Understanding & modelling rainfall to runoff, recharge and river

Understanding & modelling rainfall

to runoff, recharge and river flow

responses and potential diffuse

pollution pathways

Rob Soley: Amec Entec

A mole’s

eye view

Wow! You can

SEE the water!

Presentation (& proposed report) outline

Understanding

The big picture context

Demo catchment detail (not much!)

Storm rainfall and flood responses

Modelling & data availability

With comments on possible diffuse pollution pathways

Topographic 50m DTM elevation 3D drape looking eastward

Big picture topo – geology – structure context

Test

Avon

Stour

Sem @ Cools Cott. Sem @ Priors Farm

Nadder

@ Donhead Hall

Ebble @

Ebbesbourne WakeWylye @

Hill Deverill

Wylye @

Brixton Deverill

Wylye @

Kingston Deverill

m AOD

1:250k Geology Outcrop 3D Drape

Wylye @

Hill Deverill

Wylye @

Brixton Deverill

Wylye @

Kingston Deverill

Sem @ Cools Cott. Sem @ Priors Farm

Nadder

@ Donhead Hall

Ebble @

Ebbesbourne Wake

ClayClay

GreensandGreensand

ChalkChalk


Base of the Chalk: BGS 50m grid surface with structure lines

Anticlines

Synclines

Faults


1:250k Geology Outcrop 3D Drape with structure lines

Anticlines

Synclines

Faults



groundwater

table geology

≠

outcrop geology

Cross SectionNorth South

UGs

ZZCk

WMCk

NpCk

HCk

LeCk

SCk

PCk

CCk

NCk

Flinty hardground or

marly flow horizons

Whitway Rock

~ 35 – 55 m a b SCk

Chalk Rock

~ 5 m a b LeCk

Melbourne Rock & Plenus

Marls ~ 0 m a b HCk

Groundwater

table

High GW table

Low GW table

Reading Beds

Chalk

Upper Greensand


…variation in

marly clay

content, porosity,

fracture

stratigraphy and

major spring lines

Plenus MarlMelbourn Rock

Chalk Rock

Whitway Rock

Chalk - not just ‘white stuff’

from Mortimore &

Pomerol, 1998

& Mortimore 2001,

2007.

Important flow

and marl

horizons from

Hants & Dorset

modelling

Springheads: Upper Greensand 'header

tanks', Plenus Marls, faults, hardgrounds

West Park Farm Member

Chalk

Upper Greensand

Plenus

Marls*

Faults

London Clay

Gault Clay

1:50k mapped rivers

Scarp slope springs at the edge

of the aquifer system

Dip slope springs from the Upper

Greensand/Chalk boundary, the

Plenus Marls, or faults

Dip slope springs at edge of

confined zone

Frome

Piddle

0 5km0 5km

*Plenus Marls drawn at approx.

intersection with min. GW level

No

rth W

inte

rbo

urn

eB

ere

Stre

am

South Winterbourne

Upwey

Empool

Hooke

Bride

Syd

ling

Win

Devil's

Bk.

(a)

Springheads: Upper Greensand 'header

tanks', Plenus Marls, faults, hardgrounds

(b)

New

Pit C

halk

Holyw

ell Chalk

Zig Zag Chalk

Upper G

reensand

Lewes N

odular

Chalk

Seaford C

halk

Devil's Brook

Perched & leaking reach

Strong

gain

Perched

Gaining

Observation boreholes with

monitored section and water level

water table

Plenus M

arls

Public Water

Supply

0 500 m0 500 m

80

60

40

m

AOD

100

North South

Chalk interfluve – valley groundwater flows

suggests 'high GW level + intense recharge overflow'

karstic response (but not limited to particular formations)

60

50

40

30

20

m AOD

~ 1 kmTarrant Crawford Drove

groundwater hydrograph

Tarrant Keyneston Manor

groundwater hydrograph

10

0

The Tarrant

(winterbourne)

Dominant GW flow

direction out of page

towards Stour (~ 2 km

south @ ~22 m AOD)

K

Interfluves

Valleys

~ east~ west

Variable

Hydraulic

Conductivity

with Depth

Hydraulic

Conductivity,

K

Max GW Level

Min GW Level

Mostly abandoned

(unsaturated) fissure

system (high GW

level 'overflow')

-10

High GWL

'overflow'

fissures

Present

day zone

of active

flow for

most of

the time

Key

'Hardground'

enhanced fissuring

characteristic "UCU"

hydrograph

Upsidedown

Cow's

Udder

Daily measured river flow contrasts

Nadder

Upper Wylye

Ebble

…lots of GW baseflow but

some big runoff spikes too

Local catchment geology and slope details

…from British Geological Survey 1:50 k map


…based on 50 m grid of elevations from Ordnance Survey


white = flat red = steep

Looking east down the Wylye

Upper Greensand

Chalk

Looking east down the Wylye

Looking south west up the Wylye

Looking south west up the Wylye

Looking east down the Nadder & Ebble

Upper Greensand

Chalk

Clay

Looking east down the Nadder & Ebble

Looking west up the Nadder & Ebble

Looking west up the Nadder & Ebble

Wessex Basin Modelling

focused on low flow impacts

Recent Actual Q95

minus

Natural Q95,

Ml/d

Wessex Basin Modelling

focused on low flow impacts

Recent Actual Q95

Compliance with

WFD flow

screening

thresholds

DRAFT!

But what happens

during storms?

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

0

200

400

600

800

1000

1200

1400

1600

Jan 00 Jan 01 Jan 02 Jan 03 Jan 04 Jan 05 Jan 06 Jan 07

Flo

w (

Ml/d

)

Amesbury Observed (Ml/Day)

Amesbury Modelled (Ml/day)

0

200

400

600

800

1000

1200

1400

1600

Jan 00 Jan 01 Jan 02 Jan 03 Jan 04 Jan 05 Jan 06 Jan 07

Flo

w (

Ml/d

)



Amesbury observed & modelled

0

50

100

150

200

250

300

350

400

450

500

Jan 06 Jan 07

Flo

w (

Ml/d

)



Amesbury observed & modelled

0

50

100

150

200

250

300

350

400

Jan 06 Jan 07

Flo

w (

Ml/

d)

Stockton Park Observed (Ml/Day)

Stockton Park Modelled (Ml/day)

Stockton Park observed & modelled

0

20

40

60

80

100

120

140

160

180

200

Jan 06 Jan 07

Flo

w (

Ml/

d)

Laverstock Observed (Ml/Day)

Laverstock Modelled (Ml/day)

Laverstock observed & modelled

What happened in July 2007?

20 July 2007

00:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

00:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

01:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

01:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

02:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

02:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

03:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

03:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

04:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

04:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

05:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

05:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

06:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

06:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

07:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

07:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

08:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

08:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

09:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

09:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

10:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

10:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

11:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

11:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

12:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

12:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

13:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

13:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

14:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

14:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

15:00

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

15:30

Flow gauging

stations

Amesbury

Stockton Park

Laverstock

T

C

Bo

F

Bl

Sw

T

C

Bo

F

Bl

Sw

Processed TBRs

Tisbury

Castleton

Bowerhill

Friar Waddon

Black Lane

Swanage

May – July

200% of LTA

2007 floods were extreme:

Rainfall 19-20 July

Top of catchment ~30mm

(compared to >125mm at

Teweskbury!)

Bourne Bottom Borehole

86

87

88

89

90

91

92

93

94

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Wa

ter

lev

el

(mA

OD

)

GW recharge & baseflow occurred…

…what does this mean for pollution?

0

2

4

6

8

10

12

1990 1995 2000 2005 2010

Nit

rate

Co

nc

en

tra

tio

n (

mg

/l N

)

40

60

80

100

120

140

160

Wa

ter

Le

ve

l a

t W

oo

dy

ate

s O

BH

(m

AO

D)

Drinking Water Standard

Site Measured Nitrate

Woodyates OBH Water Level

NO3

at

PWS

Water

Level

at

OBH

Short term nitrate spikes at PWS sources are

evidence for smd bypass and rapid fracture

unsaturated flow recharge to groundwater.

Infiltration

recharge

drives slow

movement of

historically

leached NO3

Slow plug flow

through the

Chalk matrix

Rapid flow

through Chalk

fissures

Rapid fracture

recharge

sends through

spikes of this

month's (?)

leaching

Short term nitrate spikes at PWS sources are

evidence for smd bypass and rapid fracture

unsaturated flow recharge to groundwater.

What about Phosphate?

Even on the ‘baseflow

dominated’ chalk,

worked fields, tracks

etc generate turbid

runoff during intense

storms

…probably the way

most diffuse P and fine

sediment gets into the

rivers (i.e. NOT via

‘groundwater’)?

Topography

Modelling maps and data (250 m grid, 1970 – 2009 daily rainfall-runoff,

total river flow for 3 time steps/month)

4R Model: Routing



Soils



Soils (simplified)



Landuse (500m)



4R: Soil/Land

Combos



Infiltration Recharge (LTA Annual

Average mm/a)



Bypass Recharge (LTA Annual Average

mm/a)



Runoff (LTA Annual Average mm/a)



Interflow (LTA Annual Average mm/a)



Runoff Recharge (LTA Annual Average

mm/a)



Total Available Water (LTA Annual

Average mm/a)





GW Model Build Information



GW Model transmissivity – how easy is

flow through the ground?

Modelled GW levels



Wet winter



Modelled GW levelsDry Summer



Modelled flows from

GW into the rivers

Wet winter



Modelled flows from

GW into the rivers

Dry Summer

Abstractions & Source Protection Zones



Unsaturated Zone Travel Times - Low GW Levels

(assuming slow plug flow)





Unsaturated Zone Travel Times - High GW Levels

(assuming slow plug flow)

Contributing GW catchment Areas – fraction

of the recharge which ends up in the river





Daily rainfall, runoff, recharge from 4R



Gauged & modelled total river flow from MODFLOW

(Wylye @ Brixton Deverill)




(Nadder @ Wilton)




(Ebble @ Nunton Bridge)

Presentation & proposed report outline

Understanding

The big picture context

Demo catchment detail

Storm rainfall and flood responses

Modelling & data availability

With comments on possible diffuse pollution pathways

Report out by end of March!

Understanding & modelling rainfall to runoff, recharge and river

Documents