ADVANCED MONITORING SYSTEMS FOR LANDSLIDE RISK REDUCTION IN THE 'SIQ' OF PETRA (JORDAN)

The UNESCO World Heritage Site of Petra is characterized by a spectacular geo-archaeological landscape that lead to its inscription as World Heritage Site in 1985. Petra is also a fragile site facing a wide diversity of risks, ranging from those posed by environmental factors as well as those attributed to tourism. In recent years, hazardous natural phenomena were registered as increasingly impacting the site, and most specifically the 'Siq', a 1.2 km naturally formed gorge serving as the only tourist entrance to the archaeological park, posing a major threat to cultural heritage and visitors. These recent events have prompted UNESCO Amman Office, in cooperation with the national authorities, to develop a strategy towards prevention and mitigation of instability phenomena at the 'Siq' and, thus, further contribute to the management and conservation of the site through the implementation of the multi-year Italian funded "Siq Stability" project Actions have been primarily focusing on the analysis of the stability conditions of the 'Siq' slopes, the installation of an integrated monitoring system and the definition and implementation of mitigation measures against rock instability. This paper reports a detailed description of the integrated monitoring system installed paying particular attention on the wireless monitoring devices and the EASA applications, which proved to be some of the most successful systems implemented in the framework of the project. Some preliminary results regarding the data retrieved, policies applied and actions taken to ensure longterm sustainability and capacity development of the national authorities are also reported. * Corresponding author


The Petra Archaeological Park
The World Heritage Site of Petra lies in a large valley surrounded by mountain ranges.Its geology is dominated by Palaeozoic sandstone rocks that form most of the hand-carved Nabataean rock monuments of Petra.The 'Siq' is a 1.2 km naturally formed gorge in the sandstone rocks that represents the main entrance to the archaeological site.Because of the religious niches and water management features, the 'Siq', in its entirety, is considered a monument of religious and historic significance, considerably contributing to the Outstanding Universal Value of the site.

UNESCO Risk Prevention Strategies in Petra
Petra is also a very fragile site facing a wide diversity of risks, ranging from those posed by environmental factors, such as natural and geological hazards, as well as those attributed to tourism and the lack of adequate site management and emergency measures for tourist and monument safety.In recent years, natural phenomena, such as earthquakes, floods and landslides were registered as increasingly impacting the site, and most specifically the 'Siq' posing a major and permanent threat to cultural heritage and visitors.Preserving Petra's Outstanding Universal Value for which the site has been inscribed in the World Heritage List (UNESCO, 2016), is one of the corporate UNESCO priorities for culture actions in Jordan, in line with the UNESCO Strategy for Risk Reduction at World Heritage properties (UNESCO, 2006).Since 2009, the UNESCO Office in Amman has supported the Petra Archaeological Park and the Department of Antiquities in assessing, managing and mitigating natural hazards in the 'Siq' with the final objective to develop a strategy towards prevention and mitigation of instability phenomena at the 'Siq' and, thus, further contribute to the management and conservation of the site.From 2009 to 2015, UNESCO engagements focused on addressing for the first time the impact of landslides phenomena in the 'Siq'.In 2009 a technical expertise in engineering geology was provided to the national authorities to support the consolidation of a fractured block in the 'Siq'.Through the implementation of the projects "Rapid Risk Assessment" (2011) and "Siq Stability", Phase I (2009-2015) actions centered on the analysis of the stability conditions of the 'Siq' slopes based on a comprehensive site documentation, the installation of an integrated monitoring system and the definition of mitigation measures against rock instability (Delmonaco et al., 2015;Delmonaco et al., 2014;Delmonaco et al., 2013a;2013b;2013c).Most recently, the Petra "Siq Stability" project Phase II (2015)(2016) aimed to operationally implement the mitigation of landslide risk in the 'Siq' through the (a) application of priority and urgent landslide mitigation interventions in the upper 'Siq' plateau and on the 'Siq' slopes to address immediate slope hazards in the short term; (b) capacity development of the national authorities to address the management of landslide risk at the site and implement mitigation measures in coordination with international experts; (c) awareness raising among different levels of stakeholders on landslide and flash flood risk (Cesaro et al., 2017).Monitoring of instability phenomena in the 'Siq' through the installation of an advanced integrated monitoring system -from remote to field-has represented one of the most innovative, successful and sustainable approaches of the project for the detection and control of deformation processes.

The geological and geomorphological features of the 'Siq'
The 'Siq' of Petra is 1,2 km in length and 3 m to 15.70 m in width.It is formed by very steep slopes with variable height from the ground level, from few meters at the entrance to several tens of meters in some areas of the path.The 'Siq' is prevalently formed by the Disi and Umm Ishrin sandstone formations (Cambrian-Ordovician) with a typical rupestrian and massive forms (Bender, 1974).The majority of the rock monuments of Petra were almost entirely cut in the Umm Ishrin formation due to its good mechanical strength and facility to hand-carving (Amireh et al., 2001).The geomorphology of the 'Siq' is the result of long and shortterm factors such as tectonic uplift, erosion due to runoff, differential erosion and weathering of sandstone rocks.The mainly E-W orientation of the 'Siq' and its meandering course are a consequence of the intersection of numerous faults and master joints.Discontinuities in the 'Siq' rock slopes are represented by bedding (generally sub-horizontal), faults and master joints (mainly sub-vertical), other discontinuities (from vertical to medium slope angle) correlated with the geomorphological evolution of the 'Siq'.

Slope instability conditions
According to local orientation, density and persistence of discontinuities, slope instability conditions can occur and can affect rock blocks with variable dimension depending on types and degree of structural control.The 'Siq' being one of the main channels of the Wadi Musa catchment, collects a series of lateral steep channels that convey superficial water during short and intense rainfall events.Due to the above conditions, the 'Siq' of Petra presents a very diffuse hazard of rock slope failures and instability, mainly represented by the following phenomena: a) fall of loose debris (very small blocks/stones) from the cliff edges and terraces caused by heavy rainfall and flash-floods; b) fall/toppling/sliding of small/medium and large size blocks along pre-existing discontinuities of the rock mass (Figure 1), due to progressive instability caused by climatic, geological and geomorphological factors (Delmonaco et al., 2014;2013a;2013b, 2013c).
Figure 1.Landslide inventory map of the Petra area Differently from debris fall, which is in Petra mostly caused by heavy rainfall and flash-floods, phenomena of rock detachment are characterized by a long-term evolution governed by various factors such as local lithology, geostructural setting, weathering, water circulation, climatic parameters, and human effects.Slope failures in rock masses outcropping in Petra generally occur along pre-existing discontinuities and their triggering is mostly associated with short-term factors depending mainly on climatic parameters (i.e.temperature/humidity changes) and seismicity factors (Delmonaco et al., 2014;2013a;2013b;2013c).In the last decade, several landslide events, mostly rock falls and rock slides, with different magnitude (volumes from < 1 m 3 to > 10 m 3 ) have occurred in the 'Siq ' (2009, 2015) and in the core area of the site (2009,2010,2016).A brief description of such events is summarized in Table 1.
Table 1.Inventory of recent landslide events in Petra.
In Wadi Musa, rainfall precipitation is characterized by an average yearly recurrence of 4-5 heavy rainfall events, from October to April, with high intensity and short duration that can cause removal and fall of loose debris from the upper slopes and outlets of secondary channels (Delmonaco et al, 2013c).The analysis of the rainfall data recorded in the meteorological station installed in June 2013 in the framework of the 'Siq' Stability Project, Phase I, reports a climatic scenario for the 'Siq' characterized by an increase of critical precipitation in terms of rainy days with high rainfall intensity as well as by heavy rainfall events that have occurred in late April-early May.
The reasons of such anomalies can be correlated either to natural climate trends or, more probably, to climate change effects.Regardless of possible climatic change effects in Petra (Matouqa et al., 2013;Beck and Collet, 2011) and based on available meteorological records and recent rock failures inventory (although greatly incomplete), in the 'Siq' of Petra it is possible to estimate a yearly return time TR for debris fall as TR =4÷5 /yr whereas for rock slope failures (rock fall, rock slide) the return time can be assumed as TR =0.1÷ 0.2/yr (Delmonaco, 2016) as shown in Figure 2.

The integrated monitoring system
Considering the morphological setting and slope instability processes, during the Phase I of the "Siq Stability" project the following monitoring techniques have been proposed, designed, implemented and installed for the monitoring of the 'Siq' slopes (Delmonaco et al., 2015).
 Satellite SqueeSAR™ analysis with permanent scatters techniques, to evaluate potential regional deformation pattern of the site and possible 'Siq' border effects;  Automated crack-gauge network, with wireless connection, to monitor main cracks and isolated potentially unstable blocks, with a low environmental impact technology;  High resolution total station network measuring a prisms network, individual reflectorless points network and reflectorless grid network in the 'Siq' slopes, for monitoring slope/blocks deformation;  Manual crack gauge network on 25 main discontinuities.
Among all the systems implemented, the most coherent, accurate and robust results have been obtained through the automated crack-gauge network provided by EnvEve.Results achieved through the other systems led to questionable results on detection of slope deformation in the 'Siq'.

Direct Rock Block Monitoring with Wireless Network
In order to measure with high precision and accuracy the rock blocks response to daily and seasonal displacement, a wireless monitoring system was installed in the 'Siq' in 2013 (Figure 3).The sensors are provided with 5-years long-life batteries and solar cells in order to assure a continuity in data recording in the event of a breakdown.The system was not originally designed to work as a near-time alarm or early warning system, but to assess rock displacement in the 'Siq' in connection with meteorological data.

The NaturAlert and EASA platforms
Besides the installation of the devices, storage, visualization and analysis of the data collected are managed through two different platforms, NaturAlert and EASA (EnvEve Advanced Software Analytics) developed during the implementation of the "Siq Stability" project.
The NaturAlert platform allows a predefined number of users (technical project team) to view, download and analyze the data through a web connection to the project main server.The data collected include crack deformation, slope angle variation, air temperature and humidity variation, rainfall and wind speed.At the present stage of the project, a specific EASA APP is being developed to manually collect data directly in the field such as manual monitoring measurements and/or upload qualitative data related to the monitoring of landslide risk mitigation works conducted in the upper 'Siq' or additional environmental data.The APP can be used without internet connection and can automatically upload and synchronize the data collected with the EASA Cloud.The data are later converted into data series and can be easily compared with data collected from the sensors installed, thus extending the potential of the system and supporting the national authorities in the decision making process.

Rationale on causes of rock failures
Slope failures in rock masses that develop along pre-existing discontinuities may occur due to various environmentally induced mechanisms such as high magnitude earthquakes (Rodriguez et al., 1999;Yagoda-Biran et al., 2010;Hatzor, 2003), pore pressure build-up in rock joints (Iverson, 2000;Veveakis et al., 2007), and freezing and thawing of water in joints (Matsuoka, 2008;Murton et al., 2006;Williams, 1995).These suggested mechanisms fail to describe time-dependent, thermally controlled sliding along discontinuities or opening of tensile fractures which may ultimately culminate in slope failure.
Considering daily and seasonal temperature influences, several studies have evidenced extremely slow, creep-like, slope displacements due to cyclic temperature changes in long-term monitoring surveys (Vargas et al., 2013;Gisching et al., 2011;Mufundirwa et al., 2011;Gunzburger et al, 2005;Watson et al., 2004).Some of such studies were carried out for the preservation of cultural heritage sites around the world, for example in Slovakia (Vlcko et al., 2009), Japan (Greif et al, 2006) and Israel (Hatzor et al., 2002).

Blocks displacement vs thermal effects
In the case of the 'Siq' of Petra, data were collected from June 2013 up to date.However, since August 2016 the series is not entirely complete due to the partial malfunctioning of some of the devices, which were vandalized.
The data collection shows the correlation between temperature and joint displacement (Figure 5).Daily air temperature data of 2014 are compared with rock displacement measured by the sensor 6213 (crack meter of block sector 5-left slope) as example for analysis of displacement trend vs. temperature oscillation.The diagram shows a direct relationship between increase of T° and closure of the joint (ascending trend of displacement).The same trend has been already detected for displacements recorded with the manual crack gauge (manual monitoring) (Margottini and Spizzichino, 2015).
Monitoring data suggest that joint opening and closure are strongly correlated with air cooling and heating.This correlation implies that contraction and expansion of the rock on both sides of the crack manifests in joint opening and closure, as clearly indicated by the diagram of Figure 4.The inverse relationship between joint opening and air temperature for one annual cycle implies that the dominant factor affecting displacements of jointed sandstone material in the 'Siq' is thermo-elastic, the majority of which is recovered by the end of an annual loading cycle and resulting in null or slight permanent deformation.According to the above and considering that recent inventoried landslides in Petra have occurred in early autumn and late spring time, when the daily temperature records show the highest difference between minimum and maximum data, a further analysis (semi-quantitative) was performed on the effect of daily temperature differences on the triggering of recent rock fall.The analysis was first focused on the rock fall occurred on the 28 th May 2015 in the 'Siq' of Petra, sector 11.For this event, it is possible to reconstruct accurately the influence of temperature and humidity on the triggering of the rock fall.In order to get a wider overview of daily temperature fluctuation in the 'Siq' of Petra, an analysis of temperature data has been carried out since June 2013 up to end of October 2016.All available temperature data have been retrieved from NaturAlert system and transformed in excel format.The complete data set (around 145,000 records) of temperature measurements was restricted to daily maximum and minimum temperature (ca.2,500 records) and plotted in a graph (Figure 7) reporting maximum temperature, minimum temperature and daily difference (T°).The same analysis was extended also for the other landslides events, reported in Table 2, considering temperature records available for the area (e.g.'Siq'-Treasury area, Udruh).The results are summarized in the following Table 3.
Table 3.Recent landslide events and possible triggering causes

CONCLUSIONS
This study reports on the essential role of monitoring for landslide risk prevention in the 'Siq' of Petra.Among the monitoring devices installed, the wireless system proved to be the most reliable, best performing and feasible system for monitoring rock deformation in the 'Siq' of Petra due to its accuracy and possibility to detect rock displacement, mostly if in connection to thermal effects.Additional studies on the data collected combined with a further development of the EASA software could lead to enhancing the potentials of the system.
Although not initially designed to work as near-time alarm, the system could progressively lead to the identification of instability thresholds and improve its function as risk preventive measure in Petra.Future actions shall therefore focus on the possibilities of applying the wireless monitoring system also in other areas of the site while reducing its flaws.Despite some of the challenges faced in the use of the system, as its vulnerability to vandalism and the complexity of installation in the unique geomorphic environment of the 'Siq', the implementation of this monitoring system can be regarded as a successful example of landslide risk preventive measure for the improved management of a World Heritage Site.Similar actions shall be then integrated in a management plan for the protection of the site for which is currently being elaborated by UNESCO Amman in cooperation with the national authorities.
continuously cooperation in the implementation of this pioneering project.

Figure 2 .
Figure 2. Relationship between magnitude and frequency of instability phenomena of rock slope failures (points) and debris falls (blue square) in Petra according to recent recorded events

Figure 3 .
Figure 3. Distribution of the wireless monitoring devices

Figure 4 .
Figure 4. Large unstable block located in sector 5 equipped with wire deformometer, tilt meter and air and humidity sensors.
The system is particularly useful to verify in real time the functionality of any device installed in the 'Siq' and detect any breakage.During a second stage of the project, the EnvEve Advanced Software Analytics (EASA) has been developed to further enhance the initial NaturAlert software platform, making information accessible on-time and through a more userfriendly interface.EASA is a powerful cloud software for analytics and Internet of Things (IoT) enabling real-time data interoperability, advanced processing and smart visualization aimed to identify correlations and discover predictive modellingThe International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-2/W5, 201726th International CIPA Symposium 2017, 28 August-01 September 2017, Ottawa, Canada of environmental phenomena.This advanced IoT analytics cloud solution complements the innovative approach applied as part of the UNESCO "Siq Stability" project allowing to extract information out of different data systems in a cooperative and efficient manner.Specifically, EASA allows a) hardware interoperability by receiving data from additional sources and devices; b) easier treatment of different data formats to deal with historical data import, connection to external servers for real time data exchange, data format conversion; c) advanced step by step supported data series processing to i.e. label and manage data series, clean configurable data series with real time view, data series consistency check; d) real time analytics engine to implement analytics formula without coding or software programming, e) real time data customs and view on results on dynamic data series to facilitate graphic interaction and share.

Figure 6 .
Figure 6.Air temperature (upper diagram) and humidity (lower diagram) trends measured in May 2015.The orange area corresponds to the time of the rock fall.

Figure 6
Figure 6 reconstructs the trends of temperature and humidity in May 2015.The orange area corresponds to the period when the rock fall has occurred (28-29 May 2015).From the diagram, the following observations can be made:

Figure 7 .
Figure 7. Trend of air temperature in the 'Siq' of Petra from June 2013 to October 2016.The above diagram shows that the rock fall event happened on the 28 th May 2015 was preceded by the highest daily temperature fluctuation measured since the beginning of the observation (14.8°).The dotted line on 15° (T°) indicates a possible threshold of daily temperature difference that can promote rock failures in the 'Siq' of Petra.The same analysis was extended also for the other landslides events, reported in Table2, considering temperature records available for the area (e.g.'Siq'-Treasury area, Udruh).

Table 2 .
Overview of displacement recorded by EnvEve SA sensors functioning in October 2016