Application of Nature-based engineering solutions for urban river restoration in El Salvador | RiSalva

El Salvador is the smallest country in Central America (21,041 km2) with the highest population density in the region (301 inhabitants per km2). The rapid urbanisation and demographical concentration in the metropolitan area of San Salvador (2.1 million inhabitants), has taken over important forested zones and agricultural land. Still a large part of the population lives in illegal neighbourhood (almost 800,000 inhabitants), cottages and shelters which are in many times in high-risk locations, such as along brooks, riverbanks and on unstable slopes. The unbalanced urban growth and the weak enforcement of soil treatment policies to ensure the protection of the main natural resources are the causes of environmental degradation. Water resources and riverine ecosystems are under heavy stress in particular. The conditions of urban rivers and their perception are subject to a multitude of interlinked factors and stressors. Pollutions, destruction of riparian ecosystems and channelization are impacting riverine ecosystems severely. For a long time, rivers have been used mainly to drain of sewage and rains resulting in many degraded water courses. However, the sustainable management of rivers is gaining increasing importance in El Salvador. This is reflected in various initiatives and research projects. Urban rivers are increasingly considered as an opportunity to rescue a certain part of green areas, provide habitat of riparian ecosystems and a place of recreation and contact with nature for the local population. Due to the condition of many surface waters, a major focus is put on the remediation of degraded water courses besides the conservation of remaining riverine ecosystems. Many studies have shown that urban streams, while impossible to return to pristine condition, can be restored to regain many of their native functions and are recolonized by many species. Due to very limited space and a large number of infrastructure elements the revitalisation of water courses in urban environments is challenging in the context of urban planning and hydraulic engineering.

Soil bioengineering techniques are nature-based engineering solutions fulfilling both erosion control and ecological functions. The techniques of soil bioengineering have meanwhile regained worldwide recognition for their use in river and civil engineering projects (e.g. Durlo et al., 2005; Li et al., 2002; Petrone et al., 2008). Soil bioengineering techniques, which are the use of living plant material for civil engineering structures, can be a helpful instrument for civil engineers considering not only technical but also ecological, sustainable and socio-economical aspects. Previous research activities show the great potentials and challenges of soil bioengineering techniques for controlling soil erosion, shallow subsurface movements and river remediation works in Latin America, especially in its tropical territories where, despite its high biodiversity and benevolent climate conditions, climate change is already affecting in many destructive ways such as droughts, floods and landslides, etc. The high bio-diversity becomes a great tool for the use in soil erosion control. Several studies confirm that soil bio-engineering methods are a low cost, environmentally conscience, and effective solution for even large-scale erosion control, and riverbank and slope protection (e.g. Preti & Petrone, 2010). The use of locally available materials, such as vegetation and rocks, results in independence on imported inputs or the expenditure of foreign exchange. Soil bioengineering is labour-intensive and therefore offers seasonal employment opportunities to small-scale contractors and local communities who have rural construction skills (e.g. Prates Bisso et al. 2016). In El Salvador vetiver grass is frequently used for soil erosion control in the agricultural and construction sectors. In typical slope mitigation works in the rural area, car tires in combination with plants are used (Chávez et al. 2016). The use of soil bioengineering for the remediation of water courses is not state of the art.