Beach-dune interaction for dynamic coastal management

Faculty of Geosciences

Faculty of Geosciences

Beach-dune interaction for dynamic coastal management

Gerben Ruessink

Faculty of Geosciences

Beach-dune interaction

Urgency:• nature restoration• long-term coastal safety

No sand sharing: (1) loss in geomorphological dynamics(2) loss in biodiversity(3) no vertical growth with sea-level rise

Dune erosion Dune growth

Faculty of Geosciences

Building with Nature: Sand Engine

5 July 2011 10 January 2012

1 October 2013 1 oktober 20134 May 2015

Faculty of Geosciences

Building with Nature: Sand Engine

Beach-dune interaction:

• Short gradients (new embryo dunes)

• Foredune growth ~ 15 m3/m/year

• No dune erosion

Faculty of Geosciences

Building for Nature: NWNKern

Faculty of Geosciences

Building for Nature: NWNKern

Trenches:V- to U-shape

Construction After 2 years

Foredunescarping

Sedimentationlobes

Faculty of Geosciences

Combination: HPZ

Faculty of Geosciences

Questions

• How much sand is actually blown toward the dunes?

• Which factors affect this amount?

• What to expect from dune remobilization?

• Are present-day large-scale measures effective?

• Can nourishments and dune remobilization be combined?

• …

Faculty of Geosciences

Needs

• Experiments: Learning by doing

• Long-term (years) monitoring with high resolution (seasons)

• Close co-operation between stakeholders and scientists

• Models with different complexity

• …

Faculty of Geosciences

Beach-dune interaction: models

Keysers et al. (2014)Plos ONE

Poseidon Aeolus

Faculty of Geosciences

My projectBeach-dune interaction: models

Need

Accurate predictive

model of aeolian sand

supply

Challenges

Supply limitation

1. How wet?

2. When?

3. How much?

4. Upscaling

Faculty of Geosciences

Timing of aeolian events

Potential transport

• Events (4 hrs > 8 m/s)

• Hsu (1974)

Observed transport

• Sand-strip activity

Faculty of Geosciences

Timing of aeolian events

Mismatch between potential and actual events:

• Moderate wind speeds: considerable aeolian activity

• Large speeds are large: no aeolian activity

Faculty of Geosciences

Considerable aeolian activity under moderate, shore-oblique/parallel winds

Timing of aeolian events

Faculty of Geosciences

Timing of aeolian events

No aeolian activity under strong shore-normal / oblique winds because of surge

Faculty of Geosciences

Summary

• From preventing dune-erosion to beach-dune interaction

• Building with and for Nature

• Practice-inspired questions and scientific ideas

• Pilot experiments: ‘Learning by doing’ with long-term

monitoring to eventually predictively understand

Only then ready for the challenges of the decades to come

Faculty of Geosciences

Faculty of Geosciences

Surface moisture content

saturated

Reflection (dB)

Mo

istu

re c

on

ten

t (%

)

dry

Faculty of Geosciences

Surface moisture content

Faculty of Geosciences

Mismatch between potential and actual events:

• Moderate wind speeds: considerable aeolian activity

• Large speeds are large: no aeolian activity

Timing of aeolian events

Faculty of Geosciences

Transport magnitude

Faculty of Geosciences

Results (Xaver)

-80 -70 -60 -50 -40 -300

5

10

15

20E

lev

atio

n (

m M

SL

)

-80 -70 -60 -50 -40 -300

5

10

15

20

Ele

vat

ion

(m

MS

L)

Distance (m)

beforeafter

I. Destruction of new foredune and embryo dunes-80 -70 -60 -50 -40 -300

5

10

15

20

Ele

vat

ion

(m

MS

L)

-80 -70 -60 -50 -40 -300

5

10

15

20E

lev

atio

n (

m M

SL

)

Distance (m)-80 -70 -60 -50 -40 -300

5

10

15

20

Ele

vat

ion

(m

MS

L)

-80 -70 -60 -50 -40 -300

5

10

15

20

Ele

vat

ion

(m

MS

L)

Distance (m)

II. Failure of dune front with successive rotational slides

beforeafter

Faculty of Geosciences

-80 -70 -60 -50 -40 -300

5

10

15

20E

lev

atio

n (

m M

SL

)

-80 -70 -60 -50 -40 -300

5

10

15

20

Ele

vat

ion

(m

MS

L)

Distance (m)

beforeafter storm

recovery

Results (post-Xaver)