A hydroelectric dam borrow pit rehabilitation. Two decades after the project, what went wrong?

Abstract

Although environmental rehabilitation projects that did not succeed are not uncommon, there are few research papers that deal with the subject. Works on the rehabilitation of borrow pits are even more rare. In an attempt to fulfill some gaps, the present study sought to evaluate the effectiveness of a program for the restoration of a clay borrow pit used for the construction of a hydroelectric plant, twenty years after its execution. In order to assess the current degradation stage and to identify the possible errors of this intervention, the area was mapped using an unmanned aerial vehicle, which allowed the identification of the remaining physical structures, dimensioning of the actual degraded area and characterization of vegetation cover and types of exposed soil. Physical and chemical parameters of the degraded area soils were compared to those of a contiguous preserved area, which was used as a control. Soils of the degraded area are significantly more compacted (with significant reduction in macroporosity) and depleted in organic matter and nutrients. The results showed that the methodologies used in the rehabilitation project were not sufficient to recover the resilience of a deeply degraded ecosystem. The long-term success of a rehabilitation project is only possible with the guarantee of the ecological sustainability of the area, which is largely related to the restoration of soil ecological processes. Most of the time, this cannot be achieved with the simple use of classical erosion control and revegetation techniques and without the addition of sediment material to aid the process.