrain down from the highest areas of the Forest. Debris dams (discussed further in section3.4.7) can have a significant influence on channel width resulting in a greater variation inwidths than might be found on a non-forested stream.

Distinct areas of floodplain border the natural channels of the Forest streams and display atypical range of floodplain features such as

◆ ephemeral channels - (sinuous , linear scour features around 50cm wide and 5-50cm deep)◆ pools and hollows ◆ wake deposits - material deposited behind obstacles such as trees, tussocks and woody debris◆ abandoned channels – old river channels left one part of the floodplain when the river

moved laterally elsewhere◆ woody debris, trees & vegetation◆ shallow man made drainage channel lawns

Even where the channels have been over deepened and flooding is less frequent remnantfeatures can often be discerned.

3.4.4 Flow

The New Forest streams are fed by a combination of mires, bogs and surface water run offand through flow. Many of the streams typically have a mean daily flow rate of less than0.5 m3s-1 during dry weather (Langford, 1996) and flows can be considerable lower duringperiods of summer drought. Flows measured at the gauging stations on the Dockens Waterand the Lymington River are shown in Table 3-8 which give values for two contrastingstreams. Further flow data for the Hampshire Avon Tributaries is given in Appendix D. Therivers and streams are characterised by their flashy nature and can rise rapidly in responseto heavy or prolonged rainfall as shown in the hydrographs for the Lymington River andDockens Water (Figure 8 & 9). Flood peaks tend to pass through quickly and during out ofbank events the total magnitude of the flow cannot always be recorded.

During the summer months those streams fed by well developed seepage steps or mirescontinue to flow although at a much reduced level with only a few centimetres depth ofwater. However a number of streams, particularly the Hampshire Avon Tributaries areseasonally dry or reduced to a series of small pools separated by dry gravel bars or smalltrickles under the surface gravel (Plate I). Often only the deeper pools scoured out behinddebris dams or on the inside of meanders contain any water.

3.16


Figure 8Sample Hydrograph of Gauged Daily Flows of Lymington River at Brockenhurst

Figure 9Sample Hydrograph of Gauged Daily Flows – Dockens Water at Moyles Court

Source: Centre of Ecology & Hydrology

3.17

avon lymington beaulieu bartley cadnam hampshire water ...€¦ · life 02 nat/uk/8544 new forest...

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