TESTS OP RIVER CREST STAGE GAGE U^fDER WAVE ACTION 



by 



Thorndike Saville, Jr. 



Assistant Chief 



Research Division 



Beach Erosion Board 



ABSTRACT 



Tests were made of a river crest stage gage to 

 determine the effect of superficial wave action on 

 the maximum stage recorded, with the idea that gages 

 of this type might be adopted for measurements of 

 maximum water elevations in estuaries and adjacent 

 low-lying sireas resulting from hurricane surges. Even 

 slight wave action introduced considerable error in 

 the maximum level recorded with the gage as originally 

 planned, but it was found that the gage could be modi- 

 fied in such a way as to result in a maximum error of 

 only a few tenths of a foot even with relatively high 

 wave action. 



The Beach Erosion Board was requested by the U. S, Weather 

 Bureau to make some observations of the effect of wave action on 

 the maximum water level recorded by a gage designed to provide 

 a record of the peak stage reached in stream flow. If the response 

 of the gage to such surface wave action was found to be slight, 

 the Bureau recognized that the gage could possibly be used to 

 record maximum stages reached by hurricane surges. The Hurricane 

 Survey Coordinating Committee of the Corps of Engineers also felt 

 that such a gage would be of considerable use in gathering hurri- 

 cane and other storm surge data for design purposes, and was 

 instrumental in having the tests continued with a modified gage. 

 The gage initially supplied by the Weather Bureau was a U. S, 

 Geological Survey river crest stage gage consisting of a 2-inch 

 diameter plastic tube with a screw-on bottom cap having an 

 effective bottom opening of 0.17 square inch, this opening being 

 provided to allow an interchange of water between the outside and 

 inside of the tube. The top of the tube was provided with a 

 screw-on cap vented to permit escape of air. Inside the tube was 

 a metal measuring stick which rested freely on the bottom cap, 

 and extended nearly to the top cap. The inside of the tube had 

 an effective area (pipe area minus rod area) of 3,07 square inches. 



In field operation, the tubing would be of ordinary 2-inch 

 ipetal pipe and would be mounted to a pier, piling, tree, building, 

 or other suitable structure. Plastic tubing was used for the tests 

 to permit easy visual observation of the effect of wave action. 

 The crest stage in the field is recorded by means of a small 

 quantity of ground burnt cork placed in the bottom of the tube. 



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