Erosion Processes and Water Quality in Cacula Stream Watershed (Ilha Solteira - SP, Brazil)

Urban sprawl and agricultural activities give rise to strong pressures on natural resources, particularly on the water resources due to erosion processes. In Ilha Solteira (Brazil), the occurrence of porous sandy soils induces erosion processes, whose are aggravated by inadequate urban drainage works. Urban occupation intensification has facilitated the presence of erosion and sediment transport into Cacula Stream. The environment zoning of the area was obtained by applying the terrain evaluation technique at land element level. The natural conditions indicated low potential for developing erosion processes given the flat relief, slightly dissected, with a predominance of pedogenesis and low to medium steepness (usually less than 10 %). However, field surveys showed the evidence of erosion occurrences caused by inadequate rainwater conduit networks at drainage discharge points. Over time these erosive processes evolved to higher terrain parts with thicker soil profiles and coarser textures (sandy) significantly increasing the erosion occurrences. Water quality shows significant values in turbidity and total solids due to sediment transport during the rainy season. The current conditions imply potential degradation of water resources in the Cacula Stream, and recent occupation of much of the Watershed area with sugarcane planting induces erosion during the soil exposure to prepare the planting can also include the transport of agricultural inputs to the stream, which can further compromise the water quality.