3.2.4 Local sediment sources related to project operation and maintenance

Local sediment sources associated with project facilities should be quantified to determine if they individually and collectively contribute significant amounts of sediment to project-affected stream reaches.  Local sediment sources may include erosion features in the vicinity of project dams, spillways, powerhouses, penstocks and canals, project roads and trails, transmission line corridors, and reservoir shorelines (shoreline protection is discussed in Section 8.2).  Sequential aerial photography, interviews with operations staff, and field surveys are typically used to map sediment sources and differentiate natural from anthropogenic sediment sources.  A field inspection of major project-related sediment sources should be conducted to estimate delivery to water bodies.  The field inspection should consist of assessment of the erosion processes and activity level, measurements of each major erosion feature (length, width, and depth), estimation of the grain size distribution of the eroding material, and estimation of sediment delivery to water bodies.  The significance of each project-related sediment source should be evaluated based on the relative sediment volumes produced and delivered, the relative sensitivity of channels receiving sediment, and the likelihood of continued sediment production.