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.

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).

The kick-off meeting of the project “XENIOS – An integrated application platform to protect and promote cultural and tourist sites” took place on September 17, 2018 and was hosted by AUTh at KEDEK, Balkan Center, Building A, 10th km Thessaloniki-Thermi, T.K. 57001.

During the meeting, the team was introduced. It was an opportunity to get the key information necessary for the understanding of the project. It involved discussion of project aims and scope, methodological approach, partners’ role assignments, teamwork and the detailed design the initial actions.

Recording and analyzing the requirements of the Xenios’ end users has been a top priority driving the design and implementation of the system from the beginning. This analysis contributed in:

• determining the necessary services and the content of the final applications, as well as their specifications (spatial accuracy, timeliness, etc.);
• the definition of data specifications (satellite, meteorological, other spatial data, descriptive statistics) to meet the above requirements;
• the conceptual design of the platform.

Questionnaires were designed to determine the Xenios users’ needs that were filled in by the end users of the Xenios system (web platform and mobile app) and subsequently analyzed. The questionnaires were processed anonymously and respecting the privacy of the respondents, in full compliance with the restrictions of the General Data Protection Regulation (GDPR — Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016).

Xenios’ end users were categorized into the following groups and a separate questionnaire was designed for each group:

• Cultural and touristic site stakeholders (representatives with high level of operation-al experience from operators and managers of cultural and touristic places, as well as civil protection departments):
  • Site managers (users of the Xenios central platform) who manage sites similar to those of the project’s pilot areas. These users are provisioned with all available information related to natural hazards (risk indicators, dispersion of visitors within the site, etc.) through the central web platform of Xenios, which will be installed on a personal computer in their workplace.
  • First responders / field operators: People working in sites of cultural and archaeological interest (security guards, guides, security personnel, etc.). Users in this category will receive instructions from the site manager(s) and report back any significant information from the field.
• The visitors of the site of cultural / archaeological interest. Users of this category will only have access to the Xenios mobile app, through which they will receive tourist information and—conditionally—risk alerts issued from the site manager.

The results of the Xenios system’s evaluation were very encouraging, as all its services were found to be interesting and useful. It is worth noting that when asked if the organization would be willing to allocate some money for the supply of such a platform, the answers collected were negative by one third, positive by one third and the remaining third were conditionally positive. The justifications for the negative responses were that such a platform should be free of charge, as the funding of most public organizations is very restricted and it would be extremely difficult to finance such a service.

Responses of the site manager user category (users of the Xenios central platform) to the most important questions of the questionnaire

The personnel of the tourist sites (first responders / field operators) reported the main difficulties encountered in their working environment, which are the visitors’ entry control, the issuance and validation of tickets, as well as the visitors’ access to unauthorized zones. Also, the role of the staff in case of emergency is to notify the authorities and try to safely evacuate the visitors from the site.

The issues related to the safety and protection of visitors that the field operators consider should be addressed are—in order of priority—always knowing the dispersion of visitors within the site, the evacuation of the site in case of emergency, knowing the most appropriate process to evacuate the visitors from the area, procession of dedicated firefighting means, the communication with the site managers/control center (sending reports / receiving instructions) and the guidance of visitors into safety.

The personnel of the tourist sites also reported that they need more training on visitor safety and site protection. They also believe that a system like Xenios would significantly increase the safety of the visitors and staff and could help increase its visibility and the number of visitors.

Finally, the visitors of the sites characterized as very interesting and useful the services of Xenios related to the safety of the visitors and the promotion of the site’s points of interest. When asked if they would install a dedicated mobile app for the site they are visiting, the majority responded positively. Nevertheless, more than half disagreed with the app maintaining the history of the route they are following and were only willing to provide access rights to their current location via GPS. Finally, when being asked if they would be willing to pay a fee to get a mobile app for the area they are visiting, the vast majority replied negatively.

Responses of the site visitor user category to the most important questions of the questionnaire.