Marginal dikes promote disconnection between slopes and artificial channels: Study case in Central Brazil. 

Abstract

<p><em>Human activities in the most different environments produce gradual morphology and associated water changes. In different cultures, spread throughout history, the morphological and artificial channels are a valid example of how the superficial changes impact the hydrogeomorphological processes that take place in the hydrographic basins. Recognizing that these modifications make more complex the comprehension of how the systems/channels operate, considering that hydrological connectivity becomes subordinate to anthropic interventions, this investigation aims to verify if marginal dikes, originated from the opening and cleaning of artificial channels, generate changes in the hydro-sedimentation behavior between the slopes, artificial and natural mechanisms. This research’s effort generated analyses during rain events in a system of derivation, with focus in the production of flow data, transport data and turbidity which were associated with the presence of the marginal dikes along the channel troughs and of elements present in the interior of these troughs, such as vegetation. The study was carried on slopes located in the Central Brazil area, in a continental tropical environment. The morphology imposed by the cleaning activities has an impact on the capacity of artificial gain that follows the losses and not the volume of water (80% reductions in the flow in a 1000-meter stretch). This is meaningful data because the measurements took place in scenarios where the slopes had lines of concentrated surface runoff promoted by precipitation. Also, the presence of sediments in artificial channels is low and influenced by the vegetation that has a filtering role and by this disconnection between slope and channel. Thus, a reduction of 98.5% in the suspended sediment load was observed in the artificial channel along a stretch of 870 meters. In the natural channels, source of the water transposed in the artificial gutters, there was a gain in the sedimentary load of 29% along a stretch of 900 meters, suggesting a greater connectivity between slope and channel, especially in an area of traditional human occupation with suppression of riparian vegetation in several stretches. It is also important to point out that the flow in the natural channel continued to increase along with the contributions of the flows connected to them along the stretch in question (increase of 284%). Also, the turbidity in the artificial channel dropped from 90 to 3.5 Nephelometric Units (N.T.U’s), while in the natural channel there was an increase from 110 to 140 N.T.U’s. The disparity in the hydrogeomorphological behavior between the artificial channel, based on the interruption of connectivity made by the marginal dikes, and the natural one with the exposure of its banks, reinforce the human potential to transform the hydrogeomorphological dynamics of drainage systemsIt is also evident the need to consider how human topographic signatures, even if at first classified as small, actually have the potential to transform surface and subsurface dynamics, with changes in natural responses that reverberate and accumulate as they are repeated in the most different watersheds.</em></p>