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Slide 1

Nuclear-1 EIA

Key Stakeholder Workshop& Public Meeting

25 May 2010

Dune geomorphology

by Dr Werner Illenberger

Illenberger & Associates

Slide 2

Experience:

26 years research and consulting in physical coastal environment

Worked on dunes of the whole SA coast and Namibia

Broad multi-disciplinary knowledge of the coastal environment

Illenberger & Associates

Slide 3

Headland-bypass dunefields in the Cape St Francis area

Sand moves from west to east through the dunefields

Mapped from 1961 aerial photographs.

Thyspunt

Slide 4

Figure 2.xx31. Geomorphologic map of dunefields on the Cape St Francis headland, based on the1985 aerial photographs . The Santareme dunefield is mapped as it was in 1961. T he northern margin of the dune sands is from geological maps (Council for Geoscience, 2008). From Bur kinshaw (1998).

Oyster Bay dunefield

headland-bypass dunefield – mobile sand dunes

Vegetated parabolic dunes

Sidewalls of previously mobile dunefields

Thyspunt

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Slide 5

Burkinshaw, J.R. (1998) Morphodynamics of headland-bypass dunefields with particular reference to Cape St. Francis headland, Eastern Cape, South Africa. PhD thesis, University of Port Elizabeth, 373 pp.

La Cock, G. & Burkinshaw, J.R. (1996) Management implications ofdevelopment resulting in disruption of a headland-bypass dunefield and its associated river, Cape St. Francis, South Africa. Landscape and urban planning, 34, pp.373-381.

McLachlan A., Illenberger W.K., Burkinshaw J.R. & Burns M.E.R. (1994) Management implications of tampering with littoral sand sources. J Coastal Research Special Issue No. 12, pp 51-59.

Illenberger, W.K. (1993) Variations of sediment dynamics in Algoa Bay during the Holocene. S Afr J Sci 89, 187-196.

Investigations undertaken in the dune geomorphology, wetlands, groundwater, surface water & geology reports as part of this EIA.

MSc in progress: Lauren Elkington, Rhodes University.

Are the dune geomorphology, groundwater & surface water dynamics well-understood?

Slide 6

An MSc thesis entitled “Morphology, patterns and processes in the Oyster Bay Dune field system” by Ms Lauren Elkington is at an advanced stage.

This is a work in progress, and the data collected cannot be presented or discussed here until the MSc is completed.

However, if the thesis is completed before the final Environmental Impact Assessment Report is completed, the results will be incorporated.

This course of action was agreed upon after discussion with Fred Ellery and his group.

MSc in progress: Lauren Elkington, Rhodes University

Slide 7

Detailed terminology for the Oyster Bay dunefield, mapped from 1942 aerial photographs.

The extent of unvegetated dunes before artificial vegetating with Rooikrans can be seen by comparison with the 1985 aerial photograph (next slide).

Thyspunt(off map)

Slide 8

Overall view of headland-bypass dunefields at Cape St Francis in 1985. Comparison with the 1942 photograph (precious slide) shows the changes in the margins of the dunefields between 1942 and 1985.

The next slide depicts these changes.

Dunes artificially vegetated when Oyster Bay was developed

Dunes artificially vegetated when St Francis Bay was developed

Dunes artificially vegetated

Dunes artif iciallyvegetated

Thyspunt

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Slide 9

Headland-bypass dunefields showing changes in the margins of the dunefields between 1942 and 1985. Since 1942 the dunefield has become progressively more vegetated, both within the dunefield and along the northern margin, mostly by various invasive alien Acacia species, dominantly Rooikrans.Note the areas where the dunefields have transgressed over previously vegetated areas due to the natural advance of the dunefields.

Thyspunt

Slide 10

Dunes are on average 20 m high in the west, and gradually becomeDunes are on average 20 m high in the west, and gradually become smaller smaller towards the east, where the average height is 5 m. towards the east, where the average height is 5 m.

Because the volume of sand moving is approximately constant, a lBecause the volume of sand moving is approximately constant, a larger arger dune moves slower, and conversely a smaller dune moves fasterdune moves slower, and conversely a smaller dune moves faster

Dunes move by wind blowing sand up the Dunes move by wind blowing sand up the windward slope, whereupon the sand windward slope, whereupon the sand avalanches down the avalanches down the slipfaceslipface

windward slopewindward slope slipface

slipface

Slide 11

the same interdune pond, full

and empty

Wetlands very

dynamic

Slide 12

rainfall history: rainfall history: March 2007: 176 mm; 175 mm over 3 daysMarch 2007: 176 mm; 175 mm over 3 days

May 2007: 179 mm;161 mm over 3 days May 2007: 179 mm;161 mm over 3 days August 2007: 142 mm; 56 mm over 3 daysAugust 2007: 142 mm; 56 mm over 3 days

((followed by184 mm over 1 day (120 mm in 4 hours) on 23 November followed by184 mm over 1 day (120 mm in 4 hours) on 23 November 2007)2007)

Wetlands & surface water,Wetlands & surface water,

Aerial photo of 1 September 2007Aerial photo of 1 September 2007

Oyster Bay DunefieldOyster Bay Dunefield

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Slide 13

Ridge crestlineabout 100 m amslCrestline slopes

gently to the southeast

Slope 1:85

Slope 1:135

level

Slopes of the interdune surfaces in the Oyster Bay dunefield. The slope is steeper in the eastern sector of the dunefield. Base photo is the Google image of 2004.

Thyspunt Slide 14

Sand River; f lows another 3.5 km into Kromme estuary: steeper gradient, smaller dunes, larger catchment

2 km

Ridge crestline

Surf ace flow. Channels are not persistent, but v ary according to dune migration. No f low during dry periods.

Penny Sands River soaks aw ay in the large dunes of the western sector: lower gradient, bigger dunes, smaller catchment.

Surface flow in the Oyster Bay dunefield. Only the main drainage channels of the Sand River and Penny Sands River are shown in the farmlands. Base photo 5 Sept 2000.

Base photo 5 Sept 2000 Thyspunt

Slide 15

The “terminal pond” of the Penny Sands River.

Slide 16Base photo 5 Sept 2000

2 km

Ridge crestline

Sand River