Marios Sapountzis

This study examines the effectiveness of torrential erosion control structures (concrete check dams) to mitigate post-fire sediment transport within the Seich Sou Forest in Thessaloniki, Greece. Four years after the fire of 1997, which burned 68% of the forest, check dams were constructed (in 2001) to control erosion and sediment transport in the catchments of Eleonas and Panteleimon. In 2022, our team conducted field surveys, in which the size, effective storage capacity, and siltation of 40 check dams were recorded. The results revealed that the dams stored 14.36% and 18.81% of their total effective capacity in the Eleonas and Panteleimon catchments, respectively, with average annual erosion levels of 0.33 t/ha/year and 0.21 t/ha/year. These low rates of erosion could be attributed to the shallow, rocky soils and rapid post-fire vegetation recovery. However, this study highlights that timely construction of check dams immediately after the fire could have significantly increased their effectiveness. The results showed that if the dams were constructed immediately after the fire, they would retain 6.17 t/ha/year (Eleonas) and 7.08 t/ha/year (Panteleimon), during the first three post-fire years. These values of erosion are in agreement with previously published studies in Mediterranean ecosystems. This study highlighted the importance of the timely construction of post-fire erosion control structures to increase sediment storage and reduce soil transportation.

The aim of this study is to investigate the response of the rational method in flood hazard assessment in Potamia watershed of Thasos island, with climate data from Regional Climate Models. The precipitation intensity–duration–frequency (IDF) curves used were calculated using available EURO-CORDEX 0.11 regional climate model simulations, under the RCP8.5 scenario. The Corine Land Cover dataset was utilized for the determination of the runoff coefficient of the watershed and geomorphological and hydrographic characteristics are calculated using a Geographic Information System software. A comparison against actual flood events of the period 1991–2019, as mapped with satellite Synthetic Aperture Radar (SAR) imagery, is also carried out.

The present study was conducted in the suburban forest “Seich Sou”, which is located at the north-east of Thessaloniki city (north Greece). “Seich Sou” is one of the most significant suburban forests of North Greece. However, many disastrous events have taken place in the suburban forest during the last 25 years, caused by either human interference or other biotic/abiotic factors, such as insect outbreaks. In the present study, erosion measurements and field data were collected using a combination of silt fences (USLE plots) and depositions retained behind the constructed check-dams, aiming to monitor the impact of the significant biotic and abiotic disturbances (forest fires, insect outbreaks, logging) in Seich Sou forest. Specifically, the aim of this study is to present a cost-effective and time saving methodology towards the achievement of accurate and reliable soil erosion measurements and field data acquisition. Additionally, the installation details, data recording and collection, field work, supplementary materials and the advantages of silt fences and check-dams are presented in detail, as well as the limitations of the methods and the difficulties during the installation, maintenance and data collection period. The proposed methodology could be effectively applied in many environments and in the context of varied purposes, to quantify the erosion and runoff processes with high accuracy, as well as to increase the accuracy of soil erosion modeling performance, through implementation of calibration and/or validation processes, which is a major issue for the scientific community.

The present study was conducted in the suburban forest of Thessaloniki city (Seich Sou), which constitutes one of the most significant suburban forests in Greece. In 1997, more than the half of the forest area was destroyed by a wildfire, after which soil erosion and flood control works (check-dams) were constructed in the burned areas. The aim of the study is to estimate the annual soil erosion rate for the last 30 years (pre- and post-fire periods) applying the WaTEM/SEDEM model, in order to investigate the impact of this wildfire on soil erosion, the effectiveness of the flood- and erosion-control works and the level of forest regeneration. It is the first time that WaTEM/SEDEM was calibrated and validated in Greece, taking into account soil erosion records from the 18 check-dams that were constructed in the study area in 2001. The mean annual erosion rate was 0.0419 t/ha/year, 0.998 t/ha/year and 0.08 t/ha/year for the pre-fire period, the first 3 years and 20 years after the fire, respectively. The results showed a very low erosion rate for the pre-fire period, an expected significant increase 3 years after the wildfire and a gradual decrease in the subsequent years until 2021. However, it seems that the post-fire regeneration of the forest has not been fully achieved, since the annual soil erosion rate at the long-term post-fire period is double compared with the pre-fire period. Concerning the check-dams’ effectiveness, it was observed that after 20 years of operation, they were non-silted, and most of them retained a small amount of sediments. This fact could be attributed to multiple factors such as the very thin soil depth, fire severity and catchment geomorphology, though the main reason seems to be the time elapsed between fire occurrence and the check-dams’ construction. The results of this study advance/strengthen the knowledge concerning the pre/post-fire soil erosion processes in already degraded ecosystems, while the calibrated model could serve as a useful tool able to be applied in other Mediterranean catchments of similar characteristics.

Our study was conducted in the suburban forest of Thessaloniki (Seich Sou), which constitutes one of the most significant suburban forests of Greece and is located northeast of Thessaloniki. In 1997, more than the half of the forest area was destroyed by a wildfire, while recently (May 2019), a significant insect outbreak by the bark beetle Tomicus piniperda was detected. The insect action still goes on, while the infestation has destroyed so far more than 300 ha of forest area. Extensive selective logging and removal of infected trees from the forest were carried out in order to mitigate and restrict the outbreak spread. In the current study, silt-fenced erosion plots were installed on representative locations of disturbed (by fire and insect action) and undisturbed areas, in order to quantify the effect of the above-mentioned forest disturbances on soil erosion and correlate the height and intensity of precipitation with the soil erosion rate. The results show that there was no statistically significant increase in soil erosion in the areas of insect outbreak compared with the control plots. However, there was a statistically significant increase in soil erosion in areas where logging works had been applied as an infestation preventive measure. In addition, the study revealed that 25 years after the forest fire, the erosion rate is still at higher level compared with the undisturbed forest areas. This study could be considered as one of the first attempts to evaluate the impact of an insect outbreak infestation on soil erosion, while there is also a great lack of information concerning the assessment of long-term post-fire effects on the soil erosion of a forest ecosystem.

FLOOD HAZARD ASSESSMENT AND DELIMITATION OF THE LIKELY FLOOD HAZARD ZONES OF THE UPPER PART IN GALLIKOS RIVER BASIN

Inappropriate artificial activities can escalate the frequency, the intensity, and the magnitude of floods and aggravate their aftermath. Additionally, urban sprawl is responsible for increasing the manifestation of flood events in coastal areas. In this study, the effects of diachronically formulated artificial stream-channel modifications and registered urban expansion on flood hazards were quantified. Initially, land-use changes were monitored over time and a detailed field topographic survey was performed. The peak discharge for a 50-year return period storm event was found to be equal to 42.3 m3/s, as computed by the rational method. A steady flow analysis with a mixed flow regime was then performed so as to compute the water velocity and surface runoff elevation at 49 discrete cross sections for the years of 1945, 1981, and 2009, whereas the inundation extent was found equal to 12,208, 10,519, and 9,530 m2 for the same years by implementing another model. Although the water level and inund...