Filenews 23 October 2022 - by Angelos Nicolaou
The flooding phenomena of the last few days were intense, when several areas throughout Cyprus were confronted and afflicted citizens, this time without endangering human lives but left behind repercussions on infrastructure, property and the environment. Extreme weather events cause sudden flooding of watercourses or a combination of them with urban stormwater floods and the rest concern urban stormwater floods. In fact, the largest number of floods occurs in the districts of Nicosia and Larnaca, while the flood mechanism in almost all cases is the natural overflow.
The European Union, recognizing the need for Community legislation on flood risk management, proceeded to the adoption of Directive 2007/60 / EC that provides for the assessment and management of flood risks.
The Water Development Department in our country has in recent years established a framework for the assessment and management of flood risks with the aim of reducing the negative consequences of floods on human health, the environment, cultural heritage and economic activities of Cyprus. They proceeded to identify the areas at risk of flooding. In the first stage, it proceeded to 19 areas, while subsequently another 19 areas were additionally identified as Areas of Potential Significant Flood Risk (APSCP). Some of the new areas are adjacent to the existing ones. The total number of APSFRs is therefore now 38.
All new areas concern sudden river floods with the exception of the urban area in Larnaca, in the Canal of General Timagia, which is a combination of sudden flooding and urban flooding of rainwater for the city of Larnaca.
The WDD prepared Flood Hazard Maps showing for each of the "Flood Areas" the area that could be covered by water for three different flood scenarios:
1) from a flood with a low probability of occurring e.g. with a probability of happening 1 time in 500 years.
2) from a flood of average probability, i.e. with a probability of e.g. occurring 1 time in 100 years.
3) from a flood with a high probability e.g. with a probability of occurring 1 time in 20 years.
For each of the three scenarios in addition to the flood extent, the Flood Hazard Maps show the depth of the water in the "Flood Areas".
It is noted that, although the probability of a flood occurring is described in relation to a number of years, this flood has the specific probability of occurring in any year. In other words, a flood with a probability of happening 1 time in 500 years has a probability of 1 in 500, that is, a probability of 0.2%, to occur in any year.
The Flood Risk Maps refer to the possible negative consequences in the "Flood Areas" for each of the three flood scenarios (low probability, medium probability and high probability) and present information on: a) the likely number of inhabitants that may be affected, b) the type of economic/ cultural/ archaeological activity in the area that may be affected, c) facilities that may cause accidental pollution in case of flooding, (d) other possible significant sources of pollution.
According to the law, each Member State of the European Union including Cyprus must set appropriate targets for the management of flood risks in the areas that have been recognized as "Flood Areas" focusing on reducing the potential negative consequences of floods and reducing the likelihood of floods and to draw up Flood Risk Management Plans for these areas. Management plans providing for prevention, protection and preparedness to deal with the consequences of floods shall include measures to achieve these objectives and shall be prepared taking into account all relevant aspects such as costs and benefits, the extent of flooding, land use as well as nature conservation.
The main cause of flooding is extreme heavy rainfall which as natural phenomena cannot be predicted. For this reason, our only protection from the negative consequences of floods is the prevention and preparedness to deal with them through proper risk management.
Flood hazards
Factors influencing the risk of floods, among others, concern the past and recent variations in river beds (dams, diversions, drainage arrangements, etc.). In the areas controlled by the Republic, 84 dams have been built for irrigation and water supply, enrichment and extra-river reservoirs, which have been constructed between 1945 and 2010 covering the majority of important river basins. These projects, depending on their capacity and location, affect the amount of floods that occur, especially in the downstream areas. The presence of these works should be considered as generally reducing the flood magnitudes that have occurred from time to time in the downstream areas since they act as places to contain and retain flood flows. The vast majority of them, and especially the large dams of Cyprus, do not aim at flood protection and are not managed in such a way that they have a guaranteed empty volume for flood containment. It is possible that a dam is complete during the occurrence of an extreme flood and cannot provide significant flood protection even though with the dam's reservoir complete, some containment is achieved by the delay of the outflow from the dam spillway.
At the same time, in recent years there have been several interventions in rivers and streams that should be taken into account in the assessment of future floods. The case of Garyllis and Pedieos, which have been diverted to a new riverbed in the past, is typical. However, there are also more recent cases such as the diversion of Diarizos to the Kryos River, the arrangements of the western part of the river Vathia in Limassol where there does not seem to be a riverbed since most of it has been covered with buildings and houses, the construction of the riverbed that passes through Ormidia with concrete for the most part, the coverage of the largest part (1.9 km) of the Klimos stream in the residential area of Makedonitissa, etc.
Protective measures
The vulnerability of property exposed to future floods is expected to be reduced since, based on the experience gained, architectural designs have been improved and smart construction methods, protective measures, but also more flood-resistant materials are used using technological developments.
Examples are automatically retractable protective barriers, watertight traps, etc. In addition, risk awareness through the creation of hazard maps and information campaigns help the public to take measures to reduce vulnerability, such as the removal of valuable objects from underground spaces exposed to flooding.
Reflections on the rapid residential development
In recent years, following the entry of Cyprus into the EU, there has been a general development of the construction sector, especially in tourist beaches and peri-urban areas. This number has remained high in recent years, although stabilising and slightly downward trends have emerged since 2005. In general, the increased building development observed in recent years has resulted in the formation of new hydrological conditions in the river basins with a main impact on the runoff coefficients. The runoff coefficient in undeveloped land is in the range of 0.10 – 0.30 depending on the soils and slopes, while for residential area it ranges from 0.40 for individual dwellings to 0.70 for densely populated areas with apartment buildings. That is, an increase in the runoff coefficient of up to 5 - 7 times, depending on the variation of land use, is possible with a direct and proportional impact on the flow quantities and the speed of arrival of a flood.
As a result of the rapid residential development observed in coastal tourist areas but also in peri-urban areas, it is natural to expect an increase in the size of floods in these areas for similar rain events of the past.
Most climate change trend scenarios show an increase in the presence of extreme water-related events (e.g. floods, droughts, etc.). In particular, due to climate change (mismanagement of the environment) floods (river and sudden) are expected to occur increasing in number, duration and impact.
The significant population growth expected for Cyprus in the coming decades will lead to an increase in the density of construction and human activities in flood risk areas resulting in a future increase in flood exposure.
In addition to the aforementioned increase in risk as a result of increased runoff, population growth combined with increased construction increases the exposure of people and property to flooding, since riparian zones and floodplains of rivers are built.
Other interventions concern the use of part of the riverbed (usually part of the floodplain) for the purposes of public utility projects, such as sports, linear parks, construction of public buildings, etc. with or without the necessary hydrological studies. Interventions that result in the reduction of the cross-section of the riverbed involve increased risks for future significant floods. A similar problem is created by the abolition of streams, especially in urban areas where the pressure of land exploitation is increased.
The existence of river sections, either passing through or bordering existing and future development areas, should be taken into account as one of the main planning parameters for the preparation/revision of Development Plans.
Changes in the hydrological character of urban areas due to the development of agglomerations should be taken into account in estimates of the magnitudes of future floods. In addition, the geometry of the streambed and the natural flood zone should be taken into account in conjunction with the proposed configurations of each urban planning zone in order to correctly predict the effects of significant future floods. As a rule, it is expected that with the increase in the size of urban zones and settlement extensions, the flow will be increased while the natural floodplain of a stream remains at least the same if not smaller. The existence of a riverbed protection zone in urban planning, when it exists, offers some protection as a zone where development is prohibited, thus reducing the exposure of property to flooding since this zone receives most of the volume of flow reducing the effects of a possible flood.
Increased risk due to climate change
The value of the recipients affected is expected to increase in the future due to economic growth, but also due to the use of more electrical appliances and other technology products that are sensitive to flooding.
Taking into account all the above, it seems that the future flood risk from sudden flooding of watercourses will be increased compared to the current one for the same area due mainly to an increase in risk due to climate change and soil sealing and due to an increase in exposure due to developments.
The area where the above type of floods occurred in the past is not so important because, depending on how a local storm moves, these floods can occur in the future in any other area with small-sized watercourses that in the past was not affected by flooding. Therefore, any watercourse even with a sufficiently small catchment area and without historical flooding that passes through developed areas with significant exposure to flooding may cause significant adverse effects in the future.
Based on the above, all riparian areas along watercourses passing through developed areas and having a catchment size of more than 5 km2 are defined as areas with potentially significant future flooding events.
>Areas of potential significant flood risk
1) From Politika to Nicosia Municipality, Pedieos
2) Engomi, Agios Dometios, Klimos, Pedieos
3) Kokkinotrimithia, Tributary Merika, Serrachis
4) Strovolos and Industrial area of Latsia, Kalogeros, Pedieos
5) Paliometocho and Agioi Trimithias, Merikas and Tributaries of Koutis and Katouris, Serrachi
6) Industrial Area of Dali, Almyros – Alykos, Gialias
7) Paralimni Lake inflow river
8) Nisou, Pera Chorio and Dali, Gialias
9) Ormideia, Ormideia River
10) Aradippou – Livadia, Archangelos – Kamitsis and Parapotamos
11) Kamares Larnaca, Kamares River
12) Mesogi, Paphos, Chlorakas, Kosinas
13) City of Paphos, Limnarka
14) Germasogeia, Yermasoyia River
15) Mesa Geitonia, Ag. Athanasios and Eastern Limassol area, Vathia River and Tributary Vathia
16) Polemidia, Limassol (4 Ag. Antonios and Karnagio), New and old river bed Garyllis
17) Ypsonas, Argaki tou Marketos
18) Astromeritis, Peristerona, Komitis, Serrachis
19) City of Paphos, Argaki tou Vasilikos in Paphos
20) Vasilikos River estuary in Mari, Vasilikos
21) Vasilikos river in Kalavasos
22) River of Asgata in Kalavasos
23) Pentaschoinos river in Agios Theodoros
24) Anonymous watercourse in Troulloi, Voroklini
25) Anonymous watercourse in Livadia, Voroklini
26) Urban flood area in Larnaca, Canal of General Timagia
27) Anonymous Watercourse at Kokkinotrimithia 1, Serrachis
28) Anonymous Watercourse at Kokkinotrimithia 2, Serrachis
29) Rivers Vyzakotos and Kalogeros in the Municipalities of Latsia, Yeri and Aglantzia, Pedieos
30) Vathi tributary Kalogeros in the Municipality of Latsia, Kalogeros, Pedieos
31) Kalogeros Lakatamia River, Pedieos
32) Katevas River in Nicosia Municipality, Katevas, Pedieos
33) Kotsirkas River in Nicosia Municipality, Kotsirkas, Pedieos
34) Tributary of Pedieos in the Municipalities of Lakatamia and Strovolos, Argaki of Mantissa, Pedieos
35) Argaki tou Nomikos in Strovolos Municipality, Argaki tou Nomikos, Pedieos
36) Tributary of Pedieos in Deftera, Argaki of Kaviyu, Pedieos
37) Agia Fyla River in Limassol Municipality, Vathia
38) Argaki in Kato Polemidia
