Environmental Flow Components for Measuring Hydrologic Model Fit during Low Flow Events

Abstract

AbstractThe indicators of hydrologic alteration (IHA) is a statistical flow methodology for characterizing ecologically important streamflows. Typically, IHA has been used to identify the extent of human effects on a stream’s hydrology and to set management goals to restore the stream ecology. In this work, the use of the seven “extreme low flow” statistics of the IHA is extended to the evaluation of the performance of a hydrologic simulation model under low flow conditions. Specifically, this work uses the IHA framework to evaluate the accuracy of the Chesapeake Bay Program Phase 5 (CBP5) watershed model during low flow events on a regional scale that is relevant to many water supply planners and managers. Because the CBP5 model’s primary focus is predicting the Bay’s water quality, the measures used to calibrate the CBP5 model focused primarily on the calibration of the entire hydrological record and had only a secondary emphasis on specific flow regimes, such as low flows and very low flows, although t...