DGPS Surveys Research Articles

Early Byzantine city walls of Hierapolis in Phrygia: demolishing and recycling the Imperial era monuments

The study concerns the city walls of Hierapolis in Phrygia (Denizli, Turkey), which were built in the second half of the 4th century AD or at the beginning of the 5th century AD, by systematically recycling architectural blocks from Imperial-era public monuments and funerary edifices. The preserved remains of the fortifications enclose the city along its northern, eastern and southern sides, leaving out large sectors of the urban area. Within the research activities of the Italian Archaeological Mission, topographical DGPS surveys of the remains were performed, and a geodatabase of the reemployed blocks was implemented with three main aims: i) the reconstruction of the building site of the city walls; ii) the identification of the demolished monuments of the Imperial-era used as “quarries” and the study of the procurement strategies of stone materials in the early-Byzantine Hierapolis; iii) the analysis of the relationship between the large building site of the fortifications and the other coeval construction sites and their impact on the socio-economic life of the city. The research allowed us to trace the development of the building site of the city walls, which, starting from the north, mainly reemployed blocks from the necropolises, North Theatre, North Agora and the shops along the plateia not-included into the early Byzantine Hierapolis. Moreover, numerous materials from the Gymnasium and other monuments located in the central part of the city but not yet identified on the ground were especially reused in the eastern and southern sectors of the walls. Lastly, the location of the recycled blocks made it possible even to reconstruct the various transportation routes linking the demolished monuments to the different sectors of the city walls. On cover:Late Roman wall, the portion immediately south of the West Gate (Porta Oea) with re-used blocks from first-century mausolea (Drawing by Francesca Bigi) and Tombstone of Regina from South Shields (Arbeia) (Tyne and WearArchives and Museums/ Bridgeman Images). E-ISSN (online version) 2611-3686 ISSN (print version) 0065-0900

Inter-annual morphological evolution and volume changes of a meso- to macrotidal beach exhibiting multiple intertidal bars (MITB)

Although morphologically persistent in the long term, Multiple Intertidal Bar Systems (MITBs) display short-term, especially seasonal, morphodynamic behaviour. Analysis of high-density, monthly DGPS surveys conducted at Murlough and Ballykinler beaches, inter- and supratidal sediment volumes and hydrodynamic forcing (wave conditions and water levels), demonstrates a link between strong seasonality in wave climate and MITB beach behaviour. Summer, low-energy conditions limit cross-shore sediment exchange during which MITB beach morphology tends to stabilise throughout the season. With the onset of high-energy winter conditions cross-shore sediment exchanges occur between inter- and supratidal areas. Sediment transport is then enhanced during storm conditions that are coincident with spring tides, leading to high total water levels (TWL). Ultimately the storm sequencing, (frequency, magnitude and inter-storm interval), is the key parameter driving the beach morphological response. Major erosional patterns occur when the most energetic event, combined with spring high tide, occurs at the beginning of the winter season. Subsequent, less energetic storms then promote bar recovery until another extreme event occurs.Seasonality is also evident in alongshore dynamics. Cross-shore drainage channels that dissect the intertidal bars migrate alongshore, driving alongshore sediment transport and MITB longshore migration patterns. In summer migration of drainage channels is limited, whereas the winter high-energy forcing enhances channel migration rates and resulting sediment transport. Differences in dynamics between the two study sites are attributed to differences in local geology, beach morphology and sediment size, but in both locations, drainage channels are in fine migrating toward the inlet and associated ebb delta that divides the bay. Subsequent transport vectors are unknown, but the observations highlight the primary role of the inlet in the sediment circulation dynamics in the system as a whole.

Sediment Budget Implications from Posidonia oceanica Banquette Removal in a Starved Beach System

This study discusses the potential impact of removing Posidonia banquette on the sediment budget of a siliciclastic-sediment-starved beach-barrier system. The morphology as well as the sediment volumes of this system were estimated. The banquette’s composition and sediment content were determined with samples collected during five sampling campaigns conducted in one year. The carbonate content of the system was estimated by analyzing three 1 m long cores collected along the barrier. Five digital terrain models from DGPS surveys were used to compute the beach’s average morphology to estimate the sediment volumes. The carbonate and siliciclastic sediment content from the cores were used to calculate the overall beach’s sediment mass. Total sediment mass accounted for 126,000 m3, of which ca. 86% was siliciclastic quartz sand and approximately 14% was carbonate sediment. Total banquette deposition during the year accounted for 2300 m3, with a maximum and averaged sediment content of 339 kg m3 and 78 kg m−3. A permanent loss of ca. 1.31% of total mass will occur if 5000 m3 of banquette were to be removed. In such beach settings, banquette removal may limit sediment availability, reducing the overall sediment mass and decreasing beach resilience against climate change effects such as sea level rise.

IGiS FOR MANAGING CITIES SMARTLY – URBAN GEOINFORMATICS

Abstract. A city is a geographic entity and should be efficiently analysed and optimised through the use of geo-spatial technology. The certification for a city to be ‘Smart’ is measured on the basis of the liveable index, adequacy of water supply, assured supply of electricity, proper sanitation and solid waste management, efficient urban mobility, public transport, affordable housing, robust information technology connectivity, transparent and good governance, safety and security of citizens, modernised health and education infrastructure and citizen participation which will lead to sustainable development. Smart Cities require a perfect balancing of modernisation of city infrastructure and leveraging technology. Smart cities require Geo-smart mapping and visualization capabilities with applications for protecting groundwater resources, locating schools and health centres, locating garbage dumps and toilets, designing bus routes. The indigenously developed integrated platform of GIS, Image Processing, Photogrammetry and CAD, called IGiS has been leveraged by Scanpoint Geomatics Limited, Ahmedabad (SGL), India for implementing the Enterprise GIS for 7 smart cities in India. A centralised geo spatial database with a standard data model compliant set of maps/layers has been created for each city. The spatial layers are derived from 30cm resolution satellite data. Point data (locational information) is generated using DGPS surveys. The city assets are geographically mapped at a scale of 1:2000 and organised in a spatial database. Inputs required for operations and maintenance of every utility/facility are geo tagged and stored in the database. Web & Mobile GIS applications & Citizen portal are developed using the indigenous platform. Integration with other e-governance applications and spatial layer requirements of the Integrated Command and Control Centre are supported through RestAPI & OGC compliant web services. SGL’s Mobile GIS framework named Qpad comes handy for spatial data verification. IoT devices are used to gain insights for real-time handling of critical situations or emergencies. Having laid the foundation for driving smart cities in terms of the spatial database at a scale of 1:2000, the stage is set to look forward to the results. Plugging revenue leakages, better traffic management, information at a click during peak of the Corona pandemic, effective usage of open spaces and barren areas, planning the utility requirements by the corporation to accommodate for the urban explosion is the kind of harvest that is anticipated with abated breath. This paper demonstrates the suitability and capability of the indigenously developed common platform for image processing and GIS (IGiS Enterprise Suite) in building Smart City Applications and quantifying the results.

Analysis of Two Contrasting Seasonal Recovery Periods of an Open Sandy Beach, using High Frequency DGPS Surveys

Biausque, M. and Senechal, N., 2020. Analysis of two contrasting seasonal recovery periods of an open sandy beach, using high frequency DGPS surveys. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 377-381. Coconut Creek (Florida), ISSN 0749-0208.High frequency DGPS surveys were undertaken for 2.5 years (November 2015 until April 2018) on an open sandy double barred beach in the SW of France (Biscarrosse Beach) covering three winter and two summer periods. On those latitudes, summers are usually described as seasonal recovery periods. The morphological response of the beach during two consecutive summer periods (2016 and 2017) has been analyzed to identify processes involved in seasonal recovery. Analysis of alongshore mean profiles indicates that the summer 2016 is marked by a progressive berm reconstruction, manly driven by cross-shore sediment transport. The beach recovery in 2016 can be characterized as complete with a stable berm through the summer season associated with steady beach cusps, and a seaward dune foot migration. During this summer the variations in volume of each section of the beach (intertidal/supratidal beach and dune) show sediment transport firstly orientated from the intertidal beach toward the supratidal one, and, later, driven from the supratidal beach to the dune. This cycle is coherent with recent observations described by Philips (2017). In contrast, the summer 2017 is characterized by an incomplete recovery, an unstable berm and so, a much more complex dynamic: the berm, rapidly rebuild (by the end of June), started to erode in July. Six sequences of cross-shore sediment exchanges are measurable along the season between the intertidal and the supratidal beach, inducing successive erosion/ accretion of both sections of the beach. Thus, according to those results summers 2016 and 2017 present variable spatial and temporal dynamics. Moreover, analysis of hydrodynamic and environmental factors indicate that recovery periods not only depend on hydrodynamic conditions, such as wave energy and tide, but also on winter/summer morphological coupling, and sandbar/beach coupling.

Multi-month sedimentological characterization of the backshore of an artificial coarse-clastic beach in Italy

In this paper, a sedimentologic characterization of an artificial coarse-clastic beach at Marina di Pisa (Tuscany, Italy) is carried out within a 5 month timespan (October 2018–February 2019). The beach was built in 2007 as a form of coastal protection due to severe erosion processes occurred along this sector of the coast in the past 150 years. The grain-size characterization was performed using pyDGS, a digital grain-size analysis software developed by Buscombe (2013). It is an open-source Python framework that uses a continuous wavelet transform method to calculate grain-size parameters (e.g., mean grain size, sorting) from images. By matching grain-size data with the topographic evolution of the beach provided by DGPS surveys of the backshore, we pointed out a seaward shift of coarser pebbles after medium-energy events (max significant wave height about 3 m). This trend suggests that wave reflection processes onto the seawall are generated during those events, producing a significant cross-shore transport of pebbles along the backshore. Such reflection processes had already been reported in the scientific literature during higher energy wave states though, which means that the artificial beach had decreased the protection level over time. These observations might be useful for coastal managers to optimize future coarse-clastic beach fill interventions. Digital grain-size analysis proved to be reliable and less time-consuming compared to traditional techniques, such as dry-sieving grain-size analysis and caliper measurements. Further improvements are still required specially to extend the survey in the underwater environment.

Storms impacts on a sandy beach including seasonal recovery: alongshore variability and management influences

Despite a global context of shoreline retreat, coastal areas and in particular sandy coasts are increasingly attractive. To handle the problem of coastline retreat different management strategies are deployed and among them soft methods as windbreakers or hard ones as seawalls. But all those methods are known to interfere in the natural evolution of the beach/dune systems at different timescales. To underline potential influences of management strategies on erosion and recovery periods, high frequency DGPS surveys coupled with video images are recorded at a workshop-site exhibiting various management strategies, Biscarrosse beach (SW of France) from November 2015 until September 2016. Results for the winter 2016 highlight a global erosion of the beach associated to a dune foot retreat and an alongshore variability in the beach response to events. The same patterns can be observed during the seasonal recovery period (April to August), in particular a lag in the berm reconstruction in front of the seawall. The LVI (Longshore Variation Index) reflects possible sediment processes taking place between the different sections of the beach: while recovery seems to be dominated by cross-shore exchanges in the unmanaged section, longshore sediment processes seem to be the origin of the recovery in the managed section. This variability could be linked to a permanent rip current visible (98% of observation) in front of the seawall that could cause an offshore sediment export explaining both the lag in term of recovery timescale and the different sediment processes involved during the recovery period. During the erosion season, sediment exchanges between the beach and the dune are limited due to the presence of seawalls and beach erosion and dune retreat in the two ends on the wall accelerated.

Uplift rates of marine terraces as a constraint on fault-propagation fold kinematics: Examples from the Hawkswood and Kate anticlines, North Canterbury, New Zealand

Marine terraces on growing fault-propagation folds provide valuable insight into the relationship between fold kinematics and uplift rates, providing a means to distinguish among otherwise non-unique kinematic model solutions. Here, we investigate this relationship at two locations in North Canterbury, New Zealand: the Kate anticline and Haumuri Bluff, at the northern end of the Hawkswood anticline. At both locations, we calculate uplift rates of previously dated marine terraces, using DGPS surveys to estimate terrace inner edge elevations. We then use Markov chain Monte Carlo methods to fit fault-propagation fold kinematic models to structural geologic data, and we incorporate marine terrace uplift into the models as an additional constraint. At Haumuri Bluff, we find that marine terraces, when restored to originally horizontal surfaces, can help to eliminate certain trishear models that would fit the geologic data alone. At Kate anticline, we compare uplift rates at different structural positions and find that the spatial pattern of uplift rates is more consistent with trishear than with a parallel-fault propagation fold kink-band model. Finally, we use our model results to compute new estimates for fault slip rates (~1–2m/ka at Kate anticline and 1–4m/ka at Haumuri Bluff) and ages of the folds (~1Ma), which are consistent with previous estimates for the onset of folding in this region. These results are consistent with previous work on the age of onset of folding in this region, provide revised estimates of fault slip rates necessary to understand the seismic hazard posed by these faults, and demonstrate the value of incorporating marine terraces in inverse fold kinematic models as a means to distinguish among non-unique solutions.

Influence of the 18.6-year lunar nodal tidal cycle on tidal flats: Mont-Saint-Michel Bay, France

The influence of the 18.6-year nodal tidal cycle on estuarine accretion, and indirectly on channel migration patterns, in Mont-Saint-Michel Bay, a UNESCO World Heritage Site famous for its monastery, is explored over three tidal cycles from a 68-year dataset that combines aerial photographs (1947–2007), one DGPS survey (1997), and nine LiDAR Digital Elevation Models (2002–2015). Sand-flat elevation and sediment-budget changes in this megatidal environment were further determined over the last nodal cycle using DGPS and LiDAR surveys. We infer that the changes observed are linked to variations in tidal prism and current velocities in this shallow, large tide-range setting. Increasing (rising tidal range) or decreasing (falling tidal range) flood-dominated asymmetry are deemed to lead, respectively, to waxing and waning of sediment import, in the form of large sand banks, into the bay over the 18.6-year nodal tidal cycle that, in turn, force channel migration. Coriolis acceleration and centrifugal forces are also considered to contribute to the observed channel migration.

Recent changes in the Wanda Glacier, King George Island, Antarctica

Mudanças glaciológicas recentes na geleira Wanda, Ilha Rei George, Shetlands do Sul (latitudes 61°54’S a 62°16’S e longitudes 57°35’W a 59°02’W), fora da Península Antártica, foram quantificadas através de medidas da direção e velocidade do fluxo de gelo e das flutuações em sua posição frontal. Dados topográ- ficos e medidas de DGPS, bem como perfis transversais e longitudinais para a geleira foram obtidos para a geração de um Modelo Digital de Superfície. Os resultados demonstram que a geleira Wanda possui uma pequena bacia de drenagem, um alto grau de retração através de processos de fusão, e reduzida espessura se comparada com outras massas de gelo da Ilha Rei George. Mudanças em sua área foram obtidas pela utilização de imagens de satélite multitemporais do período de 1979 a 2011. A geleira Wanda perdeu aproximadamente 31 % de sua área original desde 1979 (1,5 km² de área em 1979). Atualmente, apresenta uma contínua e rápida fase de retração, atribuída ao recente aquecimento regional. A velocidade superficial máxima do fluxo de gelo, medida através de uma rede de estacas implantadas na geleira, foi estimada em 2,2-1 cm/dia durante o período de 2007 a 2011. Perfis transversais mostraram a influência da topografia na direção do fluxo de gelo. Devido à sua pequena área apresentada e sua condição termal, a geleira Wanda responde rapidamente às variações climáticas, revelando relevância em estudos ambientais.

Short-term geomorphic analysis in a disturbed fluvial environment by fusion of LiDAR, colour bathymetry and dGPS surveys

ObjectiveEstimating river's underwater bed elevations is a necessary but challenging task. The objective of this study is to develop a revised approach to generate accurate and detailed Digital Terrain Models (DTMs) of a river reach by merging LiDAR data for the dry area, with water depth indirectly derived from aerial imagery for wet areas. MethodsThis approach was applied along three sub-reaches of the Brenta River (Italy) before and after two major flood events. A regression model relating water depth and intensity of the three colour bands derived from aerial photos, was implemented. More than 2400 in-channel depth calibration points were taken using a differential Global Positioning System (dGPS) along a wide range of underwater bed forms. ResultsThe resulting DTMs closely matched the field-surveyed bed surface, and allowed to assess that a 10-year recurrence interval flood generated a predominance of erosion processes. Erosion dominated in the upper part of the study segment (−104,082m3), whereas a near-equilibrium is featured on the lower reach (−45,232m3). The DTMs allowed the detection of processes such as riffle–pool downstream migration, and the progressive scour of a pool located near a rip-rap. ConclusionThe presented approach provides an adequate topographical description of the river bed to explore channel adjustments due to flood events. PracticeCombining colour bathymetry and dGPS surveys proved to represent a useful tool for many fluvial engineering, ecology, and management purposes. ImplicationsThe proposed approach represents a valuable tool for river topography description, river management, ecology and restoration purposes, when bathymetric data are not available.

Evolution of Corsican pocket beaches

Balouin, Y., Belon, R., 2014. Evolution of Corsican pocket beaches. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 096–101, ISSN 0749-0208.Pocket beaches are small beaches that are formed between headlands and within coves along rocky shorelines. They can be composed of a mix of boulders, pebbles, sand and mud and therefore have the attributes of a combination of shoreline types. Their evolution depends on wave forcing and morphological characteristics, and the most commonly observed dynamic is that of beach rotation due to prevailing wave direction. In this study, 44 pocket beaches off Corsica Island, in the Mediterranean were studied. The absence of significant tides and the generally weak coastal currents restrict significant beach morphology changes to the most important storm events though the variability of coastal evolution suggests that other factors played a role. To assess these evolution parameters, the morphological characteristics of the beaches as well as the historical evolution of the shoreline were studied. This analysis, based on aerial photos and DGPS surveys, allowed for the behavior of beaches over historical (1948–2012) period to be assessed. Over this period, 15 beaches are considered to be in erosion, 16 are stable and the others show shoreline progression. The historic analysis, through several increments of time, shows that beaches have been in perpetual movement. Moreover, some periods are particularly erosive (i.e., 1996 to 2002) for a number of beaches. Several parameters must be considered to explain the beach behavior changes such as: beach orientation, closure, geology, hydro-climatic regime, grain size and length. The wave backward modeling ANEMOC was used to analyze wave characteristics and the occurrence and direction of the most important storm events. The entire dataset was used to obtain a conceptual model describing the most important factors involved in the contrasting coastal evolutions observed, i.e., symmetric or asymmetric beach rotation, homogeneous retreat or progradation and rapid shoreline movements due to the presence of beach-cast Posidonia Oceanica seagrass litter.

Quantification of three‐dimensional folding using fluvial terraces: A case study from the Mushi anticline, northern margin of the Chinese Pamir

AbstractFold deformation in three dimensions involves shortening, uplift, and lateral growth. Fluvial terraces represent strain markers that have been widely applied to constrain a fold's shortening and uplift. For the lateral growth, however, the utility of fluvial terraces has been commonly ignored. Situated along northern margin of Chinese Pamir, the Mushi anticline preserves, along its northern flank, flights of passively deformed fluvial terraces that can be used to constrain three‐dimensional folding history, especially lateral growth. The Mushi anticline is a geometrically simple fault‐tip fold with a total shortening of 740 ± 110 m and rock uplift of ~1300 m. Geologic and geomorphic mapping and dGPS surveys reveal that terrace surfaces perpendicular to the fold's strike display increased rotation with age, implying the fold grows by progressive limb rotation. We use a pure‐shear fault‐tip fold model to estimate a uniform shortening rate of 1.5 + 1.3/−0.5 mm/a and a rock‐uplift rate of 2.3 + 2.1/−0.8 mm/a. Parallel to the fold's strike, longitudinal profiles of terrace surfaces also display age‐dependent increases in slopes. We present a new model to distinguish lateral growth mechanisms (lateral lengthening and/or rotation above a fixed tip). This model indicates that eastward lengthening of the Mushi anticline ceased by at least ~134 ka and its lateral growth has been dominated by rotation. Our study confirms that terrace deformation along a fold's strike not only can constrain the lateral lengthening rate but can serve to quantify the magnitude and rate of lateral rotation: attributes that are commonly difficult to define when relying on other geomorphic criteria.

Integration of colour bathymetry, LiDAR and dGPS surveys for assessing fluvial changes after flood events in the Tagliamento River (Italy)

The estimation of underwater features of channel bed surfaces without the use of bathymetric sensors results in very high levels of uncertainty. A revised approach enabling an automatic extraction of the wet areas to create more accurate and detailed Digital Terrain Models (DTMs) is here presented. LiDAR-derived elevations of dry surfaces, water depths of wetted areas derived from aerial photos and a predictive depth-colour relationship were adopted. This methodology was applied at two different reaches of a northeastern Italian gravel-bed river (Tagliamento) before and after two flood events occurred in November and December 2010. In-channel dGPS survey points were performed taking different depth levels and different colour scales of the river bed. More than 10,473 control points were acquired, 1107 in 2010 and 9366 in 2011 respectively. A regression model that calculates channel depths using the correct intensity of three colour bands (RGB) was implemented. LiDAR and water depth points were merged and interpolated into DTMs which features an average error, for the wet areas, of ±14 cm. The different number of calibration points obtained for 2010 and 2011 showed that the bathymetric error is also sensitive to the number of acquired calibration points. The morphological evolution calculated through a difference of DTMs shows a prevalence of deposition and erosion areas into the wet areas.

The boulder berm of Punta Saguerra (Taranto, Italy): a morphological imprint of the Rossano Calabro tsunami of April 24, 1836?

An extended berm of calcarenitic boulders is recognisable at Punta Saguerra, few kilometres south of Taranto (Apulia, Italy) while isolated boulders are sparse in other near localities. The berm is at 2–5 m above present sea level (a.p.s.l), on a rocky headland gently sloping toward the sea; it is separated from the coastline by a large terrace. A detailed study of its stratigraphy and its morphology has been performed in order to define its depositional mechanism; in particular, integrated DGPS and Laser Scanner surveys have provided precise details of each boulder: position, size and distance from the shoreline. The accumulation is constitute of boulders up to 30 tons, which locally are arranged in rows of embricated patterns. The surfaces of the biggest boulders are characterised by biogenic encrustations and by solution potholes that indicate their intertidal/adlittoral/spray zone provenience. Based on direct observations of each boulder (size, shape, weight and long axis azimuth), together with hydrodynamic equations it is possible to hypothesize the extreme event—geodynamic or meteorological— which was responsible for this singular accumulation. AMS age determinations on Vermetid sp. sampled on boulder surfaces and chronicle suggest that the accumulation may be attributed to the tsunami generated by the strong earthquake that occurred on April 24, 1836, the epicentre of which has been localised near Rossano Calabro, along the Ionian coast of northern Calabria.

Predicting shoreline response to changes in longshore sediment transport for the Rio Grande do Sul coastline

Longshore sediment transport (LST) has been calculated using the CERC formula for the long (618 km), gently undulating, sandy shore of Rio Grande do Sul (RS) for wave climate scenarios typifying normal (i.e. non-ENSO years) and La Nina years. Predicted LST values have been validated with available field measurements. Whilst in most cases LST was directed to the north, simulations revealed large spatial variability in both the magnitude and direction of the net annual LST flux. This was related primarily to the orientation of the coastline relative to the incident waves and to the dominance of waves from different directions. Predicted net annual LST values were used in a simple model to calculate changes in the position of the shoreline. For normal years, results showed that areas of erosion predicted along the southern shores of the coastal projections and regions of accretion predicted in the embayments agreed well with shoreline surveys. The wavelength and amplitude of temporal and spatial oscillations in shoreline position measured by DGPS surveys were estimated well by a simple simulation of shoreline change. The simulation showed also that observed reversals in shoreline displacement from erosion to accretion or vice-versa could be explained by subtle changes in the annual wave climate. The present results provide strong evidence that slight changes to the wave climate can impact significantly on coastal processes along the RS shoreline. Similar impacts might be anticipated along other sandy shorelines worldwide.

Mobilité des cordons littoraux et submersions marines

ABSTRACT Firstly, the morphosedimentary changes of ten gravel barriers located in the bay of Brest are analysed using aerial photographs taken between 1952 and 2004 and DGPS surveys (2004–2005). An analysis of meteorological and oceanographic conditions during this period is then carried out using tide, wind speed and direction data. Finally, the synthesis of these data shows three morphological responses of the gravel spits which allows to define a sensitivity scale for the evaluation of coastal damage.