Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Moree D.

Blakely Mountain Dam controls flow on a 1,105 square mile watershed and is located upstream of Hot Springs, Arkansas. In order to better understand the hydrologic risks associated with the dam, the following items are being performed to increase confidence in the probable maximum flood for Blakely Mountain Dam and its assigned frequency. An outline of the methodology used to complete each process will be presented, with a focus on the creation of probable maximum precipitation dataset and the routing of the event to the dam.

• Preform a Site-Specific Probable Maximum Flood Analysis and compare with the standard HMR 51/52 Methodology. Use Sensitivity analyses to determine upper, lower, and best estimate.
• Create hydrologic model (HEC-HMS) with adequate calibration and validation. Calculate peaking factors to account for added runoff volume
• Complete a survey of dam and spillway crest. Use 2-dimensional modeling to validate rating curves for spillway and am overtopping.
• Create a reservoir routing model (HEC-ResSim) with the ability to model downstream flow constraints. Validate the mod
• Perform a paleoflood analysis to extend the effective record length of the reservoir inflow data, and increase confidence in estimates of extreme flood probability
• Gather historical flood records dating back to 1800's and incorporate the historical records and the paleoflood information into the inflow volume-frequency curve using HEC-SSP.
• Compare the inflow volume-frequency curve to the regional precipitation-frequency curve from NOAA Atlas 14 to see if the estimated return periods for the PMP and PMF are consistent.
• Update the stage-frequency curve using a Reservoir Frequency Analysis Tool (RMC-RFA) with the new volume-frequency curve.
• Use the stage-frequency curve to assign a reoccurrence frequency values to Spillway, Top of Dam and PMF elevations.