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The flow in the conduit from upslope terraces JL must be controlled so that there is no excess hydraulic head under a lower terrace, causing water to flow up through the riser, which could result in the terrace overtopping (Schwab et al., 1981). Based upon economic considerations, an orifice plate is used to minimize the conduit size. This experimental study was conducted to evaluate the hydraulic characteristics of different combinations of riser-orifice plate openings. One open-top and two round-hole terrace intake risers were tested under laboratory conditions using three diameters of orifice plates. The drop-inlet spillway model was used to describe discharge characteristics. Equations and curves were constructed for the head-discharge relationships of various riser-orifice plate combinations.