Relating Design Storm Events to Ordinary High Water Marks in Indiana.

摘要

Hydraulic design and environmental permitting are heavily dependent upon Ordinary High Water Marks (OHWM) because they define the active river channel. The United States Army Corps of Engineers (USACE) use OHWM for regulation of the “Waters of the United States” as well as for flood and drought management. Current methods to determine OHWM are based on detailed on-site surveys to identify physical characteristics like scouring, deposition around the banks, absence of vegetation and water staining. These characteristics are site specific so there are fluctuations in measurements based on the water body, weather conditions, channel morphology, slope, fluvial patterns and size of the channel. A more reliable way to estimate this variable for hydraulic design is required that is based on storm recurrence intervals. Hydrologic and hydraulic modeling is used to relate OHWM to storm recurrence intervals by analyzing hydraulic and hydrologic parameters corresponding to design streamflow events for 26 watersheds (drainage area less than 200 square miles) in Indiana. The results show that the recurrence intervals of OHWM are actually smaller (less than 1 year) than the bank-full discharge intervals of 1.5-2 years which suggests that OHWM correspond to channel flows much smaller than bank-full discharge. Further analysis using the discharge-return period flow duration curves shows that the OHWM recurrence intervals have a fairly distributed range (0.73-1.12 years) and do not have a fixed recurrence interval. Trend analysis using Mann-Kendall test suggested that five hydrologic/hydraulic variables have a significant trend with OHWM discharges with drainage area, watershed slope and 2-year flow being the most significant. Regional equations are developed for Northern, Central and Southern Indiana to estimate OHWM discharges based on hydrologic/hydraulic parameter estimation using multiple and step-wise liner regression. Using these equations, it is possible to estimate OHWM occurrence discharges fairly accurately.