Over Estimating Low Flow Recession
Operational forecasters are extremely dedicated to the immediacy of their river modeling and public reporting tasks. Seldom is their time for a complete FGM analysis of the watershed and river in addition to the regular job requirements. Despite the difficulty in finding time to analyze the physical reasons for incongruence between observed and modeled flows, many modelers learn how various parameters should be adjusted for their region's geomorphology and human modifications.
In the Yolo Bypass area of the Sacramento River, observed Low Flows have departures in a different direction than high flows. In Low Flows, the observed recession, in violet color, was outpaced by the modeled recession, in white. The cause of this incongruence in observed and modeled flows is likely due to the same coastal geomorphological influences and weir controls. For the CNRFC, it was initially unclear how to adjust the Lag and K parameters to better match the coastal estuary influences.
Image courtesy of NOAA