An investigation was made of the flash flood of July 9, 1943, on the Blacksburg watershed with a view toward an approximation of the actual amount of water passing as run-off during the storm, as well as the peak rate of flow. All the available data have been reviewed with the above purpose in mind. The unit graph method has been applied to this investigation as the most logical method of solution. With the data already available plus that gathered by the writer, the unit graph method was readily applied. In this connection, the writer has kept continuous rainfall records at the Mineral Industries Building and continuous water level records at the Virginia Polytechnic Institute dam. After arriving at a solution as to the actual run-off conditions at the Virginia Polytechnic Institute dam following the above storm, further investigation was made of that point of the drainage area above the Blacksburg depot of the Norfolk and Western Railroad. The capacities of both the culvert on Eakia Street and the channel above Eakia Street were determined by calculations, and an opinion based on the review of observed data was offered as to why the culvert did not properly take care of the run-off from the drainage area above it. Using the calculated maximum rate of run-off, a cross section of Strouble’s Creek at the site of the proposed Virginia Polytechnic Institute sewage disposal plant has been analyzed. A solution has been offered as to low high the maximum flood crest of Strouble’s Creek at that point will reach. This information is necessary because the sewage plant must be build above the flood waters. / M.S.