Scenarios of Sediment Transport Management in Francia Creek, Valparaiso, Chile

摘要

The port of Valparaiso is located in the central region of Chile. Its topography is dominated by several creeks that drain waters from hills that surround the city. These creeks were formed through natural terrain abrasion produced by precipitation events that occur mainly in the winter season (JuneAugust). Francia Creek drains waters from a catchment area of approximately 324 ha (3.24 km~2) covered mainly by native and exotic vegetation, eroded soil and urban areas. The waters drained by the creek feed the storm water pipes of the city system. Sediment transport and deposition has been a recurring problem through the years. This research tests the following hypothesis: if a city restores its surrounding natural systems this would lead to the reduction of the occurrence of floods and high sediment-load events. Since Francia Creek is moderately urbanized and still preserves some of the natural vegetation while also having land covers with exotic (non-native) vegetation and loose soil, a hydrological and sediment transport model is developed for its catchment and streams to computationally test the hypothesis. The model is used to simulate possible natural scenarios of land use. The results show that a scenario in which current non-native vegetation land covers is replaced by a combination of native forest and native shrub (70% and 30%, respectively) produces the least amount of sediment volume to accumulate at the sand trap. This scenario reduces the sediment volume in around 200 m3 (up to 20% percent reduction) and at the same time reduces the strength of peak floods in about 5%. In conclusion, the model output shows that the environmental-paradigm hypothesis is correct in terms of sediment volume reduction and stream flow peak floods attenuation, i.e., if the Francia Creek watershed is restored to approximate original (natural) land cover, sediment transport and floods are less severe than under current conditions.