Assessment of Golspie Beach sand feeding performance using high resolution digital terrain models

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1 Sky Journal of Soil Science and Environmental Management Vol. 4(2), pp , May, 2015 Available online ISSN Sky Journals Full Length Research Paper Assessment of Golspie Beach sand feeding performance using high resolution digital terrain models Brown Joshua 1, Nnaji Austine O. 2* and Njoku Richard E. 2 1 Department of Geo-spatial and Mapping Sciences, University of Glassgow, Scotland. 2 Department of Surveying and Geoinformatics, Federal University of Technology, Owerri, Nigeria. Accepted 22 March, 2015 Coastal environments are globally recognized for their highly dynamic and unstable nature. The Golspie Beach situated in Sutherland Highlands of Scotland is not spared from these processes. To minimize the effects of the rampaging erosions, sand feeding was proposed to protect a section of the beach. To evaluate the success of the protective project, a high resolution digital terrain model (DTM) of the current situation of beach in 2014 was necessary. This was achieved with the use of Terrestrial Laser Scanning Technique to acquire highly dense point cloud with five centimeter point resolution over one kilometer length of beach. The change in the beach surface between 2013 and 2014 was assessed using photogrammetically generated DTM from 2013 aerial photographs and DTMs of 2014 obtained from terrestrial laser scanning techniques. The DTMs were used to assess the height and volumetric changes at the study area. The results from the change analysis revealed areas with significant loss and gains in height. Some sections were observed to have experienced height loss of approximately 0.25 to 1.5 m especially around the frontage of the south end of the golf course and a section at the frontage of the Kart track. From the volumetric analysis performed, the areas with losses in sediments were highlighted. A total change of approximately 30,129.4 m 3 in sediment volume of the entire study area was recorded out of which the loss and gain represents 30 and 70%, respectively. An overall net gain of approximately 11,929.6 m 3 was recorded from the sediment budget of the entire beach with southward movements of sediments. The general outcome from the study revealed the success of using both techniques in beach studies. Key words: Golspie Beach Scotland, digital terrain model, coastal environments, sand feeding, height change, volumetric change. INTRODUCTION Coastal environments have globally been known for their highly dynamic and unstable nature, consequently they constantly undergo changes due to the external forces acting upon them (reference). Modeling such environmental changes is very critical to the understanding of the morphological dynamism and any application of adequate mitigation measures to coastal erosion hazards. Several geomatics survey techniques have been applied in understanding erosional hazards (Alkan and Karsidag, 2012), for example, Terrestrial Laser *Corresponding author. dr_nnaji@yahoo.com. Scanning (TLS). The techniques existing for assessing changes in the beach environment include direct measurement of changes from electronic distance measurement (EDM), global navigation satellite system (GNSS), aerial photography, synthetic aperture radar (SAR), light detection and ranging (LiDAR) and satellite imageries (reference). Usually baseline surveys of coasts show changes that occur at different scales with some regions experiencing more of accretion, while others experience more erosion. These changes occur both in short and long-term bases depending on the morphology and material constituents of the coast (reference). The coast of Scotland is not isolated from the above

2 Joshua et al. 21 described phenomenon; it has experienced its own share of the continuous changes that occur over time. Some of these changes have been documented in the works of Dawson et al. (2010), Hansom et al. (2011) and Collins et al. (2007). Such studies showed that the Scottish coast rather than being static, has continuously responded to long term changes in ocean volume, land uplift and the advance and retreat of glacier, which is in particular the case with the study area (Figure 1); the Golspie Coast situated at the Sutherland Highland in Scotland between the south end of the Golspie Golf Course and adjacent to kart track. A documented evidence of changes experienced in the study area in terms of coastal erosion (Figure 2) was reported by Hansom and Fitton (2013). The process of erosion in Golspie Coast has been attributed to natural factors such as storm waves, sealevel rise as well as human interferences, however its progress depends on the underlying rock structure (reference). The Golspie Beach is characterized by bedrocks and boulder outcrops at the north end and backed by emerged marine sands and gravels which have been deposited some 6,500 years ago at height relatively higher than sea level, (Hansom and Fitton, 2013). Attempts have been made, though unsuccessfully to minimize the effect of erosion on the beach. Most of these schemes are dated back to 1979 when a demolished railway bridge in Golspie was used to protect the coastal edge below the golf course. All were focused on ensuring full protection of the golf course frontage. On the contrary, such measures have not been effective, as wave storms swept away some of the defences and consequently sand feeding project was adopted. Based on the fore-going stated problem, an optimized approach of assessing changes on the beach is very important. This study aimed primarily to: i) Acquire a high resolution point cloud data of the current situation of the Golspie Beach using terrestrial laser scanning techniques ii) Develop a high resolution DTM of the beach to serve as baseline data for assessing performance of the proposed beach sand feeding/defence measure and evaluate the changes that have taken place at the beach between 2013 to MATERIALS AND METHODS The two major sources of data necessary for achieving study objectives were aerial photography flow on 19 th February 2013 and terrestrial laser scanning executed on 19 th June The aerial photographs were flown at a very low altitude; hence the spatial resolutions were very high. The scanning data was obtained directly from the study location over an approximately one kilometer length using time-of-flight scanner Leica ScanStation C10. The properties of the camera used for acquisition of the aerial photographs are as follows: Camera Model - Hasselblad H4D- 50 (28 mm), Resolution , Focal Length - 28 mm, Pixel Size µm and Acquisition Date was 19 th February, Based on their suitability for the various tasks to be executed for purposes of the study, the analytical software tools/packages were selected. The AgisoftPhotoscan software was chosen for processing of the photogrammetry data, because of the following reasons: i) Its capability to process images captured with nonmetric Cameras, ii) Sucha Digital Photogrammetric Workstation (DPWs) is relatively easy to use with friendly interface, iii) It has also a robust three dimensional modeling capabilities for reconstruction of different surfaces. The Leica Cyclone 8.1 chosen for the editing of the point cloud data acquired from the field has the capability of processing scanned point cloud data and producing relatively good three dimensional models. In spite, it was used in this study only for the purpose of editing the data to remove outliers and export the cleaned data as text file format. All the data produced from the previously mentioned software packages were imported to ESRI ArcGIS for the spatial analysis and measurement of expected changes. The ArcGIS was selected due to its robustness and capabilities for surface modeling and spatial analysis. The work flow for data analysis was accomplished as follows: Sediment Budget, Change Analysis (Geographic Information System GIS), Volumetric Analysis, Areal Height, DEM & Orthophoto Generation, Accuracy Assessment, Point Cloud Acquisition, Terrestrial Laser Scanning, Direct Referencing ASCII Point File, Removing of Outliers, DEM Generation. The flowchart showing combined photogrammetric and terrestrial laser scanning techniques for beach change analysis was as follows: Digital Photogrammetry, Acquisition of GCPs, Interior/Exterior Orientation, Optimization/NormalizationImage Matching, Results visualization both in two dimensional and three dimensional charts. To further review the changes in Golspie Coast, three along shore profiles were drawn on the beach as sections A, B and C. One profile (which A, B or C) was drawn at the frontage of the southern end of the golf course running to the frontage of the caravan park, the second (which A, B or C) was from the north end of the Kart track to the south end of the Kart track while the last profile (which A, B or C) was drawn from the north end of the section C portion to the south end of the partition (Figure 3). RESULTS AND DISCUSSION The nature of change in the Goldpie Beach is proved in increased sediment erosion in the southern end of the

3 22 Sky. J. Soil. Sci. Environ. Manage. Figure 1. The study area. golf course. The toe of the rip-raps used to protect the golf course frontage is undergoing steepness as earlier noted by Hansom and Fitton (2013). This is mainly due to the fact that the materials used to protect the beach are loosely packed and being rapidly eroded. For instance, the wave energy from high tides continually strikes the surface of the materials and softens the surface and the possibility of eroding the toe becomes very apparent (Hansom et al., 2013). An assessment of the sediment change within the study area, highlights areas where there have been more losses or gain. These include; for the entire beach, for the three partitioned sections (A, B & C) and for the various units within the various partitions such as the dune face, upper beach and lower beach. The sediment budget of the entire beach revealed a total sediment loss of approximately 9,100 m 3 which represent 30% of the total sediment change between 2013 to While the gain was approximately 21,000 m 3 representing approximately 70% of the entire change. The loss was quite significant giving the short period under review. A net gain of 11,929.6 m 3 was recorded at the entire beach Section A which experienced approximately 40% loss in sediments with gain at approximately 60%. The loss and gain in section B represents approximately 21 and 79%, respectively. While the section C recorded approximately 100% gain as there was no significant loss within the section. Further investigation of the sediment change within the sections was done by partitioning the beach into various units such as, dune face, upper beach and lower beach. The result shows how the sediment change was distributed within these units, Section B of the beach which is the frontage of the Kart track witnessed more sediment gain that could be attributed to the movement of sediments away from section A. However there was a significant loss (how much) of sediment in this section which appears to be more of anthropogenic than natural from inspection of the ground photograph acquired (Schaefer and Inkpen, 2010). Section C was observed to be a sediment bank as there was no obvious loss in sediments during the study time; an overall net loss and

7%, respectively was recorded at the dune face of all the sections. While the upper beach recorded an overall net loss and gain of approximately 2756.

4 Joshua et al. 23 Figure 2. Coastal erosion in GolspieBeach of Scotland Source: Handsom and Fitton (2013). Figure 3. Height change between 2013 to 2014 DTMs showing areas of loss and gain in height. gain of approximately 1,027.6 and 8,953.1 m 3 which represents 10.3 and 89.7%, respectively was recorded at the dune face of all the sections. While the upper beach recorded an overall net loss and gain of approximately and m 3 translating into 39.2 and 60.8%, respectively. Finally the lower beach recorded a net loss and gain of approximately and m 3 representing 39.6 and 60.4%, respectively. The most loss

5 24 Sky. J. Soil. Sci. Environ. Manage. Figure 4. Alongshore surface change in height between surface at the Kart track frontage. in sediments was recorded at the lower beach at the section A especially at the frontage of the southern end of the golf course. While the most gain in sediments from the results was at the dune face at section A. The consequent result is the significant loss of sediment at the toe of the area. Also the study revealed a massive loss of sediments as stated above at the lower beach in the frontage of the southern end of the golf course extending to the frontage of the caravan park. This indicates that the beach is lowering. To further review this changes three along shore profiles were drawn on the beach at section A, B and C. One of the profiles, was drawn at the frontage of the southern end of the golf course running to the frontage of the caravan park, the second was from the north end of the Kart track to the south end of the Kart track while the last profile was drawn from the north end of the section C partion to the south end of the partition (Figure 4). The Stack Profile tool in ArcGIS was used to produce these profiles. The profile was produced from the 2013 and 2014 DTMs by stacking them together. These profiles further validates the results from the analysis as presented above by showing the height gain and loss from both surfaces within the profile lines. The results so far from this study agree with the findings as documented by Lillesand et al. (2008). Golspie Beach has obviously undergone series of changes in the time past (Soudarissanane et al., 2008) and also presently as highlighted by these studies. Possible causes of change in sediments on the beach From the visit to the site and the results from the studies some inferences have been made as to what the possible causes of these changes in the beach sediment budget might be. Most of the changes in the movement of sediment volume across the study area would have been caused by the actions of wave-energy. The beach experiences high and low tides continually each day. This alters the structure of the beach gradually (Lindenbergh et al., 2011). Hence this would have resulted in the gradual deposition and removal of sediments at the different sections of the beach. Although some changes can be more spontaneous especially in the advent of extreme weather conditions such as violent storms. This was the case with Golspie Beach as an extreme storm was witnessed in December, 2012 (Hansom et al., 2013) which supposedly would have altered the beach. Also, there is human interference with the natural beach replenishing processes. In the bid to reduce erosion at the beach, materials were added to the beach at some sections. This resulted to an increase in sediment volume on the beach such as was captured in the results from the study (Figure 5). This could be seen as a positive impact to the beach since it minimizes erosion temporarily at those locations where these materials were added, however on the negative side, it often results to erosion at sites left

Joshua et al. 25 Figure 5. Volumetric change model showing areas of net loss and gain in sediment volume on the Golspie Beach. unprotected (Ford, 2013).

6 Joshua et al. 25 Figure 5. Volumetric change model showing areas of net loss and gain in sediment volume on the Golspie Beach. unprotected (Ford, 2013). This was the case with the Golspie Beach as noted by Hansom et al. (2013) and as was revealed by the present study as well. The intertidal area at the frontage of the south end of the golf course was observed to be eroding as there was a high loss of sediments more than the rest sections. This could also be attributed to human interference as a result of the added materials to the golf course frontage. The loss at the Kart track frontage could also be attributed to some anthropogenic activities such as the addition of bunds to

7 26 Sky. J. Soil. Sci. Environ. Manage. protect the beach. A need to identify the causal factor of the loss within this section of the Kart track would be very instrumental to militating against it. Conclusions This study has highlighted the effectiveness of the use of digital photogrammetric and terrestrial laser scanning techniques for beach change analysis. With these techniques the objectives of this study were fully realized. High resolution point cloud data with a point spacing of 5 cm was achieved with the use of terrestrial laser scanning, Lim (2005), This effectively captured the nature of the beach terrain for 2014 which would serve as a baseline data for post-change analysis of the beach after the beach nourishment project has been executed. Furthermore, a 25 cm resolution DTM and orthophoto was generated from the 2013 aerial photographs which was used alongside the TLS DTM to perform the change analysis. The findings from the result of the analysis show that the Golspie Beach is highly unstable with an interplay of erosional and accretional forces at work. The south end of the golf course experienced the greatest amount of changes in sediment volumes with a total loss and gain of approximately 6,517.3 and 9,143.7 m 3, respectively. The overall change in sediment on the beach was revealed with a southward movements observed in the sediments. Meanwhile other sections of the beach experienced more of gains with milder losses. Generally, the study revealed more of gains in sediments than losses in the study area. The percentages of gain and loss are approximately 70 and 30%, respectively, which is expected due to the increased intervention to protect the beach after the 2012 extreme storm that resulted in severe erosions. More materials were added to the beach during this period hence the increased gain in sediments. Based on the above the study goal and objectives could be said to have been achieved. Dawson A, Gomez C, Ritchie W (2010). Gualan Island study, South Ford, outer Hebridges. Final Report: Aberdeen Institute for Coastal Science and Management (AICSM) pp Ford M (2013). Shoreline changes interpreted from multi-temporal aerial photographs and high resolution satellite images: Wotje Atoll, Marshall Islands. Remote Sensing of Environment. Vol.135. pp Hansom JD, Rennie AF, Dunlop A, Drummond J (2011). A methodology to assess the causes and rates of change to Scotland s beaches and sand dunes Phase1. Scottish Natural Heritage Commissioned Report. No. 364.pp Hansom JD, Fitton JM (2013). Golspie dunes: Coastal erosion options appraisal. Scottish Natural Heritage Commissioned Report No. 635 Lillesand TM, Kiefer RW, Chipman JW (2008). Remote Sensing and Image Interpretation (Sixth edition). United States: John Wiley & sons Inc. pp Lim M, Petley DN, Rosser NJ, Allison RJ, Long AJ, Pybus D (2005). Combined digital photogrammetry and time-of-flight laser scanner for monitoring cliff evolution. The Photogrammetric Record.Vo.20, No.110.pp Lindenbergh RC, Soudarissanane SS, Vries DS, Gorte BGH, Schipper MA (2011). Aeolian beach and sand transport monitored by terrestrial laser scanning. The Photogrammetric Record.Vol.26, No.136.pp Schaefer M, Inkpen R (2010). Towards a protocol for laser scanning of rock surfaces. Earth Surface Processes and Landforms.Vol.35, No.4.pp Soudarissanane S, Lindenbergh R, Gorte B (2008). Reducing the error in terrestrial laser scanning by optimizing the measurement set-up. Beijing: The International 59 Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences Vol. 27, Part B5 (WG V/3). REFERENCES Alkan RM, Karsidag G (2012). Analysis of the accuracy of terrestrial laser scanning measurements. FIG Working Week, Rome, Italy, 6-10 May Collins BD, Kayen R, Reiss T, Sitar N (2007). Terrestrial LIDAR Investigation of the December 2003 and January 2007 Activations of the Northridge Bluff Landslide, Daly City, California: U.S. Geological Survey, Open File Report , 32pg;

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