In December 1993, on my second trip to India to work at the National Institute of Hydrology, I met a colleague who confided to me that he was having trouble modeling a dam-breach failure1 using a well-known model. He mentioned that his results appeared to be two high by a factor of about two. I asked him what value of discharge coefficient was he using. He responded: "3.09, following Chow." 2 I said: "Are you using SI units?" To which he responded: "Of course." I said: "That is your problem. You are using a discharge coefficient applicable to U.S. customary units. You should be using the SI equivalent, which is 1.7."
1 Ponce, V. M., A. Taher-Shamsi, and A. V. Shetty. (2003). Dam-breach flood wave propagation using dimensionless parameters. Journal of Hydraulic Engineering, ASCE, Vol. 129, No. 10, October, 777-782. 2 Chow, V. T. (1959). Open-channel hydraulics. McGraw-Hill, New York.
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