Cross sections for the 50-year flood, for Rio Sonaguera, Sonaguera, Honduras. Water-surface elevations for an estimated 50-year-flood discharge on Rio Sonaguera and north and south tributaries at Sonaguera were determined using HEC-RAS, a one-dimensional step-backwater computer program. The channel and floodplain cross section geometry used in HEC-RAS were developed from an airborne light detection and ranging (LIDAR) topographic survey of the area. The 50-year-flood discharge for Rio Sonaguera, 282 cubic meters per second, and the North Tributary, 168 cubic meters per second, and the South Tributary, 194 cubic meters per second were estimated using a regression equation that relates the 50-year-flood discharge to drainage area and mean annual precipitation. The area of inundation and depth of flood coverage was created with the HEC-RAS output and topographic TIN using HEC-geo-RAS software.