PRELIMINARY RESULTS OF CIRCULAR 284 VERIFICATIONS IN MISSISSIPPI by K.V. Wilson Prepared by the U.S. Geological Survey 1964 U.S. GEOLOGICAL SURVEY WRD Bulletin TABLE OF CONTENTS Summary TABLES 1. Summary of computations of verifications of Circular 284 FIGURES 1. Effect of bridge length on "C" for heavily wooded flood plains ABSTRACT circular 284 has proved to be one of the most widely used and best accepted manuals developed by the Water Resources Division in recent years. The Circular is based mainly on laboratory studies made at Georgia Institute of Technology. Since the report was prepared, very little work has been done to verify the method under field conditions. The wide use and general acceptance of the Circular would make it doubly important that the reliability and limitations of the Circular be well established. Primarily, during 1961 and early 1962, verification measurements were made at 72 bridges in Mississippi. Many of these measurements were made under conditions that were far from ideal, but the bulk of evidence strongly indicates that, on streams with broad heavily wooded flood plains, the methods outlined in Circular 284 resulted in discharges that were as much as 200 percent too large. Verifications made on streams where the approach sections were fairly clear checked the computed discharges within reasonable limits. Preliminary anaylsis has not disclosed the source of error, but it is fairly certain to be related to the effect of roughness. Studies are continuing. We hope to evaluate the source of error through further analysis of these measurements and by obtaining additional verification measurements. This article was written for a three-fold purpose: 1. To solicit discussion of our preliminary findings. 2. Point out the possible error in unrestricted use of Circular 284 on streams with broad heavily wooded flood plains. 3. Encourage further verification studies in other districts. LizardTech's Djvu plug-in is needed to view these reports. CLICK HERE TO VIEW THE ENTIRE REPORT For questions or comments, contact K. Van Wilson.