Recommendations for riparian buffer widths based on field surveys of erosion processes on steep cultivated slopes

Abstract

Results of field surveys are used to build knowledge about erosion processes occurring on steep cultivated slopes next to watercourses, and to propose conservation measures with an emphasis on widths for riparian buffer strips. The surveys were conducted on a 108-km2 watershed in Portneuf region, Québec, Canada. Using a handheld global positioning system (GPS), measuring tapes, a 0.5-m resolution satellite image and a 1-m resolution Digital Terrain Model (DTM), 12 erosion-prone areas, totalling 53 ha, located close to river banks were surveyed during four days of the rainy and snowmelt period of April–May 2012. As a result, 328 erosion features were identified and classified into 10 categories. Predominant erosion features included rills, ephemeral gullies and sheet erosion (70% of all features observed). Rills and smaller gullies had lengths of 0.5–160 m, depths of 5–55 cm, and breadths of 5–130 cm. Most erosion features (n = 194) occurred on hillslopes > 8% and had lengths of 10–60 m. At present, most riparian buffer strips in the surveyed field are 1–3 m wide, which is the minimum dimension required by the provincial policy that regulates vegetated filters. In most places surveyed, ephemeral gullying on steep slopes simply extends through the thin 1–3 m buffer strip to easily discharge sediments and pollutants into flowing streams. Based on the local slopes assessed, it is proposed herein to convert these steep cultivated hillslopes into riparian buffer strips of 10–60 m, so that vegetated strips effectively act as boundaries between watercourses and damaging uphill erosion processes, which are sources of sedimentation and, in all likelihood, eutrophication.