Communicating Drought Severity and Re-Evaluating Firm Yield — Cumberland County, Tennessee As a Case Study

The 2007 drought in Cumberland County, Tennessee greatly strained the three reservoirs that provide the large majority of the county's water supply and prompted a new analysis of the reservoirs' firm yield. With the reservoirs lacking long term streamflow and operations records, traditional yield analysis could not be performed directly. A multi-scale Standardized Precipitation Index (SPI) analysis was conducted, and the resulting multi-scale SPI plot was found to be a highly effective tool for communicating the drought severity of the current drought relative to past droughts. A simple, continuous-simulation HEC-HMS model was used to generate a synthetic streamflow record, and determine the critical drought period for each reservoir using the traditional sequent peak algorithm. Using the sequent peak algorithm, storage-yield relationships a multiple yield cumulative deficit plot were created as useful tools for explaining reservoir behavior. This is part of a County-wide water supply plan being developed by the US Army Corps of Engineers, which includes projecting future water demand, evaluating potential conservation measures, and evaluating sources to meet the growing demand.