Vanessa, thank you for joining this forum and bringing National Rivers research and expertise to this site. Guys I have been studying river law for 20 some years and have personally vetted NORs findings with lawyer friends and by researching court cases myself. M r, The OHWM is determined by the highest the water gets save for excessive floods. The highest the water gets during full generation would not be considered flood level as it occurs on a regular basis. The corps site for your river gage should give you the gage height at which the river is considered to be in flood. Anything below that level should safely be below the OHWM.