Introducing the conservation, functional and geotechnical buffer widths for watershed management measures: a new approach for efficient land use planning

Watershed management measures present vital services in mitigating the risk of environmental events and conserving existing land uses on a catchment scale. Nevertheless, alongside land uses encroach on their functioning territory, and considerations regarding the failures in their structures and resulting hazards to surrounding areas have not been well documented. Therefore, the present study aimed to develop a new formula for calculating setback width (A) to conserve the structure of watershed management measures and warranty their roles and define a safety width (B) to preserve them from instability on slopes. Relations developed estimated a wide range of setback widths of A and B in detail according to the specific and environmental variables. Setback width A of mechanical measures gained based on the height and stream and its bank's slopes, in which maximum conservation width should consider for the taller check dams and weirs set up between the river banks lower than 10 degrees. Results showed that setback width A of biomechanical measures, especially in flood spreading and contour-based actions that control runoff and flash floods is wider on slopes > 20%. Setback width A of tree planting should consider 36 times the diameter of the trunk in their mature age of growth to protect the tree root system. Further, a maximum of 40 m safety setback width (B) on > 45% slope is obtained based on the erodibility factor and considering widths for firefighting and the height of falling down the tree. The present research provides guidelines for watershed managers to conserve functions of established management actions and future operations and optimize designing adjacent land uses. Observing arranging setbacks (A and B) is a critical step for land use planning and decreasing conflict of interest in lands and appropriate use of natural resources.