▁the ▁in let . ▁The ▁value ▁ 3 . 1 ▁is ▁based ▁on ▁the ▁assumption ▁that ▁He ▁and ▁va ▁are ▁measured ▁at ▁a ▁location ▁that ▁exhib its ▁sub crit ical ▁flow ▁conditions . ▁ ▁NE H 1 4 ▁also ▁provides ▁the ▁following ▁relationship ▁for ▁side ▁channel ▁in lets : ▁ ▁Q mi ▁= ▁ 3 . 1 L h 3 / 2 ▁ ▁Where : ▁ ▁Q mi ▁= ▁dis charge ▁capacity ▁without ▁fre eb o ard ▁( ft 3 / s ) ▁( In ▁this ▁case , ▁fre eb o ard ▁is ▁the ▁vertical ▁distance ▁from ▁the ▁water ▁surface ▁to ▁the ▁dam ▁cr est ▁when ▁the ▁water ▁surface ▁is ▁at ▁a ▁lower ▁elev ation .) ▁ ▁L ▁= ▁length ▁of ▁the ▁sp ill way ▁cr est ▁( ft ) ▁ ▁H ▁= ▁height ▁of ▁the ▁side w alls ▁above ▁the ▁sp ill way ▁cr est ▁( ft ) ▁ ▁Side ▁Channel ▁In let ▁▁ ▁The ▁United ▁States ▁Bureau ▁of ▁Rec lam ation ▁( U SB R ) ▁also ▁uses ▁the ▁we ir ▁formula ▁to ▁quant ify ▁flow ▁over ▁a ▁ch ute ▁sp ill way . ▁The ▁USB R ▁flow ▁equation ▁is : ▁ ▁Q ▁= ▁CL H 3 / 2 ▁ ▁Where : ▁ ▁Q ▁= ▁flow ▁( ft 3 / s ) ▁ ▁L ▁= ▁sp ill way ▁cr est ▁length ▁( or ▁width ) ▁( ft ) ▁ ▁H ▁= ▁elev ation ▁difference ▁between ▁the ▁res er voir ▁water ▁surface ▁and ▁the ▁sp ill way ▁cr est ▁ ▁C ▁=