Urban watershed management prioritization using the rapid impact assessment matrix (RIAM-UWMAP), GIS and field survey

Abstract

Urban growth when badly planned and poorly sustainable linked with climate change, brings negative impacts to the cities. In the environment, erosion, landslide, floods, water pollution, illegal solid waste disposal, damaged drainage structures with disconnected parts, clandestine sewage or effluent discharge, among others, can be cited as impacts of urbanization. In this context, watersheds can be used as a foundation for urban development with certain scales of prioritization. In literature, the discussion for watershed prioritization was mostly found based only on computational methods and models, and does not include the important influence of field investigation and analysis of the headwaters. This is an option for urban areas, since most urban rivers are considered as headwaters (order 1). Also, erosion and poorly managed drainage systems can be obstructed by vegetation and may not be seen from satellite images. The aim of this work was to integrate on a GIS environment a Rapid Environmental Impact Assessment Matrix analysis with data based on basin morphology and field investigation of vegetation, erosion, drainage infrastructure, and presence of solid waste and wastewater in the urban headwaters of a medium size city in Brazil to create an urban watershed management prioritization order. A field survey was carried in 27 urban headwaters and digital analysis of the physical characteristics of the watersheds was using the QSWAT+ tool with SRTM data, land cover and use by MapBiomas and pedology by ITCG. Results showed that higher levels of prioritization (lowest value of the environmental score – es) were most related to poorly managed vegetation, drainage structure problems and urbanization, for example headwaters 2b (es = −390), 3b (es = −330), 4a (es = −354), 5b (es = −346) and 5c (es = −322). On the other hand, when the surroundings were primarily rural activities, the environmental score were positive. With the RIAM map, municipal decision makers may allocate financial resources to points of urgency and thus avoiding the waste of time and money in locations where management was not necessarily as urgent. Also, the RIAM is an excellent diagnostic tool for urban watershed management.