A Method for Estimating the Risk of Dam Reservoir Silting in Fire-Prone Watersheds: A Study in Douro River, Portugal

Abstract

Forest fires are an increasing problem over recent decades. The fires, among other consequences, lead to an increase in the soil vulnerability to water erosion and a consequent increase in sedimentation rates. When barriers are present, such as dams or weirs, there is an amplified risk of sediment and ash deposition in their reservoirs, causing siltation. Thus, there is an interest in studying in more detail the risk of siltation of barriers and reservoirs in the Douro River watershed following wildfires. A detailed barrier inventory was lacking for the Douro River, hampering the identification of siltation-prone areas. In order to fill in this gap, an extensive inventory of barriers in the Douro river basin was carried out for the present study. The result was an abundant and reliable dataset on the Douro River barriers, which allowed a prognosis on the watershed siltation risk. The method for calculating the siltation risk relied on the relationship between the frequency of forest fires, the erosion risk and the frequency of reservoirs. The sub-basins with the greater siltation risk are the Tâmega, Corgo, Sousa and Paiva river basins. Most reservoirs with the highest siltation risk were from small dams. The modelling results were compared with stream connectivity and concentrations of stream water phosphorus (associated with the sediments that flow into the rivers due to the fires). With regard to connectivity, only two reservoirs were at high risk of sedimentation due to fires, so the categories of connectivity risk and fire-based sedimentation risk are probably not related. With regard to risk of high phosphorus loadings, in 8 basins the upper classes for fire-based erosion risk coincided with the upper class for phosphorus loadings suggesting that high phosphorus loading could be associated with fire-based erosion. This study works as a simple but reliable example on the assessment and mapping of siltation risk in stream networks intersected by abundant barriers. It allowed for identifying barriers that can accumulate a large quantity of fine sediments and ashes, interfering with water quality and soil erosion as well as with the storage capacity of the respective barriers.

Fire danger in the supply areas of hydroelectric reservoirs under the restoration process in the south of Minas Gerais, Brazil

“…The risk of reservoir sedimentation diminishes their lifespan and effectiveness. This natural phenomenon, driven by water erosion, is associated with the watershed's characteristics in terms of topography, lithology, vegetation cover, hydrology, and also human activities that can promote or amplify soil loss (Terêncio et al, 2020).…”

A Framework for a Hazard Taxonomy to Support Risk Assessment of Tangible Outdoor Heritage

“…As a result of this additional screening, four papers were selected, for which an analytic study was performed relating to the definition of the risk. The SLR made it possible to define indicators and indices of use for a quantitative assessment of the specific risk Siltation [46][47][48][49] in order to implement it in the prepared framework.…”

Baseline geographic information on wildfire-watershed risk in Canada: needs, gaps, and opportunities

“…In particular, CANVEC and NHN provide information to several water elements, natural and manmade, that could even generate more ideas for scientific studies, or even simple risk assessments. In particular, numerous communities in Canada depend on drinking water, hydroelectricity, flood control, and recreational opportunities coming from reservoirs 9 , and these two datasets can be used to explore reservoir vulnerability, which is of increasing concern (Bonansea and Fernandez 2013;Terêncio et al 2020;Basso et al 2021). According to the Canadian Dam Association, there is over 15,000 dams in Canada, although the number of those used for drinking water supply is not available, at least publicly.…”