Isochrones of travel time and distribution of flood storage from a tracer study on a small watershed

In the practical application of many methods of flood hydrograph synthesis it is necessary to space isochrones of travel time over the watershed or to allocate the distribution of storage. The available evidence for guiding this procedure is reviewed, but most information applies to large stream systems and to flows lower than the flood discharges of interest. Times of travel data from tracing of flood runoff on a small watershed have been compared with the evidence from large streams. Average velocities were found to increase slightly in a downstream direction through the watershed, despite decreasing slope. This increase conforms with published hydraulic geometry relationships. Five geomorphological parameters have been tested as methods for spacing isochrones. Field inspection to determine mean depths, and possibly roughness, at bank‐full stages should lead to greatest accuracy, but simple parameters based on stream length also gave good results.