An oilfield material reservoir is disclosed. The oilfield material reservoir has a body, the body having an upper end, a lower end, a sidewall extending between the upper and lower ends, the sidewall defining a recess within the body, an opening defined by the upper end, and a first orifice defined by the lower end. The oilfield material reservoir is also provided with a metering gate connected to the body at the lower end. The metering gate has a base having a second orifice aligned with the first orifice, and a knife gate connected to the base. The second orifice has a substantially trapezoidal shape. The knife gate is configured to slidably cover the second orifice. A method is also disclosed for controlling a discharge rate of oilfield material within the oilfield material reservoir by adjusting a metering open area of the second orifice according to mathematical modeling equations.