## 1 Introduction  
The construction of dams is an anthropic practice that provides economic benefits for our society but has also caused significant changes to riverine landscapes worldwide. Around 800,000 dams have been built around the world with different objectives: irrigation, flow control, navigation, and hydropower, among others [1]. Inevitably, dam construction and operation have immediate and long-term effects on river morphology [2; 3; 4] both upstream [5; 6] and downstream [7; 8] of those structures. Thus, predicting the effects of dams is key to maintaining biodiversity and ecosystem services [9; 10]. Upstream of dams, the aggradation processes in the alluvium along reservoir reaches are dominant due to the reduction in flow velocities, responsible for sediment transport, and the backwater effects following impoundment [11; 12; 13; 14; 15; 16]. Bed aggradation in these regions generates a water level rise, increasing the flood frequency and the vulnerability of the existent infrastructure, imposing an additional risk to human settlements located in the surroundings and considerable challenges for managers [17; 18]. Therefore, predicting the extent of the morphological changes in the upstream area of a reservoir can benefit flood risk estimations. Morphological changes upstream of dams are evaluated in varied ways by measuring different morphological parameters. For example, by using aerial photographs, [PERSON] [6] determined changes due to the Czorstyn reservoir at a control distance of 2.2 km, reporting an increase in bar areas and the river channel, and changes in bank erosion due to flooding, highlighting the importance of the material present in the confining valley. [PERSON] et al. [11] also used aerial photographs to define the length of the upstream influence area (4 km) based on increased bar and sand areas. However, no previous studies have considered the importance of geology in upstream areas, except for [PERSON] et al. [5], who made an approximation at a regional scale. There is also a lack of studies dealing with the changes in the channel width in these areas. The downstream morphological long-term changes depend on site-specific drivers, such as the altered flow and sediment regimes, and geological controls [19]. Clear water released from reservoirs is expected to increase bed degradation and erosion rates in the downstream reaches [20; 21]. Nevertheless, this trend is not universal and varies with the distance from the dam [22], ranging from tens to hundreds of kilometers [23; 24]. This variation may be dominated by the lithological and structural controls of the downstream valley that determine channel geometry [25] and the interaction between the main channel and its floodplains [26]. Including the surface geological settings in morphological analyses may contribute to developing more effective methods to predict such changes, but this practice has not yet been addressed. Upstream and downstream morphological evolution is commonly expressed with changes in variables such as the channel width, water depth, slope, and sediment characteristics through time. Moreover, a few studies have shown that damming can even alter bar patterns [27] and river planforms [28]. With a few studies carried out in the tropics, the morphological changes reported in the literature are mainly collected from temperate and Mediterranean environments. The impacts due to dam construction and operation in tropical rivers may have different magnitudes than those observed in other regions because of the differences observed in [29]: (1) the degree of discharge alteration, (2) sediment loads and dynamics, and (3) the nature and pace of post-disturbance adjustments. Considering the ecological value of tropical systems, it is important to perform studies in these regions to assess similitudes and differences in the morphological response.