The Effectiveness of Check Dams on Post-fire Erosion Control - The Significance of Timely Construction

This study investigates the effectiveness of torrential erosion control structures (concrete check dams) in reducing post-fire sediment transport in the Seich Sou Forest close to Thessaloniki, Greece. The July 1997 wildfire destroyed 68% of the forest vegetation, posing an urgent risk of severe erosion and floods in Thessaloniki's urban complex.

The responsible agencies decided to construct erosion control structures inside the streambeds of the watersheds that drain the Seich Sou Forest. This work was critical in watersheds where the lowland segment of the stream runs through communities, and the transportation of sediments and debris might endanger property, infrastructure, and even human life. Most of the concrete check dams were built in 2001, four years after the fire. This study included a complete documentation of the constructed check dams as well as a measurement of the sediments that gathered 21 years after the fire.

This study assessed the efficiency of constructed check dams in capturing sediments after a fire, as well as the influence of construction time, in two typical catchments (Eleonas and Panteleimon). In addition, the hypothesis "What would the effectiveness of check dams be if they were constructed immediately after the fire?" was examined. The innovative part of this study was the detailed recording of all check dams and the volume of trapped sediments, while the fact that most dams were not completely filled allowed us to compute soil erosion rates in detail.

In 2022, our team carried out field investigations to assess the size, effective storage capacity, and siltation of 40 check dams. The results showed that the dams in the Eleonas and Panteleimon catchments stored 14.36% and 18.81% of their maximal effective capacity, respectively. In the first three years following the fire, the potential maximum annual retention capacity of the check dams in the Eleonas watershed was 6.17 t/ha/year, while in the Panteleimon basin, it was 7.08 t/ha/year. The delayed construction of the check dams resulted in the failure to trap the eroded soil, which means that in the first three post-fire years, all the soil was lost to the sea.

Previous investigations have determined the precise values of post-fire erosion in the study region to be 7.76 t/ha/year and 3.39 t/ha/year for the first and second post-fire years, respectively. The annual post-fire erosion values mentioned above fall within the estimated maximum retention capacity of the check dams constructed in the research catchments. As a result, the timely (immediately following the fire) and appropriate construction of check dams can effectively manage the greatly increased post-fire erosion rates. Although check dams are extremely successful in stabilizing disrupted fire environments, their full advantage can only be realized if they are built on time and efficiently. To decrease soil loss and improve landscape resilience, future studies should focus on the timely construction of post-wildfire erosion control structures.