Introduction

Many waterways are affected by regulation from dams and diversions. Streamflow records from these waterways reflect this regulation. Flow frequency analysis procedures, such as those codified in Bulletin 17C, involve fitting analytical distributions to streamflow records that are not appreciably altered by upstream regulation. Pre-regulation streamflow records are not typically long enough to use in a flow frequency analysis. Therefore, regulated streamflow records often need to be transformed to unregulated streamflow for flow frequency analyses.  

To extract unregulated streamflow from a hydrologic model, a period of record simulation could be performed. However, this requires continuous meteorological forcing data, which may be difficult to obtain. In addition, a period of record simulation can be time-consuming to perform. Another approach is to develop a simple hydrologic routing model to transform regulated streamflow records to unregulated streamflow. This second approach is demonstrated here. Hydrologic routing can be performed without a hydrologic model (in HEC-DSSVue) or with a hydrologic model (in HEC-HMS).

In this tutorial, you will investigate transforming regulated streamflow without and with a hydrologic model: