BLM/YA/PT-88/009+7200
This Technical Note provides guidance to hydrologists and engineers (and other specialists involved with water projects) faced with the task of determining a design hydrologic event for a project that involves hydrologic risk. Such projects may include bridges, culverts, land treatments, dams, fish habitat improvements, watershed management projects, etc. Included is a discussion of hydrologic risk that defines both the manager's and specialist's roles in determining risk levels for BLM-funded projects. An extensive section on frequency of hydrologic events is included for the specialist, followed by a section on guidelines and graphical aids for determining return periods. The latter section includes problem-oriented examples of return period selection. Event frequency analysis, including confidence limits on frequency curves, is briefly discussed.