Determining Sand Migration Rates and Volumes in Cape Recife and Noordhoek Dune Fields

Determining the rate of sand influx and
dune migration in the Cape Recife and
Noordhoek dune fields
By
Lorna Mpenge
Submitted in in partial fulfillment of the requirements for the degree of
BACCALAUREUS SCIENTIAE HONORES, Faculty of Science, Nelson Mandela
Metropolitan University, Port Elizabeth, December 2016.
Supervised by: Mr. Callum R. Anderson
I, the undersigned, confirm that the following treatise is entirely my own written
work, unless otherwise credited.
Sign and date

i
Acknowledgments
I would like to extend my sincere appreciation to the following people, without them,
this project was not going to be a success:
 Port Elizabeth airport for supplying wind data
 My supervisor Mr. Callum Anderson for giving me the opportunity to work with
him. I am extremely thankful to him for sharing expertise, valuable guidance and
encouragement he extended to me.
 My co-supervisor Prof Mikes for his support.
 I am very thankful to Gerrit Goosen for sharing his experience about the field and
his assistance on fieldwork activities. I would also like to express my special
thanks to Geology honours class of 2016 for motivating me.
 Muofhe Tshibalanganda for being a good friend and helping on field
experiments.
 My family especially my mother for her support and believing in me, I dedicate
this to her.
 And finally I would like to thank my boy friend Sizinzo Alex Majola for his
contineous support and being my shoulder to cry on.

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Abstract
Prior to stabilization the three bypass dune fields at the Cape Recife headland in Port
Elizabeth used to supply sand to the Algoa Bay beaches. Driftsand and Noordhoek dune
field were both stabilised to accommodate human activities. Before stabilization the
Algoa Bay beaches used to receive an estimated 107000m3
volumes of sand annually
(McLachlan et al, 1994).
Cape Recife is currently the only active dune field supplying the sand to the Algoa bay
beaches. The main aim of this study was to determine the amount of sand received by the
Noordhoek and Cape Recife dune fields and compared the values to the volumes of sand
supplied to the Algoa Bay beaches. A number of fieldwork experiments were conducted
to collect the data that was used together with theoretical calculations to determine the
behaviour of the two dune fields.
The results revealed that both dune fields migrated in an ENE direction at a rate of
31m3
/m/y in response to the dominating WSW wind blowing in the study area. An
estimated sand volume of 9062m3
/y and 10937m3
/y, were calculated to enter the Cape
Recife and Noordhoek dune field respectively. These values suggests that if the
Noordhoek dune field was not stabilised, Algoa Bay beaches would receive an estimated
volume of 19999 m3
/y, but only 45% of that migrates across the headland.
The ENE migration of the Cape Recife dune field posed negative environmental impacts
on human activities. The lighthouse and car road is covered by sand during strong WSW
wind seasons. Various measures have been employed to minimize the impacts. These
include the car tyres and the heavy manganese rocks that have been dumped on the sand
dunes to lower the migration rate but clearly the attempts did not work. The question
now is whether the dune should be allowed to migrate across the headland if not what
other alternative measures that should be employed to minimise the impacts.

iii
Table of contents
1. Introduction........................................................................................................... 1
2. The objectives of the study ................................................................................... 4
2.1 Study area and the geologic setting................................................................... 5
3. Climate in Algoa Bay ............................................................................................ 6
4. Methods.................................................................................................................. 8
4.1 Traps.................................................................................................................. 8
4.1.2 Laboratory methods................................................................................... 15
4.1.3 Density calculation.................................................................................... 15
4.2 Long term monitoring (erosion rate)............................................................... 16
4.2.1 Field work ................................................................................................. 16
4.3 Volume calculations........................................................................................ 17
4.4 Wind analysis.................................................................................................. 17
4.5 Theoretic sand transport.................................................................................. 17
5. Results .................................................................................................................. 21
5.1 Wind data ........................................................................................................ 21
5.2 Traps................................................................................................................ 22
5.3 Impacts of surface moisture on sediment transportation................................. 30
5.4 Long term monitoring ..................................................................................... 34
5.1 Sand drift potential and Cape Recife sand Budget.......................................... 44
6. Discussion............................................................................................................. 45
6.1 Determining sand flux in Cape Recife and Noordhoek dune fields................ 45
6.2 Dune migration rates ....................................................................................... 50
6.3 Estimated sand volumes moving to adjacent beaches..................................... 54
6.4 Attempted stabilization of Cape Recife bypass dune...................................... 54
7. Conclusions .......................................................................................................... 56
7.1 Environmental impacts of the drifting sand .................................................... 57
7.1.2 Improvements for future studies ............................................................... 57
7.1.3 Sand drift potential.................................................................................... 57
8. References ............................................................................................................ 58
9. Appendix 3: sandtrap data................................................................................. 60
10. Appendix: 6 Sand drift potential calculated data ............................................ 63
11. Appendix 4: Contour maps of erosional and depositional areas in site C ..... 64
12. Appendix: 6 Sand drift potential calculated data ............................................ 66

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List of Figures
Figure 1-1: Worldwide distribution of coastal sand dunes (Martínez et al., 2009)............. 1
Figure 1-2: Map of Port Elizabeth and Cape Recife showing the bypass dunes path ways
before the development (McLachlan et al., 1994). ................................................. 1
Figure 1-3: Series of historical pictures showing the evolution of Cape Recife and
Noordhoek dune fields from 1939 to 2016 ............................................................. 2
Figure 2-1: Google earth image showing location of the Cape Recife and Noordhoek
dune fields. .............................................................................................................. 5
Figure 3-1: Contoured map of Port Elizabeth showing dominant prevailing winds in
Cape Recife (Goschen & Schumann, 2011)............................................................ 7
Figure 4-1: Wedge shaped sandtrap (left) and the cylindrical sandtrap (right) operating .. 8
Figure 4-2: Sites where experiments were conducted. The black dotted lines represents
transects where sandtraps were placed.................................................................. 10
Figure 4-3: Photo showing sandtrapping instruments in operation. Note the sandtraps are
places along the dune crest.................................................................................... 11
Figure 4-4: Annotated Google Earth image showing positions of sandtraps and weather
stations at site lighthouse....................................................................................... 12
stations at site C..................................................................................................... 13
Figure 4-6:Annotated Google Earth image showing positions of sandtraps and weather
stations at site A. ................................................................................................... 14
Figure 4-7: Annotated Google Earth image showing the setup of the erosion pins in site
C. Note the blue pins represent respective location of the erosion pins................ 16
Figure 5-1: Wind data recorded at lighthouse................................................................... 21
Figure 5-2: Wind data recorded in site A.......................................................................... 21
Figure 5-3: Wind data recorded in site C.......................................................................... 22
Figure 5-4: Plot of wind and transport rate against for the sandtrapping experiment in the
lighthouse site........................................................................................................ 23
Figure 5-5: Plot of wind and transport rate against for the sandtrapping experiment in site
C. ........................................................................................................................... 24
Figure 5-6: Plot of wind and transport rate against for the sandtrapping experiment in the
Noordhoek beach site (site A)............................................................................... 25
Figure 5-7: Lighthouse flux data compared with theoretical flux calculated by Bagnold’s
equation................................................................................................................. 27
Figure 5-8: Site A flux data compared with theoretical flux calculated by Bagnold’s
equation................................................................................................................. 28
Figure 5-9: Site C flux data compared with theoretical flux calculated by Bagnold’s
equation................................................................................................................. 29
Figure 5-10: Moisture content for the lighthouse sandtrap experiment............................ 31
Figure 5-11: Moisture contents for the experiment conducted in site A........................... 32
Figure 5-12: Moisture content for the experiment conducted in site C ............................ 33
Figure 5-13: Back dune and front dune moisture content values in site C ....................... 33
Figure 5-14: Sand sediment density plotted against moisture content.............................. 34
Figure 5-15: Contour maps of erosional and depositional surfaces with the wind rose
diagrams. ............................................................................................................... 35
diagrams. ............................................................................................................... 36
Figure 5-17 : Contour maps of erosional and depositional surfaces with the wind rose

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diagrams. ............................................................................................................... 37
diagrams. ............................................................................................................... 38
diagrams ................................................................................................................ 39
Figure 5-20: Dune migration and drift direction of site C ................................................ 41
Figure 5-21: Correlated migration rates of the two dune in site C.................................... 42
Figure 5-22: Stoss and slipface volumes calculated from 31 March to 23 August 2016 at
site C...................................................................................................................... 43
Figure 5-23: Wind rose diagram showing winds blowing in Cape Recife. ...................... 44
Figure 6-1: Photo of the Cape Recife beach site, during the sand trapping experiment.
The patches of wet sand exposed on the surface (red-dotted lines)...................... 46
Figure 6-3: photo showing the upper beach section of the sand trapping experiment at
site A. .................................................................................................................... 48
Figure 6-4: Photo showing sandtrap set up on the middle beach section at Site A. Note
red dotted areas ( wet patches of sand), blue arrows represent wind direction..... 49
Figure 6-5: Photo showing sandtrap set up on the lower beach section at Site A. Note red
dotted areas ( wet patches of sand) blue arrow represents wind direction............ 49
Figure 6-6: scatter plot of the volume moved at the slipface (positive - deposition) vs.
volume moved along the stoss surface (negative - erosion) for site C.................. 52
Figure 6-7: a cartoon showing the transportation paths of sand before accumulating on
the slipface. The dotted grey line represents how dune move in response to wind.52
Figure 6-8: Photo of avalanching slipface. Note areas surrounded by purple dotted lines
(dune avalanche) ................................................................................................... 53
Figure 6-9: photo of the Cape Recife dune field. Note the area surrounded by black
dotted line contains car tyres and heavy manganese rock fragments. This was the
attempt to stabilise the dune.................................................................................. 55
Figure 6-10: photo of the lighthouse covered by sand on the western side. ..................... 55
Figure 10-1: photo of Site A sand trapping experiment. Note the cloud of sand saltating
above calcrete ridge. Red arrows indicate the sand being transported through the
calcrete ridge gaps (cloud of saltating sand). ........................................................ 63

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List of Tables
Table 4-1: threshold velocities for different grain sizes (Dong et al., 2003). ................... 18
Table 4-2: Average grain size (mm) of sediment in the Noordhoek dune field (Goosen,
2014)...................................................................................................................... 18
Table 5-1: Estimated annual sand flux rate....................................................................... 26
Table 5-2: The migration rate of the two dunes in Site C................................................. 40
Table 5-3: Sand flux rate for the Cape Recife and Noordhoek dune fields ...................... 44

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1. Introduction
Aeolian dunes occur in a range of environments on Earth and as well as other planets
like Mars (Kocurek et al., 2012). The largest dunefields on Earth occur in arid-semiarid
areas e.g. Sahara and Kalahari deserts.
Smaller dunefield are common along many coastlines around the world that are exposed
to strong winds with plentiful sediment supply (Figure 1-1). They are highly variable
when it comes to their size and mobility. The dunes that form along the coastal areas get
their sand sediments from the adjacent beaches (McLachlan et al., 1994)
They range in size from the large Alexandria dunefield (120km2
) to small foredune
systems adjacent to beaches (Watson, 1996) .
The Southern Cape coast is characterised by a series of arcuate bays separated by the
quartzites of the Table Mountain group. The sand migrates across these rocky headland
to form headland bypass dunes (McLachlan et al., 1994). They are referred to as
headland bypass dunes because of their nature of migration, whereby the sand from one
coast line migrates across the headland to get to the adjacent coast line (Boeyinga et al.,
2010) .
Figure 1-1: Worldwide distribution of coastal sand dunes (Martínez et al., 2009).

1
In the Port Elizabeth area three such bypass systems occur (Figure 1-2), but two of these
dunes are currently inactive following their stabilization. The Driftsand and the
Noordhoek dunefields were successfully stabilised in the 1960’s (McLachlan et al.,
1994). However, the western section of the Noordhoek dune field is currently forcing its
way eastward (Figure 1-3).
Figure 1-2: Map of Port Elizabeth and Cape Recife showing the bypass dunes path ways
before the development (McLachlan et al., 1994).
Historically all the three bypass dune fields used to supply sand to the Algoa bay
beaches. The Summerstrand and the Schoenmakerskop areas were entirely covered by
the Driftsands dune field. In mid1800s people felt threatened by drifting sand and they
decided to stabilise it (McLachlan et al., 1994).
The Driftsand was stabilised in 1875 by covering it with the brushwood and seeds. It
took about 35 years before the dune system came to a standstill. By the year 1910 the
Driftsand dune field was vegetated and inactive (Goschen & Schumann, 2011).
Vegetation of Noordhoek dune field began in 1969 (Figure 1-3). The Noordhoek eastern
portion was stabilised to protect the sewerage maturation ponds. By 1978 there was no
sand passing across the headland. Since then the dune has moved over some of the
previously vegetated areas.
At present, the only active bypass system is the Cape Recife dune system at the
southernmost tip of the headland.

2
Figure 1-3: Series of historical pictures showing the evolution of Cape Recife and
Noordhoek dune fields from 1939 to 2016

3
Initially sand transportation rate for the Cape Recife dune systems was estimated to be
70m3
/m/ y (CSIR, 1970). This prediction was based on the dune migration rate of which
the dune shape was not considered. According McLachlan (1994) the value was probably
an overestimation.
Sand drift potential rate of 84 m3
/m/y. was calculated by McLachlan (1994) using wind
data that was recorded by the mobile weather station that were deployed at Cape Recife.
Taking into account salt encrustation this estimate was reduced to 42m3
/m/y.
Cape Recife and Noordhoek dune fields were then estimated to receive 12000 m3
/y. and
25000 m3
/y. respectively prior to stabilisation (McLachlan et al., 1994).
However, these estimates are probably invalid by now since the study was performed
almost ten years ago. The widths of both Noordhoek and Cape Recife dune field systems
have changed, thus the sediment flux rate must be different.

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2. The objectives of the study
This study aims to characterise sand transportation rate in the two small bypass dunes in
Cape Recife: the lighthouse and the Noordhoek. The main objective is to improve on the
previous estimates done by McLachlan (1994).
In order to achieve the aim the objectives were to:
 determine the sand flux in the Cape Recife and the Noordhoek dune fields.
This involved measuring sand flux in the field, calculating theoretical flux using wind
data and Bagnold’s equation. Theoretical and the measured flux were compared. Annual
sediment flux rate was estimated from both theoretical and measured sediment fluxes.
 calculate the volume of sand moving in Noordhoek and relate it to the rate of dune
migration.
The volumes of sand calculated were then correlated with the wind data
 estimate the amount of sand that is moving from the Cape Recife to the adjacent
beaches. This was done by using the wind data and Frybergers’s equation.

5
2.1 Study area and the geologic setting
The Cape Recife is located in Port Elizabeth the southern section of the South African
coastline. Cape Recife is a rocky headland of Table mountain sandstones. With its
northern section backed up with sandy beaches.
Figure 2-1: Google earth image showing location of the Cape Recife and Noordhoek
dune fields.

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3. Climate in Algoa Bay
The climate determines the nature of the dune movement. The wind, temperature, and
precipitation play major role in transporting sand particles and development of dunes in
the coastal areas. Windy climate is the most acknowledged one that helps to shape, dry
and move sand.
Port Elizabeth has moderate temperatures, ranging from Mediterranean with hot, dry
summers and roughly rainy winters. It is a windy area dominated by West Southwest
winds almost throughout the year (Goschen & Schumann, 2011) (Figure 3-1). The
easterly winds vary seasonally. Both easterly and westerly winds reach their maximum
speeds in October and November. Minimum wind speeds occur in May, June , and July.
October is the windiest month with the average wind speed of 4 m/s for NE winds and
4.7 m/s for south-westerly winds (Goschen & Schumann, 2011).
These seasonal wind variations affect the behaviour of the sand dunes. The rate at which
sand move within these dune fields is influenced by the properties of the blowing winds.
The westerly winds are responsible for the eastward migration of the sand dunes. The dry
and windy summers increase dune migration rate, thus the environmental impacts of the
drifting sand are more pronounced in summer.

7
Figure 3-1: Contoured map of Port Elizabeth showing dominant prevailing winds in Cape Recife (Goschen & Schumann, 2011).

8
4. Methods
Series of experiments were conducted in Cape Recife and the Noordhoek dune fields.
The main objective was to characterise the rate of sand movement in these two dune
fields. According to Lancaster (2009) there are different levels that one can follow when
investigating the behaviour of Aeolian dunes. Level1 uses available climatological data
to estimate sand transportation rate. Level2 make a use of sandtraps. Traps can be
deployed in the field for long-term monitoring. Level3 involves use of electric sensors. in
this project level1&2 were employed.
4.1 Traps
The sandtrap experiments were conducted to quantify sand movement at selected sites in
the Cape Recife and Noordhoek bypass dune fields (Figure 4-2). At the Cape Recife
dune field, an experiment was carried out to determine the amount of sand moving across
the headland to the Algoa Bay beaches. Experiments were conducted on two sites in the
Noordhoek (site A and site C) dune field. The experiment in Site A was conducted to
quantify sand entering the field. In site C and the experiment was done to ascertain sand
transport further inland.
Figure 4-1: Wedge shaped sandtrap (left) and the cylindrical sandtrap (right) operating

9
(i) General experimental procedure
Sand trapping experiments were conducted in series of runs preferably during windy
days. Each run continued for a period of 10-15 minutes depending on the strength of the
wind, for stronger winds, the sampling period was made shorter. Collected sand samples
were then transferred into 300ml sampling plastic bags.
All the sand trapping experiments performed followed the same steps stated below.
 Sandtraps were assigned unique identification number e.g. C1, W1, being
cylindrical sandtrap1 and wedge sandtrap1 respectively.
 Sandtrap inlet openings were covered with the masking tape to make sure that no
sand enters the traps before the commencement of sampling experiment. A
sampling bag was attached to the bottom tube of the trap to collect sand.
 Traps were placed at their specific sampling position facing the wind incident
direction to maximise the sampling efficiency.
 To minimise scouring aluminium plates were added at the base of trap pipe
 The base of the traps were then buried to a depth of 15 mm augured hole to make
sure the trap remains upright even when there are strong winds.
 Starting and the ending time of each run was recorded.
 At the end of each trial, traps were removed from their sampling positions and the
sampling bags were then removed safely.

10
Figure 4-2: Sites where experiments were conducted. The black dotted lines represents transects where sandtraps were placed.

11
(ii) Wind data
Two mobile Davis weather stations were used to record the wind data during the
experiments. The two weather stations were assigned unique names, e.g. weather
station2 (WS2) and weather station3 (WS3).
Data collected by both weather stations was used together with the data acquired from
the Port Elizabeth airport to generate wind roses. The wind data was also used to
correlate with the sand transportation rates.
Figure 4-3: Photo showing sand trapping instruments in operation. Note the sandtraps
are places along the dune crest.

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(iii) Field experiments
Cape Recife Bypass dune experiment1
The experiment was done on the 13th of March 2016 in the Cape Recife bypass dune
field. The study site was located near the lighthouse. Two trials were performed on a
180m long transect. The site was demarcated into two, viz. the northerly active bypass
dunes and the beach area towards the south (Figure 4-4). For this experiment, six wedge-
shaped and 13 cylindrical aeolian sandtraps were used. The sandtraps were placed 2m
apart along the transect. Two trials were conducted.
stations at site lighthouse.
Site C experiment2
The experiment was conducted on the 28th
of March 2016 in the Noordhoek dune field.
The site is characterised by two dunes separated by calcrete layer. The first two trials
were performed on the front dune. The third trial was done on both front and back dunes.
For the first and second trials, the front dune was demarcated into northern and southern
section. Three cylindrical traps with WS2 were places on the northern section and other
three with WS3on the southern section (Figure 4-5). The objective of the first and second
trials was to determine sand transportation rate along the front dune crest. The aim of the
third trial was to compare sediment transport rates on consecutive dunes.

13
stations at site C.

14
Site A experiment 3
The experiment was conducted on the 27th
of June 2016 to determine the amount of sand
entering the Noordhoek dune field. The study site is located on one of the main entry
point of sand into the Noordhoek dune field. The area is characterised by three unique
surfaces viz: the beach zone at the southern section, the northern part there were active
dune small dunes about half meter high. On the eastern side the area there was a
discontinuous calcrete ridge approximately a metre or two meters high.
The sandtraps were placed 8m apart on a 130m transect (Figure 4-6). The traps were
setup in a way that the wedge-shaped sandtraps separated three sequential cylindrical
sandtraps. Two trials were conducted. The first run was 15-minutes long and the second
trial ran for 10-minutes. The second run was made shorter because the wind increased.
Figure 4-6:Annotated Google Earth image showing positions of sandtraps and weather
stations at site A.

15
4.1.2 Laboratory methods
At the end of each experiment, the sand samples collected were taken to the lab for
further analysis. The procedure was as follows:
 Samples were separately weighed.
 A maximum of 20g of each sample was transferred to a measuring beaker and
placed in an oven at 200°C overnight to dry. The dried weight of the sediment
was reweighed.
 Moisture content for each sample was then calculated.
The formula used to calculate the moisture content is as follows:
(Davidson et al., 2005)…...equation 1
Where M is the moisture content.
Wf is the sample wet weight from the field before drying.
Wd is the dry sample from the oven.
4.1.3 Density calculation
The sand samples with maximum, intermediate and low mass were selected for both
dried and moist samples from each experiment. The selected samples were then split up
into 100mm3
polytope and weighed. The following formula was used to calculate the
density.
….equation 2
D = density (g/cm3
)
M = mass (g)
V = volume (100cm3
)

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4.2 Long term monitoring (erosion rate)
Experiments were conducted on site C. The area monitored is situated on the central
stoss of the dune in Noordhoek dune field. A big sand dune backs the site on the western
side (Figure 4-7). The crest of the dune was monitored to quantify volume of sand
moved on the dune. Thirty-four dowel sticks (910 mm x 8 mm) were placed in a 10x10
grid on a front dune stoss to monitor depositing and eroding areas of the dune. The
erosion pins were marked with numbers for identity purposes.
Figure 4-7: Annotated Google Earth image showing the setup of the erosion pins in site
C. Note the blue pins represent respective location of the erosion pins.
4.2.1 Field work
Exposure of the erosion pins above the sand surface was measured every two weeks
from 28 March to 23 August 2016. Pin exposure was adjusted depending if it had been
eroded or deposited. If the pin was buried, broken, or fallen a new pin was added. Pin
positions were measured using a Magellan xxxxxx differential GPS. Throughout the
course of the study new pins were added as a result of either the pin breaking, the crest
migrating too far or from pins being buried from the migration of the slipface.
The distance to crest from the front row pins was also recorded to monitor the crest
migration rate. If the distance to crest was greater than 10m, new pins were placed. The
back pins were used to monitor the slip face migration of the back dune.

17
4.3 Volume calculations
Volumes were calculated to describe the volume of sediment moved on the Noordhoek
dune field. The erosion pins placed in site C were all used to monitor volume of sediment
moved on the dune. The differences in exposure of the pin between time intervals gave
indication of how much volumes of sand moved. The difference in pin exposure would
tell if the sand was lost or deposited.
(i) Stoss face volumes
Surfer v11 was used to calculate the volumes of sand moved on the dune stoss face. The
erosion pin data for the entire study period was imported into the software. This
program’s volume function was used to obtain the amount of sand moved on the dune
stoss.
(ii) Slipface volumes
The amount of sand moved on the slipface of the leading dune at site C was calculated. It
was determined for a period of five months.
The average elevation of both the top of the slipface and the base of the slipface was
calculated using relevant elevation points recorded across dune transects by Magellan
xxxxxx differential GPS. The difference between the average elevation at the top and the
bottom of the dune slipface, together with the angle of repose recorded by the GPS was
used to calculate the length of the slipface. The length of the crests of the dunes were
traced out on Google Earth. To determine the volume of sediment moved: the length of
the crest, the length of the dune slipface, and the distance the dune had migrated were
multiplied by each other
4.4 Wind analysis
The wind data was used to generate the wind rose diagrams. The wind data was acquired
from Port Elizabeth airport. The WRPLOT View software was used to make the wind
roses. To calculate the net wind component, the hourly easterly and westerly wind
frequencies were added. The difference between the two winds gave the dominant net
wind direction, which was then used to explain the direction at which the sand dune is
migrating.
4.5 Theoretic sand transport
The strength of the wind required to dislodge and transport sediments varies according to
the average grain sizes of the sediments (Dong et al, 2003).In Table 4-1 it is

18
demonstrated that bigger sand grains require strong winds from transportation. Grain size
distribution in Cape Recife is displayed in Table 4-2.
Table 4-1: threshold velocities for different grain sizes (Dong et al., 2003).
Grain diameter (mm) Threshold velocity (m/s)
0.80-1.00 12.15
0.63-0.80 11.35
0.56-0.63 9.90
0.50-0.56 9.06
0.40-0.50 8.21
0.25-0.40 7.59
0.20-0.25 7.11
0.15-0.20 5.56
0.1-0.15 4.73
Table 4-2: Average grain size (mm) of sediment in the Noordhoek dune field (Goosen,
2014).
Dry grain diameter (mm) Percentage (%)
1 - 2 0.064 %
0.71 - 1 0.126 %
0.5 – 0.71 0.266 %
0.355 – 0.5 0.752 %
0.025 – 0.355 2.412 %
0.18 – 0.25 26.759 %
0.125 – 0.18 53.569 %
0.09 – 0.125 15.670 %
0.063 – 0.09 0.374 %
0.045 – 0.063 0.008 %
The average sand grain sizes found in the Noordhoek and the Cape Recife was
determined by Goosen (2014) in his honours project. According to this study, 53.6% of
the sediment found in the Noordhoek has diameter ranges of 0.125-0.18mm and that
would mean that a minimum of 5.56m/s wind speed would be required to move
noticeable volumes of sediment in this site.
(i) Sand transportation rate calculated by Bagnold
The Bagnold’s equation was used to calculate the sediment transportation rates on the
three sandtrap study sites. The calculated results were then evaluated by comparing them

19
with the sediment transportation rates measured during the sandtrapping experiments.
The aim was to compare the accuracy of the equation and the efficiency of the sandtraps.
The following equations is an updated version of Bagnold (1935) modified by
Illenberger (1988) was used:
( )
( )
( )
q = is the sand transport rate (kg/m/s);
C = is an empirical coefficient (1.8 for well-sorted sand as found in dunes);
d = is sand grain diameter (e.g. 0.16 mm);
D = is the diameter of a sand grain (0.25 mm);
p = is the density of air (1.23kg/m-3
)
g = is the gravitational acceleration, and V* is the shear velocity.
z= 1m and
k = surface roughness (10mm).
It has been stated that the Bagnold equation does not take into account, surface moisture
content, the vegetation cover and the shape of sediment grains, thus the estimated values
are expected to be higher than the measured transportation rate values (Illenberger &
Rust, 1988).
(ii) Sand drift potential
The sand drift potential calculations were done using the wind data acquired from PE
airport. Hereher (2010) defined sand drift potential to be the volumes of sand moved by
the surface winds. Resultant sand drift potential (RDP) refers to the magnitude of the
drifted sand and the resultant drift direction (RDD) refers to the sand drift direction.
The DP was calculated for the beach sites: the lighthouse in Cape Recife dune field and
site A at the main entry point of the Noordhoek dune field. The resultant drift potential

20
(RDP) and resultant drift direction (RDD) was calculated for each site. The aim was to
determine their annual sand flux.
The following equation by Fryberger (1979) was used to estimate the sand drift potential.
( )
Where DP = sand drift potential (VU)
VU = 0.07m3
/m/y.
V = average wind speed (m/s)
Vt = threshold velocity (5.6 m/s)
t = is the percentage of wind occurrences
The V2
(V-Vt) is referred to as the weighting factor.
If drift potential is presented as a rose the value of a weighting factor is divided by 100.
Areas with strong winds are characterised by high weighting factor values. Weak winds
are characterised by low weighting factor values (Hereher, 2010).
The equation assumes that the sediments are transported over a dry surface with little
vegetation cover. The equation therefore gives overestimated drift potential values.

21
5. Results
A number of experiments were conducted to characterise sand transportation rate in
Cape Recife and Noordhoek dune fields. The data gathered during the study period is
presented in this chapter. Sandtrapping experiments data correlated with wind is
presented first followed dune migration rate. Sand drift potential is presented last.
5.1 Wind data
The wind data measured in the field and the data acquired from Port Elizabeth airport are
roughly equal (Figure 5-1 to Figure 5-3). However, in site C it was not the case, the wind
recorded in the field was 40% higher compared to data obtained at the airport.
Figure 5-1: Wind data recorded at lighthouse.
Figure 5-2: Wind data recorded in site A.

22
Figure 5-3: Wind data recorded in site C.
5.2 Traps
The rate of sand transportation measured by sandtraps showed a great spatial variation
along the experimental transects. The transportation rate increased in correlation with the
wind strength. (Figure 5-4 and Figure 5-5).
Great variations in wind speed were recorded along the dune profiles in site A and
lighthouse. This resulted to variations on transportation along the dune profiles. In both
sites, sand transportation was higher on the mid sections of the dunes rather than the
upper and the baseline sections.
At lighthouse maximum sediment, transportation rates were recorded during the first
trial. The wind speed dropped during the second trial, this the sediment transportation. In
site A maximum sand transportation was recorded during the second trial responding to
rapid increase on wind
Unlike the two other sites, sand transportation and wind speed were roughly constant for
the duration of the experiment in site C (Figure 5-5).

23
Figure 5-4: Plot of wind and transport rate against for the sandtrapping experiment in the lighthouse site

24
Figure 5-5: Plot of wind and transport rate against for the sand trapping experiment in site C.

25
Figure 5-6: Plot of wind and transport rate against for the sand trapping experiment in the Noordhoek beach site (site A).

26
Sand transportation rate calculated by Bagnold
Figure 5-7 to Figure 5-9 and Table 5-1 compare the measured sand transportation rates
with the calculated sand transportation rates.
The sand transportation rate predictions calculated by Bagnold’s equation do not match
well with the measured transport rate. The equation predicted greater transportation than
those observed in the field. Theoretical values were nine times bigger compared to field
measured transportation rate values.
Table 5-1: Estimated annual sand flux rate.
Location Measured flux rate (m3
/y.)
Theoretical flux rate by
Bagnold (m3
/y.)
lighthouse 176,772 3,688,157
site C 962,55 8,686,364
site A 255,357 6,173,560

27
Figure 5-7: Lighthouse flux data compared with theoretical flux calculated by Bagnold’s equation.

28
Figure 5-8: Site A flux data compared with theoretical flux calculated by Bagnold’s equation.

29
Figure 5-9: Site C flux data compared with theoretical flux calculated by Bagnold’s equation.

30
5.3 Impacts of surface moisture on sediment transportation
The surface moisture content values varied in each study areas. The sand samples
collected by different sandtraps were characterised by varying moisture content values.
Lighthouse had highest moisture contents compared to the other two sites.
At the lighthouse sandtraps C7, W2, C9 and C4 collected samples with maximum
moisture contents. Intermediate moisture content values were recorded for the sand
samples collected sandtrap C1, C8 and W1 and C5. Dry sand samples were collected by
the following sandtraps: W7, W6, C2, Cx, C3 C12, W5, C11, C10, and W3 (Figure
5-10).
Regardless of their close proximity to ocean waters site A and the lighthouse had
different values of surface moisture. Site A was relatively dry compared to the
lighthouse. The maximum moisture recorded in site A was 0.7%, the sample was
collected by W2 sandtrap (Figure 5-11). The maximum moisture content recorded at the
lighthouse was 2%.
Site C was relatively dry compared to site A and lighthouse. Surface moisture was
roughly constant for the duration of the experiment. Maximum moisture content value
recorded in site C was 0.2%.
Moisture content also varied on the two dunes in site C. the big back dune was relative
moist compared to the small front dune. Surface moisture increased roughly towards the
southern sections of both dunes.

31
Figure 5-10: Moisture content for the lighthouse sandtrap experiment

32
Figure 5-11: Moisture contents for the experiment conducted in site A

33
Figure 5-12: Moisture content for the experiment conducted in site C
Figure 5-13: Back dune and front dune moisture content values in site C

34
Density and moisture content analysis
The relationship between the sand sediment density and moisture content is shown in
Figure 5-14 below. The results demonstrate that the sediment density decreases with
increasing surface moisture. High-density values were recorded for dry sediments.
Figure 5-14: Sand sediment density plotted against moisture content
5.4 Long term monitoring
The erosion contour maps with the wind rose diagrams (Figure 5-15 to Figure 5-19)
show the depositing and eroding areas of the dune in site C. Blue coloured areas show
zones of deposition and the green areas are the zones of erosion.
The results obtained during the study period revealed that large volumes of sand lost by
the dune coincide with periods of strong westerly winds. Generally large volumes of
sand accumulated on the dune slipface. Erosion occurred mainly on the dune stoss and
crest, except during periods of strong easterly winds these two areas deposited.

35
Figure 5-15: Contour maps of erosional and depositional surfaces with the wind rose diagrams.

36

37
Figure 5-17 : Contour maps of erosional and depositional surfaces with the wind rose diagrams.

38

39
Figure 5-19: Contour maps of erosional and depositional surfaces with the wind rose diagrams

40
(a) Dune migration rate
Table 5-2 and (Figure 5-21to Figure 5-20) show migration rates of the two dunes in site
C relative to each other. The data in (Table 5-2) below reveal that the front dune is
migrating faster than the back dune.
In a period of five months the small leading dune migrated a total distance 24.5m while,
the back dune moved a distance of 14.24m for the same period. It is then estimated that
maintaining the same rate the front dune will migrate an estimated distance of 57.72m
annually. The back dune would then move a distance of 39.72m/y.
Table 5-2: The migration rate of the two dunes in Site C
Site C Migration period
Total distance
migrated (m)
Average migration
rate (m/y)
Front dune crest
31 March2016 - 23 August
2016 24.5 57.72
Back dune slip face
31 March2016 - 23 August
2016 14.24 39.72
Difference 10.30 18
Figure 5-20 and Figure 5-20 two dunes that were monitored in site C. both these dunes
migrated in an ENE direction at different rates. Figure 5-20 show both migration
distance and direction of both dunes. Results demonstrated that the small front dune in
site C moved faster compared to the big back dune.

41
Figure 5-20: Dune migration and drift direction of site C

42
Figure 5-21: Correlated migration rates of the two dune in site C

43
(b) Slipface and stossface sand volumes
It was found that the sand flux at the slipface was higher compared to volumes of eroded
from the dune stossface (Figure 5-22).
However on the between the 27 April and the 14 may 2016 it was not the case. The sand
volumes on the stossface were slightly higher compared to the amount of sand deposited
on the dune slipface
Figure 5-22: Stoss and slipface volumes calculated from 31 March to 23 August 2016 at
site C

44
5.1 Sand drift potential and Cape Recife sand Budget
Sand drift potential for Cape Recife was calculated in this project to be 31m3
/m/y. The
Noordhoek with the averaged width of 350m its annual sand flux was calculated to be
10937 m3
/y.
The averaged width of the small Cape Recife dunefields was 290m. Sand enters the Cape
Recife dune field at 9062m3
/y. If the Noordhoek dune field was fully functional a total
volume of 19998 would enter the Algoa Bay beaches annually.
Table 5-3: Sand flux rate for the Cape Recife and Noordhoek dune fields
DP (m3
/m/y) site Flux rate (m3
/y)
resultant flux
rate(m3
/y) RDD Dune type
31 Noordhoek 10937 3281 E77E transverse
Cape Recife 9062 2719 E77E transverse
The wind rose diagram in (Figure 5-23) demonstrates that Cape Recife headland is
dominated by WSW winds of averaged maximum speeds of 13.1m/s. This better
explains the ENE resulted migration of Cape Recife and Noordhoek dune fields.
Figure 5-23: Wind rose diagram showing winds blowing in Cape Recife.

45
6. Discussion
This project involved the measurement of sediment transportation at Cape Recife
headland bypass dunes. Series of experiments were conducted at Noordhoek and Cape
Recife. The results obtained during the investigation period are presented in this chapter.
6.1 Determining sand flux in Cape Recife and Noordhoek dune fields
Sandtrap experiments were done on three sites to determine the sand flux into the Cape
Recife and Noordhoek dune fields. The experiments were conducted along north to south
transects. The transect length was decided based on the size of the site. Two experiments
were done at Noordhoek (site A and C) and one at Cape Recife (Figure 4-4 to Figure
4-6).
(i) Sand trapping experiment at lighthouse
The first experiment was conducted at the Cape Recife beach on a 180m long transect.
The site was roughly moist since it rained a day before the experiment. Trial1 was from
11:40 to 11:55 with an average wind speed of 9.06m/s. The second trial started from
14:12 to 14:27 with average wind speed of 8.6m/s. Both surface moisture and sand
transportation showed great variation (Figure 5-10). First trial had highest sediment
fluxes compared to the second trial. There are few reasons to explain that, firstly,
sediment flux was higher during the first trial because winds were stronger during the
time when the trial was conducted. Secondly, there was enough sand supply. During
second trial sand fluxes were 5times less compared to the first trial. This was because the
dry sand that was present on the surface during the first trial had disappeared in some
places due to the strong winds. This resulted in exposed wet sand patched surfaces that
were difficult to transport (Figure 6-1).
Trap with lowest sediment flux was C1. The trap was located on upper beach section on
a wet patched sand surface. Trap Cx, C3, C12, W5, C11, C10, and W3 had low fluxes
following trap C1. These traps were placed on the lowest beach section. Low sand fluxes
of these traps were attributed to high surface moisture contents. Southern most section of
the beach was affected by ocean water wave action, which increased surface moisture
content values on the lower beach section. Traps that were placed on the middle section
of the beach had highest sediment fluxes. Middle section of the transect was relative dry
compared to the lower and upper beach sections. Since dry sand is easier to transport
sediment transportation was higher on the beach middle section (Figure 6-1).

46
Figure 6-1: Photo of the Cape Recife beach site, during the sand trapping experiment. The patches of wet sand exposed on the surface (red-
dotted lines)

47
(ii) Sand trapping experiment at site A
Sand flux in site A was higher during the second trial irrespective of increased surface
moisture (Figure 5-11). The increase was caused by stronger winds that occurred by the
time second trial had commenced. The first trial was from 10:48 to 11:03 with an
average wind speed of 10.2m/s. The second trial was from 12:35 to 12:45 with an
average wind speed of 13.04m/s.
Trap W2, C12, W5 and W6 had a maximum sediment flux during the second trial. These
traps were located on relatively dry areas of the beach (Figure 6-2 to Figure 6-4). When
the wind increased during the second trial these areas dried up quickly, thus the sand was
moved easily.
Trap C8 had lower sediment flux for both trials, followed by C11, C5, C1, C2 and C4.
Low sediments flux recorded by these sandtraps was attributed to high surface moisture
contents. These traps were placed adjacent to wet patched surfaces that limited sediment
supply. Sandtrap C8, C5 and C11 were placed on the upper beach section adjacent to wet
sand surfaces (Figure 6-2). Sediment supply to trap C8 was limited by wet sand surface
that was covered with small vegetation in front of the trap. Low sediment flux recorded
by trap C5 and C11 was attributed to wet sand surfaces in front of the traps.
(iii) Sand trapping experiment at site C
Sediment fluxes were determined for the two dunes in site C. The small front dune had
low sediment fluxes compared to the big back dune. This difference was attributed to
their sizes. Big back dune was highly exposed to strong winds, thus it had high sediments
fluxes compared to small leading dune. First and the second trials were done on the front
dune (Figure 4-5). Trial1 was from 11:19 to 11:29 with an averaged wind speed of
12.2m/s. Trial2 was from 12:04 to 12:14 with an average wind speed of 12.1m/s. The
third trial was from 13:45 to 13:55. The averaged wind speed recorded for the back and
front dune was 12.2m/s and 11.7m/s respectively (Figure 5-3). Comparing the two dunes
in site C the data revealed that the small front dune had low sediment transportation
because it was shadowed from strong winds by the big back dune. High sediment fluxes
recorded from the big back dune. The data demonstrated that big dune have low
migration rates but high sediment transportation compared to the small dunes. Small
dunes migrate faster because they have small volumes of sand to transport.

48
Figure 6-2: photo showing the upper beach section of the sand trapping experiment at site A.

49
Figure 6-3: Photo showing sandtrap set up on the middle beach section at Site A. Note
red dotted areas ( wet patches of sand), blue arrows represent wind direction.
Figure 6-4: Photo showing sandtrap set up on the lower beach section at Site A. Note
red dotted areas ( wet patches of sand) blue arrow represents wind direction.

50
(iv) Theoretical and measured sand transportation rates
Bagnold’s equation estimated high sediment transportation rates compared to values
sandtrap measured values (Table 5-3). This was explained based on the fact that the
Bagnold equation used to calculate sand transportation rate do not include factors like
surface moisture and vegetation cover. Thus, theoretical calculated sand transportation
rates were higher compared to values measured on the field. The sandtraps used had low
sampling efficiency that together with human error contributed to the lower sediment
transportation rates values recorded in the field.
Wang & Kraus (1999) noted that sandtrap measured transportation rate is in many cases
lower than the actual field sediment transportation, because sandtraps have low
efficiency. The accuracy of the sandtraps in this project was in most cases decreased by
strong blowing winds. During strong winds periods the sandtraps rotated away from the
wind incident direction, thus collected minimum volumes of sand.
The sand trapping experiments conducted in this study-demonstrated complexity of
coastal sand dunes. Measured sand transportation rates values showed no correlation
with theoretical calculated sand transportation rates.
6.2 Dune migration rates
The results obtained during the erosion pin monitoring period showed that both dunes in
site C migrated eastward (ENE). However, there were periods of reverse migration that
coincides with the easterly winds. The ENE migration of the dune was driven by the
WSW winds that occurred throughout the year (Figure 5-16 and Figure 5-19).
The two dunes in site C migrated at different rates. Barchyn (2015) stated that the size
and the shape of the dune do affect the rate at which dune migrates. The small dunes tend
to migrate faster than bigger dunes. The two dunes at site C showed the exact behaviour.
The small leading dune migrated a distance of 4.81m per month, the big back dune
moved an averaged distance of 3.31m per month (Table 5-2 ).
Easterly winds were significantly dominant between (31 March 2016 – 17 April 2016),
(27April 2016 – 14 May 2016) and (24 July 2016 – 13 August 2016). The easterly winds
were stronger from 27 April 2016 -14 May 2016 (≤7.81m/s). This was followed by
backward dune migration reveled by crestline reverse migration and small sand volumes
transported between the 27 April and 14 May 2016 (Figure 5-20 and Figure 5-20).

51
Strong westerly winds were recorded in April, June and August. This is shown in Figure
5-16, Figure 5-17 and Figure 5-20). Huge forward dune advancement and large volumes
of sand transportation were recorded in the same period.
The eastward migration of the dunes was driven by the westerly winds that occurred
throughout the year. Easterly winds had no influence on the dune migration direction
apart from slowing migration.
(i) Stoss and slipface volumes
Site C was further studied to examine the behaviour dune in correlation with the wind.
The data demonstrated that the erosion occurred mostly on the stoss, while sand
accumulations occurred mostly on the slipface (Figure 5-15 to Figure 5-19).
Slipface collapsed overtime due to excess accumulations of sand sediment in it.
According to van de Graaff, (1994) slipface collapse happens when the sand
accumulations on the dune exceeds the angle of repose (32˚). When sand accumulations
go beyond that angle, the dune becomes unstable and slipface avalanches occur (Figure
6-7). Slipface areas received large volumes of their sand from the stossface, however
some of their sand that accumulates is deposited directly by winds without settling on the
stossface first (Figure 6-6), attributed to that, slip face tend to receive large volumes of
sand compared to actual amount supplied by the stoss.
Theoretically, the volumes of sand eroded from the dune stoss should be comparable to
the volumes of sand deposited on the dune slipface. However, in Figure 6-5 it is not the
case. The results demonstrated no direct correlation between the sand volumes deposited
on the slipface and the amount of sand eroded on stossface. An averaged volume of
263.414m3
per month was calculated to leave the stossface. The slipface appeared to
receive twice the volume eroded from dune stoss. An averaged volume of 556.42m3
per
month was calculated to accumulate on the slip face.
There are few explanations for the high volumes of sand accumulated on the dune
stossface. First is the differential GPS error that was possibly made when measuring the
amplitude of the stoss. Secondly, not all the sand that accumulates on the slipface is
supplied by the stoss. During strong winds, sediment grains can saltate over the dune to
feed the slipface directly (Figure 6-6). The area shaded in blue is the of sand flux
supplied by stoss, the red shaded area represent volumes of sand moved over the stoss by
wind and accumulated directly to the slipface

52
Figure 6-5: scatter plot of the volume moved at the slipface (positive - deposition) vs.
volume moved along the stoss surface (negative - erosion) for site C.
Figure 6-6: a cartoon showing the transportation paths of sand before accumulating on
the slipface. The dotted grey line represents how dune moves in response to wind.
The green dotted line represents wind transported sand from the back dune.

53
Figure 6-7: Photo of avalanching slipface at site C. Note areas surrounded by purple dotted lines (dune avalanche)

54
6.3 Estimated sand volumes moving to adjacent beaches
Sand drift potential of 31m3
/m/y was calculated for the Cape Recife bypass dune system
using wind data acquired from Port Elizabeth airport. The Noordhoek was estimated to
receive a maximum sand volume of 10937m3
/y. The small active dune field at the tip of
Cape Recife headland was calculated to receive 9062m3
/y. Thus if the Noordhoek dune
field was not stabilised the Algoa Bay beaches would receive 19999 m3
/m/y. Following
the stabilization of the Noordhoek, only receive 45% of this volume migrates across the
headland.
McLachlan (1994) estimated the drift potential of 42m3
/m/y. The Noordhoek with a
width of 600m was estimated to receive sand volumes of 25000 m3
/y. The active Cape
Recife dune field with a width of 300m had a transportation rate of 12000 m3
/y. The
values calculated in this study were lower compared to the values previously estimated
by McLachlan (1994). The difference was attributed to the wind data used in this study.
In this study, sand drift potential was calculated using wind data acquired from Port
Elizabeth airport. McLachlan (1994) used wind data that was recorded at Cape Recife.
Wind data recorded on field during sand trapping experiments were higher compared to
the winds that were recorded at the airport (Figure 5-1 and Figure 5-3). The reduced sand
drift potential calculated in this study was caused by the reduction in wind energy as
wind blows onshore because of the higher surface friction inland.
6.4 Attempted stabilization of Cape Recife bypass dune
The eastward migration of the Cape Recife dune field causes operational threat to the
human developments situated too close to the field. The sand appear to build up against
the lighthouse (Figure 6-8).
In attempt to minimise the impact of sand encroaching towards the lighthouse, heavy
manganese rock fragments and car tyres were placed on the Cape Recife dune field.
However, the attempt was unsuccessful as the dune still migrates on its natural path
across the headland. The area was rather pollute by the tyres and manganese rocks placed
on the field (Figure 6-9).

55
Figure 6-8: Photo of the Cape Recife dune field. Note the area surrounded by black
dotted line contains car tyres and heavy manganese rock fragments. This was the
attempt to stabilise the dune.
Figure 6-9: Photo of the lighthouse covered by sand on the western side.

56
7. Conclusions
Sandtrap experiments conducted in three different study sites revealed the complexity of
coastal sand transportation. Both spatial (surface moisture and surface roughness) and
temporal (wind speed and gust) factors made it difficult to estimate the behavior of the
Cape Recife dune fields. What complicates things is that available theoretical equations
do not consider these factors and the instruments used for field measurements had low
efficiency of 15-20%. Thus, both calculated and measured sand transportation rate did
not represent the actual sediment flux in the field.
Erosional and depositional contour maps demonstrated erosion occurred on stossface.
Dune slipface was a zone of sand accumulation. The distance migrated and the volumes
of sand transported from the stossface correlated perfectly with the blowing winds.
However, in most cases the volumes of sand accumulated on the dune slipface was
higher compared to the sand volumes eroded on the dune stoss. This indicated that some
of the sand that accumulates on the slipface came somewhere not from the stossface but
saltated directly above it and deposited straight on the slipface.
Sand drift potential of the Cape Recife bypass dune system was calculated to be
31m3
/m/y. The results revealed that if the Noordhoek dune field was active an estimated
volume of 19999m3
/y would migrate across the headland to the Algoa Bay beaches,
however only 45% of that migrates to the Algoa bay beaches from the currently
nonstabilized Cape Recife dune field.
This project has proved Cape Recife and Noordhoek dune field receive large volumes of
sand but only a small percentage of that migrates across the headland to feed adjacent
Algoa Bay beaches. The stabilised Noordhoek dune field traps about 55% of the sand
that was supposed to feed adjacent beaches if the field was active. Environmentally
reactivating the Noordhoek would be beneficial. For example, some of the beaches in
Port Elizabeth like Pollok beach would be reactivated. Economically the city would
benefit as the beaches attracts tourists. However, reactivating the dune field would
require relocation of all the infrastructure built on its path.

57
7.1 Environmental impacts of the drifting sand
The eastward drifting of both Noordhoek and Cape Recife dune fields pose threats on
human activities. The encroaching sand creates serious threats for the lighthouse in Cape
Recife (Figure 6-9). During windy seasons, huge quantities of sand are transported by
wind, sand then accumulate up against the lighthouse. In attempt to inhibit dune
migration rate, tyres and heavy manganese rocks were placed on the sand dunes at Cape
Recife. Clearly, the technique did not work as the sand continues to move downwind
(Figure 6-8).
7.1.1 Suggested approaches
Cape Recife dune field can be stabilised by wetting. That will keep its moisture content
high. Keeping the dune wet will decrease the migration rate. Other option would be to
relocate the infrastructure and let the dune migrate on its natural path.
7.1.2 Improvements for future studies
Sandtraps used in this study had low sampling efficiency. For future studies, the
following improvements will be useful: long nozzles added on the trap inlet openings
would make sure that the trap has minimal disturbance on the airflow, thus improving its
efficiency.
Wind vane and anemometer can be attached on each trap. This will make sure that
sediment flux for each trap is correlated directly to the winds that were blowing in
specific area where the trap was placed. Adding wind vane to all the sandtraps will
enable the trap to rotate in a direction of wind incident angle at all times
Erosion pin monitoring experiment will need to be monitored frequently to minimise the
error caused by falling pins. Thicker pins to avoid breakage when hit by a hummer for
repositioning can replace dowel stick erosion pins used in this project.
7.1.3 Sand drift potential
The wind data used to calculate sand drift potential could be recorded directly on site.
This would help minimize errors for under-estimating the actual drift potential.

58
8. References
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gusts, moisture content and fetch length on sand transport on a beach.
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seas (pp. 137–140). Washington DC: U.S. Govt. Print. Off.
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Algoa Bay , with emphasis on the western coastal region. South African
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Nickling, W. G. C. M. N. (1997). Wind tunnel evaluation of a wedge-shaped aeolian
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sand transport. Earth Surface Processes and Landforms, 24(1), 65–70.
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Watson, J. J. (1996). Human activity and potential impacts on dune breeding birds in the
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9. Appendix 3: sandtrap data
Sample No: Time mass (g) g/min g/cm/min g/cm/hour Traps distance btw (m) flux (g/min) Density (g/cm3)
C1 11:55 323.77 21.58 10.79 647.54 C1-W7 7.95 18636.92 1.476
W7 11:55 1082.79 72.19 36.09 2165.58 W7-C8 9.08 35359.94 1.518
C8 11:55 1253.77 83.58 41.79 2507.54 C8-W1 9.05 38264.15 1.452
W1 11:55 1283.08 85.54 42.77 2566.16 W1-C5 8.25 39705.74 1.484
C5 11:55 1604.61 106.97 53.49 3209.22 C5-W6 8.53 37126.54 1.460
W6 11:55 1006.87 67.12 33.56 2013.74 W6-C12 8.41 25680.36 1.536
C12 11:55 825.26 55.02 27.51 1650.52 C12-W4 7.11 30549.3 1.532
W4 11:55 1752.74 116.85 58.42 3505.48 W4-Cx 9.14 34404.48 1.505
Cx 11:55 505.76 33.72 16.86 1011.52 Cx-C3 17.06 21027.02 1.526
C3 11:55 233.76 15.58 7.79 467.52 C3-C2 16.30 10993.54 1.529
C2 11:55 170.91 11.39 5.70 341.82 C2-W5 8.40 5322.1 1.521
W5 11:55 209.24 13.95 6.97 418.48 W5-C11 8.56 5255.412 1.526
C11 11:55 159.13 10.61 5.30 318.26 C11-C10 12.93 7373.979 1.533
C10 11:55 183.05 12.20 6.10 366.10 C10-W3 8.67 6744.827 1.511
W3 11:55 283.72 18.91 9.46 567.44 W3-C4 7.73 7027.73 1.504
C4 11:55 261.77 17.45 8.73 523.54 C4-C9 16.11 13923.07 1.444
C9 11:55 256.78 17.12 8.56 513.56 C9-W2 8.70 11069.59 1.437
W2 11:55 506.64 33.78 16.89 1013.28 W2-C7 7.65 13294.81 1.411
C7 11:55 536.09 35.74 17.87 1072.18 179.6 1.410
C1 14:27 54.95 3.66 1.83 109.90 C1-W7 7.95 2717.443 1.529
W7 14:27 150.14 10.01 5.00 300.28 W7-C8 9.08 5655.629 1.549
C8 14:27 223.58 14.91 7.45 447.16 C8-W1 9.05 7709.092 1.475
W1 14:27 287.52 19.17 9.58 575.04 W1-C5 8.25 8799.038 1.527
C5 14:27 352.41 23.49 11.75 704.82 C5-W6 8.53 10387.98 1.526
W6 14:27 378.28 25.22 12.61 756.56 W6-C12 8.41 6707.536 1.522
C12 14:27 100.26 6.68 3.34 200.52 C12-W4 7.11 4688.927 1.535
W4 14:27 295.43 19.70 9.85 590.86 W4-Cx 9.14 6763.448 1.544
Cx 14:27 148.56 9.90 4.95 297.12 Cx-C3 17.06 5814.901 1.542
C3 14:27 55.95 3.73 1.87 111.90 C3-C2 16.30 5000.84 1.550
C2 14:27 128.13 8.54 4.27 256.26 C2-W5 8.40 2401.84 1.535
W5 14:27 43.43 2.90 1.45 86.86 W5-C11 8.56 1305.685 1.536
C11 14:27 48.09 3.21 1.60 96.18 C11-C10 12.93 1835.198 1.540
C10 14:27 37.07 2.47 1.24 74.14 C10-W3 8.67 1313.794 1.525

61
W3 14:27 53.85 3.59 1.80 107.70 W3-C4 7.73 1121.881 1.517
C4 14:27 33.23 2.22 1.11 66.46 C4-C9 16.11 2131.622 1.486
C9 14:27 46.16 3.08 1.54 92.32 C9-W2 8.70 2801.98 1.471
W2 14:27 147.08 9.81 4.90 294.16 W2-C7 7.65 2878.313 1.427
C7 14:27 78.67 5.24 2.62 157.34 179.63 1.429
Sample No: time mass (g) g/min g/cm/min g/cm/hour Traps
average
(g/cm/min)
distance btw
(m) flux (g/min)
Density
(g/cm3)
T1C1 11:29 455.79 45.58 22.79 1367.37 C1-C2 37.757 7.5 28317.38 1.565
T1C2 11:29 1054.47 105.45 52.72 3163.41 C2-C3 48.239 8.05 38832.6 1.556
T1C3 11:29 875.10 87.51 43.76 2625.30 C3-C4 37.169 8.39 31185 1.558
T1C4 11:29 611.67 61.17 30.58 1835.01 C4-C5 24.234 8.05 19508.17 1.561
T1C5 11:29 357.68 35.77 17.88 1073.04 C5-C6 14.916 7.5 11187 1.567
T1C6 11:29 238.96 23.90 11.95 716.88 39.49 1.564
T2C7 12:14 254.55 25.46 12.73 763.65 C7-C8 31.797 7.5 23847.75 1.566
T2C8 12:14 1017.33 101.73 50.87 3051.99 C8-C9 45.601 8.05 36708.81 1.557
T2C9 12:14 806.71 80.67 40.34 2420.13 C9-C10 33.438 8.39 28054.69 1.559
T2C10 12:14 530.82 53.08 26.54 1592.46 C10-C11 19.964 8.05 16071.02 1.561
T2C11 12:14 267.74 26.77 13.39 803.22 C11-C12 11.374 7.5 8530.5 1.566
T2C12 12:14 187.22 18.72 9.36 561.66 39.49 1.563
T3C1 13:55 191.78 19.18 9.59 575.34 C1-C2 9.261 10.37 9603.398 1.568
T3C2 13:55 178.65 17.87 8.93 535.95 C2-C3 18.694 8.95 16730.91 1.567
T3C3 13:55 569.10 56.91 28.46 1707.30 C3-C4 37.151 6.3 23405.13 1.563
T3C4 13:55 916.94 91.69 45.85 2750.82 C4-C5 39.685 5.75 22819.02 1.559
T3C5 13:55 670.47 67.05 33.52 2011.41 C5-C6 23.530 6.68 15717.87 1.559
T3C6 13:55 270.72 27.07 13.54 812.16 38.05 1.561
T3C7 13:55 331.61 33.16 16.58 994.83 C7-C8 19.070 9.51 18135.81 1.563
T3C8 13:55 431.20 43.12 21.56 1293.60 C8-C9 20.452 6.53 13355.32 1.562
T3C9 13:55 386.89 38.69 19.34 1160.67 C9-C10 23.606 8.54 20159.52 1.565
T3C10 13:55 557.35 55.74 27.87 1672.05 C10-C11 23.285 12 27941.4 1.556
T3C11 13:55 374.03 37.40 18.70 1122.09 C11-C12 34.618 9.37 32437.3 1.563
T3C12 13:55 1010.70 101.07 50.54 3032.10 45.95 1.559

62
Sample No: Time mass (g) g/min g/cm/hour Traps
average
(g/cm/min) distance btw (m) flux (g/min) Density (g/cm3)
C8 11:03 113.62 7.57 227.24 C8-C11 5.190 7.89 4095.042 1.562
C11 11:03 197.79 13.19 395.58 C11-C5 7.868 7.71 6066.228 1.567
C5 11:03 274.29 18.29 548.58 C5-W5 9.436 7.84 7398.085 1.523
W5 11:03 291.89 19.46 583.78 W5-C10 12.787 7.88 10076.02 1.561
C10 11:03 475.32 31.69 950.64 C10-C1 12.680 8 10144.27 1.533
C1 11:03 285.50 19.03 571.00 C1-C9 11.657 8.01 9337.391 1.552
C9 11:03 413.93 27.60 827.86 C9-W6 9.534 7.85 7483.798 1.548
W6 11:03 158.08 10.54 316.16 W6-C6 7.940 7.9 6272.205 1.553
C6 11:03 318.29 21.22 636.58 C6-Cx 9.511 8.01 7618.578 1.548
Cx 11:03 252.39 16.83 504.78 Cx-C12 7.117 7.89 5614.919 1.528
C12 11:03 174.60 11.64 349.20 C12-W1 8.216 8.3 6818.865 1.530
W1 11:03 318.33 21.22 636.66 W1-C2 8.079 8.08 6527.967 1.545
C2 11:03 166.42 11.09 332.84 C2-C7 8.252 8.3 6849.298 1.548
C7 11:03 328.71 21.91 657.42 C7-C4 8.686 8 6948.667 1.538
C4 11:03 192.44 12.83 384.88 C4-W2 18.422 8.4 15474.48 1.535
W2 11:03 912.88 60.86 1825.76 120.1 1.521
C8 12:45 222.21 22.22 666.63 C8-C11 18.237 7.89 14388.8 1.565
C11 12:45 507.26 50.73 1521.78 C11-C5 26.832 7.71 20687.66 1.557
C5 12:45 566.03 56.60 1698.09 C5-W5 44.060 7.84 34542.84 1.555
W5 12:45 1196.36 119.64 3589.08 W5-C10 50.657 7.88 39917.72 1.533
C10 12:45 829.92 82.99 2489.76 C10-C1 33.363 8 26690 1.529
C1 12:45 504.58 50.46 1513.74 C1-C9 34.535 8.01 27662.74 1.548
C9 12:45 876.83 87.68 2630.49 C9-W6 50.881 7.85 39941.78 1.523
W6 12:45 1158.42 115.84 3475.26 W6-C6 50.976 7.9 40271.24 1.525
C6 12:45 880.63 88.06 2641.89 C6-Cx 38.369 8.01 30733.77 1.514
Cx 12:45 654.14 65.41 1962.42 Cx-C12 47.064 7.89 37133.5 1.514
C12 12:45 1228.42 122.84 3685.26 C12-W1 54.548 8.3 45274.84 1.503
W1 12:45 953.5 95.35 2860.50 W1-C2 33.833 8.08 27337.27 1.519
C2 12:45 399.83 39.98 1199.49 C2-C7 31.358 8.3 26027.14 1.533
C7 12:45 854.49 85.45 2563.47 C7-C4 32.977 8 26381.6 1.523
C4 12:45 464.59 46.46 1393.77 C4-W2 42.688 8.4 35857.92 1.517
W2 12:45 1242.93 124.29 3728.79 120.1 1.491

63
10. Appendix: 6 Sand drift potential calculated data
Figure 10-1: photo of Site A sand trapping experiment. Note the cloud of sand saltating above calcrete ridge. Red arrows indicate the sand
being transported through the calcrete ridge gaps (cloud of saltating sand).

64
11. Appendix 4: Contour maps of erosional and depositional areas in site C

66
12. Appendix: 6 Sand drift potential calculated data
Direction 5.6 - 07.09 7.09-9.12 9.12-12.2 12.2-14.0 14.0 - 18.6 All speeds
355 - 005 0.0532 0 0 0 0 0.0532
005- 015 0 0 0 0 0 0
015 - 025 0.0532 0.2128 0 0 0 0.266
025 - 035 0.2128 0 0 0 0 0.2128
035 - 045 0.1596 0.2128 0 0 0 0.3724
045 - 055 0.4256 0 0.7581 0 0 1.1837
055 - 065 0.798 1.064 3.0324 0 0 4.8944
065 - 075 1.9152 4.4688 8.3391 0 0 14.7231
075 - 085 1.8088 5.5328 18.1944 3.4314 0 28.9674
085 - 095 1.2768 2.9792 9.8553 0 0 14.1113
095 - 105 0.9044 1.2768 0.7581 0 0 2.9393
105 - 115 0.3724 0.4256 0.7581 0 0 1.5561
115 - 125 0.3724 0.2128 0 0 0 0.5852
125 - 135 0.266 0 0 0 0 0.266
135 - 145 0.3192 0 0 0 0 0.3192
145 - 155 0.0532 0 0 0 0 0.0532
155 - 165 0.0532 0.2128 0 0 0 0.266
165 - 175 0.0532 0 0 0 0 0.0532
175 - 185 0.0532 0 0 0 0 0.0532
185 - 195 0.2128 0 0 0 0 0.2128
195 - 205 0.266 0 0 0 0 0.266
205 - 215 0.532 0.4256 0.7581 0 0 1.7157
215 - 225 1.1172 1.4896 3.0324 0 0 5.6392
225 - 235 1.6492 4.4688 21.9849 6.8628 3.7772 38.7429
235 - 245 3.0856 8.7248 47.0022 36.0297 49.1036 143.9459
245 - 255 3.99 9.1504 47.7603 27.4512 37.772 126.1239
255 - 265 2.128 4.0432 19.7106 8.5785 11.3316 45.7919
265 - 275 1.2768 1.2768 6.8229 0 0 9.3765
275 - 285 0.3192 0.2128 0.7581 0 0 1.2901
285 - 295 0.1064 0 0 0 0 0.1064
295 - 305 0 0 0 0 0 0
305 - 315 0.1064 0.2128 0 0 0 0.3192
315 - 325 0.0532 0.2128 0 0 0 0.266
325 - 335 0 0 0 0 0 0
335 - 345 0 0 0 0 0 0
345 - 355 0 0 0 0 0 0
All directions 23.9932 46.816 189.525 84.0693 101.9844 446.3879
RDP 135.0349
RDP/DP 0.302505735
RDD 77

67
Wind speed
(m/s)
Mean wind in
category (V) V² V - Vt
Weighting factor
V²(V - Vt)/100
5.6-7.6 6.6 43.6 1 0.44
7.6-8.8 8.2 67.24 2.6 1.75
8.8-9.1 8.95 80.1 3.35 2.68
9.1-12.2 10.65 113.42 5.05 5.73
12.2-14.0 13.1 171.61 7.5 12.87
14.0-18.6 16.3 265.69 10.7 28.43

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