Hydrologic Routing Model of the Iowa Flood Center Real-Time Streamflow Forecasting System

The Iowa Flood Center operates a real-time streamflow forecasting system for the entire State of Iowa. The basis for the forecasts is simulation from a rainfall–runoff model called the Hillslope-Link Model. The HLM uses terrain (DEM) landscape decomposition into hillslopes, where rainfall is transformed to runoff, and channel links that form the river network that routs the water from small streams to large rivers. The key element of the streamflow routing is the velocity model that connects water velocity at a link with discharge and draingage area upstream using a power law functional form. The parameters of the relationship are estimated from USGS observations independently from the other components of the HLM. The authors demonstrate the velocity model and the variability of its parameters across major river basins in Iowa. They also discuss an extension of the model where the parameters vary according to the stream-order. The authors evaluate the HLM model performance using various versions of the routing component. The results indicate high level of sensitivity to the model parameters as well as dependence on the resolution of the DEM used to extract the river network.