Free overfall for discharge measuring in stone bed rectangular channels

In the present investigation, the overfall is employed as a practical tool for measuring discharges in stone bed rectangular channels with overfalls. Fifteen stone bed rectangular channel models with a length of 240 cm and an end drop fall of 20 cm are constructed and examined. These models assess different stone sizes 𝐷 𝑠 = 0.5 cm, 1.0 cm, and 1.5 cm in horizontal bed channels as well as channels with different bed slopes 𝑆 𝑟 = 0.0033, 0.005, 0.01, and 0.02. The examination of laboratory data for ratios of brink flow depth 𝑌 𝑒 to critical depth 𝑌 𝑐 (EDR) and to normal flow depth 𝑌 𝑛 for different values of 𝑆 𝑟 and 𝐷 𝑠 showed straight line relationships. The average 𝑌 e / 𝑌 𝑐 values varied with 𝑆 𝑟 according to a quadratic formula. For the ranges of 𝑆 𝑟 from 0.0033 to 0.02, Froude number 𝐹 𝑟 𝑛 from 0.41 to 2.78, and 𝑌 𝑒 / 𝐷 𝑠 from 0.88 to 15.55, a direct empirical power correlation is presented for estimating the dimensionless discharge 𝑞 𝑟 /( 𝑔 𝑟 1 / 2 ⁡ 𝑌 𝑒 3 / 2 ) in terms of 𝑌 e / 𝑌 𝑐 , 𝑌 e / 𝐷 𝑠 and 𝑆 𝑟 with determination coefficient R 2 of 0.960 and Mean Percentage Error MPE = ±0.45%. Another empirical power expression is presented for the dimensionless discharge in stone bed rectangular channels of horizontal beds with R 2 of 0.965. The correlations identified in this study shown good consistency when compared to the findings of many other researchers.