Temporal Analysis of the Braided River Index by Satellite Images

The Devoll River is located in southeast Albania and has various topographical features. One of them can be found downstream of the location Kokel, where the terrain changes from a v-shaped valley to an open, more flat type of valley. Here, the Devoll River is forming a complex system of multiple branches forming a braided river. The morphology is changing frequently with seasonal varying hydrology, dominated by a rather dry, long summer and winter month with intense but rather short rainfall events. Over the last two decades, researchers have become interested in the sediment transport carrying capacity of the river Devoll, since it has a large potential for hydropower development. In 2016 and 2020, two large hydropower dams were impounded and started to produce electricity. The Banja Hydropower plant is downstream of the above-mentioned river reach and the Moglice power plant is upstream of the river reach. These power plants altered the discharge in the reach and consequently the morphological changes. According to the literature, river discharge alteration due to river regulations leads to fewer morphological changes and therefore to a loss of flow diversity in the reach. Strongly alternating river reaches are known to be reduced to one single channel incising the valley. This can be quantified with a decreased braided index. Therefore, the current study aims to evaluate various frames of morphological evolution by analyzing satellite images by identifying the braided index at each individual time step. The braided index is calculated as (Ʃm +Ʃl)/ Ʃm, where Ʃm is the summation of mainstream length and Ʃl is the summation of all lateral streams lengths. According to this analysis, evidence can be found that the braided index of the Devoll River decreased, and the river starts to develop a rather straight main channel. This study will show why this is happening by analyzing the altered discharge hydrograph in the river reach.