Impact of Groundwater Abstraction on Wetlands Tim Lewis, Entec UK Groundwater Modelling Workshop: Groundwater – Surface Water Interaction, Birmingham,

Impact of Groundwater Abstraction on Wetlands

Tim Lewis, Entec UK

Groundwater Modelling Workshop: Groundwater – Surface Water Interaction, Birmingham, 28 March 2007

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Key Questions

Processes & Representation

Foulden Example

Foulden Model

Soils

Summary:Adverse Effect

Spatial Variability

Overall Summary

Outline

why are we interested & what questions are we trying to answer?

how are we representing wetlands?

how do we assess 'impact'?

what do we do well and where is there room for improvement.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Key Question(s)

Habitats Directive (HD) Review of Consents (RoC) requires positive demonstration of 'no adverse effect on integrity of the site' (impossible?)

ecological communities (and species within them) have different requirements

relative lack of hard information on ecological history and water needs means that 'targets' (against which to measure no adverse effect) are not very well constrained.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Key Question(s)

HD fits into Agency Restoring Sustainable Abstraction (RSA) programme, which also integrates with CAMS, WFD, assessment of non-RoC sites etc.

sustainability is the key (both in terms of ecology and water abstraction)

how to assess presence/absence of 'adverse effect', and what to do about it?

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Context: Anglian Region Groundwater Models

RoC sites

N.B. Some are too small to show at this scale.

Also, there are many other 'non-RoC' sites which still require 'protection'.

Groundwater Abstractions

(several thousand)

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Context

For the Habitats Directive, it is the consent which is reviewed, not just current or recent abstraction, so we also need to consider a 'fully licensed' case

RSA has a wider remit, so also need to consider stream flows etc.

Habitats Directive in theory requires assessment of 'alone' and 'in combination' effects: in many circumstances 'alone' is only of theoretical interest

realistically, a wider 'catchment' view is needed to permit sensible regulation

N.B. Other issues such as site management need to be considered, but not today!

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Processes & Representation: what's special about wetlands?

very shallow water table conditions, often maintained by upward flow and discharge of groundwater

riparian conditions, evaporation from water table

spatial variability is of interest, e.g. hummocky micro-topography important for some ecologies to maintain diversity of species within communities

in detail, water regime is complex.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Wetland Mechanisms (WETMECS) (from 'Wetland Framework for Impact Assessment' (Draft))

essentially, different configurations of springs, upflows, seepages etc.

several WETMECs may be operative at a site, and within a small space

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Representation

for practical reasons (because there are so many sites and abstractions), we have to take a catchment view using a regional model: eventually this will be used to 'optimise' abstraction

this imposes some limitations on geological structure, heterogeneity, feature location/spacing, which means we cannot easily represent all of the 'WETMEC' variability in models

however…we can represent overall behaviour by careful specification of model structure, stream discharges, evaporation etc.

regional models have multiple layers: the third dimension is very important for simulation of upflows

can learn much from modelled water balances of selected areas.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary


detail is VERY complicated groundwater processes surface water processes soil processes not coupled: tricky to maintain consistency.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary


4R recharge & runoff calculator

MODFLOW groundwater

model

PE, recharge, runoff

calculates head, flows, storage

change etc.

water level

soil moisture

calculation

Rainfall, PE

consi

sten

cy? consistency?

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Example: Foulden Common, part of the 'Norfolk Valley Fens SAC'

Foulden Common

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Norfolk Valley Fens

what's important?– moisture conditions, combination of

water level and variationsmoisture content in the soil (unsaturated zone)

– throughflow of water from Chalk (upflow)– maintain discharge to stream

impact: some kind of change in what's important!– but what kind of change?– and how much/how long?– what is 'acceptable'?

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common from the air (obviously!)

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: LIDAR

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: Ecology

i.e. variable!

Also, note that maps like these usually show communities: there is significant variation of species (possibly with

individual water 'requirements') within these.

Regional Hydrogeology

•Wetland exists due to proximity of regional groundwater table to the ground surface.

•The vertical fluctuation of the water table dictates spring flows and water supply to the pingos.

•Regional groundwater flow from west to east.

•Groundwater emerges as springs feeding the drains and the pingos.

•Seasonal Chalk Fluctuations in the order of 1-2m.

Talents Fen

•The Chalk and Drift are hydraulically connected. Fluctuations in the Chalk are quickly reflected as similar fluctuations in the drift and pingos.

Gooderstone Fen

•Strong spring flow maintained throughout the year

NE Foulden Common

•Downward vertical movement of water from Foulden Drain to drift and potnetially to Chalk.

In this area the base of the Foulden Drain intercepts the drift water table and groundwater begins to discharge to the drain. Flow may be sustained by storage in the drift and the pingos close to the drain.

Foulden Common: monitoring

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: simple groundwater level calculation

4

4.2

4.4

4.6

4.8

5

5.2

5.4

5.6

01/01/04 31/01/04 01/03/04 01/04/04 01/05/04 01/06/04 01/07/04 01/08/04 31/08/04 30/09/04 31/10/04 30/11/04

wat

er le

vel a

nd

key

ele

vati

on

s (m

AO

D)

-50

-40

-30

-20

-10

0

10

20

30

rain

fall-

PE

(m

m/d

)

TF70/158 observed water level

cutoff at 'ground level'

limit of unrestricted PE

extinction depth

Rainfall-PE

If we make some simple assumptions about how evaporation varies, we can calculate a groundwater level…

GW level

rainfall - PE

4

4.2

4.4

4.6

4.8

5

5.2

5.4

5.6

01/01/04 31/01/04 01/03/04 01/04/04 01/05/04 01/06/04 01/07/04 01/08/04 31/08/04 30/09/04 31/10/04 30/11/04

wat

er le

vel a

nd

key

ele

vati

on

s (m

AO

D)

-50

-40

-30

-20

-10

0

10

20

30

rain

fall-

PE

(m

m/d

)

calculated water level

TF70/158 observed water level

cutoff at 'ground level'

limit of unrestricted PE

extinction depth

Rainfall-PE

PEcrop factor 1Sy 0.1WTini 5.1

WL cutoff at 'GL' 5.3

ElevPEmax 4.8extdepth 4.6

looks good, but doesn't allow for 'upflow', which we know happens, or for any interaction with system external to wetland, so the 'match' may be mis-leading

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: spatial discretisation of model

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Model water levels near Foulden Common

3

4

5

6

7

8

9

Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05

4

5

6

7

8

9

10

5

6

7

8

9

10

11

12

13

14

15

Jan-84 Dec-85 Jan-88 Dec-89 Jan-92 Dec-93 Jan-96 Dec-97 Jan-00 Dec-01 Jan-04

6

7

8

9

10

11

12

13

14

15

16

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: accretion profile data

0

1

2

3

4

5

6

7

8

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600

Distance (m)

Flo

w (

Ml/d

)

Spotflow 31/07/2003

Spotflow 17/09/2003

Spotflow 28/07/2004

AD13 AD14 AD15

stream gauging on 3 separate occasions

(summer)

0

1

2

3

4

5

6

7

8

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600

Distance (m)

Flo

w (

Ml/d

)

Spotflow 31/07/2003

Modelled His 31/07/03Spotflow 17/09/2003

Modelled His 17/09/03

Spotflow 28/07/2004Modelled His 28/07/04

AD13 AD14 AD15

model results (daily calculation) agree well with accretion data

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

0

5000

10000

15000

20000

25000

6.85 6.9 6.95 7 7.05 7.1

observed gaugeboard water level

mo

de

lle

d s

tre

am

flo

w (

m3

/d)

0

5000

10000

15000

20000

25000

30000

2.5 2.6 2.7 2.8 2.9 3


mo

de

lle

d s

tre

am

flo

w (

m3

/d)

Foulden Common: gaugeboard data

0

5000

10000

15000

20000

25000

30000

2.5 2.6 2.7 2.8 2.9 3


mo

de

lle

d s

tre

am

flo

w (

m3

/d) Model Flow at L1R100C125

3-day prior average

'measured' from accretion profiles

0

5000

10000

15000

20000

25000

6.85 6.9 6.95 7 7.05 7.1


mo

de

lle

d s

tre

am

flo

w (

m3

/d)

modelled flow

3-day prior average

'measured' from accretion profile

model 'rating curves' agree well with (limited) observations

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

Foulden Common: vertical flows

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

this is the 'historic' model in a wet period

note effect of large abstraction

note variability across site

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: vertical flows

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

'historic'

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

570000 572000 574000 576000 578000 580000

296000

298000

300000

302000

304000

'naturalised'

note effect in near surface is subtle in wet conditions, more obvious in

dry periods

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: modelled upflow of groundwater

note that difference (between abstraction scenarios) is greater in dry periods

-50

0

50

100

150

200

250

300

350

400

450

J an 88 Dec 89 J an 92 Dec 93 J an 96 Dec 97 J an 00 Dec 01 J an 04

m3/

day

Upwards Flow Historic (85) Upwards Flow Naturalised (75)Upwards Flow Fully 100% Licenced (76) Upwards Flow Abs at 50% recharge (83)Target = 0 m3/d

Flow to Top Active Layer: Gooderstone Fen (Cell 'B') (R99 C126)

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Foulden Common: 'impact'

look at differences between model scenarios– usually a reliable technique (i.e. probably more confidence in

modelled differences than in absolute magnitude)

– BUT, some 'targets' are very specific to absolute levels, so makes it trickier

– targets are debatable: ecological history useful but often absent

– maybe use model results as surrogate (i.e. if we 'know' the site hasn't had a problem under a wide range of climatic conditions with 'historic' abstraction, then we may be able to use 'modelled extremes' as some kind of guide).

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Soils & Soil Moisture

water table is often important, but so may be the availability of water above the water table, within the soil

how to assess change in soil moisture consistently with the regional model?

approach developed with Jan van Wonderen (Motts)

based on standard curves relating soil properties, depth to water table and evaporative (capillary) flux.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Relation between moisture content, depth to water table and capillary flux

Fine Sandy Loam: moisture content vs. depth to water table

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 90

moisture content in root zone (%)

heig

ht o

f cap

illar

y ris

e, i.

e. d

epth

to w

ater

tabl

e be

low

root

zon

e (c

m)

4mm/d flux

3mm/d flux

2mm/d flux

1mm/d flux

0.6mm/d flux

0.2mm/d flux

Fine Sandy Loam Full Saturation (0 bar)

Fine Sandy Loam Field Capacity (0.1 bar)

Fine Sandy Loam Permanent Wilting Point (16 bar)

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Relation between moisture content, depth to water table and capillary flux

Fine Sandy Loam: moisture content vs. depth to water table

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 90

moisture content in root zone (%)

heig

ht o

f cap

illar

y ris

e, i.

e. d

epth

to w

ater

tabl

e be

low

root

zon

e (c

m)

4mm/d flux

3mm/d flux

2mm/d flux

1mm/d flux

0.6mm/d flux

0.2mm/d flux

Fine Sandy Loam Full Saturation (0 bar)

Fine Sandy Loam Field Capacity (0.1 bar)

Fine Sandy Loam Permanent Wilting Point (16 bar)

example: evaporative demand (flux) of 4mm/d, water table at 1m below root zone, moisture content in root zone c. 39% (red line)

if water table drops to 1.2m below root zone, moisture content in root zone drops to c.33% but flux of 4mm/d is maintained (orange line)

If water table drops to 1.2m below root zone, moisture content in root zone must drop to c.33% to maintain flux of 4mm/d (orange line)

N.B. Assumes 'steady-state'

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Transient behaviour

steady-state calcs. may be informative, but we are much more interested in transient behaviour, so..

Treat time as a series of steady-states ‘Knowing’ water level, rainfall and PE (evap. demand)… …and assuming root zone depth and soil type… …can find (by interpolation between graphs) an

‘instantaneous’ solution for each time of interest BUT.. Change in soil moisture contributes to evaporative

demand therefore required flux is less: this is then an iterative problem

Manual calculations are rather tedious, so automate it.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Relation of moisture content, capillary flux and water table depth (from Rijtema, 1969)

5. Humous loamy med-coarse sand0 2 10 20 31 50 100 165 250 500 1000 2500 5000 10000 16000

Flux rate (mm/d) 47.0 46.6 46.0 44.8 44.0 42.4 40.5 37.8 33.6 29.3 23.3 17.4 14.0 11.7 10.58 0.00 1.37 5.22 9.77 14.02 19.67 27.12 29.60 30.32 31.43 32.27 33.05 33.48 33.80 33.977 0.00 1.45 5.55 10.44 15.04 21.22 29.54 32.36 33.18 34.45 35.41 36.30 36.79 37.16 37.356 0.00 1.54 5.93 11.20 16.22 23.06 32.48 35.74 36.69 38.17 39.29 40.33 40.90 41.33 41.555 0.00 1.65 6.36 12.08 17.60 25.25 36.11 39.97 41.12 42.89 44.23 45.48 46.16 46.67 46.954 0.00 1.77 6.86 13.11 19.24 27.92 40.74 45.49 46.91 49.13 50.80 52.36 53.21 53.85 54.193 0.00 1.91 7.44 14.34 21.23 31.27 46.93 53.08 54.96 57.90 60.13 62.21 63.35 64.20 64.652 0.00 2.07 8.14 15.83 23.70 35.60 55.74 64.48 67.26 71.65 74.98 78.10 79.81 81.09 81.77

1.5 0.00 2.16 8.53 16.70 25.17 38.29 61.84 72.90 76.57 82.39 86.81 90.97 93.25 94.95 95.861 0.00 2.27 8.97 17.67 26.84 41.47 69.88 84.99 90.35 98.97 105.57 111.80 115.21 117.77 119.13

0.5 0.00 2.38 9.46 18.76 28.76 45.29 81.30 105.29 115.24 131.86 144.88 157.29 164.10 169.23 171.940.2 0.00 2.45 9.78 19.48 30.06 47.99 91.14 128.91 149.37 186.95 218.20 248.78 265.75 278.53 285.310.1 0.00 2.47 9.89 19.74 30.52 48.97 95.26 142.57 174.19 239.13 297.73 357.54 391.22 416.73 430.270 0.00 2.50 9.99 19.97 30.95 49.89 99.49 162.02 224.39 417.28 698.32 1129.37 1427.64 1670.67 1803.28

Flux rates

Height of capillary rise

Suction (cm)

Moisture content in root zone (%)

N.B. Same data as on graphs

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Relation of moisture content, capillary flux and water table depth (from Rijtema, 1969)

For a given water level (say 30cmbRZ), a number of ranges of ‘states’ are possible

By feeding back the contribution (over a period of time) of soil moisture to the overall demand, we can find the ‘correct’ position in this matrix (i.e. current flux and soil moisture content) by interpolation and iteration. Importantly, we end up with a time series of soil moisture content.

5. Humous loamy med-coarse sand0 2 10 20 31 50 100 165 250 500 1000 2500 5000 10000 16000

Flux rate (mm/d) 47.0 46.6 46.0 44.8 44.0 42.4 40.5 37.8 33.6 29.3 23.3 17.4 14.0 11.7 10.58 0.00 1.37 5.22 9.77 14.02 19.67 27.12 29.60 30.32 31.43 32.27 33.05 33.48 33.80 33.977 0.00 1.45 5.55 10.44 15.04 21.22 29.54 32.36 33.18 34.45 35.41 36.30 36.79 37.16 37.356 0.00 1.54 5.93 11.20 16.22 23.06 32.48 35.74 36.69 38.17 39.29 40.33 40.90 41.33 41.555 0.00 1.65 6.36 12.08 17.60 25.25 36.11 39.97 41.12 42.89 44.23 45.48 46.16 46.67 46.954 0.00 1.77 6.86 13.11 19.24 27.92 40.74 45.49 46.91 49.13 50.80 52.36 53.21 53.85 54.193 0.00 1.91 7.44 14.34 21.23 31.27 46.93 53.08 54.96 57.90 60.13 62.21 63.35 64.20 64.652 0.00 2.07 8.14 15.83 23.70 35.60 55.74 64.48 67.26 71.65 74.98 78.10 79.81 81.09 81.77

1.5 0.00 2.16 8.53 16.70 25.17 38.29 61.84 72.90 76.57 82.39 86.81 90.97 93.25 94.95 95.861 0.00 2.27 8.97 17.67 26.84 41.47 69.88 84.99 90.35 98.97 105.57 111.80 115.21 117.77 119.13

0.5 0.00 2.38 9.46 18.76 28.76 45.29 81.30 105.29 115.24 131.86 144.88 157.29 164.10 169.23 171.940.2 0.00 2.45 9.78 19.48 30.06 47.99 91.14 128.91 149.37 186.95 218.20 248.78 265.75 278.53 285.310.1 0.00 2.47 9.89 19.74 30.52 48.97 95.26 142.57 174.19 239.13 297.73 357.54 391.22 416.73 430.270 0.00 2.50 9.99 19.97 30.95 49.89 99.49 162.02 224.39 417.28 698.32 1129.37 1427.64 1670.67 1803.28

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Comparison of moisture content between scenarios

Flux and Moisture Changes

0

10

20

30

40

50

60

70

80

90

01/01/89 01/01/90 01/01/91 01/01/92 01/01/93

de

ma

nd

, fl

ux

an

d m

ois

ture

co

ntr

ibu

tio

n (

mm

/d)

0

10

20

30

40

50

60

70

80

90

mo

istu

re c

on

ten

t in

ro

ot

zon

e,

str

es

s t

hre

sh

old

an

d f

ield

ca

pa

cit

y (

%)

20. Peat

Note differences here

moisture content 'thresholds' against which scenarios may be

assessed (in some way)

Change in water content between root zone base and water table

Calculated moisture profiles: Peat Soil, 100mm Root Zone, Historic Model Water Levels

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100

moisture content (%)

de

pth

be

low

ba

se

ro

ot

zon

e (

cm

)

31 July 97

31 August 97

30 Sep. 97

WL1 (42.1cm@31/7/97)

WL2 (48.5cm@31/8/97)

WL3 (53.3@30/9/97)

full saturation


0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100


de

pth

be

low

ba

se

ro

ot

zon

e (

cm

)

31 July 97

31 August 97

30 Sep. 97

WL1 (42.1cm@31/7/97)

WL2 (48.5cm@31/8/97)

WL3 (53.3@30/9/97)

full saturation


0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100


de

pth

be

low

ba

se

ro

ot

zon

e (

cm

)

31 July 97

31 August 97

30 Sep. 97

WL1 (42.1cm@31/7/97)

WL2 (48.5cm@31/8/97)

WL3 (53.3@30/9/97)

full saturation

Release of water from storage:

August

September

this is a tricky calculation, but can be done to give time series of storage change

by manipulating data from soil 'property matrix', we can work out moisture profile below the root zone (for the current water level and calculated flux)

this is effectively 'specific yield', but note that the equivalent value is depth-dependent (this is correct, but we usually ignore it)

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Consistency of Process Quantification

apportionment of demand to capillary flux and storage change shows approximate agreement with comparable values from 4R/MODFLOW.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Summary: what is 'adverse effect'?

combination of types of 'criteria' and types of 'breach'

criteria:– water level– upflow/seepage– soil moisture– discharge to stream

breaches– magnitude– frequency– duration– cumulative excess (duration &

magnitude)– timing (seasonal)

target criteria may be established from:– measurement– experience– anecdotal information– model results

absolute criteria may vary between sites

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Good stuff

regional model context: internal consistency and equitable assessment for 'RSA'

making sensible use of all types of model 'results', including water balance components

'interpretation' of comparison between model and observations

soil moisture 'method' allows consideration of changes in soil water without the pain of a variably-saturated model

model allows internally consistent assessment of results against many different types of 'target'

'engagement' between ecologists & hydrogeologists.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Could do better?

ecological history not well established ecological water requirements not well known these mean that precise target setting is fraught

with difficulty inter-relation of coupled processes difficult to

deal with uncertainty in many (all) parameters and

processes small scale spatial variability.

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Spatial variability: possible ways forward

'single cell' model, including soil moisture calc.

'2m' model

and/or stick with informed interpretation (lateral thinking/water balances) of regional model and monitor key responses

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Spatial variability

construct simple model based on LIDAR elevation (2m grid)

ground level acts as 'drain'

upflow through base (value from regional model)

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Spatial variability

dry

wet

headdepth to water (blue

wet, pink dry)

this looks 'real', but actually contains an awful lot of uncertainty: nevertheless it may be useful for assessment purposes, to give some idea of variability on sub-grid scale

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Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Example heads within 'cell model'

4

4.2

4.4

4.6

4.8

5

5.2

5.4

5.6

5.8

6

01/01/70 01/01/72 01/01/74 01/01/76 01/01/78 01/01/80 01/01/82 01/01/84 01/01/86 01/01/88 01/01/90 01/01/92 01/01/94 01/01/96 01/01/98 01/01/00 01/01/02 01/01/04

Back

Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

'Compartmentalised' Single Cell Modelling Concept (from Jan van Wonderen)

ETaETa

ETa Rain

Runoff

Leakage

Upward flux (from regional model)

Lateral flow (from regional model)

calculates local circulation and 'interaction' of

processes

Back

Key Questions


Foulden Example

Foulden Model

Soils


Spatial Variability

Overall Summary

Summary

detail of wetland behaviour is extremely complex need to consider many aspects of water 'regime':

each may give clues/assistance to understanding

models can help, but need lateral thinking around the results

strict 'targets' of 'acceptability' are difficult to define: again models can help set criteria

ecological water requirements and tolerances (for any given site/community) not known with accuracy: there may (always?) be a need for further monitoring and analysis

small scale spatial variability needs to be considered, and possibly 'calculated'.

Impact of Groundwater Abstraction on Wetlands

Tim Lewis, Entec UK

Groundwater Modelling Workshop: Groundwater – Surface Water Interaction, Birmingham, 28 March 2007

Documents

Impact of Groundwater Abstraction on Wetlands Tim Lewis, Entec UK Groundwater Modelling Workshop: Groundwater – Surface Water Interaction, Birmingham,