Perhaps the most serious natural hazard threatening the archeological site of Dion in Pieria is that of flooding. This is due to the fact that, from the creation of the ancient city until today, Vafyras river, a navigable river that provided access to the sea during antiquity, passes through the eastern side of the archeological site. The torrent Orlias, which descends from Mount Olympus and passes along the north side of the archeological site, contributes to Vafyras, meeting it shortly before entering the site. During periods of heavy and extensive rainfall, Vafyras overflows, resulting in the flooding of parts of the eastern side of the archaeological site. The biggest problems from these flooding events occur in the Sanctuary of Isis and the Sanctuary of Zeus Hypsistos, as Vafyras passes between them, covering them with water and mud during every significant flood.

During each flooding event and also later, in the water drainage and cleaning phase, the external forces exerted on the monuments cause wear and tear. Additionally, the floods pose risks for the safety of visitors and employees and disrupt the smooth operation of the archaeological site. For this reason it was deemed necessary by the partners of the XENIOS project to add an early warning module for flood to the XENIOS system.

The development of the flood prediction module, required, among other things, to collect information on historical flooding events as well as meteorological, hydrological and topographic data, in order to model the behavior of the water catchment area ending at the archaeological site. In this way, future flooding events will be predicted successfully. The effort was challenging as the area is very complex both geologically and hydrologically, with the water coming from Mount Olympus entering into the ground through sinkholes, and after flowing underground for a large part of the torrent Orlias, in case of heavy rains, reappearing shortly before its junction with Vafyras river. The exact source of Vafyras is also uncertain.

Some of the most interesting facts about the historical floods in the area and the archaeological site of Dion are presented here. The documentation is based mainly on reports and photos provided by the Ephorate of Antiquities of Pieria, but was also sourced  from scientific reports and from articles that were retrieved from the local mass media. Through the combination of sources it has been possible to build a list of confirmed flood events that occurred in the last two decades.

The oldest historical event for which photographic material was found, took place on 10/11/1999. The next recorded flood was on 10/12/2002. Within the next period, three more flood events occurred on 19/6/2004, 26/10/2009 and 24/10/2010, for which only qualitative data without photographic material were found. As seen in the following photos, by comparing the images after the floods of 1999 and 2002 with contemporary photos, one can realize the magnitude of the problem that arises each time a flood occurs. This has a great impact on the site itself but also poses a heavy burden to the Ephorate of Antiquities of Pieria regarding time, effort and cost, for cleaning, repairing of damages and reorganizing the site, so that it becomes available to visitors again in a reasonable time.

Figure 1. The impact of the flood that took place in 10/11/1999 (Source: Maria Iatrou) and a recent view of the site in its current form (3/4/2019).

Figure 2. The Sanctuary of Isis after the flood that took place in 10/11/1999 (Source: Maria Iatrou) and a recent photo of the site (3/4/2019).

Figure 3. The path leading to the Sanctuary of Isis after the flooding event of 10/12/2002 (Source: Maria Iatrou and a recent photo of the site (3/4/2019).

Figure 4. The Sanctuary of Isis after the flood of 10/12/2002, with a corridor that has been built for the visitors covered with mud (Source: Maria Iatrou) and a contemporary image (3/4/2019).

Perhaps the most severe and catastrophic flood that has occurred in Dion to date is that of November 17, 2017. It was the result of extreme weather events that hit Pieria, which caused a strong inflow of water from Vafyras river in the archaeological site of Dion. On November 16, 218.6 mm of rain fell and on November 17, 135.2 mm more were added (source: National Athens Observatory Meteorological Station in Dion). At this point it is important to mention that the average annual rainfall of the area for the period 2008-2019 is 643.75 mm.

This flood was caused by the fact that the bottom of the stream was raised due to the transport of sediments, to a height of about 3 meters covering a large part of the northern walls of the site, while part of the metal fence of the area, about 10 m long, fell. Most of the problems were concentrated in the area of ​​the sanctuaries of Isis and the Zeus Hypsistos which were covered by water and mud. Then, when the water receded, the sanctuaries remained covered with mud and were not visible in their entirety. The connection with a metal bridge that existed between the two sanctuaries was interrupted as the bridge was swept away by the water flow.

Figure 5. The Sanctuary of Zeus Hypsistos covered with mud after the flood of 17/11/2017 (Source: Ephorate of Antiquities of Pieria).

Figure 6. The Sanctuary of Isis covered with mud after the flood of 17/11/2017 (Source: Ephorate of Antiquities of Pieria).

Figure 7. The Sanctuary of Isis covered with mud after the flood of 17/11/2017 (Source: Ephorate of Antiquities of Pieria).

During the last two years, two more flood events were recorded within the archaeological site, one on 25/11/2019 and another on 3/12/2020.

Figure 8. The Sanctuary of Isis filled with water after the flood of 25/11/2019 (Source: Ephorate of Antiquities of Pieria).

Figure 9. The Sanctuary of Zeus Hypsistos filled with water after the flood of 25/11/2019 (Source: Ephorate of Antiquities of Pieria).

Figure 10. A view of the Sanctuary of Isis after the retreat of water, following the flood of 25/11/2019 (photo taken on 26/11/2019) (Source: Ephorate of Antiquities of Pieria).

Figure 11. The metal bridge at the entrance of the Sanctuary of Isis (photo taken on 26/11/2019) (Source: Ephorate of Antiquities of Pieria).

Figure 12. The Sanctuary of Ipsistos Zeus after the retreat of water after the flood of 25/11/2019 (photo taken on 26/11/2019) (Source: Ephorate of Antiquities of Pieria).

Figure 13. The Sanctuary of Zeus Hypsistos (right) and the Sanctuary of Isis (left) during the flood of 7/12/2020 (Source: Ephorate of Antiquities of Pieria).

From the documentation above it becomes obvious that there is a need to take technical measures to avoid disasters or at least to reduce their effects. Among the latter is the existence of a flood early warning system so that appropriate measures can be taken. The XENIOS project aims, among other modules, to create such a module, that will contribute to the safety of visitors and employees of the archaeological site and will support its smooth operation.

As part of the XENIOS project, the Creative People team visited the archeological park in Dion in June 2020. More specifically from June 15th to June 19th of 2020. The purpose of the visit was to study the wireless network coverage needs in the park and to identify particularities of the site that could adversely affect communication between the site and the XENIOS system.

The following article is part of the test timeline planned and carried out during our visit to Dion with a view to achieving communication of network equipment in the field.

The main problems we faced were the dense high vegetation and the lack of visual contact between points, either because of vegetation, or because of soil unevenness. These problems were addressed and resolved on a case-by-case basis and are mentioned below.

The flora of the region varies by season. The density and color of the foliage, humidity and temperature vary during the year and certainly affect the yield of the coverage. In our study we have taken into consideration the greater range of these variables, with a view to approach the most ideal interconnection and topology of equipment available in the field.

The lack of power-outlet points in the field was a particular difficulty we had to take into account. This is why we designed and deployed mobile 12/24VDC rechargeable power supply units, built in Creative People, in accordance with safety standards, to avoid any risk to the environment or to equipment operators.

The only factor that we have not been able to simulate in the study is human interference in the morphology of the site (landscaping works, future structures, etc.).

Tests timeline

Our arrival to the archeological park, was followed by a field inspection to the site, aiming to the understanding of its geomorphologic specificities, as well as of noting down other factors, which we should consider when performing the tests.

The park is divided into two parts, the first part is the site of the Sanctuaries and the second part is the site of the Ancient City. As displayed on map 1.2, the site of The Sanctuaries’ site is outlined in green and the site of The Ancient City in red. In addition, a full walk of the site is shown in yellow on map 1.2. Its length is 7.3 km, and it takes about 2 hours of fast continuous walking to cover it.

Map 1.2, main points of interest of the park and full route.

Sites of Archeological Interest

In the Archeological Park the total number of sites of archeological interest is quite large. For this study, we selected the most visited sites, based on information received from the Archeological Park staff.

As main points of interest (see map 1.2) were designated:

The Hellenistic Theater, the Roman Theater, the Sanctuary of Aspelpius, the Thermal Baths, the Sanctuary of Demetra, the Sanctuary of Zeus, the Sanctuary of Isis, the Conservatory, the Great Thermal Baths, and the Villa of Dionysus.

The site’s morphology offers a variety of tour combinations, as there is no specific tour path.

We have therefore chosen a 4.2 km route, covering most of the Sanctuary, as well as part of the Ancient City site, including the Conservatory, the Great Thermal baths and part of the southern Wall.

Most of the area has increased humidity and even on the warm days of June, the soil in several places is still wet.

The vegetation is particularly high, especially between the Sanctuary of Demetra and the Roman Theater. The average height of the tree vegetation is over 15 meters (and at some points it is far higher) while the foliage is particularly dense.

On the following map 1.3, blue color depicts the route for which the coverage study was carried out.

Map 1.3, selected path for coverage tests.

Interconnection tests Entrance – Sanctuary of Isis

On the second day, the first interconnection test was performed between the base and the eastern point of the Isis Sanctuary.

The two points cannot be interconnected. The problem is the dense vegetation, which interferes between the 110 meters distance of the two points.

Interconnection tests Entrance — Thermal Baths

A test was then performed between an ENTRANCE and a point in front of the Thermal Baths.

The distance between the two points -in an imaginable line- is 345 meters. The interconnection between ENTRANCE and Thermal Baths was successful and did not pose any problems. The coverage performance, as well as the interconnection quality of the two points, was maintained constantly throughout the tests.

Interconnection tests ENTRANCE – Outhouse near Sanctuary of Asclepius

The third interconnection between point A (ENTRANCE) and the outhouse near the Sanctuary of Asclepius was successfully established. The distance between the two points in -an imaginable straight line- is 250 meters and very few trees are interfering between them, which does not affect their stable interconnection.

The interconnection quality and coverage performance between point A (ENTRANCE) and the outhouse remained constant throughout the tests.

Interconnection tests ENTRANCE – Mobile Point at Demetra Sanctuary area

In this particular case, we have logged interconnection quality measurements of the mobile point in a wide area relative to the base at various points, in order to achieve its optimal placing.

The quality of interconnection and coverage of this point was studied in detail. The reason is that this point will also take over the relay-interconnection with a transmitter, which will be placed on a platform, located at the Sanctuary of Zeus, next to the bridge destroyed by flooding, covering the area of the Isis Sanctuary and the Zeus Sanctuary.

Extensive testing was carried out at selection points to identify the most ideal ones. Tests were then carried out, with varying mast heights at both points, mainly to avoid interference from visitors’ passage, until the desired level of interconnection and coverage was achieved.

Interconnection tests between The Sanctuary of Demetra – Transmitter at The Sanctuary of Zeus and Sanctuary of Isis

The distance between the points is 149 meters with altitude difference. The interconnection has been established and is stable with satisfactory performance. The coverage is quite good in both areas, Sanctuary of Zeus and Sanctuary of Isis.

A serious factor we should take into consideration is the vegetation variations in the site, either during the year due to changes in meteorological conditions, or due to human intervention, which are intended to clean up and ensure the safety of the site.

With quite a large amount of data collected on day 2, we can now determine the final points at which the equipment will be temporarily installed for the testing and pilot of XENIOS.

The ISP (Internet Service Provider) line capability at the site of Dion does not exceed 3Mbps Download and 0.6Mbps Upload, making it very difficult to correctly transmit data to XENIOS’s Cloud platform, let alone provide free wireless network access to the internet for visitors. This issue will be partly resolved by using additional 4G LTE equipment installed for testing purposes.

Interconnection tests ENTRANCE — Conservatory

The next area to test coverage selected was the Conservatory, where the Wall and the Ancient City begin.

This is the last test point, which is 235 meters away -in an imaginable straight line- from the ENTRANCE.

The interconnection was successful and stable. The coverage quality is very satisfactory and is benefiting from the open field, which extends north-east of the Conservatory, as well as from the elevation advantage.

Installation of equipment at final locations – Coverage Tests

On the morning of the 3rd day at the site, we met with the Archeological’ s Park archeologist in charge, and we were guided around the area of the Sanctuaries and part of the Ancient City. We were pointed out which are the points of the highest danger, and we discussed whether or not they can be covered.

Equipment has been installed at the optimal locations selected (see map 1.5) and put into fully operational mode, in order to perform a test, simulating a visitor on various points.

For this test, a random path has been chosen in the predefined areas by making small stops near points of interest and using mobile devices to simulate a visitor tour in the area.

Along the way (see Map 1.5), several disconnection-reconnect tests were performed on the XENIOS network. These tests were performed as many mobile devices are known to disconnect from wireless networks (Wi-Fi) during a phone call. Indicatively, the reconnection to the XENIOS network from a mobile device running Android 10.9, takes place in less than 6 seconds, having selected the automatic connection to the XENIOS network.

Map 1.5, Visitor tour simulation route and equipment placement points.

The total distance, walking in the site for this trial, exceeded 5 km.

During the 3rd day tests, the weather was mild rainy for about an hour. Stability and quality of coverage were not affected.

During the field tests we noticed that the coverage between the bridge and the platform at the path near the Sanctuary of Isis is unstable, due to elevation difference combined with dense vegetation that surrounds the site.

Reoccurring equipment boot tests

The equipment has been put into fully operational mode for a repetition of the test.

The measurements confirmed the data, collected on day 3, involving stability between interconnected points and coverage quality. In addition, connection tests have been performed on the XENIOS network with different mobile devices (mobile phones and laptops) to confirm that there is no great discrepancy between devices and measurements.

Due to very low ground connection speed provided by the ISP at the site of the Archeological Park, 4G LTE equipment was tested to establish a more stable and rapid connection between the equipment and the Xenios Cloud Platform.

Following the test equipment interconnection with the XENIOS platform, indicative data collection and dispatch tests between equipment and platform were performed. Furthermore, the visitors ticketing system (ENTRANCE – EXIT) were tested and data was sent successfully to the XENIOS system.

Upon the end of the interconnection tests, a final backup of the configuration along with the exact locations of the equipment involved were performed.

From the moment that the archeological site of Dion, in Pieria Greece was selected as a demonstration area for the XENIOS project, it became clear from discussions with the officials of the Ephorate of Antiquities of Pieria that the main natural risk they face, is flooding. The magnitude of the problem was documented, in addition to oral descriptions and photographs that were made available by the officials (Figures 1 and 2), through news articles and photographs found in the local mass media and social networks. In fact, reports on the most important floods also appear in national media. Additionally, several administrative acts related to the floods in the area were identified (financial aid, flood mitigation project financing, etc.). Thus, the project partners decided that flooding must be a risk for which the XENIOS system should be able to provide forecasts, in addition to forest fire danger prediction that was included in the project’s original design.

Figure 1. The Temple of Isis flooded in November 2019 (source: Ephorate of Antiquities of Pieria).

Figure 2. Vafyras river, flooded in the Temple of Zeus Hypsistos (source: Ephorate of Antiquities of Pieria).

Following this decision, the XENIOS project partners proceeded to collect data on the topography of the area, the climate, its meteorological and hydrological characteristics and, of course, on past floods. A site visit was added to the office work to capture and evaluate the current situation leading to the occurrence of floods. Thus, the source of the river Vafyras that passes through the archeological site was explored, along with the riverbed and the characteristics of the torrent Ourlias (Figure 3) that contributes to Vafyras.  Vafyras was found to originate from small sources fed with water from the alluvial soil of the area, a short distance north of the archaeological site, and has a relatively small steady flow. On the contrary, the water that flows from Olympus to the riverbed of Ourlias disappears in sinkholes immediately after leaving the mountain. Thus, the torrent remains dry almost all year round, with the exception of periods of continuous heavy rainfall (Figure 4). The photos below are indicative of the exploration effort (Figures 5-8). The observations that were made are taken into account in the modeling of flooding in the area, on which the forecasts offered by the XENIOS system will be based.

Figure 3. The Ourlias torrent and the river Vafyras that passes through the archeological site of Dion, highlighted on a Google Earth image (source: Ephorate of Antiquities of Pieria).